Merge pull request 'webui: a grouped keyboard shortcut panel for the sheet' (#33) from sheet-shortcuts into sheet-editing

Reviewed-on: #33
Reviewed-by: branderson <brad@branderson.io>

.dejima/allowed-domains

@@ -0,0 +1,6 @@
+deb.debian.org
+security.debian.org
+pypi.org
+files.pythonhosted.org
+download.pytorch.org
+download-r2.pytorch.org

.gitea/workflows/tests.yml

@@ -0,0 +1,86 @@
+name: tests
+
+# `pull_request_target` reads this file from the base branch, so a pull
+# request cannot change what runs or where (including `runs-on:`). The run's
+# ref is therefore the base branch, and the checkout has to name the head.
+on:
+  pull_request_target:
+
+jobs:
+  test:
+    # No Docker socket, and egress limited to .dejima/allowed-domains on main.
+    runs-on: dejima-confined
+
+    # Node for actions/checkout; Debian bookworm's python3 is the 3.11 the
+    # Dockerfile ships.
+    container:
+      image: node:22-bookworm
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+
+      # Inline rather than a script in the repository: the files come from the
+      # branch under test, so a script would be missing from older branches.
+      - name: Check the hosts this job fetches from are reachable
+        run: |
+          set -u
+          bad=""
+          for host in deb.debian.org security.debian.org pypi.org \
+                      files.pythonhosted.org download.pytorch.org \
+                      download-r2.pytorch.org; do
+            resolved=""
+            for attempt in 1 2 3 4; do
+              getent hosts "$host" >/dev/null 2>&1 && { resolved=yes; break; }
+              sleep 2
+            done
+            if [ -z "$resolved" ]; then
+              echo "no    $host - does not resolve"; bad="$bad $host(dns)"; continue
+            fi
+            # Any HTTP answer proves the connection; curl reports 000 for none.
+            code="$(curl -sS -o /dev/null --max-time 20 --retry 2 -w '%{http_code}' "https://$host/" 2>/dev/null || true)"
+            case "${code:-000}" in
+              000) echo "no    $host - resolves, but nothing answered over https"
+                   bad="$bad $host(net)" ;;
+              *)   echo "ok    $host (http $code)" ;;
+            esac
+          done
+          [ -z "$bad" ] && exit 0
+          {
+            echo
+            echo "Unreachable:$bad"
+            echo
+            echo "The confined tier reaches only what .dejima/allowed-domains on"
+            echo "main declares, rendered onto the runner separately from the"
+            echo "merge. On the runner:"
+            echo "  sudo dejima-ci-allowlist show    - is the name listed?"
+            echo "  sudo dejima-ci-allowlist check   - is a change pending?"
+            echo "  sudo dejima-ci-allowlist render  - apply it now"
+            echo "A (dns) failure is the resolver; a (net) one is the packet"
+            echo "filter, which sudo dejima-ci-firewall reapplies."
+            echo
+            echo "download.pytorch.org redirects its wheels to"
+            echo "download-r2.pytorch.org, so both have to be allowed."
+          } >&2
+          exit 1
+
+      - name: Install Python
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends python3 python3-venv
+          python3 -m venv /opt/venv
+          # bookworm's pip 23.0 rejects the PyTorch index's typing_extensions
+          # wheel over its name's spelling, then cannot build it from source
+          /opt/venv/bin/pip install --retries 5 --upgrade pip
+          echo /opt/venv/bin >> "$GITHUB_PATH"
+
+      # The CPU build first: torch from PyPI is the CUDA build, several GB of
+      # libraries no test uses. The install below then finds torch satisfied.
+      - name: Install CPU-only torch
+        run: pip install --retries 5 torch torchaudio --index-url https://download.pytorch.org/whl/cpu
+
+      - name: Install songtrace
+        run: pip install --retries 5 -e '.[dev]'
+
+      - run: pytest

README.md

@@ -34,6 +34,60 @@ printing the low-confidence regions it found (e.g.
 editor such as [Yass](https://www.yass-along.com/) or
 [USDX](https://usdx.eu/) and touch those spots up before playing.
 
+## Reviewing a song
+
+The web UI plays the finished song folder back against the review, so you can
+check the timing without loading it into a game first. Pick a song in the
+queue and the review panel gets the packaged video with a transport above the
+lyrics; as it plays, the line being sung is highlighted, words light up as
+they are reached, and a playhead sweeps each line against its notes. Click any
+line or word to play from there.
+
+Playback is modelled on the game: the `#MP3` is the audio and the clock, and
+the `#VIDEO` is muted background slaved to it. It also uses the same seconds
+the notes were generated from, so a word that lights up late in the browser is
+late in the game too.
+
+The packaged video has its audio track stripped for the same reason. It is the
+same recording as the `#MP3`, so a player that does not mute the video plays
+both at once, a few frames apart, which is heard as an echo. Songs built
+before this change still have it — check with `ffprobe <song>.mp4` for an
+audio stream, and rebuild with **Restart from** set to `package` to clear it
+without re-downloading.
+
+## Editing a song
+
+Above the lyrics, the note sheet shows one line at a time on a pitch-by-beat
+grid, with the pitch songtrace detected drawn over the notes: where a note is
+right the curve runs through it, so a wrong one stands out. Fix it there and
+**SAVE LINE**; the song folder's chart is rewritten on the spot.
+
+Drag a note to move it and its ends to resize it; everything snaps to the
+chart's beat grid and to semitones. Double-click empty space to add a note,
+or a note to change its syllable. With the sheet focused: ←/→ move, ↑/↓
+change pitch (Shift for an octave), Shift+←/→ change length, Tab selects the
+next note, S splits, M merges with the next note, G/F/R make a note golden,
+freestyle or rap, Delete removes, Ctrl+Z undoes, Ctrl+S saves and P plays
+the line.
+
+The ↵ markers either side of a line are its line breaks: drag one to move it
+(it snaps to beats and stays between the lines it separates) and double-click
+one to put it back where songtrace places it. Moving a break does not mark
+either line's notes as edited, so they still follow a rebuild.
+
+The **GRID** bar above the notes sets the chart's BPM and GAP. Changes redraw
+the grid as you type and are charted on **APPLY**; ×2 and ÷2 fix a tempo
+detected at double or half speed, and **ALIGN TO NOTE** moves GAP the least
+that puts the selected note on a beat. Notes keep their timing in seconds and
+re-snap to the new grid. **RESET** returns to the BPM songtrace chose (your
+BPM override, or the detected tempo) with GAP at the first note.
+
+Edits survive every rebuild, REBUILD ALL FROM… included: they are kept apart
+from what the pipeline generates and laid back over it each time. **REVERT**
+returns a line to the generated notes. Changing a line's lyrics sets its edit
+aside rather than applying it to different words; the sheet lists those so
+you can discard them.
+
 ## Configuration
 
 Config is TOML. Resolution order:
@@ -51,7 +105,9 @@ $EDITOR config.toml   # set whisper_url at minimum
 
 See `config.example.toml` for every available field (`whisper_url`,
 `whisper_api_key`, `whisper_model`, `whisper_api`, `output_dir`, `work_dir`,
-`creator`, `demucs_model`, `crepe_model`, `device`, `bind_host`, `port`).
+`creator`, `demucs_model`, `crepe_model`, `device`, `bind_host`, `port`,
+`ytdlp_clients`, `ytdlp_cookies`, `ytdlp_impersonate`,
+`ytdlp_pot_provider_url`, `ytdlp_version`).
 
 `whisper_api` selects the wire format: `"openai"` (default) speaks the
 OpenAI-compatible `POST {whisper_url}/audio/transcriptions` API; `"asr-webservice"`
@@ -85,6 +141,30 @@ Toolkit](https://docs.nvidia.com/datacenter/cloud-native/container-toolkit/)
 installed on the host; `docker-compose.yml` requests one GPU via the
 `nvidia` device driver.
 
+## Sharing the GPU
+
+`songtrace serve` is long-lived but only wants the GPU in bursts, so it hands
+it back after every stage rather than holding it for the life of the process.
+Three stages load a model — `separate` (Demucs), `align` (wav2vec2) and
+`pitch` (torchcrepe) — and each one's weights are dropped as soon as that
+stage finishes, followed by `torch.cuda.empty_cache()` to return the
+allocator's freed blocks to the driver instead of keeping them for reuse. This
+matters most between `separate` and `align`: `transcribe` sits between them
+waiting on your Whisper server, which can be minutes of a GPU nothing is
+using.
+
+Stages that gave memory back say so in the job log:
+
+```
+[separate] released 3704 MiB of GPU memory
+```
+
+The cost is reloading each model once per job instead of once per process,
+which is seconds against stages that run for minutes. What this does not
+release is the CUDA context itself, a few hundred MB that belongs to the
+process until it exits; freeing that would mean running each stage in a
+subprocess. If you need every last MB back, stop the container between runs.
+
 ## Bare-metal
 
 ```sh
@@ -117,10 +197,74 @@ songtrace make --title "..." --artist "..." --lyrics lyrics.txt \
 Valid stages, in pipeline order: `acquire`, `separate`, `transcribe`,
 `align`, `pitch`, `notes`, `grid`, `package`.
 
+In the web UI this is what selecting a queue entry does: its title, artist,
+lyrics and the rest come back up in the form, so you can adjust them and hit
+REBUILD SONG. Only the stages your edit actually invalidates are rerun —
+fixing a line of lyrics realigns without re-downloading or re-separating.
+CREATE SONG, at the top of the queue, clears the page to start a fresh one.
+
+That planning works off the fields you changed, which cannot see a change in
+songtrace itself: after an upgrade, a rebuild of an older song finds every
+stage cached and does nothing. **Restart from** on the rebuild form is the way
+to redo a stage anyway — pick `package` to repackage without re-downloading.
+It can only widen what is rerun, so an edit that invalidates an earlier stage
+still wins.
+
+**REBUILD ALL FROM…**, under CREATE SONG, does the same for every song at once:
+pick the stage an update improved and each song is rebuilt from there with the
+inputs it has now. Every song starts ticked; untick any already rebuilt by hand
+(each shows when it was last built). Songs still in progress are skipped, as
+are songs whose uploaded video is gone when the stage is `acquire`.
+
+## YouTube download failures
+
+`HTTP Error 403: Forbidden` from the acquire stage means YouTube served the
+page but refused the media URL. In rough order of likelihood:
+
+1. **yt-dlp is stale.** YouTube changes its defences every few weeks, so
+   songtrace keeps yt-dlp current itself. Once a day, and again whenever a
+   download fails outright, it checks PyPI for a newer stable release,
+   installs it under `$XDG_CACHE_HOME/songtrace/` (`/data/models/cache` in the
+   container), and tries it before the copy installed with songtrace. That
+   copy is never modified and is always the fallback, so a release that breaks
+   compatibility costs a retry rather than the download. The job log names
+   the yt-dlp version behind each attempt.
+
+   `ytdlp_version` overrides this: `"bundled"` uses only the installed copy,
+   and a release number such as `"2026.08.19"` pins that release instead of
+   the newest.
+
+2. **Missing JS runtime.** yt-dlp needs `yt-dlp-ejs` plus a JavaScript engine
+   to solve YouTube's player challenges; without them it silently falls back to
+   formats that 403. The `[default,curl-cffi,deno]` extras in `pyproject.toml`
+   cover this, for both the installed copy and the ones fetched at runtime.
+   Check with `docker compose exec songtrace yt-dlp -v --simulate <url>` — the debug
+   header must show a `JS runtimes:` line that is not `none`.
+
+3. **The IP is rate-limited or flagged.** Datacenter and VPN ranges get
+   throttled hardest. Try from another network before changing config.
+
+4. **A PO token is required.** If the log says so explicitly, run
+   [bgutil-ytdlp-pot-provider](https://github.com/Brainicism/bgutil-ytdlp-pot-provider)
+   as a sidecar, install its plugin into the image, and point
+   `ytdlp_pot_provider_url` at it.
+
+`ytdlp_clients` retries the download against each listed player client in
+turn, so a client that YouTube has broken is skipped automatically.
+`ytdlp_cookies` (a Netscape cookie jar, for age-gated videos) and
+`ytdlp_impersonate` (a browser TLS fingerprint, e.g. `"chrome"`) are the other
+two levers. Do not use a cookie jar from an account you care about — YouTube
+bans for automated access.
+
+Failed downloads leave the work dir intact, so re-running the job resumes
+rather than starting over.
+
 ## Regenerating the web UI screenshot
 
 `scripts/screenshot_webui.py` seeds the real app with a fixed set of jobs
-covering every status and screenshots it to `docs/images/webui.png`:
+covering every status and screenshots it to `docs/images/webui.png`. It uses
+`ffmpeg` to give the selected song a playable folder so the shot includes the
+player; without `ffmpeg` on `PATH` it still runs, just without it.
 
 ```sh
 pip install -e '.[dev]'

config.example.toml

@@ -11,3 +11,13 @@ creator = "brad"
 # device = "cuda"
 bind_host = "0.0.0.0"
 # port = 8000
+
+# YouTube downloads. Each player client is tried in order until one works;
+# "default" means whatever yt-dlp currently picks for itself.
+# ytdlp_clients = ["default", "tv"]
+# ytdlp_cookies = "/config/youtube-cookies.txt"  # Netscape cookie jar
+# ytdlp_impersonate = "chrome"                   # TLS fingerprint to present
+# ytdlp_pot_provider_url = "http://bgutil-provider:4416"
+# Newer yt-dlp releases are fetched from PyPI at runtime and tried before the
+# bundled one; "bundled" turns that off, a release number pins one.
+# ytdlp_version = "auto"

pyproject.toml

@@ -5,7 +5,12 @@ description = "Generate UltraStar/Melody Mania karaoke songs from a video and re
 requires-python = ">=3.11"
 license = "AGPL-3.0-or-later"
 dependencies = [
-    "yt-dlp",
+    # yt-dlp declares no runtime deps of its own; the extras are what make
+    # YouTube work. "default" pulls yt-dlp-ejs (JS challenge solving) and the
+    # requests/urllib3 handlers, "deno" ships the JS runtime that executes it,
+    # and "curl-cffi" provides the --impersonate targets. Without them YouTube
+    # extraction degrades to HTTP 403 on the media URLs.
+    "yt-dlp[default,curl-cffi,deno]",
     "demucs",
     "torch",
     "torchaudio",

scripts/screenshot_webui.py

@@ -7,6 +7,8 @@ One-time setup: pip install -e '.[dev]' && playwright install chromium
 Run: python scripts/screenshot_webui.py
 """
 import json
+import shutil
+import subprocess
 import tempfile
 import threading
 import time
@@ -110,6 +112,7 @@ SONGS = [
     ("Vampire in the Corner", "Magdalena Bay", "queued", {}),
 ]
 SELECTED = "Greensleeves"
+REVIEW_HEADING = "REVIEW"
 
 running_event = threading.Event()
 
@@ -157,14 +160,42 @@ def make_runner():
     return runner
 
 
-def start_server(tmp_path: Path) -> str:
+def start_server(tmp_path: Path) -> tuple[str, Config]:
     cfg = Config(whisper_url="http://localhost:9000/v1", output_dir=tmp_path / "out",
                  work_dir=tmp_path / "work", bind_host="127.0.0.1", port=8811)
     app = create_app(cfg, runner=make_runner())
     server = uvicorn.Server(uvicorn.Config(app, host=cfg.bind_host, port=cfg.port,
                                             log_level="warning"))
     threading.Thread(target=server.run, daemon=True).start()
-    return f"http://{cfg.bind_host}:{cfg.port}"
+    return f"http://{cfg.bind_host}:{cfg.port}", cfg
+
+
+def install_media(cfg: Config) -> bool:
+    """Give the selected song a playable folder, so the shot shows the player.
+
+    A flat fill rather than a test pattern: the point is the transport and the
+    lyric tracking underneath it, not the picture. Skipped without ffmpeg.
+    """
+    if shutil.which("ffmpeg") is None:
+        print("ffmpeg not found; screenshotting without the player")
+        return False
+    artist, title = next((a, t) for t, a, _, _ in SONGS if t == SELECTED)
+    slug = f"{artist} - {title}"
+    out = cfg.output_dir / slug
+    out.mkdir(parents=True, exist_ok=True)
+    subprocess.run(
+        ["ffmpeg", "-y", "-loglevel", "error", "-f", "lavfi",
+         "-i", "color=c=0x1A1430:s=640x360:d=60", "-c:v", "libx264",
+         "-pix_fmt", "yuv420p", "-preset", "ultrafast", "-an",
+         str(out / f"{slug}.mp4")], check=True)
+    subprocess.run(
+        ["ffmpeg", "-y", "-loglevel", "error", "-f", "lavfi",
+         "-i", "anullsrc=r=44100:cl=stereo:d=60", "-b:a", "64k",
+         str(out / f"{slug}.mp3")], check=True)
+    (out / f"{slug}.txt").write_text(
+        f"#TITLE:{title}\n#ARTIST:{artist}\n#MP3:{slug}.mp3\n#VIDEO:{slug}.mp4\n"
+        f"#BPM:240\n#GAP:10000\n: 0 4 16 Alas,\nE\n", encoding="utf-8")
+    return True
 
 
 def seed_jobs(base_url: str) -> None:
@@ -187,13 +218,25 @@ def seed_jobs(base_url: str) -> None:
                 time.sleep(0.05)
 
 
-def capture(base_url: str) -> None:
+def capture(base_url: str, with_player: bool) -> None:
     with sync_playwright() as p:
         browser = p.chromium.launch()
-        page = browser.new_page(viewport={"width": 1280, "height": 900})
+        page = browser.new_page(viewport={"width": 1280, "height": 1000})
         page.goto(base_url, wait_until="networkidle")
         page.get_by_text(SELECTED, exact=True).click()
-        page.wait_for_timeout(300)
+        page.wait_for_timeout(500)
+        if with_player:
+            # paused mid-line, so the shot carries the playhead and the sung /
+            # current word colouring rather than an untouched transport
+            page.evaluate("document.getElementById('player-media').currentTime = 11.6")
+            page.wait_for_timeout(400)
+            # scrolled to the review: the player pins to the top of #main and
+            # the tracked lines sit under it, which is the panel in use
+            page.evaluate("""() => {
+              const main = document.getElementById('main');
+              main.scrollTo(0, document.getElementById('review').offsetTop - 12);
+            }""")
+            page.wait_for_timeout(400)
         OUT_IMAGE.parent.mkdir(parents=True, exist_ok=True)
         page.screenshot(path=str(OUT_IMAGE))
         browser.close()
@@ -201,10 +244,11 @@ def capture(base_url: str) -> None:
 
 def main() -> None:
     with tempfile.TemporaryDirectory() as tmp:
-        base_url = start_server(Path(tmp))
+        base_url, cfg = start_server(Path(tmp))
         time.sleep(1)
         seed_jobs(base_url)
-        capture(base_url)
+        with_player = install_media(cfg)
+        capture(base_url, with_player)
     print(f"wrote {OUT_IMAGE}")
 
 

src/songtrace/config.py

@@ -1,6 +1,6 @@
 import os
 import tomllib
-from dataclasses import dataclass, fields
+from dataclasses import dataclass, field, fields
 from pathlib import Path
 
 
@@ -18,9 +18,18 @@ class Config:
     device: str = "cuda"
     bind_host: str = "127.0.0.1"
     port: int = 8000
+    # YouTube player clients to try, in order, until one yields a download.
+    # "default" means yt-dlp's own choice; see its extractor-args docs.
+    ytdlp_clients: list[str] = field(default_factory=lambda: ["default", "tv"])
+    ytdlp_cookies: Path | None = None
+    ytdlp_impersonate: str | None = None
+    ytdlp_pot_provider_url: str | None = None
+    # "auto" keeps yt-dlp current from PyPI, "bundled" uses only the copy
+    # installed with songtrace, and a release such as "2026.08.19" pins that.
+    ytdlp_version: str = "auto"
 
 
-_PATH_FIELDS = {"output_dir", "work_dir"}
+_PATH_FIELDS = {"output_dir", "work_dir", "ytdlp_cookies"}
 
 
 def load_config(path: Path | None = None) -> Config:

src/songtrace/edits.py

@@ -0,0 +1,233 @@
+"""Manual edits to a song, kept apart from what the pipeline generates.
+
+Edits live in work/<slug>/edits.json, which no stage produces, so no rebuild
+removes them; grid lays them over the freshly generated notes every time. An
+edit is a whole lyric line as the user left it, timed in seconds so that a
+rebuild with a different BPM re-snaps it rather than breaking it.
+"""
+import difflib
+import json
+import math
+import time
+from pathlib import Path
+
+from .notes import MIN_NOTE_SEC, TimedNote, low_confidence_warnings
+
+EDITS_FILE = "edits.json"
+FINAL_FILE = "notes_final.json"
+KINDS = {":", "*", "F", "R", "G"}
+
+
+def _empty(lyrics: list[list[str]]) -> dict:
+    # grid: the BPM and GAP set in the editor, or None for the pipeline's own;
+    # breaks: line breaks moved by hand, keyed by the line each comes before
+    return {"lyrics": lyrics, "lines": {}, "stale": [], "grid": None, "breaks": {}}
+
+
+def load(work: Path, lyrics: list[list[str]]) -> dict:
+    """The song's edits, keyed to `lyrics`.
+
+    Edits are stored with the lyrics they were made against. When those
+    differ, each edited line is matched to its line in the new lyrics by
+    text and order; an edit whose line's words changed is set aside as stale
+    rather than applied to words it was not made for.
+    """
+    path = work / EDITS_FILE
+    if not path.exists():
+        return _empty(lyrics)
+    data = json.loads(path.read_text())
+    if data["lyrics"] != lyrics:
+        data = _remap(data, lyrics)
+        save(work, data)
+    return data
+
+
+def save(work: Path, data: dict) -> None:
+    path = work / EDITS_FILE
+    if not (data["lines"] or data["stale"] or data.get("grid") or data.get("breaks")):
+        path.unlink(missing_ok=True)
+        return
+    tmp = path.with_suffix(".tmp")
+    tmp.write_text(json.dumps(data))
+    tmp.replace(path)
+
+
+def _remap(data: dict, lyrics: list[list[str]]) -> dict:
+    old = [tuple(line) for line in data["lyrics"]]
+    new = [tuple(line) for line in lyrics]
+    moved = {}
+    for tag, i1, i2, j1, _ in difflib.SequenceMatcher(
+            a=old, b=new, autojunk=False).get_opcodes():
+        if tag == "equal":
+            moved.update({i1 + k: j1 + k for k in range(i2 - i1)})
+    lines, stale = {}, list(data["stale"])
+    for key, edit in data["lines"].items():
+        to = moved.get(int(key))
+        if to is None:
+            stale.append(edit)
+        else:
+            lines[str(to)] = {**edit, "line_index": to}
+    # a moved break goes with the line it comes before; with that line gone,
+    # there is nothing left for it to separate
+    breaks = {str(moved[int(k)]): t for k, t in data.get("breaks", {}).items()
+              if int(k) in moved}
+    return {"lyrics": lyrics, "lines": lines, "stale": stale, "grid": data.get("grid"),
+            "breaks": breaks}
+
+
+def validate_notes(notes: list[dict]) -> list[dict]:
+    """The notes of a line edit, checked and reduced to what is stored."""
+    clean = []
+    for n in notes:
+        try:
+            note = {"start": float(n["start"]), "duration": float(n["duration"]),
+                    "pitch": int(n["pitch"]), "text": str(n["text"]),
+                    "kind": str(n.get("kind", ":"))}
+        except (KeyError, TypeError, ValueError):
+            raise ValueError(f"malformed note {n!r}")
+        if note["start"] < 0 or note["duration"] <= 0:
+            raise ValueError(f"a note needs start >= 0 and duration > 0: {n!r}")
+        if note["kind"] not in KINDS:
+            raise ValueError(f"unknown note kind {note['kind']!r}")
+        if not note["text"].strip():
+            raise ValueError("a note needs text")
+        clean.append(note)
+    return sorted(clean, key=lambda n: n["start"])
+
+
+def set_line(data: dict, index: int, notes: list[dict]) -> None:
+    data["lines"][str(index)] = {
+        "line_index": index, "words": data["lyrics"][index],
+        "notes": validate_notes(notes), "saved_at": time.time()}
+
+
+def clear_line(data: dict, index: int) -> bool:
+    return data["lines"].pop(str(index), None) is not None
+
+
+def set_breaks(data: dict, changes: dict) -> None:
+    """Move line breaks, each keyed by the line it comes before, to a time in
+    seconds; None puts one back to where the notes alone would place it."""
+    breaks = dict(data.get("breaks", {}))
+    for key, t in changes.items():
+        try:
+            line = int(key)
+        except (TypeError, ValueError):
+            raise ValueError(f"a break is keyed by the line it comes before, not {key!r}")
+        if not 0 < line < len(data["lyrics"]):
+            raise ValueError(f"no line {line} for a break to come before")
+        if t is None:
+            breaks.pop(str(line), None)
+            continue
+        try:
+            t = float(t)
+        except (TypeError, ValueError):
+            raise ValueError(f"a break needs a time in seconds, not {t!r}")
+        if not (math.isfinite(t) and t >= 0):
+            raise ValueError(f"a break needs a time of 0 or more, not {t}")
+        breaks[str(line)] = t
+    data["breaks"] = breaks
+
+
+def set_grid(data: dict, bpm, gap_ms) -> None:
+    """Set the chart's BPM (UltraStar's, a quarter of a beat per beat) and GAP."""
+    try:
+        bpm, gap_ms = float(bpm), float(gap_ms)
+    except (TypeError, ValueError):
+        raise ValueError("bpm and gap_ms must be numbers")
+    if not (math.isfinite(bpm) and 0 < bpm <= 2000):
+        raise ValueError(f"bpm must be above 0 and at most 2000, not {bpm}")
+    if not (math.isfinite(gap_ms) and gap_ms >= 0):
+        raise ValueError(f"gap_ms must be 0 or more, not {gap_ms}")
+    data["grid"] = {"bpm": bpm, "gap_ms": gap_ms}
+
+
+def clear_grid(data: dict) -> bool:
+    had = bool(data.get("grid"))
+    data["grid"] = None
+    return had
+
+
+def merge(notes: list[dict], breaks: list[float], data: dict
+          ) -> tuple[list[dict], list[float]]:
+    """Generated notes and breaks with every edited line laid over them.
+
+    An edited line replaces the generated notes of that line, and the user's
+    timing wins: generated notes of earlier lines are cut back to end where it
+    starts, and those of later lines to start where it ends. Line breaks next
+    to an edited line move to the middle of the gap it leaves; a break moved
+    by hand stays where it was put, kept between the lines it separates.
+    """
+    edited = {int(k): e["notes"] for k, e in data["lines"].items()}
+    moved = {int(k): t for k, t in data.get("breaks", {}).items()}
+    if not edited and not moved:
+        return notes, breaks
+    spans = {li: (ns[0]["start"], ns[-1]["start"] + ns[-1]["duration"])
+             for li, ns in edited.items() if ns}
+    kept = []
+    for n in notes:
+        li = n["line_index"]
+        if li in edited:
+            continue
+        start, end = n["start"], n["start"] + n["duration"]
+        for eli, (a, b) in spans.items():
+            if li < eli:
+                end = min(end, a)
+            elif li > eli:
+                start = max(start, b)
+        if (start, end) == (n["start"], n["start"] + n["duration"]):
+            kept.append(n)
+        elif end - start >= MIN_NOTE_SEC:
+            kept.append({**n, "start": start, "duration": end - start})
+    for li, ns in edited.items():
+        kept += [{**n, "line_index": li, "low_confidence": False} for n in ns]
+    kept.sort(key=lambda n: (n["start"], n["line_index"]))
+
+    def line_after(t: float) -> int | None:
+        return next((n["line_index"] for n in notes if n["start"] >= t), None)
+
+    first = {}
+    last = {}
+    for n in kept:
+        first.setdefault(n["line_index"], n)
+        last[n["line_index"]] = n
+    order = sorted(first, key=lambda li: first[li]["start"])
+    out_breaks = []
+    for prev, nxt in zip(order, order[1:]):
+        end = last[prev]["start"] + last[prev]["duration"]
+        if nxt in moved:
+            # where it was put, but never inside either line's notes
+            out_breaks.append(min(max(moved[nxt], end), max(first[nxt]["start"], end)))
+            continue
+        if prev not in edited and nxt not in edited:
+            # the generated break between these two lines, untouched
+            gen = [t for t in breaks if line_after(t) == nxt]
+            if gen:
+                out_breaks.append(gen[0])
+                continue
+        out_breaks.append((end + first[nxt]["start"]) / 2)
+    return kept, out_breaks
+
+
+def finalize(work: Path, lyrics: list[list[str]]) -> dict:
+    """The song as it is to be charted: generated notes with the edits laid
+    over them, warnings brought up to date, written to notes_final.json."""
+    generated = json.loads((work / "notes_sec.json").read_text())
+    data = load(work, lyrics)
+    notes, breaks = merge(generated["notes"], generated["breaks"], data)
+    warnings = generated.get("warnings", [])
+    if data["lines"]:
+        # low-confidence warnings must describe the merged notes, so a line
+        # the user fixed stops being reported; the others are about lyrics
+        warnings = (low_confidence_warnings([TimedNote(**n) for n in notes])
+                    + [w for w in warnings if "low-confidence" not in w])
+    if data["stale"]:
+        n = len(data["stale"])
+        warnings.append(f"{n} edited line{' no longer matches' if n == 1 else 's no longer match'}"
+                        " the lyrics; set aside in the editor")
+    final = {"notes": notes, "breaks": breaks, "warnings": warnings,
+             "edited_lines": sorted(int(k) for k in data["lines"]),
+             "stale": data["stale"], "grid": data.get("grid"),
+             "moved_breaks": sorted(int(k) for k in data.get("breaks", {}))}
+    (work / FINAL_FILE).write_text(json.dumps(final))
+    return final

src/songtrace/grid.py

@@ -3,7 +3,11 @@ from pathlib import Path
 
 import numpy as np
 
-from .ultrastar import LineBreak, Note, UltraStarSong, format_bpm
+from .ultrastar import (LineBreak, Note, UltraStarSong, format_bpm, get_header,
+                        parse_bpm, parse_ultrastar, serialize_ultrastar)
+
+
+TEMPO_FILE = "tempo.json"
 
 
 def detect_bpm(instrumental_path: Path) -> float:
@@ -25,11 +29,20 @@ def scale_bpm(bpm: float) -> float:
 
 
 def to_ultrastar(notes: list[dict], breaks: list[float], file_bpm: float,
-                 headers: list[tuple[str, str]]) -> UltraStarSong:
+                 headers: list[tuple[str, str]],
+                 gap_ms: float | None = None) -> UltraStarSong:
+    """Snap notes to the beat grid. GAP defaults to the first note's start; a
+    GAP set later than that would put notes on negative beats, which players
+    reject, so it moves back by whole beats, keeping the grid where it was."""
     if not notes:
         raise ValueError("no notes to place on the beat grid")
-    gap_ms = round(notes[0]["start"] * 1000)
     spb = 60 / (4 * file_bpm)
+    first_ms = notes[0]["start"] * 1000
+    if gap_ms is None:
+        gap_ms = first_ms
+    elif gap_ms > first_ms:
+        gap_ms -= math.ceil((gap_ms - first_ms) / (spb * 1000)) * spb * 1000
+    gap_ms = max(0, round(gap_ms))
 
     def beat(t: float) -> int:
         return round((t - gap_ms / 1000) / spb)
@@ -49,10 +62,27 @@ def to_ultrastar(notes: list[dict], breaks: list[float], file_bpm: float,
         else:
             b = max(beat(t), cursor)
             length = max(1, beat(t + n["duration"]) - beat(t))
-            body.append(Note(kind=":", beat=b, length=length, pitch=n["pitch"],
-                             text=n["text"]))
+            body.append(Note(kind=n.get("kind", ":"), beat=b, length=length,
+                             pitch=n["pitch"], text=n["text"]))
             cursor = b + length
     out_headers = list(headers)
     out_headers.append(("BPM", format_bpm(file_bpm)))
     out_headers.append(("GAP", str(gap_ms)))
     return UltraStarSong(headers=out_headers, body=body)
+
+
+def rechart(txt_path: Path, notes: list[dict], breaks: list[float],
+            bpm: float | None = None, gap_ms: float | None = None) -> None:
+    """Replace a chart's notes, keeping its headers and, unless given new
+    ones, its BPM.
+
+    For an edit saved from the editor: the packaged chart's headers may differ
+    from the work copy's (a re-encoded #VIDEO, a dropped #COVER), so each
+    keeps its own.
+    """
+    song = parse_ultrastar(txt_path.read_text(encoding="utf-8"))
+    if bpm is None:
+        bpm = parse_bpm(get_header(song, "BPM"))
+    headers = [(k, v) for k, v in song.headers if k.upper() not in ("BPM", "GAP")]
+    txt_path.write_text(serialize_ultrastar(to_ultrastar(notes, breaks, bpm, headers, gap_ms)),
+                        encoding="utf-8")

src/songtrace/models.py

@@ -0,0 +1,47 @@
+"""Handing the GPU back between stages.
+
+The GPU this runs on is shared, and `songtrace serve` outlives every job it
+runs, so a stage that caches its weights holds VRAM until the process exits —
+including while a later stage is waiting on the Whisper server, which can be
+minutes of a GPU nothing is using. Two things have to be undone: the caches
+themselves, and PyTorch's allocator, which keeps freed blocks for reuse rather
+than returning them to the driver.
+
+A stage that caches a model registers how to drop it with @on_release, so this
+module needs to know nothing about the pipeline. Registration happens at import
+time, which run_pipeline has already done by the time it calls release().
+"""
+import gc
+import sys
+from typing import Callable
+
+_callbacks: list[Callable[[], None]] = []
+
+
+def on_release(fn: Callable[[], None]) -> Callable[[], None]:
+    """Register a callback that drops a cached model."""
+    _callbacks.append(fn)
+    return fn
+
+
+def release() -> int:
+    """Drop every cached model and return its VRAM to the driver.
+
+    Answers the bytes handed back, which is the only part of this a caller can
+    show someone. Safe whenever: a stage that never loaded anything has nothing
+    to drop, and the allocator is left alone unless this process actually
+    initialised CUDA.
+    """
+    for callback in _callbacks:
+        callback()
+    # weights reach the allocator's free list only once the last reference
+    # goes, and a module graph is cyclic enough to outlive refcounting
+    gc.collect()
+    torch = sys.modules.get("torch")
+    if torch is None or not torch.cuda.is_available():
+        return 0
+    if not torch.cuda.is_initialized():
+        return 0
+    before = torch.cuda.memory_reserved()
+    torch.cuda.empty_cache()
+    return max(before - torch.cuda.memory_reserved(), 0)

src/songtrace/notes.py

@@ -7,7 +7,17 @@ import pyphen
 from .languages import LANGUAGES
 
 CONF_MASK = 0.5          # pitch frames below this are unvoiced
-LOW_SCORE = 0.5          # word alignment score below this -> low_confidence
+# A word is low-confidence when it scores below this share of the song's
+# median alignment score: the scale differs a lot from song to song, so no
+# fixed cutoff holds across them.
+LOW_SCORE_OF_MEDIAN = 0.25
+# ...or when no one sings a word that fast, or it was stretched over more than
+# it can be holding.
+MIN_WORD_SEC = 0.08
+MAX_WORD_SEC = 3.0
+# Flagged notes closer than this share one warning, so the list reads as
+# places to look rather than one line per note.
+WARN_GAP_SEC = 2.0
 SPLIT_SEMITONES = 0.8
 MIN_SEG_SEC = 0.05
 MIN_NOTE_SEC = 0.05      # alignment may hand us zero-length words
@@ -24,6 +34,7 @@ class TimedNote:
     text: str             # display text incl. leading space / "~"
     low_confidence: bool
     line_index: int
+    kind: str = ":"       # UltraStar note type; generated notes are all normal
 
 
 def hz_to_midi_float(hz: float) -> float:
@@ -84,19 +95,12 @@ def build_notes(rows: list[dict], times, f0, conf, language: str | None,
                 ) -> tuple[list[TimedNote], list[float], list[str]]:
     notes: list[TimedNote] = []
     breaks: list[float] = []
-    prev_line, prev_end, last_seen_line = None, 0.0, None
+    floor = LOW_SCORE_OF_MEDIAN * float(np.median([r["score"] for r in rows])) if rows else 0.0
+    prev_line, prev_end = None, 0.0
     for row in rows:
-        # last_seen_line tracks every row (skipped or not) so a run of
-        # skipped rows can't trigger a duplicate break on the next row of
-        # the same still-unseen line; prev_line/prev_end only advance on
-        # rows that actually emit notes, so a skipped row can't corrupt
-        # line_initial or break timing for its own line's later words.
-        if last_seen_line is not None and row["line_index"] > last_seen_line:
+        if prev_line is not None and row["line_index"] > prev_line:
             breaks.append((prev_end + row["start"]) / 2)
-        last_seen_line = row["line_index"]
         line_initial = row["line_index"] != prev_line
-        if any(a <= row["start"] < b for a, b in missing_spans):
-            continue
         prev_line, prev_end = row["line_index"], row["end"]
         segs = segment_span(times, f0, conf, row["start"], row["end"])
         if not segs:
@@ -105,7 +109,8 @@ def build_notes(rows: list[dict], times, f0, conf, language: str | None,
                                _text(row["word"], 0, line_initial), True,
                                row["line_index"]))
             continue
-        low = row["score"] < LOW_SCORE
+        low = (row["score"] < floor
+               or not MIN_WORD_SEC <= row["end"] - row["start"] <= MAX_WORD_SEC)
         sylls = syllabify(row["word"], language)
         if len(segs) < len(sylls):
             segs = _subdivide(segs, len(sylls))
@@ -166,18 +171,25 @@ def _fmt(t: float) -> str:
     return f"{int(t // 60)}:{int(t % 60):02d}"
 
 
+def low_confidence_warnings(notes: list[TimedNote]) -> list[str]:
+    runs: list[list[TimedNote]] = []
+    for n in notes:
+        if not n.low_confidence:
+            continue
+        last = runs[-1][-1] if runs else None
+        if last is not None and n.start - (last.start + last.duration) < WARN_GAP_SEC:
+            runs[-1].append(n)
+        else:
+            runs.append([n])
+    return [
+        f"{len(run)} low-confidence note{'' if len(run) == 1 else 's'} "
+        f"near {_fmt(run[0].start)}–{_fmt(run[-1].start + run[-1].duration)}"
+        for run in runs]
+
+
 def _warnings(notes: list[TimedNote], dropped_lines=(), missing_spans=(),
              ref_lines=()) -> list[str]:
-    warnings, run = [], []
-    for n in list(notes) + [None]:
-        if n is not None and n.low_confidence:
-            run.append(n)
-        elif run:
-            first, last = run[0], run[-1]
-            warnings.append(
-                f"{len(run)} low-confidence note{'' if len(run) == 1 else 's'} "
-                f"near {_fmt(first.start)}–{_fmt(last.start + last.duration)}")
-            run = []
+    warnings = low_confidence_warnings(notes)
     for group in _consecutive_runs(dropped_lines):
         n = len(group)
         text = " ".join(ref_lines[group[0]]) if group[0] < len(ref_lines) else ""

src/songtrace/pipeline.py

@@ -3,6 +3,7 @@ from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Callable
 
+from . import models
 from .config import Config
 
 class PipelineError(Exception):
@@ -46,7 +47,11 @@ def song_slug(inp: SongInput) -> str:
     return name.replace("/", "").replace("\0", "")
 
 def read_warnings(work: Path) -> list[str]:
-    notes_file = work / "notes_sec.json"
+    # grid's copy accounts for the user's edits; notes' is all a song built
+    # before edits existed has
+    notes_file = work / "notes_final.json"
+    if not notes_file.exists():
+        notes_file = work / "notes_sec.json"
     if not notes_file.exists():
         return []
     return json.loads(notes_file.read_text()).get("warnings", [])
@@ -74,6 +79,14 @@ def run_pipeline(inp: SongInput, cfg: Config, log=print,
             log(f"[{stage.name}] cached, skipping")
             continue
         log(f"[{stage.name}] running")
-        stage.run(ctx)
+        # per stage rather than per job: each model is used by one stage, so
+        # holding it past that only keeps VRAM from whatever else wants it
+        try:
+            stage.run(ctx)
+        finally:
+            # logged only when it actually gave something back, so the line is
+            # evidence rather than noise on a box where this matters
+            if freed := models.release():
+                log(f"[{stage.name}] released {freed / 2**20:.0f} MiB of GPU memory")
     return PipelineResult(output_dir=cfg.output_dir / song_slug(inp),
                           warnings=read_warnings(work))

src/songtrace/rebuild.py

@@ -38,6 +38,17 @@ def plan(old: SongInput, new: SongInput) -> str | None:
     return min((FIELD_STAGE[f] for f in changed), key=STAGE_ORDER.index)
 
 
+def earliest(*stages: str | None) -> str | None:
+    """The earliest of the stages given, ignoring None ("nothing forced").
+
+    An operator's explicit choice is combined with plan()'s rather than
+    replacing it: the planner's stage is the latest that is still correct for
+    the edit, so a choice may only ever redo more.
+    """
+    named = [s for s in stages if s]
+    return min(named, key=STAGE_ORDER.index) if named else None
+
+
 def relocate_work(old: SongInput, new: SongInput, cfg: Config) -> bool:
     """Move the cached work dir when title/artist changed its slug.
 

src/songtrace/stages/acquire.py

@@ -2,14 +2,19 @@ import json
 import shutil
 from pathlib import Path
 
+from .. import ytdlp
+from ..config import Config
 from ..media import ffmpeg
 from ..pipeline import Ctx, PipelineError, Stage
 
 IMAGE_EXTENSIONS = {".jpg", ".jpeg", ".png", ".webp", ".avif", ".gif"}
+# yt-dlp's in-progress scratch files, which a failed attempt leaves behind.
+PARTIAL_EXTENSIONS = {".part", ".ytdl", ".temp"}
 
 
 def _classify_downloads(dest: Path) -> tuple[Path, Path | None]:
-    files = list(dest.glob("source_video.*"))
+    files = [p for p in dest.glob("source_video.*")
+             if p.suffix.lower() not in PARTIAL_EXTENSIONS]
     thumbs = [p for p in files if p.suffix.lower() in IMAGE_EXTENSIONS]
     videos = [p for p in files if p.suffix.lower() not in IMAGE_EXTENSIONS]
     if not videos:
@@ -18,17 +23,50 @@ def _classify_downloads(dest: Path) -> tuple[Path, Path | None]:
     return video, thumbs[0] if thumbs else None
 
 
-def download_youtube(url: str, dest: Path) -> tuple[Path, Path | None]:
-    import yt_dlp
-    opts = {
-        "outtmpl": str(dest / "source_video.%(ext)s"),
-        "format": "bestvideo*+bestaudio/best",
-        "writethumbnail": True,
-        "noplaylist": True,
-    }
-    with yt_dlp.YoutubeDL(opts) as ydl:
-        ydl.extract_info(url, download=True)
-    return _classify_downloads(dest)
+def _ydl_args(cfg: Config, dest: Path, client: str, url: str) -> list[str]:
+    args = [
+        "--output", str(dest / "source_video.%(ext)s"),
+        "--format", "bestvideo*+bestaudio/best",
+        "--write-thumbnail", "--no-playlist", "--no-progress",
+        "--retries", "10", "--fragment-retries", "10",
+        "--extractor-retries", "5",
+    ]
+    if client != "default":
+        args += ["--extractor-args", f"youtube:player_client={client}"]
+    if cfg.ytdlp_pot_provider_url:
+        args += ["--extractor-args",
+                 f"youtubepot-bgutilhttp:base_url={cfg.ytdlp_pot_provider_url}"]
+    if cfg.ytdlp_cookies:
+        args += ["--cookies", str(cfg.ytdlp_cookies)]
+    if cfg.ytdlp_impersonate:
+        args += ["--impersonate", cfg.ytdlp_impersonate]
+    return [*args, "--", url]
+
+
+def download_youtube(url: str, dest: Path, cfg: Config,
+                     log=print) -> tuple[Path, Path | None]:
+    clients = list(cfg.ytdlp_clients) or ["default"]
+    tried: list[str] = []
+    last: Exception | None = None
+    # If every copy fails, look for a release newer than the daily check found.
+    for refresh in (False, True):
+        for ydl in ytdlp.candidates(cfg, log, refresh):
+            if ydl.version in tried:
+                continue
+            tried.append(ydl.version)
+            for client in clients:
+                try:
+                    ydl.run(_ydl_args(cfg, dest, client, url), log)
+                    return _classify_downloads(dest)
+                except PipelineError as e:
+                    last = e
+                    log(f"yt-dlp {ydl.version} player_client={client} "
+                        f"failed: {e}")
+    raise PipelineError(
+        f"yt-dlp {', '.join(tried)} could not download {url} after trying "
+        f"player_client={', '.join(clients)}. Last error: {last}. "
+        "See the yt-dlp options in config.toml (cookies, impersonation, "
+        "PO token provider).")
 
 
 def _run(ctx: Ctx) -> None:
@@ -36,7 +74,8 @@ def _run(ctx: Ctx) -> None:
         raise PipelineError("provide exactly one of youtube_url / video_path")
     thumb = None
     if ctx.inp.youtube_url:
-        video, thumb = download_youtube(ctx.inp.youtube_url, ctx.work)
+        video, thumb = download_youtube(ctx.inp.youtube_url, ctx.work,
+                                       ctx.cfg, ctx.log)
     else:
         video = ctx.work / f"source_video{ctx.inp.video_path.suffix}"
         shutil.copyfile(ctx.inp.video_path, video)

src/songtrace/stages/align.py

@@ -1,12 +1,27 @@
 import json
 from pathlib import Path
 
+import numpy as np
+import soundfile as sf
+
 from ..lyrics import alignment_token, normalize_lyrics
+from ..models import on_release
 from ..pipeline import Ctx, PipelineError, Stage
-from .transcribe import classify_lyrics_match, load_transcript, lyrics_similarity, vocal_sections
+from ..whisper_client import TranscriptSegment
+from .transcribe import (classify_lyrics_match, load_transcript, lyrics_similarity,
+                         recovered_spans, vocal_sections)
 
 SIMILARITY_THRESHOLD = 0.4
+# MMS_FA's wildcard token: any audio the transcript does not cover
+STAR = "*"
+# Singing is audio within this much of the stem's loud level; separation
+# bleed sits far below it.
+SINGING_BELOW_LOUD_DB = 25.0
+# Shorter stretches are breaths, ad-libs or Whisper's loose segment edges.
+MIN_UNHEARD_SEC = 3.0
 
+# a stage aligns section by section, so the model is cached across the calls
+# within one run and dropped at the end of it
 _model_cache = {}
 
 
@@ -17,6 +32,11 @@ def _get_model(device: str):
     return _model_cache[device]
 
 
+@on_release
+def unload_model() -> None:
+    _model_cache.clear()
+
+
 def force_align_section(vocals_path: Path, start: float, end: float,
                         tokens: list[str], device: str) -> list[tuple[float, float, float]]:
     import torch
@@ -32,7 +52,7 @@ def force_align_section(vocals_path: Path, start: float, end: float,
         waveform[:, lo:hi], sr, bundle.sample_rate)
     # MMS_FA only models a-z and apostrophe; anything else becomes the star token.
     vocab = bundle.get_dict()
-    tokens = ["".join(c if c in vocab else "*" for c in t) for t in tokens]
+    tokens = ["".join(c if c in vocab else STAR for c in t) for t in tokens]
     with torch.inference_mode():
         emission, _ = _get_model(device)(waveform.to(device))
         spans = bundle.get_aligner()(emission[0], bundle.get_tokenizer()(tokens))
@@ -42,6 +62,39 @@ def force_align_section(vocals_path: Path, start: float, end: float,
              sum(t.score for t in s) / len(s)) for s in spans]
 
 
+def untranscribed_singing(vocals_path: Path, segments,
+                          frame: float = 0.05) -> list[tuple[float, float]]:
+    """Stretches of the vocal stem with singing in them but no transcript."""
+    data, sr = sf.read(str(vocals_path), dtype="float32", always_2d=True)
+    hop = int(sr * frame)
+    n = len(data) // hop
+    if n == 0:
+        return []
+    rms = np.sqrt((data[:n * hop].mean(1).reshape(n, hop) ** 2).mean(1))
+    db = 20 * np.log10(rms + 1e-10)
+    sung = db >= np.quantile(db, 0.9) - SINGING_BELOW_LOUD_DB
+    times = np.arange(n) * frame
+    for s in segments:
+        sung[(times >= min(s.start, s.end)) & (times < max(s.start, s.end))] = False
+    spans, start = [], None
+    for t, on in zip(times, sung):
+        if on and start is None:
+            start = float(t)
+        elif not on and start is not None:
+            spans.append((start, float(t)))
+            start = None
+    if start is not None:
+        spans.append((start, float(times[-1] + frame)))
+    # a breath or a quiet syllable must not split one unsung passage in two
+    merged: list[list[float]] = []
+    for a, b in spans:
+        if merged and a - merged[-1][1] < 1.0:
+            merged[-1][1] = b
+        else:
+            merged.append([a, b])
+    return [(a, b) for a, b in merged if b - a >= MIN_UNHEARD_SEC]
+
+
 def _assign_lines_to_sections(line_indices: list[int], sections) -> list[list[int]]:
     """Split matched lyric line indices across vocal sections proportionally to section duration."""
     total = sum(b - a for a, b in sections) or 1.0
@@ -84,9 +137,20 @@ def _enforce_monotonic(rows: list[dict]) -> None:
 def _align_section(vocals: Path, sec: tuple[float, float], words: list[tuple[str, int]],
                    language: str | None, device: str) -> list[dict]:
     tokens = [alignment_token(w, language) for w, _ in words]
-    alignable = [t for t in tokens if t]
-    aligned = iter(force_align_section(vocals, sec[0], sec[1], alignable, device)
-                   if alignable else [])
+    # A star before, between and after lines lets speech, laughter or an
+    # ad-lib there go unexplained rather than claim the next line's letters.
+    seq, prev_line = [], None
+    for (_, line_index), token in zip(words, tokens):
+        if not token:
+            continue
+        if line_index != prev_line:
+            seq.append(STAR)
+            prev_line = line_index
+        seq.append(token)
+    if seq:
+        seq.append(STAR)
+    spans = force_align_section(vocals, sec[0], sec[1], seq, device) if seq else []
+    aligned = iter(span for span, token in zip(spans, seq) if token != STAR)
     rows, blank = [], (None, None, 0.0)
     for (word, line_index), token in zip(words, tokens):
         start, end, score = next(aligned, blank) if token else blank
@@ -104,11 +168,18 @@ def _run(ctx: Ctx) -> None:
         raise PipelineError(
             f"lyrics don't match audio (similarity {sim:.2f}) — "
             "wrong lyrics or wrong recording?")
-    # normalised so an inverted span can never collapse a section onto one instant
-    sections = [(min(a, b), max(a, b)) for a, b in vocal_sections(segments)]
-    dropped_lines, missing_spans = classify_lyrics_match(segments, ref)
-    matched = [i for i in range(len(ref.lines)) if i not in set(dropped_lines)]
     vocals = ctx.work / "vocals.wav"
+    unheard = untranscribed_singing(vocals, segments)
+    dropped_lines, missing_spans = classify_lyrics_match(segments, ref,
+                                                         unheard=unheard)
+    # lines Whisper missed are aligned against the singing it had no text for;
+    # only that singing, so an untranscribed ad-lib cannot draw lines into it
+    recovered = [TranscriptSegment(a, b, "")
+                 for a, b in recovered_spans(segments, ref, unheard)]
+    # normalised so an inverted span can never collapse a section onto one instant
+    sections = [(min(a, b), max(a, b))
+                for a, b in vocal_sections(segments + recovered)]
+    matched = [i for i in range(len(ref.lines)) if i not in set(dropped_lines)]
     rows = []
     for sec, line_idxs in zip(sections, _assign_lines_to_sections(matched, sections)):
         words = [(w, li) for li in line_idxs for w in ref.lines[li]]

src/songtrace/stages/grid.py

@@ -1,13 +1,16 @@
 import json
 from pathlib import Path
 
-from .. import grid
+from .. import edits, grid
+from ..lyrics import normalize_lyrics
 from ..pipeline import Ctx, PipelineError, Stage, song_slug
 from ..ultrastar import serialize_ultrastar
 
 
 def _run(ctx: Ctx) -> None:
-    data = json.loads((ctx.work / "notes_sec.json").read_text())
+    data = edits.finalize(ctx.work, normalize_lyrics(ctx.inp.lyrics_text).lines)
+    if data["edited_lines"]:
+        ctx.log(f"[grid] kept {len(data['edited_lines'])} edited line(s)")
     meta = json.loads((ctx.work / "meta.json").read_text())
     if ctx.inp.bpm_override is not None:
         bpm = ctx.inp.bpm_override
@@ -16,6 +19,12 @@ def _run(ctx: Ctx) -> None:
             bpm = grid.scale_bpm(grid.detect_bpm(ctx.work / "instrumental.wav"))
         except ValueError:
             raise PipelineError("could not detect a usable tempo - is the audio silent?")
+    # the pipeline's own tempo, which RESET in the editor returns to
+    (ctx.work / grid.TEMPO_FILE).write_text(json.dumps({"bpm": bpm}))
+    gap_ms = None
+    if data["grid"]:
+        bpm, gap_ms = data["grid"]["bpm"], data["grid"]["gap_ms"]
+        ctx.log("[grid] using the BPM and GAP set in the editor")
     slug = song_slug(ctx.inp)
     video_ext = Path(meta["video_file"]).suffix
     headers = [("TITLE", ctx.inp.title), ("ARTIST", ctx.inp.artist)]
@@ -28,7 +37,7 @@ def _run(ctx: Ctx) -> None:
     headers += [("CREATOR", ctx.cfg.creator), ("MP3", f"{slug}.mp3"),
                 ("COVER", f"{slug}.jpg"), ("VIDEO", f"{slug}{video_ext}")]
     try:
-        song = grid.to_ultrastar(data["notes"], data["breaks"], bpm, headers)
+        song = grid.to_ultrastar(data["notes"], data["breaks"], bpm, headers, gap_ms)
     except ValueError:
         raise PipelineError("no notes were generated - the lyrics may not match the audio")
     (ctx.work / "song.txt").write_text(serialize_ultrastar(song), encoding="utf-8")
@@ -36,5 +45,6 @@ def _run(ctx: Ctx) -> None:
 
 def grid_stage() -> Stage:
     return Stage(name="grid",
-                 outputs=lambda ctx: [ctx.work / "song.txt"],
+                 outputs=lambda ctx: [ctx.work / "song.txt",
+                                      ctx.work / edits.FINAL_FILE],
                  run=_run)

src/songtrace/stages/package.py

@@ -51,11 +51,15 @@ def _run(ctx: Ctx) -> None:
     meta = json.loads((ctx.work / "meta.json").read_text())
     src_video = ctx.work / meta["video_file"]
     fmt, codec = ffprobe_codec(src_video)
+    # The video is background only: the song's audio is #MP3, and the two are
+    # the same recording. A player that does not mute the video plays both at
+    # once, which is heard as an echo, so the audio track is dropped here.
     if (fmt, codec) in GOOD_VIDEO:
-        shutil.copyfile(src_video, out / f"{slug}{src_video.suffix}")
+        ffmpeg("-i", str(src_video), "-c", "copy", "-an",
+               str(out / f"{slug}{src_video.suffix}"))
     else:
         ffmpeg("-i", str(src_video), "-c:v", "libx264", "-crf", "20",
-               "-preset", "medium", "-c:a", "aac", str(out / f"{slug}.mp4"))
+               "-preset", "medium", "-an", str(out / f"{slug}.mp4"))
         _set_header(txt, "VIDEO", f"{slug}.mp4")
     cover_src = ctx.inp.cover_path
     if cover_src is None and meta.get("thumbnail"):

src/songtrace/stages/pitch.py

@@ -1,9 +1,32 @@
+import sys
 from pathlib import Path
 
 import numpy as np
 
+from ..models import on_release
 from ..pipeline import Ctx, Stage
 
+# Separated vocal stems keep faint bleed that crepe still finds a pitch in, so
+# frames this far below the song's loud vocal level count as silence. Relative
+# rather than absolute, so it holds however loud the song was mastered.
+SILENCE_BELOW_LOUD_DB = 25.0
+
+
+@on_release
+def unload_model() -> None:
+    """torchcrepe caches its model as attributes on its own infer function."""
+    torchcrepe = sys.modules.get("torchcrepe")
+    if torchcrepe is None:
+        return
+    for attr in ("model", "capacity"):
+        if hasattr(torchcrepe.infer, attr):
+            delattr(torchcrepe.infer, attr)
+
+
+def mute_silence(conf: np.ndarray, loudness: np.ndarray) -> None:
+    """Zero the confidence of frames quiet enough to be bleed, in place."""
+    conf[loudness < np.quantile(loudness, 0.9) - SILENCE_BELOW_LOUD_DB] = 0.0
+
 
 def track_pitch(vocals_path: Path, model: str, device: str):
     import torchaudio
@@ -20,6 +43,7 @@ def track_pitch(vocals_path: Path, model: str, device: str):
         return_periodicity=True, batch_size=512)
     f0 = f0[0].cpu().numpy()
     conf = periodicity[0].cpu().numpy()
+    mute_silence(conf, torchcrepe.loudness.a_weighted(waveform, 16000, 160)[0].cpu().numpy())
     times = np.arange(len(f0)) * 0.01
     return times, f0, conf
 

src/songtrace/stages/transcribe.py

@@ -39,29 +39,74 @@ def lyrics_similarity(segments, ref: RefLyrics) -> float:
     return matcher.ratio()
 
 
-def classify_lyrics_match(segments, ref: RefLyrics, pad: float = 1.0
+def _line_times(segments, matcher, seg_of, line_of) -> dict[int, tuple[float, float]]:
+    """For each reference line that was heard, the start of the first and the
+    end of the last transcript segment its words were heard in. Words in a
+    'replace' block are paired with heard words proportionally."""
+    times: dict[int, tuple[float, float]] = {}
+    for tag, ai1, ai2, bj1, bj2 in matcher.get_opcodes():
+        if tag not in ("equal", "replace"):
+            continue
+        for j in range(bj1, bj2):
+            seg = segments[seg_of[ai1 + (j - bj1) * (ai2 - ai1) // (bj2 - bj1)]]
+            a, b = times.get(line_of[j], (seg.start, seg.end))
+            times[line_of[j]] = (min(a, seg.start), max(b, seg.end))
+    return times
+
+
+def _unheard_runs(segments, ref: RefLyrics, unheard
+                  ) -> tuple[list[list[int]], list[list[tuple[float, float]]]]:
+    """Runs of reference lines with nothing heard for them, each with the
+    untranscribed singing between the heard lines either side of it."""
+    matcher, seg_of, line_of = match_lyrics(segments, ref)
+    times = _line_times(segments, matcher, seg_of, line_of)
+    alignable = set(line_of)
+    runs, spans, run, prev_end = [], [], [], 0.0
+
+    def close(next_start: float) -> None:
+        if run:
+            runs.append(list(run))
+            spans.append([(max(a, prev_end), min(b, next_start)) for a, b in unheard
+                          if a < next_start and b > prev_end])
+            run.clear()
+
+    for li in range(len(ref.lines)):
+        if li in times:
+            close(times[li][0])
+            prev_end = times[li][1]
+        elif li in alignable:
+            run.append(li)
+    close(float("inf"))
+    return runs, spans
+
+
+def recovered_spans(segments, ref: RefLyrics, unheard) -> list[tuple[float, float]]:
+    """The untranscribed singing that stands in for lines Whisper missed, so
+    alignment can place them there."""
+    return _merge_spans([sp for spans in _unheard_runs(segments, ref, unheard)[1]
+                         for sp in spans])
+
+
+def classify_lyrics_match(segments, ref: RefLyrics, pad: float = 1.0, unheard=()
                           ) -> tuple[list[int], list[tuple[float, float]]]:
     """Split reference lines into matched vs. dropped, and flag sung spans no
     reference line explains.
 
     dropped_lines: reference line indices covered only by 'insert' opcodes
-    (present in the lyrics, never heard). missing_spans: the padded, merged
-    bounds of the heard segments behind 'delete' opcodes (heard, but matching
-    no reference word) — scoped tightly to the unmatched audio itself, not
-    the whole vocal section it falls in, so matched lines sharing a section
-    with an ad-lib keep their notes.
-    """
-    matcher, seg_of, line_of = match_lyrics(segments, ref)
-    covered = [False] * len(line_of)
-    for tag, _, _, bj1, bj2 in matcher.get_opcodes():
-        if tag in ("equal", "replace"):
-            for j in range(bj1, bj2):
-                covered[j] = True
-    by_line = {}
-    for j, li in enumerate(line_of):
-        by_line.setdefault(li, []).append(covered[j])
-    dropped_lines = sorted(li for li, cov in by_line.items() if not any(cov))
+    (present in the lyrics, never heard), unless `unheard` (sung spans the
+    transcript has no text for) has singing between the heard lines either
+    side of them: then Whisper missed them, not the singer.
 
+    missing_spans: the padded, merged bounds of the heard segments behind
+    'delete' opcodes (heard, but matching no reference word). A segment can
+    also hold matched lines, so a span marks where to look, not words to
+    discard.
+    """
+    runs, run_spans = _unheard_runs(segments, ref, unheard)
+    dropped_lines = sorted(li for run, sp in zip(runs, run_spans) if not sp
+                           for li in run)
+
+    matcher, seg_of, _ = match_lyrics(segments, ref)
     spans = []
     for tag, ai1, ai2, _, _ in matcher.get_opcodes():
         if tag != "delete":

src/songtrace/static/edit-model.js

@@ -0,0 +1,158 @@
+// Editing one line's notes. Every operation returns a new array and leaves
+// its input alone, so undo is just keeping the old one. Times are seconds,
+// snapped to the chart's beat grid as the chart itself will be. Notes carry
+// a client-side `id` so a selection survives reordering; it is never saved.
+
+const MIN_BEATS = 1;
+
+const spbOf = (grid) => 60 / (4 * grid.bpm);
+const gapOf = (grid) => grid.gap_ms / 1000;
+const byStart = (a, b) => a.start - b.start;
+
+let nextId = 1;
+export const newId = () => nextId++;
+
+export function beatOf(t, grid) {
+  return (t - gapOf(grid)) / spbOf(grid);
+}
+
+export function timeOf(beat, grid) {
+  return gapOf(grid) + beat * spbOf(grid);
+}
+
+export function snap(t, grid) {
+  return timeOf(Math.round(beatOf(t, grid)), grid);
+}
+
+// A note as the chart will have it: start on a beat, at least one beat long.
+function onGrid(n, grid) {
+  const start = snap(n.start, grid);
+  const beats = Math.max(MIN_BEATS, Math.round((n.end - n.start) / spbOf(grid)));
+  return { ...n, start, end: start + beats * spbOf(grid) };
+}
+
+export function withIds(notes) {
+  return notes.map(n => ({ ...n, id: n.id ?? newId() })).sort(byStart);
+}
+
+export function move(notes, ids, beats, semitones, grid) {
+  const spb = spbOf(grid);
+  return notes.map(n => {
+    if (!ids.has(n.id)) return n;
+    const g = onGrid(n, grid);
+    const shift = Math.max(beats * spb, -g.start);   // never before the song starts
+    return { ...g, start: g.start + shift, end: g.end + shift, pitch: n.pitch + semitones };
+  }).sort(byStart);
+}
+
+// Drag one edge of a note to time t; the other edge stays put.
+export function resize(notes, id, edge, t, grid) {
+  const spb = spbOf(grid);
+  return notes.map(n => {
+    if (n.id !== id) return n;
+    const g = onGrid(n, grid);
+    if (edge === "end") return { ...g, end: Math.max(snap(t, grid), g.start + spb) };
+    return { ...g, start: Math.max(0, Math.min(snap(t, grid), g.end - spb)) };
+  }).sort(byStart);
+}
+
+// Longer or shorter by whole beats, keeping the start.
+export function stretch(notes, ids, beats, grid) {
+  const spb = spbOf(grid);
+  return notes.map(n => {
+    if (!ids.has(n.id)) return n;
+    const g = onGrid(n, grid);
+    return { ...g, end: Math.max(g.end + beats * spb, g.start + spb) };
+  });
+}
+
+// In two at the beat nearest the middle; the second half holds the syllable.
+export function split(notes, id, grid) {
+  const i = notes.findIndex(n => n.id === id);
+  if (i < 0) return { notes, ids: [] };
+  const g = onGrid(notes[i], grid);
+  const beats = Math.round((g.end - g.start) / spbOf(grid));
+  if (beats < 2) return { notes, ids: [] };
+  const mid = g.start + Math.floor(beats / 2) * spbOf(grid);
+  const a = { ...g, end: mid };
+  const b = { ...g, id: newId(), start: mid, text: "~", low_confidence: false };
+  return { notes: [...notes.slice(0, i), a, b, ...notes.slice(i + 1)], ids: [a.id, b.id] };
+}
+
+// Into one with the note after it; a held "~" adds no text.
+export function merge(notes, id) {
+  const i = notes.findIndex(n => n.id === id);
+  if (i < 0 || i + 1 >= notes.length) return notes;
+  const a = notes[i];
+  const b = notes[i + 1];
+  const text = b.text.trim() === "~" ? a.text : a.text + b.text;
+  return [...notes.slice(0, i), { ...a, end: b.end, text }, ...notes.slice(i + 2)];
+}
+
+export function remove(notes, ids) {
+  return notes.filter(n => !ids.has(n.id));
+}
+
+export function insert(notes, t, pitch, grid) {
+  const start = Math.max(0, snap(t, grid));
+  const note = { id: newId(), start, end: start + 2 * spbOf(grid), pitch,
+                 text: "~", kind: ":", low_confidence: false };
+  return { notes: [...notes, note].sort(byStart), id: note.id };
+}
+
+// Applying a kind every selected note already has turns it back to normal.
+export function setKind(notes, ids, kind) {
+  const chosen = notes.filter(n => ids.has(n.id));
+  const to = chosen.length && chosen.every(n => n.kind === kind) ? ":" : kind;
+  return notes.map(n => (ids.has(n.id) ? { ...n, kind: to } : n));
+}
+
+// A syllable that starts a word keeps the space before it that marks it so.
+export function setText(notes, id, text) {
+  const clean = text.trim();
+  if (!clean) return notes;
+  return notes.map(n => {
+    if (n.id !== id) return n;
+    const lead = n.text.startsWith(" ") && !text.startsWith(" ") ? " " : "";
+    return { ...n, text: lead + (text.startsWith(" ") ? " " + clean : clean) };
+  });
+}
+
+// What the server stores for a line.
+export function toSaved(notes) {
+  return notes.map(n => ({ start: n.start, duration: n.end - n.start, pitch: n.pitch,
+                           text: n.text, kind: n.kind ?? ":" }));
+}
+
+export function history(initial) {
+  const past = [];
+  const future = [];
+  let present = initial;
+  return {
+    get present() { return present; },
+    get canUndo() { return past.length > 0; },
+    get canRedo() { return future.length > 0; },
+    push(next) {
+      if (next === present) return;
+      past.push(present);
+      future.length = 0;
+      present = next;
+    },
+    undo() {
+      if (past.length) { future.push(present); present = past.pop(); }
+      return present;
+    },
+    redo() {
+      if (future.length) { past.push(present); present = future.pop(); }
+      return present;
+    },
+  };
+}
+
+// Where a dragged line break lands: on a beat, but kept between the end of
+// the line before it and the start of the line it introduces.
+export function placeBreak(t, lo, hi, grid) {
+  const snapped = snap(t, grid);
+  if (hi < lo) return lo;
+  return Math.min(Math.max(snapped, lo), hi);
+}

src/songtrace/static/index.html

@@ -111,6 +111,62 @@ body {
 }
 
 #sidebar .eyebrow, #jobs .empty-note { padding: 0 18px; }
+#create-song { display: block; width: calc(100% - 36px); margin: 0 18px 20px; padding: 9px 12px; }
+
+#rebuild-all { display: block; margin: -8px 18px 20px; }
+#rebuild-all-note { margin: -12px 18px 20px; }
+
+#rebuild-all-dialog {
+  width: min(480px, calc(100vw - 32px));
+  padding: 26px 28px;
+  color: var(--text);
+  background: var(--panel);
+  border: 1px solid var(--border);
+}
+#rebuild-all-dialog::backdrop { background: rgb(10 10 15 / 0.75); }
+#rebuild-all-dialog h2 {
+  margin: 0 0 14px;
+  font-family: var(--font-display);
+  font-weight: 700;
+  font-size: 0.8rem;
+  letter-spacing: 0.22em;
+  color: var(--text-muted);
+}
+#rebuild-all-form { display: grid; gap: 16px; }
+#rebuild-all-form p { margin: 0; font-size: 0.88rem; line-height: 1.5; }
+#rebuild-all-count { color: var(--warn); }
+#rebuild-all-songs { margin: 0; padding: 0; border: 0; min-width: 0; }
+#rebuild-all-songs legend {
+  margin-bottom: 6px;
+  padding: 0;
+  font-family: var(--font-display);
+  font-weight: 600;
+  font-size: 0.68rem;
+  letter-spacing: 0.14em;
+  text-transform: uppercase;
+  color: var(--text-muted);
+}
+#rebuild-all-list {
+  max-height: 40vh;
+  overflow-y: auto;
+  border-top: 1px solid var(--border);
+  border-bottom: 1px solid var(--border);
+}
+.rebuild-all-row {
+  display: grid;
+  grid-template-columns: auto 1fr;
+  gap: 1px 10px;
+  align-items: baseline;
+  padding: 7px 4px;
+  font-size: 0.88rem;
+  cursor: pointer;
+}
+.rebuild-all-row input { accent-color: var(--purple); }
+.rebuild-all-row:has(input:disabled) { cursor: default; color: var(--text-muted); }
+.rebuild-all-row .meta { grid-column: 2; font-size: 0.76rem; color: var(--text-muted); }
+.rebuild-all-every { padding-top: 0; color: var(--text-muted); }
+#rebuild-all-error { min-height: 1.2em; color: var(--fail); }
+#rebuild-all-error:empty { display: none; }
 
 #jobs { display: flex; flex-direction: column; gap: 1px; margin-top: 8px; }
 
@@ -199,6 +255,8 @@ body {
 .song-form-lyrics textarea { height: 100%; flex: 1 1 auto; }
 .pair { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; }
 .field { display: flex; flex-direction: column; gap: 6px; }
+/* [hidden] is only display:none, which the rule above would otherwise win */
+.field[hidden], .keep-note[hidden] { display: none; }
 .field > span {
   font-family: var(--font-display);
   font-weight: 600;
@@ -307,6 +365,7 @@ button { cursor: pointer; }
   transition: background 120ms ease;
 }
 .primary:hover { background: #BE7BF9; }
+.primary:disabled { background: var(--control); color: var(--text-muted); cursor: not-allowed; }
 
 #form-error { margin: 12px 0 0; min-height: 1.2em; font-size: 0.85rem; color: var(--fail); }
 
@@ -319,8 +378,187 @@ button { cursor: pointer; }
 }
 #review h3 span { color: var(--text-muted); font-weight: 400; }
 
+/* sticks to the top of #main so the video stays in frame as the lyrics scroll */
+#player { position: sticky; top: 0; z-index: 2; margin: 0 0 14px; padding: 6px 0 10px; background: var(--bg); }
+#player-video {
+  display: block;
+  width: 100%;
+  max-height: 30vh;
+  background: #000;
+  border: 1px solid var(--border);
+  border-radius: 2px;
+}
+#player-video[hidden] { display: none; }
+/* the native transport renders light otherwise, against everything around it */
+#player-media { display: block; width: 100%; margin-top: 8px; color-scheme: dark; }
+
+#sheet { margin: 14px 0; padding: 12px 14px 10px; background: var(--panel); border: 1px solid var(--border); }
+#sheet[hidden] { display: none; }
+.sheet-nav { display: flex; align-items: center; gap: 12px; margin-bottom: 12px; }
+.sheet-title {
+  min-width: 9em;
+  text-align: center;
+  font-family: var(--font-display);
+  font-weight: 700;
+  font-size: 0.72rem;
+  letter-spacing: 0.18em;
+  color: var(--text-muted);
+}
+.sheet-nav .action:disabled { opacity: 0.35; cursor: default; }
+.sheet-badges { display: flex; gap: 8px; margin-left: auto; }
+.sheet-badge {
+  padding: 2px 8px;
+  font-family: var(--font-display);
+  font-weight: 600;
+  font-size: 0.66rem;
+  letter-spacing: 0.1em;
+  text-transform: uppercase;
+  border: 1px solid currentColor;
+  border-radius: 2px;
+}
+.sheet-badge-edited { color: var(--aqua); }
+.sheet-badge-low { color: var(--fail); }
+.sheet-grid {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 8px 10px;
+  margin-bottom: 12px;
+  padding: 8px 10px;
+  border: 1px solid var(--border);
+}
+.sheet-grid[hidden] { display: none; }
+.sheet-grid-head {
+  font-family: var(--font-display);
+  font-weight: 700;
+  font-size: 0.66rem;
+  letter-spacing: 0.16em;
+  color: var(--aqua);
+}
+.sheet-grid-field {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  margin-left: 6px;
+  font-family: var(--font-display);
+  font-weight: 600;
+  font-size: 0.66rem;
+  letter-spacing: 0.1em;
+  color: var(--text-muted);
+}
+.sheet-grid-field input { width: 6.5em; padding: 3px 2px; font: 0.85rem var(--font-mono); }
+.sheet-grid .action:disabled { opacity: 0.35; cursor: default; }
+.sheet-grid .sheet-save:not(:disabled) { color: var(--bg); background: var(--purple); border-color: var(--purple); }
+.sheet-grid-source { flex: 1; min-width: 7em; font-size: 0.76rem; text-align: right; color: var(--text-muted); }
+.sheet-grid-pending { color: var(--warn); }
+.sheet-tools { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 14px; margin-bottom: 12px; }
+.sheet-tool-group { display: flex; gap: 6px; }
+.sheet-tools .action:disabled { opacity: 0.35; cursor: default; }
+.sheet-tools .sheet-save:not(:disabled) { color: var(--bg); background: var(--purple); border-color: var(--purple); }
+.sheet-status { flex: 1; min-width: 6em; font-size: 0.78rem; color: var(--text-muted); text-align: right; }
+.sheet-status-error { color: var(--fail); }
+.sheet-badge-dirty { color: var(--warn); }
+.sheet-plot { position: relative; cursor: crosshair; touch-action: none; }
+.sheet-plot:focus-visible { outline: 2px solid var(--aqua); outline-offset: 2px; }
+.sheet-note-selected { stroke: var(--text); stroke-width: 2; stroke-dasharray: none; }
+.sheet-syllable-selected { color: var(--aqua); }
+.sheet-text-input {
+  position: absolute;
+  top: -2px;
+  width: 7em;
+  padding: 1px 4px;
+  font-size: 0.8rem;
+  background: var(--panel-raised);
+  border: 1px solid var(--aqua);
+}
+.sheet-stale { margin-bottom: 12px; padding: 8px 10px; font-size: 0.82rem; border: 1px solid var(--warn); }
+.sheet-stale[hidden] { display: none; }
+.sheet-stale-head { color: var(--warn); margin-bottom: 6px; }
+.sheet-stale-row { display: flex; align-items: center; gap: 10px; margin-top: 4px; }
+.sheet-stale-text { flex: 1; color: var(--text-muted); }
+.sheet-nav > .action[aria-expanded] { margin-left: 4px; }
+.sheet-keys {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
+  gap: 14px 22px;
+  margin-bottom: 14px;
+  padding: 12px 14px;
+  background: var(--panel-raised);
+  border: 1px solid var(--border);
+}
+.sheet-keys[hidden] { display: none; }
+.sheet-keys-head {
+  margin-bottom: 6px;
+  font-family: var(--font-display);
+  font-weight: 700;
+  font-size: 0.66rem;
+  letter-spacing: 0.16em;
+  text-transform: uppercase;
+  color: var(--aqua);
+}
+.sheet-keys dl { display: grid; grid-template-columns: auto 1fr; gap: 4px 10px; margin: 0; font-size: 0.78rem; }
+.sheet-keys dt { white-space: nowrap; color: var(--text-muted); }
+.sheet-keys dd { margin: 0; color: var(--text); }
+.sheet-keys kbd {
+  display: inline-block;
+  min-width: 1.4em;
+  padding: 0 5px;
+  font: 0.72rem var(--font-mono);
+  text-align: center;
+  color: var(--text);
+  background: var(--panel);
+  border: 1px solid var(--control);
+  border-bottom-width: 2px;
+  border-radius: 3px;
+}
+.sheet-help[hidden] { display: none; }
+.sheet-help { margin-top: 10px; font-size: 0.74rem; line-height: 1.5; color: var(--text-muted); }
+.sheet-svg { display: block; }
+.sheet-row { fill: var(--panel-raised); }
+.sheet-row-black { fill: var(--bg); }
+.sheet-octave { stroke: var(--control); stroke-width: 1; }
+.sheet-key { fill: var(--text-muted); font: 10px var(--font-mono); text-anchor: end; dominant-baseline: middle; }
+.sheet-key-c { fill: var(--text); font-weight: 600; }
+.sheet-beat { stroke: var(--border); stroke-width: 1; opacity: 0.35; }
+.sheet-beat-1 { stroke: var(--control); opacity: 0.55; }
+.sheet-beat-2 { stroke: var(--text-muted); opacity: 0.8; }
+.sheet-breaks { pointer-events: none; }
+.sheet-break { stroke: var(--text-muted); stroke-width: 1.5; stroke-dasharray: 5 4; }
+.sheet-break-moved { stroke: var(--aqua); stroke-dasharray: none; }
+.sheet-break-label { fill: var(--text-muted); stroke: none; font: 12px var(--font-mono); }
+.sheet-break-label.sheet-break-moved { fill: var(--aqua); stroke: none; }
+.sheet-curve { pointer-events: none; }
+.sheet-curve polyline { fill: none; stroke: var(--aqua); stroke-width: 1.5; opacity: 0.9; }
+.sheet-note { fill: var(--purple); }
+.sheet-note-golden { fill: #E8B931; }
+.sheet-note-free { fill: none; stroke: var(--purple); stroke-width: 1.5; stroke-dasharray: 4 3; }
+.sheet-note-rap { fill: var(--aqua); }
+.sheet-note-golden-rap { fill: #E8B931; stroke: var(--aqua); stroke-width: 2; }
+.sheet-note-low { stroke: var(--fail); stroke-width: 2; stroke-dasharray: 3 2; }
+.sheet-note-context { opacity: 0.28; }
+.sheet-playhead { position: absolute; top: 0; height: 300px; width: 2px; margin-left: -1px; background: var(--aqua); pointer-events: none; }
+.sheet-playhead[hidden] { display: none; }
+.sheet-syllables, .sheet-words { position: relative; overflow: hidden; }
+.sheet-syllables { height: 22px; margin-top: 6px; overflow: visible; }
+.sheet-syllable { position: absolute; top: 0; font-size: 0.8rem; white-space: pre; color: var(--text); cursor: text; }
+.sheet-words { height: 24px; margin-top: 4px; }
+.sheet-word {
+  position: absolute;
+  top: 0;
+  padding-top: 4px;
+  font-size: 0.78rem;
+  white-space: nowrap;
+  color: var(--text-muted);
+  border-top: 2px solid var(--border);
+}
+
 #lyrics-review { display: flex; flex-direction: column; gap: 10px; }
 .review-line { padding: 8px 12px; background: var(--panel); border: 1px solid var(--border); }
+.review-line-active { background: var(--panel-raised); border-color: var(--aqua); }
+.review-word-sung { color: var(--text-muted); }
+.review-word-active { color: var(--aqua); font-weight: 600; }
+.review-playhead { position: absolute; top: 0; bottom: 0; width: 2px; margin-left: -1px; background: var(--aqua); }
+.review-seek { cursor: pointer; }
 .review-line-text { display: block; font-size: 0.9rem; }
 .review-line-dropped { opacity: 0.55; }
 .review-line-dropped .review-line-text { text-decoration: line-through; }
@@ -354,7 +592,7 @@ button { cursor: pointer; }
   border: 1px solid var(--border);
 }
 .output-path code { flex: 1; overflow-wrap: anywhere; font-family: var(--font-mono); font-size: 0.82rem; }
-#copy-path, .action, #cancel-rebuild {
+#copy-path, .action {
   flex: none;
   padding: 5px 12px;
   font-family: var(--font-display);
@@ -367,10 +605,11 @@ button { cursor: pointer; }
   border: 1px solid var(--control);
   border-radius: 2px;
 }
-#copy-path:hover, .action:hover, #cancel-rebuild:hover { border-color: var(--text-muted); }
+#copy-path:hover, .action:hover { border-color: var(--text-muted); }
 
 .form-actions { display: flex; align-items: center; gap: 14px; }
 .keep-note { margin: -8px 0 0; font-size: 0.78rem; color: var(--aqua); }
+#form-lock { margin: 0; font-size: 0.78rem; color: var(--text-muted); }
 #review-actions { display: flex; gap: 10px; margin-top: 14px; }
 #review-lineage { margin: -10px 0 14px; }
 .lineage {
@@ -493,11 +732,40 @@ button { cursor: pointer; }
     <div class="kana" aria-hidden="true">カラオケ</div>
   </div>
   <div>
+    <button type="button" id="create-song" class="primary">CREATE SONG</button>
+    <button type="button" id="rebuild-all" class="action">REBUILD ALL FROM…</button>
+    <p id="rebuild-all-note" class="empty-note" role="status" hidden></p>
     <h2 class="eyebrow">QUEUE</h2>
     <div id="jobs"></div>
   </div>
 </aside>
 
+<dialog id="rebuild-all-dialog" aria-labelledby="rebuild-all-heading">
+  <form id="rebuild-all-form" method="dialog">
+    <h2 id="rebuild-all-heading">REBUILD ALL SONGS</h2>
+    <p>Reruns the songs ticked below from the chosen stage onwards with the
+      inputs they have now, for when a songtrace update improves that stage.</p>
+    <label class="field">
+      <span>Restart from</span>
+      <select name="force_from" required></select>
+    </label>
+    <fieldset id="rebuild-all-songs">
+      <legend>Songs</legend>
+      <label class="rebuild-all-row rebuild-all-every">
+        <input type="checkbox" id="rebuild-all-toggle" checked>
+        <span>All songs</span>
+      </label>
+      <div id="rebuild-all-list"></div>
+    </fieldset>
+    <p id="rebuild-all-count"></p>
+    <p id="rebuild-all-error" role="alert"></p>
+    <div class="form-actions">
+      <button type="submit" class="primary">REBUILD SELECTED</button>
+      <button type="button" class="action" id="rebuild-all-cancel">CANCEL</button>
+    </div>
+  </form>
+</dialog>
+
 <main id="main">
   <section id="new-song">
     <h2>NEW SONG</h2>
@@ -511,6 +779,10 @@ button { cursor: pointer; }
           <label class="field"><span>YouTube URL</span><input name="youtube_url"></label>
           <label class="field"><span>Video file</span><input type="file" name="video"></label>
           <p class="keep-note" data-keep="video" hidden></p>
+          <label class="field" id="restart-field" hidden>
+            <span>Restart from</span>
+            <select name="force_from"></select>
+          </label>
           <details>
             <summary>Advanced</summary>
             <div class="stack">
@@ -531,7 +803,7 @@ button { cursor: pointer; }
       </div>
       <div class="form-actions">
         <button type="submit" class="primary">CREATE SONG</button>
-        <button type="button" id="cancel-rebuild" hidden>CANCEL</button>
+        <p id="form-lock" hidden></p>
       </div>
     </form>
     <p id="form-error" role="alert"></p>
@@ -542,6 +814,11 @@ button { cursor: pointer; }
     <h3 id="review-title"></h3>
     <p id="review-lineage" hidden></p>
     <p id="review-error" class="review-error" hidden></p>
+    <div id="player" hidden>
+      <video id="player-video" muted playsinline preload="metadata"></video>
+      <audio id="player-media" controls preload="metadata"></audio>
+    </div>
+    <div id="sheet" hidden></div>
     <div id="lyrics-review"><p class="empty-note">no songs queued yet — nothing to review</p></div>
     <div id="output-path"></div>
     <div id="review-actions"></div>
@@ -572,10 +849,15 @@ const nowTitle = document.getElementById("now-title");
 const stageTrack = document.getElementById("stage-track");
 const reviewActions = document.getElementById("review-actions");
 const reviewLineage = document.getElementById("review-lineage");
-const cancelRebuild = document.getElementById("cancel-rebuild");
+const createSong = document.getElementById("create-song");
+const formLock = document.getElementById("form-lock");
 const formHeading = document.querySelector("#new-song h2");
 const submitButton = form.querySelector("button[type=submit]");
 let rebuildOf = null;
+let formDirty = false;
+// set by CREATE SONG: the page is a blank sheet on purpose, so the poll must
+// not quietly select the newest song back into it
+let composing = false;
 let JOBS = [];
 let selectedId = null;
 let STAGES = [];
@@ -610,10 +892,16 @@ form.addEventListener("submit", async (e) => {
   if (!resp.ok) {
     const body = await resp.json().catch(() => ({}));
     formError.textContent = body.detail || `error: ${resp.status}`;
-    return;  // before the reset below, so a rejected submission is never retyped
+    return;
   }
   selectedId = (await resp.json()).id;
-  exitRebuild();
+  composing = false;
+  // the fields stay as submitted: the song just sent is the obvious starting
+  // point for the next one, and nothing has to be retyped to correct it. The
+  // queue's CREATE SONG button is what empties the form.
+  rebuildOf = null;
+  formDirty = false;
+  setFormMode(null, null);
   refreshJobs();
 });
 
@@ -638,7 +926,115 @@ for (const input of form.querySelectorAll('input[type="file"]')) {
   });
 }
 
-cancelRebuild.addEventListener("click", exitRebuild);
+// selecting another queue entry reloads the form, so track whether there is
+// anything of the operator's in there worth warning about first
+form.addEventListener("input", () => { formDirty = true; });
+
+// Always available, and the form is usually holding a selected song by now, so
+// this clears the whole page down to a blank sheet — fields, review, player and
+// queue selection — and brings the form back into view from wherever playback
+// scrolled the panel to. Leaving another song's review under an empty form
+// reads as though the two belong together.
+createSong.addEventListener("click", () => {
+  if (sheet?.isDirty() && !confirm("Discard unsaved changes to this line?")) return;
+  if (formDirty && !confirm("Discard your unsaved edits to this form?")) return;
+  composing = true;
+  selectedId = null;
+  for (const card of jobsDiv.querySelectorAll(".job")) card.removeAttribute("aria-current");
+  exitRebuild();
+  clearDetail("nothing selected");
+  document.getElementById("new-song").scrollIntoView({ block: "start", behavior: "smooth" });
+  form.elements.title.focus();
+});
+
+const rebuildAllButton = document.getElementById("rebuild-all");
+const rebuildAllNote = document.getElementById("rebuild-all-note");
+const rebuildAllDialog = document.getElementById("rebuild-all-dialog");
+const rebuildAllForm = document.getElementById("rebuild-all-form");
+const rebuildAllCount = document.getElementById("rebuild-all-count");
+const rebuildAllError = document.getElementById("rebuild-all-error");
+
+const rebuildAllList = document.getElementById("rebuild-all-list");
+const rebuildAllToggle = document.getElementById("rebuild-all-toggle");
+const rebuildAllSubmit = rebuildAllForm.querySelector("button[type=submit]");
+
+function rebuildAllBoxes() {
+  return [...rebuildAllList.querySelectorAll("input:not(:disabled)")];
+}
+
+function updateRebuildAllCount() {
+  const boxes = rebuildAllBoxes();
+  const chosen = boxes.filter(b => b.checked).length;
+  rebuildAllToggle.checked = chosen === boxes.length && chosen > 0;
+  rebuildAllToggle.indeterminate = chosen > 0 && chosen < boxes.length;
+  rebuildAllCount.textContent = chosen === 1 ? "1 song will be rebuilt."
+                                             : `${chosen} songs will be rebuilt.`;
+  // with nothing ticked no ids are sent, which the API reads as every song
+  rebuildAllSubmit.disabled = chosen === 0;
+}
+
+function rebuildAllRow(song) {
+  const busy = song.status === "queued" || song.status === "running";
+  const row = document.createElement("label");
+  row.className = "rebuild-all-row";
+  const box = document.createElement("input");
+  box.type = "checkbox";
+  box.name = "ids";
+  box.value = song.id;
+  box.checked = !busy;
+  box.disabled = busy;
+  const name = document.createElement("span");
+  name.textContent = `${song.title} · ${song.artist}`;
+  const meta = document.createElement("span");
+  meta.className = "meta";
+  const when = song.finished_at && new Date(song.finished_at * 1000).toLocaleString(
+    undefined, { dateStyle: "medium", timeStyle: "short" });
+  meta.textContent = busy ? "in progress, skipped"
+    : `${song.status === "failed" ? "failed" : song.rebuilt_from ? "rebuilt" : "built"} ${when || ""}`.trim();
+  row.append(box, name, meta);
+  return row;
+}
+
+rebuildAllButton.addEventListener("click", async () => {
+  rebuildAllError.textContent = "";
+  rebuildAllForm.reset();
+  const resp = await fetch("/api/rebuild-all");
+  const songs = resp.ok ? await resp.json() : [];
+  rebuildAllList.replaceChildren(...songs.map(rebuildAllRow));
+  updateRebuildAllCount();
+  rebuildAllDialog.showModal();
+});
+
+rebuildAllList.addEventListener("change", updateRebuildAllCount);
+rebuildAllToggle.addEventListener("change", () => {
+  for (const box of rebuildAllBoxes()) box.checked = rebuildAllToggle.checked;
+  updateRebuildAllCount();
+});
+
+document.getElementById("rebuild-all-cancel").addEventListener(
+  "click", () => rebuildAllDialog.close());
+
+rebuildAllForm.addEventListener("submit", async (e) => {
+  e.preventDefault();
+  const stage = rebuildAllForm.elements.force_from.value;
+  const resp = await fetch("/api/rebuild-all", {
+    method: "POST", body: new FormData(rebuildAllForm) });
+  if (!resp.ok) {
+    const body = await resp.json().catch(() => ({}));
+    rebuildAllError.textContent = body.detail || `error: ${resp.status}`;
+    return;
+  }
+  const { ids, skipped } = await resp.json();
+  rebuildAllDialog.close();
+  let note = `Queued ${ids.length} rebuild${ids.length === 1 ? "" : "s"} from ${stage}.`;
+  if (skipped.length) {
+    const reasons = [...new Set(skipped.map(s => s.reason))].join("; ");
+    note += ` Skipped ${skipped.length}: ${reasons}.`;
+  }
+  rebuildAllNote.textContent = note;
+  rebuildAllNote.hidden = false;
+  refreshJobs();
+});
 
 function jobCard(job) {
   const card = document.createElement("button");
@@ -713,6 +1109,13 @@ function renderJobs(jobs) {
 async function loadStages() {
   const resp = await fetch("/api/stages");
   STAGES = (await resp.json()).stages;
+  // a rebuild redoes only what the edit invalidated, which cannot see a change
+  // in songtrace itself — this is how you redo a stage anyway
+  const select = form.elements.force_from;
+  select.replaceChildren(new Option("only what changed", ""),
+                         ...STAGES.map(s => new Option(s, s)));
+  rebuildAllForm.elements.force_from.replaceChildren(
+    new Option("choose a stage", ""), ...STAGES.map(s => new Option(s, s)));
 }
 
 function renderStageTrack(job) {
@@ -772,20 +1175,30 @@ async function refreshJobs() {
   const resp = await fetch("/api/jobs");
   const jobs = await resp.json();
   JOBS = jobs;
-  if (selectedId === null && jobs.length) selectedId = jobs[0].id;
+  // deliberately not via selectJob: the auto-selection on load fills the review
+  // panel but leaves the form blank, so landing on the page is still the way to
+  // start a new song. Clicking a queue entry is what loads its inputs.
+  if (!composing && selectedId === null && jobs.length) selectedId = jobs[0].id;
   renderJobs(jobs);
   renderNowBar(jobs);
   if (selectedId) refreshDetail();
-  else clearDetail();
+  else clearDetail(composing ? "nothing selected" : undefined);
   schedulePoll(jobs);
 }
 
 async function selectJob(id) {
+  if (id !== selectedId && sheet?.isDirty() &&
+      !confirm("Discard unsaved changes to this line?")) return;
+  // the form already holds this job; reloading it would drop edits in progress
+  const reload = id !== rebuildOf;
+  if (reload && formDirty && !confirm("Discard your unsaved edits to this form?")) return;
+  composing = false;
   selectedId = id;
   for (const card of jobsDiv.querySelectorAll(".job")) {
     if (card.dataset.id === id) card.setAttribute("aria-current", "true");
     else card.removeAttribute("aria-current");
   }
+  if (reload) await loadInputs(id, JOBS.find(j => j.id === id)?.status);
   refreshDetail();
 }
 
@@ -857,6 +1270,10 @@ function lineTimeline(words, notes, minPitch, span) {
   }
   box.append(wordsRow);
   if (notes.length) box.append(pianoRoll(notes, minPitch, span, t0, t1));
+  const playhead = document.createElement("div");
+  playhead.className = "review-playhead";
+  playhead.hidden = true;
+  box.append(playhead);
   return box;
 }
 
@@ -890,6 +1307,22 @@ function lineNode(line, minPitch, span) {
   return row;
 }
 
+// What playback needs from a rendered line: the time range it was laid out
+// over, the word labels along it, and the bar that sweeps across it.
+function lineEntry(row, line) {
+  const laid = line.words.length ? line.words : line.notes;
+  if (!laid.length || line.dropped) return null;
+  const labels = [...row.querySelectorAll(".review-word")];
+  return {
+    row,
+    index: line.index,
+    t0: laid[0].start,
+    t1: Math.max(...laid.map(x => x.end)),
+    words: line.words.map((w, i) => ({ el: labels[i], start: w.start, end: w.end })),
+    playhead: row.querySelector(".review-playhead"),
+  };
+}
+
 function buildLyricsReview(data) {
   const allNotes = data.lines.flatMap(l => l.notes);
   const pitches = allNotes.map(n => n.pitch);
@@ -898,6 +1331,7 @@ function buildLyricsReview(data) {
   const span = Math.max(1, maxPitch - minPitch);
   const spans = [...data.missing_spans].sort((a, b) => a.start - b.start);
   const nodes = [];
+  const entries = [];
   let spanIdx = 0;
   for (const line of data.lines) {
     const lineStart = line.notes.length ? Math.min(...line.notes.map(n => n.start)) : null;
@@ -905,24 +1339,205 @@ function buildLyricsReview(data) {
       nodes.push(missingSpanNode(spans[spanIdx]));
       spanIdx++;
     }
-    nodes.push(lineNode(line, minPitch, span));
+    const row = lineNode(line, minPitch, span);
+    const entry = lineEntry(row, line);
+    if (entry) entries.push(entry);
+    nodes.push(row);
   }
   while (spanIdx < spans.length) {
     nodes.push(missingSpanNode(spans[spanIdx]));
     spanIdx++;
   }
-  return nodes;
+  return { nodes, entries };
+}
+
+// The song folder's own media, played against the same seconds the review was
+// built from, so the highlighted line is the one you are hearing.
+//
+// Modelled on the game: #MP3 is the audio and the clock, the video is muted
+// background slaved to it. Playing the video's own audio alongside the mp3 is
+// the same recording twice, a few frames apart, which is heard as an echo.
+const player = document.getElementById("player");
+const media = document.getElementById("player-media");
+const video = document.getElementById("player-video");
+const DRIFT = 0.25;  // seconds before the picture is worth re-seeking
+
+// the note sheet lives in its own module, loaded before any review renders
+let sheet = null;
+let stopAt = null;   // set by playing one line: where playback pauses again
+const sheetReady = import("/static/sheet.js").then((m) => {
+  sheet = m.createSheet(document.getElementById("sheet"), {
+    seek: (t) => {
+      media.currentTime = t;
+      if (media.paused) syncPlayback();
+    },
+    playLine: (from, to) => {
+      if (player.hidden) return;
+      media.currentTime = from;
+      stopAt = to;
+      media.play().catch(() => {});
+    },
+    // a saved line changes the notes the lyric list draws
+    onSaved: (data) => {
+      const box = document.getElementById("lyrics-review");
+      const { nodes, entries } = buildLyricsReview(data);
+      box.replaceChildren(...nodes);
+      bindTimeline(player.hidden ? [] : entries);
+      if (!player.hidden) syncPlayback();
+    },
+  });
+});
+
+function slaveVideo(force) {
+  if (video.hidden || !video.getAttribute("src")) return;
+  if (force || Math.abs(video.currentTime - media.currentTime) > DRIFT) {
+    video.currentTime = media.currentTime;
+  }
+}
+
+for (const event of ["seeked", "ratechange"]) {
+  media.addEventListener(event, () => {
+    video.playbackRate = media.playbackRate;
+    slaveVideo(true);
+  });
+}
+media.addEventListener("pause", () => {
+  video.pause();
+  stopAt = null;
+});
+let timeline = [];
+let activeEntry = null;
+let syncFrame = null;
+
+// the first line that has not finished yet: the one being sung, or the one
+// coming up while the track is between lines
+function entryAt(t) {
+  return timeline.find(e => t <= e.t1) ?? timeline[timeline.length - 1] ?? null;
+}
+
+function paintEntry(entry, t) {
+  for (const w of entry.words) {
+    w.el.classList.toggle("review-word-sung", t >= w.end);
+    w.el.classList.toggle("review-word-active", t >= w.start && t < w.end);
+  }
+  if (!entry.playhead) return;
+  const inside = t >= entry.t0 && t <= entry.t1;
+  entry.playhead.hidden = !inside;
+  if (inside) {
+    const frac = (t - entry.t0) / Math.max(entry.t1 - entry.t0, 0.001);
+    entry.playhead.style.left = `${frac * 100}%`;
+  }
+}
+
+function clearEntry(entry) {
+  entry.row.classList.remove("review-line-active");
+  if (entry.playhead) entry.playhead.hidden = true;
+  for (const w of entry.words) {
+    w.el.classList.remove("review-word-sung", "review-word-active");
+  }
+}
+
+function syncPlayback() {
+  const t = media.currentTime;
+  const entry = entryAt(t);
+  if (entry !== activeEntry) {
+    if (activeEntry) clearEntry(activeEntry);
+    activeEntry = entry;
+    if (entry) {
+      entry.row.classList.add("review-line-active");
+      sheet?.showLine(entry.index);
+      focusActive();
+    }
+  }
+  if (entry) paintEntry(entry, t);
+  sheet?.setTime(t);
+}
+
+// centred so there is context either side, like a scrolling lyric sheet; only
+// while running, so it does not fight a reader who has scrolled away to look
+// at something else
+function focusActive() {
+  if (!activeEntry || media.paused) return;
+  activeEntry.row.scrollIntoView({ block: "center", behavior: "smooth" });
+}
+
+function pumpPlayback() {
+  if (stopAt !== null && media.currentTime >= stopAt) media.pause();
+  syncPlayback();
+  slaveVideo(false);
+  syncFrame = media.paused ? null : requestAnimationFrame(pumpPlayback);
+}
+
+// timeupdate fires about four times a second, too coarse for a playhead
+media.addEventListener("play", () => {
+  if (syncFrame === null) syncFrame = requestAnimationFrame(pumpPlayback);
+  if (!video.hidden && video.getAttribute("src")) video.play().catch(() => {});
+  focusActive();  // the line may already be active from a seek while paused
+});
+for (const event of ["pause", "seeked", "loadedmetadata"]) {
+  media.addEventListener(event, syncPlayback);
+}
+
+function bindTimeline(entries) {
+  if (activeEntry) clearEntry(activeEntry);
+  activeEntry = null;
+  timeline = entries;
+  for (const entry of entries) {
+    entry.row.classList.add("review-seek");
+    entry.row.title = "click to play from here";
+    entry.row.addEventListener("click", (e) => {
+      const word = entry.words.find(w => w.el === e.target);
+      media.currentTime = word ? word.start : entry.t0;
+      if (media.paused) syncPlayback();
+    });
+  }
+}
+
+// Returns true when the folder gave us something to play. #MP3 is required —
+// it is the audio the game uses, so it is the one the review has to track.
+function setPlayerSource(job, available) {
+  const src = available?.audio ? `/api/jobs/${job.id}/media/audio` : "";
+  player.hidden = !src;
+  if (media.dataset.src === src) return !!src;
+  media.dataset.src = src;
+  if (src) media.src = src;
+  else { media.removeAttribute("src"); media.load(); }
+
+  video.hidden = !(src && available.video);
+  video.poster = available?.cover ? `/api/jobs/${job.id}/media/cover` : "";
+  if (!video.hidden) video.src = `/api/jobs/${job.id}/media/video`;
+  else { video.removeAttribute("src"); video.load(); }
+  return !!src;
+}
+
+function resetPlayer() {
+  sheet?.clear();
+  // the 3s poll reaches here for every running job; reloading a cleared
+  // element each time would be pure churn
+  if (player.hidden && !timeline.length) return;
+  bindTimeline([]);
+  player.hidden = true;
+  media.pause();
+  video.pause();
+  media.dataset.src = "";
+  for (const el of [media, video]) {
+    el.removeAttribute("src");
+    el.removeAttribute("poster");
+    el.load();
+  }
 }
 
 async function renderLyricsReview(job) {
   const box = document.getElementById("lyrics-review");
   if (job.status === "failed") {
     delete box.dataset.jobId;
+    resetPlayer();
     box.replaceChildren(emptyNote("job failed — nothing to review"));
     return;
   }
   if (job.status !== "done") {
     delete box.dataset.jobId;
+    resetPlayer();
     box.replaceChildren(emptyNote("waiting for this song to finish…"));
     return;
   }
@@ -930,6 +1545,7 @@ async function renderLyricsReview(job) {
   const resp = await fetch(`/api/jobs/${job.id}/review`);
   if (job.id !== selectedId) return;
   if (!resp.ok) {
+    resetPlayer();
     box.replaceChildren(emptyNote("no review data available"));
     return;
   }
@@ -937,10 +1553,20 @@ async function renderLyricsReview(job) {
   if (job.id !== selectedId) return;
   box.dataset.jobId = job.id;
   if (!data.lines.length) {
+    resetPlayer();
     box.replaceChildren(emptyNote("no lyrics to review"));
     return;
   }
-  box.replaceChildren(...buildLyricsReview(data));
+  const { nodes, entries } = buildLyricsReview(data);
+  box.replaceChildren(...nodes);
+  await sheetReady;
+  if (job.id !== selectedId) return;
+  sheet.load(job.id, data);
+  // with nothing to play, a highlighted line and a click-to-seek cursor would
+  // both be promising something the song folder cannot deliver
+  const playable = setPlayerSource(job, data.media);
+  bindTimeline(playable ? entries : []);
+  if (playable) syncPlayback();
 }
 
 async function copyPath(path, button) {
@@ -1000,40 +1626,63 @@ function renderOutputPath(job) {
   outputPathDiv.replaceChildren(wrap);
 }
 
-function clearDetail() {
+function clearDetail(why = "no songs queued yet") {
   reviewTitle.replaceChildren();
   reviewError.hidden = true;
   reviewError.textContent = "";
-  document.getElementById("warnings").replaceChildren(
-    emptyNote("no songs queued yet — nothing to review"));
+  resetPlayer();
+  // the review box, not an element that no longer exists: getting this wrong
+  // threw partway through and left the rest of the panel showing the old song
+  const box = document.getElementById("lyrics-review");
+  delete box.dataset.jobId;
+  box.replaceChildren(emptyNote(`${why} — nothing to review`));
   outputPathDiv.replaceChildren();
   reviewActions.replaceChildren();
   delete reviewActions.dataset.jobId;
   reviewLineage.replaceChildren();
   reviewLineage.hidden = true;
   delete reviewLineage.dataset.jobId;
-  detail.textContent = "no songs queued yet — nothing to log";
+  detail.textContent = `${why} — nothing to log`;
 }
 
-function setFormMode(inp) {
+// a rebuild is refused with 409 until the job settles, so the form says so
+// rather than letting the submission fail
+function setSubmitLock(status) {
+  const locked = rebuildOf !== null && (status === "queued" || status === "running");
+  submitButton.disabled = locked;
+  formLock.textContent = locked ? "editable once this run finishes" : "";
+  formLock.hidden = !locked;
+}
+
+function setFormMode(inp, status) {
   formHeading.textContent = rebuildOf ? "REBUILD" : "NEW SONG";
   submitButton.textContent = rebuildOf ? "REBUILD SONG" : "CREATE SONG";
-  cancelRebuild.hidden = !rebuildOf;
+  setSubmitLock(status);
+  // only a rebuild has stages to restart from; a new song always runs them all
+  document.getElementById("restart-field").hidden = !rebuildOf;
+  if (!rebuildOf) form.elements.force_from.value = "";
   for (const [field, key] of [["video", "video_filename"], ["cover", "cover_filename"]]) {
     const note = form.querySelector(`[data-keep="${field}"]`);
     const kept = rebuildOf && inp ? inp[key] : null;
     note.textContent = kept ? `keeping ${kept} — attach a file to replace it` : "";
     note.hidden = !kept;
   }
+  // the advanced fields carry into a rebuild whether or not the section is open,
+  // so anything actually set must not sit hidden behind a closed summary
+  form.querySelector("details").open = !!inp?.cover_filename ||
+    ["genre", "year", "language", "bpm"].some(n => form.elements[n].value);
 }
 
 function exitRebuild() {
   rebuildOf = null;
   form.reset();
-  setFormMode(null);
+  formDirty = false;
+  setFormMode(null, null);
 }
 
-async function startRebuild(id) {
+// selecting a queue entry brings its inputs back up, so a song can be adjusted
+// and rebuilt without being retyped
+async function loadInputs(id, status) {
   const resp = await fetch(`/api/jobs/${id}/input`);
   if (!resp.ok) return;
   const inp = await resp.json();
@@ -1044,9 +1693,9 @@ async function startRebuild(id) {
     if (el && value !== null) el.value = value;
   }
   rebuildOf = id;
-  setFormMode(inp);
+  formDirty = false;
+  setFormMode(inp, status);
   formError.textContent = "";
-  form.elements.title.focus();
 }
 
 async function rerunJob(id) {
@@ -1083,19 +1732,19 @@ async function deleteJob(id) {
     return;
   }
   if (selectedId === id) selectedId = null;
+  // the form is holding a job that no longer exists; a rebuild would 404
+  if (rebuildOf === id) exitRebuild();
   refreshJobs();
 }
 
 const ACTION_LABELS = {
   rerun: "RERUN",
-  edit: "EDIT & REBUILD",
   "rebuild-full": "REBUILD FROM SCRATCH",
   delete: "DELETE",
 };
 
 const ACTION_HANDLERS = {
   rerun: rerunJob,
-  edit: startRebuild,
   "rebuild-full": rebuildFullJob,
   delete: deleteJob,
 };
@@ -1112,7 +1761,7 @@ function actionButton(action, jobId) {
 
 function renderActions(job) {
   // no controls mid-run: every endpoint answers 409 until the job settles
-  const doneActions = ["edit", "rebuild-full", "delete"];
+  const doneActions = ["rebuild-full", "delete"];
   const wanted = job.status === "failed" ? ["rerun", ...doneActions]
                : job.status === "done" ? doneActions : [];
   const shown = [...reviewActions.children].map(b => b.dataset.action);
@@ -1149,6 +1798,7 @@ async function refreshDetail() {
   reviewTitle.replaceChildren(`${job.title} `, artist);
   reviewError.hidden = !job.error;
   reviewError.textContent = job.error ?? "";
+  if (rebuildOf === job.id) setSubmitLock(job.status);
   renderLyricsReview(job);
   renderOutputPath(job);
   renderLineage(job);

src/songtrace/static/sheet.js

@@ -0,0 +1,951 @@
+// The note sheet: one lyric line at a time on a pitch-by-beat grid, the way
+// an UltraStar editor lays a song out, with the detected pitch drawn over
+// the notes so a wrong one stands out. The line on show can be edited.
+
+import * as edit from "./edit-model.js";
+
+const SVG = "http://www.w3.org/2000/svg";
+const NAMES = ["C", "C♯", "D", "D♯", "E", "F", "F♯", "G", "G♯", "A", "A♯", "B"];
+const BLACK = new Set([1, 3, 6, 8, 10]);
+const GUTTER = 46;        // px of note names left of the grid
+const PLOT_HEIGHT = 300;  // px; rows divide this between the pitches shown
+const CONTEXT = 0.75;     // seconds shown either side of the line
+const EDGE = 6;           // px from a note's end that grabs it for resizing
+const KINDS = { "*": "golden", F: "free", R: "rap", G: "golden-rap" };
+const KEYS_OPEN = "songtrace.sheet-keys";
+
+// The sheet's controls, grouped as an editor's reference card lists them.
+// "+" joins keys pressed together, " / " separates alternatives, and a
+// lowercase word is something done with the mouse rather than a key.
+export const SHORTCUTS = [
+  ["Select", [
+    ["click", "select a note"],
+    ["Shift+click", "add to the selection"],
+    ["Tab / Shift+Tab", "next, previous note"],
+    ["Esc", "clear the selection"]]],
+  ["Move", [
+    ["drag", "move in time and pitch"],
+    ["← / →", "a beat earlier, later"],
+    ["↑ / ↓", "a semitone up, down"],
+    ["Shift+↑ / Shift+↓", "an octave up, down"]]],
+  ["Length", [
+    ["drag an end", "resize"],
+    ["Shift+← / Shift+→", "a beat shorter, longer"]]],
+  ["Notes", [
+    ["double-click", "add a note, on empty space"],
+    ["S", "split in two"],
+    ["M", "merge with the next"],
+    ["Delete", "remove"]]],
+  ["Kind", [
+    ["G", "golden"],
+    ["F", "freestyle"],
+    ["R", "rap"],
+    ["G / F / R", "again: back to normal"]]],
+  ["Line break", [
+    ["drag a ↵ marker", "move it, between the lines it separates"],
+    ["double-click a ↵", "back to where songtrace puts it"]]],
+  ["Syllable", [
+    ["double-click", "edit, on a note"],
+    ["Enter", "edit the selected note"]]],
+  ["Line", [
+    ["Ctrl+Z", "undo"],
+    ["Ctrl+Shift+Z / Ctrl+Y", "redo"],
+    ["Ctrl+S", "save"],
+    ["P", "play"],
+    ["Page Up / Page Down", "previous, next line"],
+    ["?", "show or hide these keys"]]],
+];
+
+// "Shift+Tab / Esc" as key caps, with mouse actions left as words
+export function comboParts(combo) {
+  return combo.split(" / ").map(alt => alt.split("+").map(part => ({
+    text: part, key: !/^[a-z]/.test(part),
+  })));
+}
+
+const wrap = (n, d) => ((n % d) + d) % d;
+const mod12 = (p) => wrap(p, 12);
+
+// UltraStar pitch 0 is C4 (MIDI 60)
+export function noteName(pitch) {
+  return NAMES[mod12(pitch)] + (Math.floor((pitch + 60) / 12) - 1);
+}
+
+export function isBlackKey(pitch) {
+  return BLACK.has(mod12(pitch));
+}
+
+// The pitches to show: the line's notes with room around them, and never
+// less than an octave and a bit, so rows stay a consistent size to aim at.
+export function pitchRange(pitches, { pad = 3, min = 15 } = {}) {
+  if (!pitches.length) return { lo: -7, hi: 7 };
+  let lo = Math.min(...pitches) - pad;
+  let hi = Math.max(...pitches) + pad;
+  const short = min - (hi - lo + 1);
+  if (short > 0) {
+    lo -= Math.floor(short / 2);
+    hi += Math.ceil(short / 2);
+  }
+  return { lo, hi };
+}
+
+// UltraStar beats between t0 and t1 on the chart's grid. A beat is a quarter
+// of the #BPM beat; weight 2 marks every 16th, 1 every 4th, as editors do.
+export function beatLines(t0, t1, grid) {
+  const spb = 60 / (4 * grid.bpm);
+  const gap = grid.gap_ms / 1000;
+  const out = [];
+  for (let k = Math.ceil((t0 - gap) / spb); gap + k * spb <= t1; k++) {
+    const weight = wrap(k, 16) === 0 ? 2 : wrap(k, 4) === 0 ? 1 : 0;
+    out.push({ t: gap + k * spb, beat: k, weight });
+  }
+  return out;
+}
+
+// The seconds a line occupies, from its notes and the words it was aligned to.
+export function lineSpan(line) {
+  const ts = [...line.notes.flatMap(n => [n.start, n.end]),
+              ...line.words.flatMap(w => [w.start, w.end])];
+  return ts.length ? { start: Math.min(...ts), end: Math.max(...ts) } : null;
+}
+
+function el(name, attrs = {}, parent = null) {
+  const node = document.createElementNS(SVG, name);
+  for (const [k, v] of Object.entries(attrs)) node.setAttribute(k, v);
+  if (parent) parent.append(node);
+  return node;
+}
+
+function div(cls, text = null) {
+  const node = document.createElement("div");
+  node.className = cls;
+  if (text !== null) node.textContent = text;
+  return node;
+}
+
+export function createSheet(root, { seek, playLine, onSaved }) {
+  const button = (label, title, onClick, cls = "action") => {
+    const b = document.createElement("button");
+    b.type = "button";
+    b.className = cls;
+    b.textContent = label;
+    b.title = title;
+    b.addEventListener("click", onClick);
+    return b;
+  };
+  const title = div("sheet-title");
+  const badges = div("sheet-badges");
+  const prev = button("◀ PREV", "previous line (Page Up)", () => page(-1));
+  const next = button("NEXT ▶", "next line (Page Down)", () => page(1));
+  const nav = div("sheet-nav");
+  const keysButton = button("KEYS ?", "keyboard shortcuts (?)", () => toggleKeys());
+  keysButton.setAttribute("aria-expanded", "false");
+  nav.append(prev, title, next, badges, keysButton);
+
+  const tools = {
+    undo: button("UNDO", "Ctrl+Z", () => undo()),
+    redo: button("REDO", "Ctrl+Shift+Z", () => redo()),
+    split: button("SPLIT", "split the selected note (S)", () => splitSelected()),
+    merge: button("MERGE", "merge with the next note (M)", () => mergeSelected()),
+    remove: button("DELETE", "delete the selected notes (Delete)", () => removeSelected()),
+    golden: button("GOLDEN", "golden note (G)", () => kind("*")),
+    free: button("FREESTYLE", "freestyle note (F)", () => kind("F")),
+    rap: button("RAP", "rap note (R)", () => kind("R")),
+    play: button("▶ LINE", "play this line (P)", () => playCurrent()),
+    discard: button("DISCARD", "drop unsaved changes to this line", () => discard()),
+    revert: button("REVERT", "go back to the generated notes for this line", () => revert()),
+    save: button("SAVE LINE", "Ctrl+S", () => save(), "action sheet-save"),
+  };
+  const toolbar = div("sheet-tools");
+  const group = (...items) => { const g = div("sheet-tool-group"); g.append(...items); return g; };
+  const status = div("sheet-status");
+  status.setAttribute("role", "status");
+  toolbar.append(group(tools.undo, tools.redo),
+                 group(tools.split, tools.merge, tools.remove),
+                 group(tools.golden, tools.free, tools.rap),
+                 group(tools.play), status,
+                 group(tools.discard, tools.revert, tools.save));
+
+  const plot = div("sheet-plot");
+  plot.tabIndex = 0;
+  plot.setAttribute("aria-label", "note sheet: select notes and edit them with the mouse or keyboard");
+  const svg = el("svg", { class: "sheet-svg" });
+  const playhead = div("sheet-playhead");
+  playhead.hidden = true;
+  plot.append(svg, playhead);
+  const syllables = div("sheet-syllables");
+  const words = div("sheet-words");
+  const help = div("sheet-help", "Press ? for keyboard shortcuts.");
+  const keys = div("sheet-keys");
+  keys.id = "sheet-keys";
+  keysButton.setAttribute("aria-controls", keys.id);
+  for (const [group, entries] of SHORTCUTS) {
+    const section = div("sheet-keys-group");
+    const heading = div("sheet-keys-head", group);
+    const list = document.createElement("dl");
+    for (const [combo, action] of entries) {
+      const dt = document.createElement("dt");
+      comboParts(combo).forEach((alt, i) => {
+        if (i) dt.append(" / ");
+        alt.forEach((part, j) => {
+          if (j) dt.append("+");
+          const node = document.createElement(part.key ? "kbd" : "span");
+          node.textContent = part.text;
+          dt.append(node);
+        });
+      });
+      const dd = document.createElement("dd");
+      dd.textContent = action;
+      list.append(dt, dd);
+    }
+    section.append(heading, list);
+    keys.append(section);
+  }
+  const stale = div("sheet-stale");
+  const gridBar = div("sheet-grid");
+  const field = (label, step, unit) => {
+    const wrap = document.createElement("label");
+    wrap.className = "sheet-grid-field";
+    const input = document.createElement("input");
+    input.type = "number";
+    input.step = step;
+    input.min = "0";
+    wrap.append(label, input);
+    if (unit) wrap.append(unit);
+    return { wrap, input };
+  };
+  const bpmField = field("BPM", "0.01");
+  const gapField = field("GAP", "1", "ms");
+  const gridSource = div("sheet-grid-source");
+  const gridTools = {
+    double: button("×2", "double the BPM", () => tryGrid({ bpm: grid().bpm * 2 })),
+    half: button("÷2", "halve the BPM", () => tryGrid({ bpm: grid().bpm / 2 })),
+    earlier: button("−10", "GAP 10ms earlier", () => tryGrid({ gap_ms: grid().gap_ms - 10 })),
+    later: button("+10", "GAP 10ms later", () => tryGrid({ gap_ms: grid().gap_ms + 10 })),
+    align: button("ALIGN TO NOTE", "move GAP the least that puts the selected note on a beat",
+                  () => alignToNote()),
+    cancel: button("CANCEL", "drop the BPM and GAP being tried", () => { gridDraft = null; render(); }),
+    reset: button("RESET", "back to the BPM songtrace chose, with GAP at the first note",
+                  () => resetGrid()),
+    apply: button("APPLY", "chart the song on this BPM and GAP", () => applyGrid(),
+                  "action sheet-save"),
+  };
+  const gridHead = div("sheet-grid-head", "GRID");
+  gridBar.append(gridHead, bpmField.wrap, gridTools.double, gridTools.half,
+                 gapField.wrap, gridTools.earlier, gridTools.later, gridTools.align,
+                 gridSource, gridTools.cancel, gridTools.reset, gridTools.apply);
+  for (const [f, key] of [[bpmField, "bpm"], [gapField, "gap_ms"]]) {
+    f.input.addEventListener("input", () => {
+      const v = Number(f.input.value);
+      if (f.input.value !== "" && Number.isFinite(v) && v >= 0 && (key === "gap_ms" || v > 0)) {
+        tryGrid({ [key]: v }, f.input);
+      }
+    });
+  }
+  root.replaceChildren(nav, stale, gridBar, toolbar, keys, plot, syllables, words, help);
+
+  // stays as the person left it, across lines, songs and visits
+  function showKeys(open) {
+    keys.hidden = !open;
+    help.hidden = open;
+    keysButton.setAttribute("aria-expanded", String(open));
+    try { localStorage.setItem(KEYS_OPEN, open ? "1" : ""); } catch {}
+  }
+  function toggleKeys() {
+    showKeys(keys.hidden);
+  }
+  let keysOpen = false;
+  try { keysOpen = !!localStorage.getItem(KEYS_OPEN); } catch {}
+  showKeys(keysOpen);
+
+  let review = null;
+  let curve = null;
+  let index = null;
+  let jobId = null;
+  let view = null;        // what the last render laid out: window and scale
+  let layout = null;      // window and pitch range, kept steady while editing
+  let hist = null;        // the current line's notes, with undo
+  let baseline = null;    // what the line holds on the server
+  let preview = null;     // notes mid-drag, not yet in the history
+  let breakPreview = null;  // a break mid-drag: { which, t }
+  let selected = new Set();
+  let drag = null;
+  let saving = false;
+
+  const visible = () => review.lines.filter(l => !l.dropped && lineSpan(l));
+  // the line being edited: its notes and the breaks either side of it, as
+  // one state so undo covers both. A break is its time, undefined where there
+  // is none to move, or null when it is to go back to automatic.
+  const notes = () => preview ?? hist?.present.notes ?? [];
+  const dirty = () => !!hist && hist.present !== baseline;
+  let gridDraft = null;   // BPM and GAP being tried out, not yet applied
+  // the grid being drawn and snapped to: the one being tried out, if any
+  const grid = () => gridDraft ?? review?.grid;
+  // notes snap to the grid, so they wait while a new one is being tried
+  const canEdit = () => !!review?.grid && !gridDraft && !saving;
+
+  function say(text, error = false) {
+    status.textContent = text;
+    status.classList.toggle("sheet-status-error", error);
+  }
+
+  // the window and pitch range that hold the line, grown (never shrunk while
+  // editing) so rows do not jump under the pointer
+  function fit(reset) {
+    const line = review.lines[index];
+    const ts = [...notes().flatMap(n => [n.start, n.end]),
+                ...line.words.flatMap(w => [w.start, w.end])];
+    const span = ts.length ? { start: Math.min(...ts), end: Math.max(...ts) } : lineSpan(line);
+    const range = pitchRange(notes().map(n => n.pitch));
+    const want = { t0: span.start - CONTEXT, t1: span.end + CONTEXT, ...range };
+    // the breaks either side are part of the line's page, so they stay on it
+    for (const slot of breakSlots()) {
+      const t = breakTime(slot);
+      want.t0 = Math.min(want.t0, t - 0.3);
+      want.t1 = Math.max(want.t1, t + 0.3);
+    }
+    layout = reset || !layout ? want : {
+      t0: Math.min(layout.t0, want.t0), t1: Math.max(layout.t1, want.t1),
+      lo: Math.min(layout.lo, want.lo), hi: Math.max(layout.hi, want.hi),
+    };
+  }
+
+  // edits whose line's lyrics have since changed: kept, not applied, until
+  // the person who made them decides
+  function paintStale() {
+    const items = review?.stale ?? [];
+    stale.hidden = !items.length;
+    stale.replaceChildren();
+    if (!items.length) return;
+    stale.append(div("sheet-stale-head",
+      `${items.length} edited line${items.length === 1 ? " was" : "s were"} set aside ` +
+      "because the lyrics changed:"));
+    items.forEach((item, n) => {
+      const row = div("sheet-stale-row");
+      row.append(div("sheet-stale-text", `"${item.text}"`),
+                 button("DISCARD", "throw this edit away", () => discardStale(n)));
+      stale.append(row);
+    });
+  }
+
+  async function discardStale(n) {
+    const resp = await fetch(`/api/jobs/${jobId}/stale/${n}`, { method: "DELETE" });
+    if (!resp.ok) { say(`error ${resp.status}`, true); return; }
+    review = await resp.json();
+    paintStale();
+    onSaved(review);
+  }
+
+  function open(i) {
+    index = i;
+    const line = review.lines[i];
+    const lines = visible();
+    const at = lines.findIndex(l => l.index === i);
+    const breakBefore = (l) => review.breaks?.find(b => b.line === l?.index)?.time;
+    baseline = {
+      notes: edit.withIds(line.notes.map(n => ({ ...n, kind: n.kind ?? ":" }))),
+      before: at > 0 ? breakBefore(line) : undefined,
+      after: breakBefore(lines[at + 1]),
+    };
+    hist = edit.history(baseline);
+    breakPreview = null;
+    preview = null;
+    selected = new Set();
+    say("");
+    fit(true);
+    paintStale();
+    render();
+  }
+
+  // asked for by the person using the sheet, so it may cost them their edits
+  function goTo(i) {
+    if (!review || i === index) return;
+    if (dirty() && !confirm("Discard unsaved changes to this line?")) return;
+    open(i);
+  }
+
+  function page(step) {
+    const lines = visible();
+    const at = lines.findIndex(l => l.index === index);
+    const to = lines[Math.min(Math.max(at + step, 0), lines.length - 1)];
+    if (to) goTo(to.index);
+  }
+
+  function change(next, keep = selected) {
+    hist.push({ ...hist.present, notes: next });
+    selected = new Set([...keep].filter(id => next.some(n => n.id === id)));
+    fit(false);
+    render();
+  }
+
+  function changeBreak(which, t) {
+    if (hist.present[which] === t) return;
+    hist.push({ ...hist.present, [which]: t });
+    render();
+  }
+
+  // the breaks either side of the line, each with the gap it may move in:
+  // from the end of the line before it to the start of the line after
+  function breakSlots() {
+    const ns = notes();
+    if (!hist || !ns.length) return [];
+    const lines = visible();
+    const at = lines.findIndex(l => l.index === index);
+    const prev = lines[at - 1];
+    const next = lines[at + 1];
+    const slots = [];
+    if (prev?.notes.length && hist.present.before !== undefined) {
+      slots.push({ which: "before", line: index,
+                   lo: Math.max(...prev.notes.map(n => n.end)), hi: ns[0].start });
+    }
+    if (next?.notes.length && hist.present.after !== undefined) {
+      slots.push({ which: "after", line: next.index,
+                   lo: Math.max(...ns.map(n => n.end)), hi: Math.min(...next.notes.map(n => n.start)) });
+    }
+    return slots;
+  }
+
+  // where a break is drawn; one going back to automatic is shown mid-gap,
+  // roughly where it will land
+  function breakTime(slot) {
+    const v = breakPreview?.which === slot.which ? breakPreview.t : hist.present[slot.which];
+    const t = v === null ? (slot.lo + slot.hi) / 2 : v;
+    return Math.min(Math.max(t, slot.lo), Math.max(slot.hi, slot.lo));
+  }
+
+  const undo = () => { if (hist?.canUndo) { hist.undo(); fit(false); render(); } };
+  const redo = () => { if (hist?.canRedo) { hist.redo(); fit(false); render(); } };
+  const one = () => (selected.size === 1 ? [...selected][0] : null);
+
+  function splitSelected() {
+    if (one() === null || !grid()) return;
+    const out = edit.split(notes(), one(), grid());
+    if (out.notes !== notes()) change(out.notes, new Set([out.ids[0]]));
+  }
+  function mergeSelected() {
+    if (one() !== null) change(edit.merge(notes(), one()));
+  }
+  function removeSelected() {
+    if (selected.size) change(edit.remove(notes(), selected), new Set());
+  }
+  function kind(k) {
+    if (selected.size) change(edit.setKind(notes(), selected, k));
+  }
+  function playCurrent() {
+    if (!layout) return;
+    const ns = notes();
+    const start = ns.length ? ns[0].start : layout.t0 + CONTEXT;
+    const end = ns.length ? Math.max(...ns.map(n => n.end)) : layout.t1 - CONTEXT;
+    playLine(Math.max(0, start - 0.3), end + 0.2);
+  }
+
+  function discard() {
+    if (!dirty()) return;
+    open(index);
+  }
+
+  // a change saved to the server, which answers with the refreshed review
+  async function send(path, method, body, busy, done) {
+    saving = true;
+    render();
+    say(busy);
+    try {
+      const resp = await fetch(`/api/jobs/${jobId}/${path}`, {
+        method, headers: { "Content-Type": "application/json" },
+        body: body ? JSON.stringify(body) : undefined,
+      });
+      if (!resp.ok) {
+        const err = await resp.json().catch(() => ({}));
+        say(err.detail || `error ${resp.status}`, true);
+        return false;
+      }
+      const data = await resp.json();
+      const at = index;
+      review = data;
+      gridDraft = null;
+      open(at);
+      say(done);
+      onSaved(data);
+      return true;
+    } catch {
+      say("could not reach songtrace", true);
+      return false;
+    } finally {
+      saving = false;
+      render();
+    }
+  }
+
+  // only what changed: a moved break alone must not mark the line edited
+  async function save() {
+    if (!dirty() || saving) return;
+    const state = hist.present;
+    const lines = visible();
+    const next = lines[lines.findIndex(l => l.index === index) + 1];
+    const moved = {};
+    if (state.before !== baseline.before) moved[index] = state.before;
+    if (state.after !== baseline.after && next) moved[next.index] = state.after;
+    if (state.notes !== baseline.notes &&
+        !await send(`lines/${index}`, "PUT", { notes: edit.toSaved(state.notes) }, "saving…", "saved")) {
+      return;
+    }
+    if (Object.keys(moved).length) await send("breaks", "PUT", moved, "saving…", "saved");
+  }
+
+  function revert() {
+    if (!review.lines[index].edited || saving) return;
+    if (!confirm("Go back to the generated notes for this line? Your edit is lost.")) return;
+    send(`lines/${index}`, "DELETE", null, "reverting…", "reverted to the generated notes");
+  }
+
+  // redraws on the trial grid straight away; nothing is saved until APPLY
+  function tryGrid(change, typing = null) {
+    const next = { ...grid(), ...change };
+    next.gap_ms = Math.max(0, next.gap_ms);
+    const same = review.grid && next.bpm === review.grid.bpm && next.gap_ms === review.grid.gap_ms;
+    gridDraft = same ? null : next;
+    render(typing);
+  }
+
+  function alignToNote() {
+    const note = notes().find(n => selected.has(n.id));
+    if (!note) return;
+    const g = grid();
+    const spbMs = 60000 / (4 * g.bpm);
+    const atMs = note.start * 1000;
+    const offset = (atMs - g.gap_ms) - Math.round((atMs - g.gap_ms) / spbMs) * spbMs;
+    tryGrid({ gap_ms: Math.round((g.gap_ms + offset) * 100) / 100 });
+  }
+
+  async function applyGrid() {
+    if (!gridDraft || saving) return;
+    if (dirty()) { say("save or discard this line's changes first", true); return; }
+    await send("grid", "PUT", gridDraft, "charting on the new grid…", "grid applied");
+  }
+
+  async function resetGrid() {
+    if (!review.grid_edited || saving) return;
+    if (dirty()) { say("save or discard this line's changes first", true); return; }
+    await send("grid", "DELETE", null, "resetting the grid…",
+               "grid reset to the BPM songtrace chose");
+  }
+
+  function paintGrid(typing) {
+    const g = grid();
+    gridBar.hidden = !review.grid;
+    if (!g) return;
+    const round = (v, d) => String(Math.round(v * 10 ** d) / 10 ** d);
+    // the field being typed in keeps what was typed, half-finished or not
+    if (typing !== bpmField.input) bpmField.input.value = round(g.bpm, 2);
+    if (typing !== gapField.input) gapField.input.value = round(g.gap_ms, 2);
+    gridSource.textContent = gridDraft ? "not applied"
+      : review.grid_edited ? "set in the editor"
+      : review.auto_bpm ? "songtrace's choice" : "";
+    gridSource.classList.toggle("sheet-grid-pending", !!gridDraft);
+    gridTools.align.disabled = saving || selected.size !== 1;
+    gridTools.cancel.disabled = !gridDraft || saving;
+    gridTools.apply.disabled = !gridDraft || saving;
+    gridTools.reset.disabled = !review.grid_edited || !!gridDraft || saving;
+    for (const b of [gridTools.double, gridTools.half, gridTools.earlier, gridTools.later]) {
+      b.disabled = saving;
+    }
+  }
+
+  function render(typing = null) {
+    if (!review || index === null) return;
+    const line = review.lines[index];
+    const { t0, t1, lo, hi } = layout;
+    const width = Math.max(plot.clientWidth, 320);
+    const rowH = PLOT_HEIGHT / (hi - lo + 1);
+    const x = (t) => GUTTER + ((t - t0) / (t1 - t0)) * (width - GUTTER);
+    const y = (p) => (hi - p) * rowH;   // top of the row for pitch p
+    view = { t0, t1, x, width, rowH, hi,
+             time: (px) => t0 + ((px - GUTTER) / (width - GUTTER)) * (t1 - t0),
+             pitch: (py) => hi - Math.floor(py / rowH) };
+
+    svg.setAttribute("viewBox", `0 0 ${width} ${PLOT_HEIGHT}`);
+    svg.setAttribute("width", width);
+    svg.setAttribute("height", PLOT_HEIGHT);
+    svg.replaceChildren();
+
+    const rows = el("g", { class: "sheet-rows" }, svg);
+    for (let p = lo; p <= hi; p++) {
+      el("rect", { x: GUTTER, y: y(p), width: width - GUTTER, height: rowH,
+                   class: isBlackKey(p) ? "sheet-row sheet-row-black" : "sheet-row" }, rows);
+      if (mod12(p) === 0) {
+        el("line", { x1: GUTTER, x2: width, y1: y(p) + rowH, y2: y(p) + rowH,
+                     class: "sheet-octave" }, rows);
+      }
+      // every C names its octave; the naturals between get a name when
+      // there is room for it
+      if (mod12(p) === 0 || (rowH >= 16 && !isBlackKey(p))) {
+        const label = el("text", { x: GUTTER - 6, y: y(p) + rowH / 2,
+                                   class: mod12(p) === 0 ? "sheet-key sheet-key-c" : "sheet-key" },
+                         rows);
+        label.textContent = noteName(p);
+      }
+    }
+
+    if (grid()) {
+      const beats = el("g", { class: "sheet-beats" }, svg);
+      const spbPx = x(60 / (4 * grid().bpm)) - x(0);
+      for (const b of beatLines(t0, t1, grid())) {
+        if (b.weight === 0 && spbPx < 10) continue;
+        el("line", { x1: x(b.t), x2: x(b.t), y1: 0, y2: PLOT_HEIGHT,
+                     class: `sheet-beat sheet-beat-${b.weight}` }, beats);
+      }
+    }
+
+    const layer = el("g", { class: "sheet-notes" }, svg);
+    const pad = Math.min(2, rowH * 0.12);
+    const drawNote = (n, current) => {
+      const cls = ["sheet-note", `sheet-note-${KINDS[n.kind] ?? "normal"}`];
+      if (!current) cls.push("sheet-note-context");
+      if (current && n.low_confidence) cls.push("sheet-note-low");
+      if (current && selected.has(n.id)) cls.push("sheet-note-selected");
+      const rect = el("rect", { x: x(n.start), y: y(n.pitch) + pad,
+                                width: Math.max(x(n.end) - x(n.start), 2), height: rowH - 2 * pad,
+                                rx: Math.min(4, rowH / 3), class: cls.join(" ") }, layer);
+      if (current) rect.dataset.id = n.id;
+      el("title", {}, rect).textContent = `${n.text.trim() || "~"} · ${noteName(n.pitch)}`;
+    };
+    for (const l of review.lines) {
+      if (l.dropped || l.index === index) continue;
+      for (const n of l.notes) if (n.end >= t0 && n.start <= t1) drawNote(n, false);
+    }
+    for (const n of notes()) drawNote(n, true);
+
+    const marks = el("g", { class: "sheet-breaks" }, svg);
+    for (const slot of breakSlots()) {
+      const t = breakTime(slot);
+      const value = hist.present[slot.which];
+      const byHand = value !== null &&
+        (value !== baseline[slot.which] || review.breaks?.find(b => b.line === slot.line)?.moved);
+      const cls = `sheet-break${byHand ? " sheet-break-moved" : ""}`;
+      el("line", { x1: x(t), x2: x(t), y1: 0, y2: PLOT_HEIGHT, class: cls }, marks);
+      el("text", { x: x(t) + 3, y: 11, class: `${cls} sheet-break-label` }, marks)
+        .textContent = "↵";
+    }
+
+    syllables.replaceChildren(...notes().map(n => {
+      const s = div("sheet-syllable" + (selected.has(n.id) ? " sheet-syllable-selected" : ""),
+                    n.text.trim() || "~");
+      s.style.left = `${x(n.start)}px`;
+      s.dataset.id = n.id;
+      return s;
+    }));
+
+    // over the notes: the curve matters most where it agrees with one
+    if (curve) {
+      const g = el("g", { class: "sheet-curve" }, svg);
+      const from = Math.max(0, Math.floor((t0 - curve.start) / curve.step));
+      const to = Math.min(curve.pitch.length, Math.ceil((t1 - curve.start) / curve.step));
+      let pts = [];
+      const flush = () => {
+        if (pts.length > 1) el("polyline", { points: pts.join(" ") }, g);
+        pts = [];
+      };
+      for (let k = from; k < to; k++) {
+        const p = curve.pitch[k];
+        if (p === null || p < lo - 0.5 || p > hi + 0.5) { flush(); continue; }
+        pts.push(`${x(curve.start + k * curve.step).toFixed(1)},${(y(p) + rowH / 2).toFixed(1)}`);
+      }
+      flush();
+    }
+
+    words.replaceChildren(...line.words.map(w => {
+      const node = div("sheet-word", w.text);
+      node.style.left = `${x(w.start)}px`;
+      node.style.width = `${Math.max(x(w.end) - x(w.start), 2)}px`;
+      return node;
+    }));
+
+    const lines = visible();
+    const at = lines.findIndex(l => l.index === index);
+    title.textContent = `LINE ${at + 1} / ${lines.length}`;
+    prev.disabled = at <= 0;
+    next.disabled = at >= lines.length - 1;
+    const tags = [];
+    if (dirty()) tags.push(["unsaved", "sheet-badge-dirty"]);
+    if (line.edited) tags.push(["edited", "sheet-badge-edited"]);
+    if (notes().some(n => n.low_confidence)) tags.push(["low confidence", "sheet-badge-low"]);
+    badges.replaceChildren(...tags.map(([text, cls]) => div(`sheet-badge ${cls}`, text)));
+
+    paintTools();
+    paintGrid(typing);
+  }
+
+  function paintSelection() {
+    for (const node of root.querySelectorAll("[data-id]")) {
+      const on = selected.has(Number(node.dataset.id));
+      node.classList.toggle(node.tagName === "rect" ? "sheet-note-selected"
+                                                     : "sheet-syllable-selected", on);
+    }
+    paintTools();
+    paintGrid();
+  }
+
+  function paintTools() {
+    const line = review.lines[index];
+    const editable = canEdit();
+    tools.undo.disabled = !editable || !hist.canUndo;
+    tools.redo.disabled = !editable || !hist.canRedo;
+    tools.split.disabled = tools.merge.disabled = !editable || one() === null;
+    for (const b of [tools.remove, tools.golden, tools.free, tools.rap]) {
+      b.disabled = !editable || !selected.size;
+    }
+    tools.discard.disabled = !dirty() || saving;
+    tools.save.disabled = !dirty() || saving;
+    tools.revert.disabled = !line.edited || saving;
+  }
+
+  // --- pointer -------------------------------------------------------------
+
+  function hit(e) {
+    const box = plot.getBoundingClientRect();
+    const px = e.clientX - box.left;
+    const py = e.clientY - box.top;
+    // by geometry, not the event's target: a render replaces the elements
+    // under the pointer, and the topmost note drawn wins
+    if (canEdit()) {
+      const brk = breakSlots().find(s => Math.abs(px - view.x(breakTime(s))) <= 5);
+      if (brk) return { px, py, note: null, brk, mode: "break" };
+    }
+    const pitch = view.pitch(py);
+    const note = [...notes()].reverse().find(n => n.pitch === pitch &&
+      px >= view.x(n.start) - 1 && px <= view.x(n.end) + 1) ?? null;
+    let mode = null;
+    if (note) {
+      const left = view.x(note.start);
+      const right = view.x(note.end);
+      mode = right - left > 3 * EDGE && px >= right - EDGE ? "end"
+           : right - left > 3 * EDGE && px <= left + EDGE ? "start" : "move";
+    }
+    return { px, py, note, brk: null, mode };
+  }
+
+  plot.addEventListener("pointermove", (e) => {
+    if (!view) return;
+    if (!drag) {
+      const { note, brk, mode } = hit(e);
+      plot.style.cursor = brk ? "col-resize"
+                        : !note || !canEdit() ? "crosshair"
+                        : mode === "move" ? "grab" : "ew-resize";
+      return;
+    }
+    const box = plot.getBoundingClientRect();
+    const px = e.clientX - box.left;
+    const py = e.clientY - box.top;
+    if (Math.abs(px - drag.px) + Math.abs(py - drag.py) > 3) drag.moved = true;
+    if (drag.moved && drag.brk) {
+      const { which, lo, hi } = drag.brk;
+      breakPreview = { which, t: edit.placeBreak(view.time(px), lo, hi, grid()) };
+      render();
+      return;
+    }
+    if (!drag.moved || !drag.note) return;
+    if (drag.mode === "move") {
+      const spbPx = view.x(60 / (4 * grid().bpm)) - view.x(0);
+      const beats = Math.round((px - drag.px) / spbPx);
+      const semis = Math.round((drag.py - py) / view.rowH);
+      preview = edit.move(drag.base, selected, beats, semis, grid());
+    } else {
+      preview = edit.resize(drag.base, drag.note.id, drag.mode, view.time(px), grid());
+    }
+    render();
+  });
+
+  plot.addEventListener("pointerdown", (e) => {
+    if (!view || e.button !== 0) return;
+    // the browser's own focus handling would otherwise take focus off the
+    // sheet, and with it the keyboard
+    e.preventDefault();
+    plot.focus();
+    const { px, py, note, brk, mode } = hit(e);
+    if (px < GUTTER) return;
+    if (brk) plot.setPointerCapture(e.pointerId);
+    if (note && canEdit()) {
+      if (e.shiftKey) {
+        selected = new Set(selected);
+        if (selected.has(note.id)) selected.delete(note.id); else selected.add(note.id);
+      } else if (!selected.has(note.id)) {
+        selected = new Set([note.id]);
+      }
+      plot.setPointerCapture(e.pointerId);
+      plot.style.cursor = mode === "move" ? "grabbing" : "ew-resize";
+      paintSelection();
+    }
+    drag = { px, py, note, brk, mode, base: notes(), moved: false };
+  });
+
+  const endDrag = (e, cancelled) => {
+    if (!drag) return;
+    const d = drag;
+    drag = null;
+    if (breakPreview) {
+      const { which, t } = breakPreview;
+      breakPreview = null;
+      if (cancelled) render(); else changeBreak(which, t);
+    } else if (preview) {
+      const next = preview;
+      preview = null;
+      if (cancelled) render(); else change(next);
+    } else if (!d.moved && !d.note && !d.brk && !cancelled) {
+      selected = new Set();
+      render();
+      seek(view.time(d.px));
+    }
+    if (plot.hasPointerCapture?.(e.pointerId)) plot.releasePointerCapture(e.pointerId);
+  };
+  plot.addEventListener("pointerup", (e) => endDrag(e, false));
+  plot.addEventListener("pointercancel", (e) => endDrag(e, true));
+
+  plot.addEventListener("dblclick", (e) => {
+    if (!view || !canEdit()) return;
+    const { px, py, note, brk } = hit(e);
+    if (px < GUTTER) return;
+    if (brk) { changeBreak(brk.which, null); return; }   // back to automatic
+    if (note) { editText(note.id); return; }
+    const out = edit.insert(notes(), view.time(px), view.pitch(py), grid());
+    change(out.notes, new Set([out.id]));
+    editText(out.id);
+  });
+
+  // --- syllable text -------------------------------------------------------
+
+  function editText(id) {
+    const note = notes().find(n => n.id === id);
+    if (!note) return;
+    const input = document.createElement("input");
+    input.className = "sheet-text-input";
+    input.value = note.text.trim();
+    input.style.left = `${view.x(note.start)}px`;
+    input.setAttribute("aria-label", "syllable");
+    syllables.append(input);
+    input.focus();
+    input.select();
+    let done = false;
+    const finish = (commit) => {
+      if (done) return;
+      done = true;
+      const value = input.value;
+      input.remove();
+      if (commit) {
+        const next = edit.setText(notes(), id, value);
+        if (next !== notes()) change(next);
+      }
+      plot.focus();
+    };
+    input.addEventListener("keydown", (e) => {
+      e.stopPropagation();
+      if (e.key === "Enter") finish(true);
+      else if (e.key === "Escape") finish(false);
+    });
+    input.addEventListener("blur", () => finish(true));
+  }
+
+  syllables.addEventListener("dblclick", (e) => {
+    const id = e.target.dataset?.id;
+    if (id) editText(Number(id));
+  });
+
+  // --- keyboard ------------------------------------------------------------
+
+  plot.addEventListener("keydown", (e) => {
+    if (!view) return;
+    const ctrl = e.ctrlKey || e.metaKey;
+    const key = e.key;
+    const handled = () => { e.preventDefault(); e.stopPropagation(); };
+    if (ctrl && key.toLowerCase() === "s") { handled(); save(); return; }
+    if (ctrl && key.toLowerCase() === "z") { handled(); e.shiftKey ? redo() : undo(); return; }
+    if (ctrl && key.toLowerCase() === "y") { handled(); redo(); return; }
+    if (key === "PageUp") { handled(); page(-1); return; }
+    if (key === "PageDown") { handled(); page(1); return; }
+    if (ctrl || e.altKey || !canEdit()) return;
+    const ns = notes();
+    if (key === "Tab") {
+      handled();
+      if (!ns.length) return;
+      const at = ns.findIndex(n => selected.has(n.id));
+      const to = at < 0 ? (e.shiftKey ? ns.length - 1 : 0)
+                        : (at + (e.shiftKey ? -1 : 1) + ns.length) % ns.length;
+      selected = new Set([ns[to].id]);
+      render();
+      return;
+    }
+    if (key === "?") { handled(); toggleKeys(); return; }
+    if (key === "Escape") {
+      handled();
+      if (!keys.hidden) showKeys(false);
+      else { selected = new Set(); render(); }
+      return;
+    }
+    if (key.toLowerCase() === "p") { handled(); playCurrent(); return; }
+    if (!selected.size) return;
+    const arrows = { ArrowLeft: -1, ArrowRight: 1 };
+    if (key in arrows) {
+      handled();
+      change(e.shiftKey ? edit.stretch(ns, selected, arrows[key], grid())
+                        : edit.move(ns, selected, arrows[key], 0, grid()));
+    } else if (key === "ArrowUp" || key === "ArrowDown") {
+      handled();
+      change(edit.move(ns, selected, 0, (key === "ArrowUp" ? 1 : -1) * (e.shiftKey ? 12 : 1), grid()));
+    } else if (key === "Delete" || key === "Backspace") {
+      handled(); removeSelected();
+    } else if (key === "Enter" && one() !== null) {
+      handled(); editText(one());
+    } else if (key.toLowerCase() === "s") {
+      handled(); splitSelected();
+    } else if (key.toLowerCase() === "m") {
+      handled(); mergeSelected();
+    } else if ({ g: "*", f: "F", r: "R" }[key.toLowerCase()]) {
+      handled(); kind({ g: "*", f: "F", r: "R" }[key.toLowerCase()]);
+    }
+  });
+
+  window.addEventListener("beforeunload", (e) => {
+    if (dirty()) e.preventDefault();
+  });
+
+  new ResizeObserver(() => render()).observe(plot);
+
+  return {
+    // keeps the line on show when the song is the same one, refreshed
+    load(id, data) {
+      const same = id === jobId;
+      review = data;
+      root.hidden = false;
+      if (!same) {
+        jobId = id;
+        curve = null;
+        gridDraft = null;
+        fetch(`/api/jobs/${id}/pitch`)
+          .then(r => (r.ok ? r.json() : null))
+          .then(c => { if (jobId === id) { curve = c; render(); } })
+          .catch(() => {});
+      }
+      const lines = visible();
+      if (!lines.length) { root.hidden = true; return; }
+      open(same && lines.some(l => l.index === index) ? index : lines[0].index);
+    },
+    clear() {
+      review = null;
+      jobId = null;
+      curve = null;
+      index = null;
+      view = layout = hist = baseline = preview = gridDraft = null;
+      root.hidden = true;
+    },
+    // playback following the song: never at the cost of unsaved edits
+    showLine(i) {
+      if (review && i !== index && !dirty()) open(i);
+    },
+    isDirty: dirty,
+    setTime(t) {
+      if (!view) return;
+      const inside = t >= view.t0 && t <= view.t1;
+      playhead.hidden = !inside;
+      if (inside) playhead.style.left = `${view.x(t)}px`;
+    },
+  };
+}

src/songtrace/web.py

@@ -9,19 +9,25 @@ import uuid
 from dataclasses import asdict, dataclass, field
 from pathlib import Path
 
-from fastapi import FastAPI, File, Form, HTTPException, UploadFile
+import numpy as np
+from fastapi import Body, FastAPI, File, Form, HTTPException, UploadFile
 from fastapi.concurrency import run_in_threadpool
 from fastapi.responses import FileResponse
 from fastapi.staticfiles import StaticFiles
 
+from . import edits, grid
 from . import rebuild as rebuild_policy
 from .config import Config
 from .lyrics import normalize_lyrics
+from .notes import CONF_MASK
 from .pipeline import (STAGE_ORDER, PipelineError, SongInput, read_warnings,
                        run_pipeline, song_slug)
+from .ultrastar import get_header, parse_ultrastar
 
 STATIC = Path(__file__).parent / "static"
 STAGE_LINE = re.compile(r"^\[(\w+)\] (?:running|cached, skipping)")
+# the song folder names its own media, exactly as the game reads it
+MEDIA_HEADERS = {"audio": "MP3", "video": "VIDEO", "cover": "COVER"}
 
 
 @dataclass
@@ -74,7 +80,7 @@ def _cleanup_uploads(cfg: Config, job_id: str, video_path: Path | None) -> None:
     Covers are left behind: they are small, and a rebuild inherits cover_path, so
     removing one would silently strip #COVER from the rebuilt song. A rebuild can
     also inherit its parent's upload, so the directory is not always uploads/<job_id>.
-    Never raises — the caller has already marked the job done.
+    Never raises, so cleaning up cannot fail a job that otherwise succeeded.
     """
     uploads = (cfg.work_dir / "uploads").resolve()
     dirs = {uploads / job_id}
@@ -129,6 +135,7 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
     jobs: dict[str, Job] = {}
     order: list[str] = []
     lock = threading.Lock()
+    edit_lock = threading.Lock()
     todo: queue.Queue[str] = queue.Queue()
 
     for job in _discover_jobs(cfg):
@@ -137,18 +144,18 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
 
     def _prepare_rebuild(job: Job, log) -> str | None:
         """Relocate cached work and report the stage this rebuild restarts from."""
-        if job.force_stage:
-            log(f"[rebuild] restarting from {job.force_stage} (forced rebuild from scratch)")
-            return job.force_stage
         if not job.rebuilt_from:
-            return None
+            return job.force_stage
         with lock:
             parent = jobs.get(job.rebuilt_from)
         if parent is None:
-            return None
-        force_from = rebuild_policy.plan(parent.inp, job.inp)
+            return job.force_stage
+        planned = rebuild_policy.plan(parent.inp, job.inp)
         changed = rebuild_policy.changed_fields(parent.inp, job.inp)
         rebuild_policy.relocate_work(parent.inp, job.inp, cfg)
+        # a stage the operator asked for can only widen what plan() decided,
+        # which is how "redo the packaging" reaches work nothing invalidated
+        force_from = rebuild_policy.earliest(planned, job.force_stage)
         log(f"[rebuild] restarting from {force_from or 'the first incomplete stage'}"
             f" ({', '.join(changed) if changed else 'nothing'} changed)")
         return force_from
@@ -190,6 +197,7 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
                     if m := STAGE_LINE.match(msg):
                         job.stage = m[1]
 
+            status, error = "done", None
             try:
                 force_from = _prepare_rebuild(job, log)
                 _write_sidecar(job)
@@ -198,18 +206,15 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
                     job.output_dir = str(result.output_dir)
                     job.warnings = list(result.warnings)
                 _drop_superseded_output(job, log)
-                with lock:
-                    job.status = "done"
                 # uploads survive a failure so the job stays rerunnable; acquire
                 # has already copied the video into the work dir by now.
                 _cleanup_uploads(cfg, job_id, job.inp.video_path)
             except BaseException as e:
-                with lock:
-                    job.status = "failed"
-                    job.error = str(e)
-            finally:
-                with lock:
-                    job.finished_at = time.time()
+                status, error = "failed", str(e)
+            # last, and all at once: a client that sees the job finished must
+            # find everything finishing it does already done
+            with lock:
+                job.status, job.error, job.finished_at = status, error, time.time()
 
     threading.Thread(target=worker, daemon=True).start()
 
@@ -245,6 +250,7 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
                       cover: UploadFile | None = File(None)):
         youtube_url, genre, language = (youtube_url or None, genre or None,
                                         language or None)
+        lyrics = lyrics.replace("\r\n", "\n")
         has_video = bool(video and video.filename)
         if bool(youtube_url) == has_video:
             raise HTTPException(400, "provide exactly one of youtube_url / video")
@@ -290,13 +296,20 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
                       lyrics: str = Form(...), youtube_url: str | None = Form(None),
                       genre: str | None = Form(None), year: int | None = Form(None),
                       language: str | None = Form(None), bpm: float | None = Form(None),
+                      force_from: str | None = Form(None),
                       video: UploadFile | None = File(None),
                       cover: UploadFile | None = File(None)):
         parent = _finished_job(job_id)
+        force_from = force_from or None
+        if force_from is not None and force_from not in STAGE_ORDER:
+            raise HTTPException(400, f"unknown stage {force_from!r}")
         # a cleared field arrives as "" from some clients; "" and None must not
         # look like different inputs to plan()
         youtube_url, genre, language = (youtube_url or None, genre or None,
                                         language or None)
+        # a browser submits a textarea with CRLF; without this every rebuild
+        # from the page looks like a lyrics edit and redoes the alignment
+        lyrics = lyrics.replace("\r\n", "\n")
         has_video = bool(video and video.filename)
         if youtube_url and has_video:
             raise HTTPException(400, "provide exactly one of youtube_url / video")
@@ -314,8 +327,54 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
                         youtube_url=youtube_url, video_path=video_path,
                         genre=genre, year=year, language=language,
                         cover_path=cover_path, bpm_override=bpm)
-        _require_source(parent.inp, inp, rebuild_policy.plan(parent.inp, inp))
-        return _enqueue(new_id, inp, rebuilt_from=job_id)
+        _require_source(parent.inp, inp, rebuild_policy.earliest(
+            rebuild_policy.plan(parent.inp, inp), force_from))
+        return _enqueue(new_id, inp, rebuilt_from=job_id, force_stage=force_from)
+
+    def _current_songs() -> list[Job]:
+        """The job that stands for each song now, newest first."""
+        with lock:
+            # a job that was rebuilt is history: its rebuild is the song now,
+            # possibly under another slug
+            rebuilt = {j.rebuilt_from for j in jobs.values()}
+            latest = {song_slug(j.inp): j for j in (jobs[i] for i in order)
+                      if j.id not in rebuilt}
+            position = {job_id: n for n, job_id in enumerate(order)}
+            return sorted(latest.values(), key=lambda j: position[j.id], reverse=True)
+
+    @app.get("/api/rebuild-all")
+    def rebuild_all_candidates():
+        return [{"id": j.id, "title": j.title, "artist": j.artist,
+                 "status": j.status, "rebuilt_from": j.rebuilt_from,
+                 "finished_at": j.finished_at}
+                for j in _current_songs()]
+
+    @app.post("/api/rebuild-all", status_code=201)
+    def rebuild_all(force_from: str = Form(...), ids: list[str] | None = Form(None)):
+        """Rebuild every song, or the ones in `ids`, from `force_from` on, for
+        when songtrace itself improved that stage. Each is an ordinary rebuild
+        with unchanged inputs."""
+        if force_from not in STAGE_ORDER:
+            raise HTTPException(400, f"unknown stage {force_from!r}")
+        songs = _current_songs()
+        queued, skipped = [], []
+        if ids is not None:
+            current = {j.id for j in songs}
+            skipped = [{"id": i, "reason": "no longer the current job for its song"}
+                       for i in ids if i not in current]
+            songs = [j for j in songs if j.id in set(ids)]
+        for job in songs:
+            if job.status in ("queued", "running"):
+                skipped.append({"id": job.id, "reason": "still in progress"})
+                continue
+            try:
+                _require_source(job.inp, job.inp, force_from)
+            except HTTPException as e:
+                skipped.append({"id": job.id, "reason": e.detail})
+                continue
+            queued.append(_enqueue(uuid.uuid4().hex, job.inp, rebuilt_from=job.id,
+                                   force_stage=force_from)["id"])
+        return {"ids": queued, "skipped": skipped}
 
     @app.get("/api/stages")
     def list_stages():
@@ -376,13 +435,44 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
         shutil.rmtree(cfg.work_dir / slug, ignore_errors=True)
         shutil.rmtree(cfg.output_dir / slug, ignore_errors=True)
 
+    def _resolve_media(job: Job, header: str) -> Path | None:
+        """The file a song folder's #MP3/#VIDEO/#COVER header points at."""
+        slug = song_slug(job.inp)
+        out = (cfg.output_dir / slug).resolve()
+        txt = out / f"{slug}.txt"
+        if not txt.exists():
+            return None
+        name = get_header(parse_ultrastar(txt.read_text(encoding="utf-8")), header)
+        if not name:
+            return None
+        # a header names a file in the song folder and nothing else
+        path = (out / name).resolve()
+        if path.parent != out or not path.is_file():
+            return None
+        return path
+
+    @app.get("/api/jobs/{job_id}/media/{kind}")
+    def get_media(job_id: str, kind: str):
+        header = MEDIA_HEADERS.get(kind)
+        if header is None:
+            raise HTTPException(404)
+        job = _finished_job(job_id)
+        if job.status != "done":
+            raise HTTPException(404)
+        path = _resolve_media(job, header)
+        if path is None:
+            raise HTTPException(404)
+        return FileResponse(path)
+
     @app.get("/api/jobs/{job_id}/review")
     def get_review(job_id: str):
         job = _finished_job(job_id)
         if job.status != "done":
             raise HTTPException(404)
         work = cfg.work_dir / song_slug(job.inp)
-        notes_file = work / "notes_sec.json"
+        notes_file = work / edits.FINAL_FILE
+        if not notes_file.exists():
+            notes_file = work / "notes_sec.json"
         if not notes_file.exists():
             raise HTTPException(404)
         notes_data = json.loads(notes_file.read_text())
@@ -402,11 +492,166 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
         for n in notes_data["notes"]:
             by_line.setdefault(n["line_index"], []).append({
                 "start": n["start"], "end": n["start"] + n["duration"],
-                "pitch": n["pitch"], "low_confidence": n["low_confidence"]})
+                "pitch": n["pitch"], "low_confidence": n["low_confidence"],
+                "text": n["text"], "kind": n.get("kind", ":")})
+        edited = set(notes_data.get("edited_lines", []))
         lines = [{"index": i, "text": " ".join(words), "dropped": i in dropped,
+                  "edited": i in edited,
                   "notes": by_line.get(i, []), "words": words_by_line.get(i, [])}
                  for i, words in enumerate(ref.lines)]
-        return {"lines": lines, "missing_spans": missing_spans}
+        stale = [{"text": " ".join(e["words"]), "notes": e["notes"]}
+                 for e in notes_data.get("stale", [])]
+        media = {kind: _resolve_media(job, header) is not None
+                 for kind, header in MEDIA_HEADERS.items()}
+        # each break with the line it comes before, the key a move is saved by
+        moved = set(notes_data.get("moved_breaks", []))
+        starts = sorted((n["start"], n["line_index"]) for n in notes_data["notes"]
+                        if "line_index" in n)
+        breaks = []
+        for t in notes_data.get("breaks", []):
+            after = next((li for start, li in starts if start >= t), None)
+            if after is not None:
+                breaks.append({"line": after, "time": t, "moved": after in moved})
+        return {"lines": lines, "missing_spans": missing_spans, "media": media,
+                "stale": stale, "breaks": breaks, "grid": _chart_grid(work),
+                "grid_edited": bool(notes_data.get("grid")), "auto_bpm": _auto_bpm(work)}
+
+    @app.get("/api/jobs/{job_id}/pitch")
+    def get_pitch(job_id: str):
+        """The detected vocal pitch, to draw behind the notes: UltraStar
+        semitones (0 = C4) every `step` seconds, null where nothing is sung."""
+        job = _finished_job(job_id)
+        path = cfg.work_dir / song_slug(job.inp) / "pitch.npz"
+        if not path.exists():
+            raise HTTPException(404)
+        data = np.load(path)
+        times, f0, conf = data["times"], data["f0"], data["conf"]
+        # every other 10ms frame is still finer than a note can be drawn
+        stride = 2
+        f0, conf = f0[::stride], conf[::stride]
+        voiced = (conf >= CONF_MASK) & (f0 > 0)
+        semis = 9 + 12 * np.log2(np.where(voiced, f0, 440.0) / 440.0)
+        hop = float(times[1] - times[0]) if len(times) > 1 else 0.01
+        return {"start": float(times[0]) if len(times) else 0.0, "step": hop * stride,
+                "pitch": [round(float(v), 2) if ok else None
+                          for v, ok in zip(semis, voiced)]}
+
+    def _chart_grid(work: Path) -> dict | None:
+        """The beat grid the chart was built on, for snapping edits to it."""
+        txt = work / "song.txt"
+        if not txt.exists():
+            return None
+        song = parse_ultrastar(txt.read_text(encoding="utf-8"))
+        bpm, gap = get_header(song, "BPM"), get_header(song, "GAP")
+        if bpm is None or gap is None:
+            return None
+        return {"bpm": float(bpm.replace(",", ".")), "gap_ms": float(gap.replace(",", "."))}
+
+    def _editable(job_id: str) -> Job:
+        job = _finished_job(job_id)
+        slug = song_slug(job.inp)
+        with lock:
+            # a build of this song would overwrite the chart being edited
+            if any(j.status in ("queued", "running") and song_slug(j.inp) == slug
+                   for j in jobs.values()):
+                raise HTTPException(409, "this song is being rebuilt")
+        if job.status != "done":
+            raise HTTPException(409, "only a finished song can be edited")
+        return job
+
+    def _edit(job_id: str, change) -> dict:
+        """Apply `change` to the song's edits, then rewrite its charts."""
+        job = _editable(job_id)
+        work = cfg.work_dir / song_slug(job.inp)
+        lyrics = normalize_lyrics(job.inp.lyrics_text).lines
+        with edit_lock:
+            data = edits.load(work, lyrics)
+            try:
+                change(data, lyrics)
+            except ValueError as e:
+                raise HTTPException(400, str(e))
+            edits.save(work, data)
+            final = edits.finalize(work, lyrics)
+            # the editor's grid, else the pipeline's own tempo with GAP at
+            # the first note, as the grid stage would chart it
+            chosen = final["grid"] or {"bpm": _auto_bpm(work), "gap_ms": None}
+            charts = [work / "song.txt"]
+            if job.output_dir:
+                charts.append(Path(job.output_dir) / f"{song_slug(job.inp)}.txt")
+            for txt in charts:
+                if txt.exists():
+                    grid.rechart(txt, final["notes"], final["breaks"],
+                                 chosen["bpm"], chosen["gap_ms"])
+        with lock:
+            job.warnings = list(final["warnings"])
+        return get_review(job_id)
+
+    def _auto_bpm(work: Path) -> float | None:
+        """The tempo the pipeline chose: recorded by grid, or for a song built
+        before that was, the one its chart already has."""
+        try:
+            return float(json.loads((work / grid.TEMPO_FILE).read_text())["bpm"])
+        except (OSError, ValueError, KeyError):
+            g = _chart_grid(work)
+            return g["bpm"] if g else None
+
+    @app.put("/api/jobs/{job_id}/breaks")
+    def save_breaks(job_id: str, body: dict = Body(...)):
+        """Move line breaks: {line: seconds}, keyed by the line each comes
+        before; null puts one back where the notes alone would place it."""
+        return _edit(job_id, lambda data, lyrics: edits.set_breaks(data, body))
+
+    @app.put("/api/jobs/{job_id}/grid")
+    def save_grid(job_id: str, body: dict = Body(...)):
+        """Set the chart's BPM and GAP, kept through rebuilds like any edit."""
+        job = _editable(job_id)
+        work = cfg.work_dir / song_slug(job.inp)
+        tempo = work / grid.TEMPO_FILE
+        # a song built before grid recorded its tempo: the chart's, taken now
+        # while it is still the pipeline's, is what RESET must return to
+        if not tempo.exists() and (bpm := _auto_bpm(work)) is not None:
+            tempo.write_text(json.dumps({"bpm": bpm}))
+        return _edit(job_id, lambda data, lyrics: edits.set_grid(
+            data, body.get("bpm"), body.get("gap_ms")))
+
+    @app.delete("/api/jobs/{job_id}/grid")
+    def reset_grid(job_id: str):
+        """Go back to the BPM the pipeline chose and GAP at the first note."""
+        def change(data, lyrics):
+            if not edits.clear_grid(data):
+                raise HTTPException(404, "the grid was not set in the editor")
+        return _edit(job_id, change)
+
+    def _line(lyrics, index: int) -> int:
+        if not 0 <= index < len(lyrics):
+            raise HTTPException(404, f"no line {index}")
+        return index
+
+    @app.put("/api/jobs/{job_id}/lines/{index}")
+    def save_line(job_id: str, index: int, body: dict = Body(...)):
+        """Save a line as edited: its full note list, in seconds."""
+        notes = body.get("notes")
+        if not isinstance(notes, list):
+            raise HTTPException(400, "body must be {\"notes\": [...]}")
+        return _edit(job_id, lambda data, lyrics: edits.set_line(
+            data, _line(lyrics, index), notes))
+
+    @app.delete("/api/jobs/{job_id}/lines/{index}")
+    def revert_line(job_id: str, index: int):
+        """Drop a line's edit, so it follows what the pipeline generates."""
+        def change(data, lyrics):
+            if not edits.clear_line(data, _line(lyrics, index)):
+                raise HTTPException(404, f"line {index} has no edit")
+        return _edit(job_id, change)
+
+    @app.delete("/api/jobs/{job_id}/stale/{n}")
+    def discard_stale(job_id: str, n: int):
+        """Throw away an edit whose line's lyrics have since changed."""
+        def change(data, lyrics):
+            if not 0 <= n < len(data["stale"]):
+                raise HTTPException(404, f"no stale edit {n}")
+            data["stale"].pop(n)
+        return _edit(job_id, change)
 
     return app
 

src/songtrace/ytdlp.py

@@ -0,0 +1,185 @@
+"""The one place songtrace touches yt-dlp.
+
+YouTube breaks old yt-dlp releases faster than songtrace is released, so
+besides the copy installed with songtrace (the bundled one), newer stable
+releases are fetched from PyPI into a cache dir at runtime and tried first,
+with the bundled copy as the fallback. yt-dlp runs in a subprocess and is
+driven through its command line, its most stable interface, so a cached
+release never mixes with anything songtrace has imported.
+"""
+import importlib.metadata
+import os
+import re
+import shutil
+import subprocess
+import sys
+import tempfile
+import threading
+import time
+from dataclasses import dataclass
+from pathlib import Path
+
+import httpx
+
+from .config import Config
+from .pipeline import PipelineError
+
+# The extras are what make YouTube work; see pyproject.toml.
+REQUIREMENT = "yt-dlp[default,curl-cffi,deno]"
+CHECK_INTERVAL = 24 * 3600
+_lock = threading.Lock()
+
+
+class YtDlpError(PipelineError):
+    pass
+
+
+def _key(version: str) -> tuple[int, ...]:
+    return tuple(int(p) for p in version.split("."))
+
+
+def cache_dir() -> Path:
+    base = os.environ.get("XDG_CACHE_HOME") or Path.home() / ".cache"
+    # Installs hold compiled wheels, so they are only good for one Python.
+    return Path(base) / "songtrace" / f"yt-dlp-py{sys.version_info[0]}{sys.version_info[1]}"
+
+
+@dataclass(frozen=True)
+class YtDlp:
+    version: str
+    path: Path | None = None  # None for the bundled copy
+
+    def _env(self) -> dict[str, str]:
+        env = dict(os.environ)
+        if self.path:
+            env["PYTHONPATH"] = os.pathsep.join(
+                filter(None, [str(self.path), env.get("PYTHONPATH")]))
+            env["PATH"] = os.pathsep.join(
+                [str(self.path / "bin"), env.get("PATH", "")])
+        return env
+
+    def run(self, args: list[str], log) -> None:
+        """Runs yt-dlp with `args`, passing each line it prints to `log`."""
+        proc = subprocess.Popen(
+            [sys.executable, "-P", "-m", "yt_dlp", "--ignore-config", *args],
+            stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True,
+            errors="replace", env=self._env())
+        last = error = ""
+        for line in proc.stdout:
+            last = line.rstrip()
+            log(last)
+            if last.startswith("ERROR:"):
+                error = last
+        if proc.wait() == 0:
+            return
+        if proc.returncode == 2:
+            raise YtDlpError(f"yt-dlp {self.version} rejected songtrace's "
+                             f"options, so it may be incompatible: {last}")
+        raise YtDlpError(error or f"yt-dlp exited with status {proc.returncode}")
+
+
+def bundled() -> YtDlp:
+    return YtDlp(importlib.metadata.version("yt-dlp"))
+
+
+def _latest_release() -> str:
+    r = httpx.get("https://pypi.org/pypi/yt-dlp/json", timeout=15,
+                  follow_redirects=True)
+    r.raise_for_status()
+    return r.json()["info"]["version"]
+
+
+def _pip_install(target: Path, version: str) -> None:
+    proc = subprocess.run(
+        [sys.executable, "-m", "pip", "install", "--quiet", "--no-input",
+         "--disable-pip-version-check", "--target", str(target),
+         f"{REQUIREMENT}=={version}"],
+        capture_output=True, text=True)
+    if proc.returncode:
+        raise YtDlpError(f"pip could not install yt-dlp {version}: "
+                         f"{proc.stderr.strip()[-500:]}")
+
+
+def _install(version: str, log) -> YtDlp:
+    """Installs `version` into the cache unless it is already there.
+
+    The install is checked to run before it is moved into place, so a
+    directory in the cache is always a usable yt-dlp."""
+    dest = cache_dir() / version
+    if dest.is_dir():
+        return YtDlp(version, dest)
+    dest.parent.mkdir(parents=True, exist_ok=True)
+    log(f"installing yt-dlp {version}")
+    tmp = Path(tempfile.mkdtemp(dir=dest.parent, prefix=".tmp-"))
+    try:
+        _pip_install(tmp, version)
+        proc = subprocess.run(
+            [sys.executable, "-P", "-m", "yt_dlp", "--version"],
+            capture_output=True, text=True, env=YtDlp(version, tmp)._env())
+        got = proc.stdout.strip()
+        if proc.returncode or _key(got) != _key(version):
+            raise YtDlpError(f"yt-dlp {version} failed its check after install: "
+                             f"{(got or proc.stderr.strip())[-500:]}")
+        try:
+            tmp.rename(dest)
+        except OSError:
+            if not dest.is_dir():
+                raise
+    finally:
+        shutil.rmtree(tmp, ignore_errors=True)
+    return YtDlp(version, dest)
+
+
+def _cached() -> list[YtDlp]:
+    root = cache_dir()
+    if not root.is_dir():
+        return []
+    found = [YtDlp(p.name, p) for p in root.iterdir()
+             if p.is_dir() and re.fullmatch(r"\d+(\.\d+)*", p.name)]
+    return sorted(found, key=lambda y: _key(y.version))
+
+
+def _newest(base: YtDlp, refresh: bool, log) -> YtDlp | None:
+    """The newest cached release newer than `base`, checking PyPI for a newer
+    one first if that has not been done for a day or `refresh` is set."""
+    marker = cache_dir() / ".checked"
+    if (refresh or not marker.exists()
+            or time.time() - marker.stat().st_mtime > CHECK_INTERVAL):
+        # Recorded even on failure, so a broken release is not reinstalled
+        # for every job; a failed download refreshes regardless.
+        marker.parent.mkdir(parents=True, exist_ok=True)
+        marker.touch()
+        try:
+            latest = _latest_release()
+            if _key(latest) > _key(base.version):
+                _install(latest, log)
+        except Exception as e:
+            log(f"could not update yt-dlp: {e}")
+    newer = [y for y in _cached() if _key(y.version) > _key(base.version)]
+    for old in newer[:-1]:
+        shutil.rmtree(old.path, ignore_errors=True)
+    return newer[-1] if newer else None
+
+
+def candidates(cfg: Config, log, refresh: bool = False) -> list[YtDlp]:
+    """The yt-dlp copies to try, in order: the newest release (or the one
+    `cfg.ytdlp_version` pins), then the bundled copy."""
+    base = bundled()
+    want = cfg.ytdlp_version
+    if want == "bundled":
+        return [base]
+    with _lock:
+        if want == "auto":
+            first = _newest(base, refresh, log)
+        elif not re.fullmatch(r"\d+(\.\d+)*", want):
+            raise YtDlpError(f"ytdlp_version must be \"auto\", \"bundled\" or a "
+                             f"release such as \"2026.08.19\", not {want!r}")
+        elif _key(want) == _key(base.version):
+            first = None
+        else:
+            try:
+                first = _install(want, log)
+            except Exception as e:
+                log(f"could not install the pinned yt-dlp {want}: {e}")
+                first = None
+    return [first, base] if first else [base]

tests/fixtures/chart_crlf.txt

@@ -0,0 +1,36 @@
+#TITLE:Placeholder Chart
+#ARTIST:Test Artist
+#LANGUAGE:English
+#YEAR:2000
+#CREATOR:songtrace tests
+#GENRE:Test
+#COVER:Test Artist - Placeholder Chart [CO].jpg
+#MP3:Test Artist - Placeholder Chart.mp3
+#VIDEO:Test Artist - Placeholder Chart.mp4
+#BPM:217,98
+#GAP:4880
+#MEDLEYSTARTBEAT:113
+#MEDLEYENDBEAT:240
+: 0 3 16 ah
+: 5 3 20  ah
+: 11 3 23  la
+: 17 3 16  la
+: 22 28 15  ah
+: 51 2 16  doo
+: 54 31 16 ~
+- 95  
+F 113 3 18 la
+F 117 3 21  la
+F 121 3 21  la
+* 125 3 21  doo
+* 129 12 19 ~
+- 150
+: 155 4 12 Na
+R 160 4 0  na
+G 165 4 0  na
+: 170 6 14  la
+- 190
+: 194 3 16 La
+: 198 3 18  la
+* 202 10 20  ah
+E

tests/fixtures/chart_latin1.txt

@@ -0,0 +1,21 @@
+#TITLE:Café Placeholder
+#ARTIST:Tést Artist
+#LANGUAGE:English
+#GENRE:Test
+#YEAR:2000
+#MP3:Tést Artist - Café Placeholder.mp3
+#CREATOR:songtrace tests
+#BPM:256
+#GAP:49673
+: 0 4 2 Doo
+: 6 4 4  doo
+: 12 8 5  laé
+- 28 30
+: 32 4 0 Na
+: 38 4 -2  na
+* 44 12 -9  ah
+- 64
+F 70 4 3 La
+: 76 6 -5  la
+: 84 10 -9 ~
+E

tests/js/edit-model.test.mjs

@@ -0,0 +1,129 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import * as m from "../../src/songtrace/static/edit-model.js";
+
+// 300 BPM: one UltraStar beat is 0.05s, starting at GAP = 1s
+const GRID = { bpm: 300, gap_ms: 1000 };
+const near = (a, b) => Math.abs(a - b) < 1e-9;
+
+function line() {
+  return m.withIds([
+    { start: 1.52, end: 1.71, pitch: 0, text: "one", kind: ":", low_confidence: false },
+    { start: 1.8, end: 2.0, pitch: 2, text: " two", kind: ":", low_confidence: true },
+  ]);
+}
+
+test("snapping lands on the beat grid from GAP", () => {
+  assert.ok(near(m.snap(1.52, GRID), 1.5));
+  assert.ok(near(m.snap(1.53, GRID), 1.55));
+  assert.ok(near(m.snap(0.97, GRID), 0.95));   // beats before GAP too
+});
+
+test("moving snaps to the grid, then shifts by beats and semitones", () => {
+  const notes = line();
+  const out = m.move(notes, new Set([notes[0].id]), 2, -3, GRID);
+  assert.ok(near(out[0].start, 1.6) && near(out[0].end, 1.8));
+  assert.equal(out[0].pitch, -3);
+  assert.equal(out[1], notes[1]);          // untouched note is the same object
+  assert.equal(notes[0].start, 1.52);      // input left alone
+});
+
+test("moving never goes before the start of the song", () => {
+  const notes = m.withIds([{ start: 0.1, end: 0.2, pitch: 0, text: "x", kind: ":" }]);
+  const out = m.move(notes, new Set([notes[0].id]), -100, 0, GRID);
+  assert.ok(near(out[0].start, 0));
+});
+
+test("resizing moves one edge and keeps at least a beat", () => {
+  const notes = line();
+  const id = notes[0].id;
+  assert.ok(near(m.resize(notes, id, "end", 1.9, GRID)[0].end, 1.9));
+  assert.ok(near(m.resize(notes, id, "end", 1.0, GRID)[0].end, 1.55));
+  const startMoved = m.resize(notes, id, "start", 1.4, GRID)[0];
+  assert.ok(near(startMoved.start, 1.4) && near(startMoved.end, 1.7));
+});
+
+test("stretching changes length by whole beats", () => {
+  const notes = line();
+  const out = m.stretch(notes, new Set([notes[1].id]), 2, GRID);
+  assert.ok(near(out[1].start, 1.8) && near(out[1].end, 2.1));
+  assert.ok(near(m.stretch(notes, new Set([notes[1].id]), -10, GRID)[1].end, 1.85));
+});
+
+test("splitting halves a note on a beat and holds the syllable", () => {
+  const notes = line();
+  const { notes: out, ids } = m.split(notes, notes[1].id, GRID);
+  assert.equal(out.length, 3);
+  assert.ok(near(out[1].end, 1.9) && near(out[2].start, 1.9));
+  assert.deepEqual([out[1].text, out[2].text], [" two", "~"]);
+  assert.equal(ids.length, 2);
+  // one beat cannot be split
+  const short = m.withIds([{ start: 1.0, end: 1.05, pitch: 0, text: "x", kind: ":" }]);
+  assert.equal(m.split(short, short[0].id, GRID).notes, short);
+});
+
+test("merging joins a note with the next, dropping a held ~", () => {
+  const notes = m.withIds([
+    { start: 1.0, end: 1.2, pitch: 0, text: "sev", kind: ":" },
+    { start: 1.2, end: 1.4, pitch: 0, text: "en", kind: ":" },
+    { start: 1.4, end: 1.6, pitch: 0, text: "~", kind: ":" },
+  ]);
+  const once = m.merge(notes, notes[0].id);
+  assert.deepEqual(once.map(n => n.text), ["seven", "~"]);
+  const twice = m.merge(once, once[0].id);
+  assert.deepEqual(twice.map(n => [n.text, n.end]), [["seven", 1.6]]);
+  assert.equal(m.merge(twice, twice[0].id), twice);   // nothing after it
+});
+
+test("inserting adds a two-beat held note on the grid", () => {
+  const { notes, id } = m.insert(line(), 1.76, 4, GRID);
+  const added = notes.find(n => n.id === id);
+  assert.ok(near(added.start, 1.75) && near(added.end, 1.85));
+  assert.deepEqual([added.pitch, added.text, added.kind], [4, "~", ":"]);
+  assert.deepEqual(notes.map(n => n.text), ["one", "~", " two"]);
+});
+
+test("a kind toggles back to normal when every selected note has it", () => {
+  const notes = line();
+  const both = new Set(notes.map(n => n.id));
+  const golden = m.setKind(notes, both, "*");
+  assert.deepEqual(golden.map(n => n.kind), ["*", "*"]);
+  assert.deepEqual(m.setKind(golden, both, "*").map(n => n.kind), [":", ":"]);
+  const mixed = m.setKind(golden, new Set([notes[0].id]), "F");
+  assert.deepEqual(m.setKind(mixed, both, "F").map(n => n.kind), ["F", "F"]);
+});
+
+test("editing text keeps a word-initial space and refuses blank", () => {
+  const notes = line();
+  assert.equal(m.setText(notes, notes[1].id, "too")[1].text, " too");
+  assert.equal(m.setText(notes, notes[0].id, "won")[0].text, "won");
+  assert.equal(m.setText(notes, notes[0].id, " won")[0].text, " won");
+  assert.equal(m.setText(notes, notes[0].id, "   "), notes);
+});
+
+test("saved notes carry duration and kind, not ids", () => {
+  const saved = m.toSaved(line());
+  assert.deepEqual(Object.keys(saved[0]).sort(), ["duration", "kind", "pitch", "start", "text"]);
+  assert.ok(near(saved[0].duration, 0.19));
+});
+
+test("history undoes and redoes, and a new change drops the redo", () => {
+  const h = m.history("a");
+  h.push("b");
+  h.push("c");
+  assert.equal(h.undo(), "b");
+  assert.equal(h.undo(), "a");
+  assert.equal(h.canUndo, false);
+  assert.equal(h.redo(), "b");
+  h.push("d");
+  assert.equal(h.canRedo, false);
+  assert.equal(h.present, "d");
+});
+
+test("a dragged break snaps to a beat but stays between its lines", () => {
+  assert.ok(near(m.placeBreak(1.52, 1.4, 1.8, GRID), 1.5));
+  assert.equal(m.placeBreak(1.0, 1.42, 1.8, GRID), 1.42);   // not into the line before
+  assert.equal(m.placeBreak(2.5, 1.4, 1.78, GRID), 1.78);   // nor into the line after
+  assert.equal(m.placeBreak(1.6, 1.9, 1.8, GRID), 1.9);     // lines overlap: at the end of the first
+});

tests/js/sheet.test.mjs

@@ -0,0 +1,72 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { beatLines, isBlackKey, lineSpan, noteName, pitchRange }
+  from "../../src/songtrace/static/sheet.js";
+
+test("note names follow UltraStar's C4 = 0", () => {
+  assert.equal(noteName(0), "C4");
+  assert.equal(noteName(9), "A4");
+  assert.equal(noteName(-1), "B3");
+  assert.equal(noteName(13), "C♯5");
+  assert.equal(noteName(-13), "B2");
+});
+
+test("black keys are the sharps, in any octave", () => {
+  assert.deepEqual([0, 1, 2, 3, 4, 5, 6].map(isBlackKey),
+                   [false, true, false, true, false, false, true]);
+  assert.equal(isBlackKey(-11), true);   // C#3
+  assert.equal(isBlackKey(-12), false);  // C3
+});
+
+test("the pitch range pads the line's notes and keeps a minimum height", () => {
+  assert.deepEqual(pitchRange([0, 5]), { lo: -4, hi: 10 });      // 15 rows
+  assert.deepEqual(pitchRange([0, 20]), { lo: -3, hi: 23 });     // padded only
+  assert.deepEqual(pitchRange([]), { lo: -7, hi: 7 });
+});
+
+test("beat lines sit on the chart's grid with bar weights", () => {
+  // 300 BPM: an UltraStar beat is 60 / (4 * 300) = 0.05s, from GAP 1.0s
+  const lines = beatLines(1.0, 1.85, { bpm: 300, gap_ms: 1000 });
+  assert.equal(lines.length, 18);
+  assert.deepEqual(lines.slice(0, 5).map(b => b.weight), [2, 0, 0, 0, 1]);
+  assert.equal(lines[16].weight, 2);
+  assert.ok(Math.abs(lines[4].t - 1.2) < 1e-9);
+});
+
+test("beats before GAP keep their weights", () => {
+  const lines = beatLines(0.75, 1.0, { bpm: 300, gap_ms: 1000 });
+  assert.deepEqual(lines.map(b => [b.beat, b.weight]),
+                   [[-5, 0], [-4, 1], [-3, 0], [-2, 0], [-1, 0], [0, 2]]);
+});
+
+test("a line spans its notes and words", () => {
+  assert.deepEqual(lineSpan({ notes: [{ start: 2, end: 3 }], words: [{ start: 1.5, end: 2.5 }] }),
+                   { start: 1.5, end: 3 });
+  assert.equal(lineSpan({ notes: [], words: [] }), null);
+});
+
+import { readFileSync } from "node:fs";
+import { SHORTCUTS, comboParts } from "../../src/songtrace/static/sheet.js";
+
+test("shortcut combos split into keys and mouse actions", () => {
+  assert.deepEqual(comboParts("Shift+click / Tab"), [
+    [{ text: "Shift", key: true }, { text: "click", key: false }],
+    [{ text: "Tab", key: true }],
+  ]);
+  assert.deepEqual(comboParts("Page Up"), [[{ text: "Page Up", key: true }]]);
+});
+
+test("every letter key the shortcut list names is one the sheet handles", () => {
+  const source = readFileSync(new URL("../../src/songtrace/static/sheet.js", import.meta.url), "utf8");
+  const handler = source.slice(source.indexOf('plot.addEventListener("keydown"'));
+  const letters = SHORTCUTS.flatMap(([, entries]) => entries)
+    .flatMap(([combo]) => comboParts(combo).flat())
+    .filter(p => p.key && /^[A-Z]$/.test(p.text))
+    .map(p => p.text.toLowerCase());
+  assert.ok(letters.length >= 6);
+  for (const letter of new Set(letters)) {
+    assert.ok(handler.includes(`"${letter}"`) || handler.includes(`${letter}:`),
+              `the list names ${letter.toUpperCase()} but the sheet does not handle it`);
+  }
+});

tests/test_acquire.py

@@ -24,7 +24,7 @@ def test_local_video(tmp_path, monkeypatch):
     assert any("audio.wav" in str(a[-1]) for a in calls)
 
 def test_youtube(tmp_path, monkeypatch):
-    def fake_dl(url, dest):
+    def fake_dl(url, dest, cfg, log):
         video = dest / "source_video.webm"
         video.write_bytes(b"v")
         thumb = dest / "source_video.jpg"
@@ -83,3 +83,120 @@ def test_classify_picks_largest_video_when_multiple(tmp_path):
     (tmp_path / "source_video.mp4").write_bytes(b"much larger contents here")
     video, _ = acquire._classify_downloads(tmp_path)
     assert video.name == "source_video.mp4"
+
+def test_classify_ignores_partials_left_by_a_failed_attempt(tmp_path):
+    (tmp_path / "source_video.webm").write_bytes(b"v")
+    (tmp_path / "source_video.f137.mp4.part").write_bytes(b"a much bigger partial")
+    (tmp_path / "source_video.f251.webm.ytdl").write_bytes(b"resume state")
+    video, _ = acquire._classify_downloads(tmp_path)
+    assert video.name == "source_video.webm"
+
+def test_ydl_args_default_client_adds_no_player_client(tmp_path):
+    cfg = Config(whisper_url="http://x/v1")
+    args = acquire._ydl_args(cfg, tmp_path, "default", "https://yt/x")
+    assert "--extractor-args" not in args
+    assert "--retries" in args and "--fragment-retries" in args
+    assert args[-2:] == ["--", "https://yt/x"]
+
+def test_ydl_args_named_client_pot_provider_and_cookies(tmp_path):
+    cfg = Config(whisper_url="http://x/v1",
+                 ytdlp_pot_provider_url="http://pot:4416",
+                 ytdlp_cookies=tmp_path / "cookies.txt",
+                 ytdlp_impersonate="chrome")
+    args = acquire._ydl_args(cfg, tmp_path, "tv", "https://yt/x")
+    joined = " ".join(args)
+    assert "--extractor-args youtube:player_client=tv" in joined
+    assert ("--extractor-args youtubepot-bgutilhttp:base_url=http://pot:4416"
+            in joined)
+    assert f"--cookies {tmp_path / 'cookies.txt'}" in joined
+    assert "--impersonate chrome" in joined
+
+def test_ydl_args_parse_with_real_yt_dlp(tmp_path):
+    """Every option songtrace passes must exist in the bundled yt-dlp."""
+    import pytest
+    pytest.importorskip("yt_dlp")
+    from yt_dlp import parse_options
+    cfg = Config(whisper_url="http://x/v1", ytdlp_pot_provider_url="http://p:1",
+                 ytdlp_cookies=tmp_path / "c.txt")
+    parse_options(acquire._ydl_args(cfg, tmp_path, "tv", "https://yt/x"))
+
+class FakeYtDlp:
+    def __init__(self, version, behaviour, seen):
+        self.version, self._behaviour, self._seen = version, behaviour, seen
+    def run(self, args, log):
+        client = next((a for a in args if a.startswith("youtube:")), None)
+        self._seen.append((self.version, client))
+        self._behaviour(self.version, client)
+
+def _fake_candidates(monkeypatch, behaviour, versions=("2026.09.01", "2026.08.19"),
+                     refreshed=None):
+    """Stub ytdlp.candidates; `refreshed` is what a refresh turns up."""
+    seen = []
+    def candidates(cfg, log, refresh=False):
+        vs = refreshed if refresh and refreshed else versions
+        return [FakeYtDlp(v, behaviour, seen) for v in vs]
+    monkeypatch.setattr(acquire.ytdlp, "candidates", candidates)
+    return seen
+
+def test_download_falls_through_to_the_next_client(tmp_path, monkeypatch):
+    from songtrace.ytdlp import YtDlpError
+    def behaviour(version, client):
+        if client is None:
+            raise YtDlpError("ERROR: HTTP Error 403: Forbidden")
+        (tmp_path / "source_video.webm").write_bytes(b"v")
+    seen = _fake_candidates(monkeypatch, behaviour)
+    cfg = Config(whisper_url="http://x/v1", ytdlp_clients=["default", "tv"])
+    logged = []
+    video, thumb = acquire.download_youtube("https://yt/x", tmp_path, cfg,
+                                            logged.append)
+    assert video.name == "source_video.webm"
+    assert thumb is None
+    assert seen == [("2026.09.01", None),
+                    ("2026.09.01", "youtube:player_client=tv")]
+    assert any("403" in m for m in logged)
+
+def test_download_falls_back_to_the_bundled_copy(tmp_path, monkeypatch):
+    from songtrace.ytdlp import YtDlpError
+    def behaviour(version, client):
+        if version == "2026.09.01":
+            raise YtDlpError("rejected songtrace's options")
+        (tmp_path / "source_video.webm").write_bytes(b"v")
+    seen = _fake_candidates(monkeypatch, behaviour)
+    cfg = Config(whisper_url="http://x/v1", ytdlp_clients=["default"])
+    acquire.download_youtube("https://yt/x", tmp_path, cfg, lambda m: None)
+    assert [v for v, _ in seen] == ["2026.09.01", "2026.08.19"]
+
+def test_download_retries_with_a_release_found_after_failing(tmp_path, monkeypatch):
+    from songtrace.ytdlp import YtDlpError
+    def behaviour(version, client):
+        if version != "2026.10.01":
+            raise YtDlpError("ERROR: HTTP Error 403: Forbidden")
+        (tmp_path / "source_video.webm").write_bytes(b"v")
+    seen = _fake_candidates(monkeypatch, behaviour,
+                            refreshed=("2026.10.01", "2026.08.19"))
+    cfg = Config(whisper_url="http://x/v1", ytdlp_clients=["default"])
+    acquire.download_youtube("https://yt/x", tmp_path, cfg, lambda m: None)
+    assert [v for v, _ in seen] == ["2026.09.01", "2026.08.19", "2026.10.01"]
+
+def test_download_reports_versions_and_clients_when_all_fail(tmp_path, monkeypatch):
+    import pytest
+    from songtrace.pipeline import PipelineError
+    from songtrace.ytdlp import YtDlpError
+    def behaviour(version, client):
+        raise YtDlpError("ERROR: HTTP Error 403: Forbidden")
+    seen = _fake_candidates(monkeypatch, behaviour)
+    cfg = Config(whisper_url="http://x/v1", ytdlp_clients=["default", "tv"])
+    with pytest.raises(PipelineError) as e:
+        acquire.download_youtube("https://yt/x", tmp_path, cfg, lambda m: None)
+    assert "2026.09.01, 2026.08.19" in str(e.value)
+    assert "default, tv" in str(e.value)
+    assert "403" in str(e.value)
+    assert len(seen) == 4
+
+def test_download_with_no_configured_clients_still_tries_default(tmp_path, monkeypatch):
+    seen = _fake_candidates(
+        monkeypatch,
+        lambda v, c: (tmp_path / "source_video.mp4").write_bytes(b"v"))
+    cfg = Config(whisper_url="http://x/v1", ytdlp_clients=[])
+    acquire.download_youtube("https://yt/x", tmp_path, cfg, lambda m: None)
+    assert seen == [("2026.09.01", None)]

tests/test_align.py

@@ -1,11 +1,23 @@
 import json
 
+import numpy as np
 import pytest
+import soundfile as sf
 
 from songtrace.config import Config
 from songtrace.lyrics import normalize_lyrics
 from songtrace.pipeline import Ctx, PipelineError, SongInput
 from songtrace.stages import align
+from songtrace.whisper_client import TranscriptSegment
+
+REAL_UNTRANSCRIBED_SINGING = align.untranscribed_singing
+
+
+@pytest.fixture(autouse=True)
+def no_untranscribed_singing(monkeypatch):
+    """The tests have no vocals.wav; those about missed singing set their own."""
+    monkeypatch.setattr(align, "untranscribed_singing", lambda vocals, segments: [])
+
 
 LYRICS = "it's one two three\nfour five six seven eight"
 
@@ -160,3 +172,66 @@ def test_align_flags_missing_span_for_unmatched_singing(tmp_path, monkeypatch):
     meta = json.loads((tmp_path / "w" / "align_meta.json").read_text())
     assert meta["dropped_lines"] == []
     assert meta["missing_spans"] == [[19.0, 24.0]]
+
+
+def _tone(seconds, sr, level):
+    t = np.arange(int(seconds * sr)) / sr
+    return level * np.sin(2 * np.pi * 220 * t)
+
+
+def test_untranscribed_singing_finds_sung_audio_the_transcript_skips(
+        tmp_path):
+    sr = 16000
+    rng = np.random.default_rng(0)
+    audio = np.concatenate([
+        _tone(2, sr, 0.3),           # 0-2s: sung and transcribed
+        np.zeros(2 * sr),            # 2-4s: silence
+        _tone(5, sr, 0.3),           # 4-9s: sung, never transcribed
+        np.zeros(3 * sr),            # 9-12s: silence
+        _tone(1, sr, 0.3),           # 12-13s: too short to count
+        np.zeros(3 * sr),
+    ]) + 0.001 * rng.standard_normal(16 * sr)   # separation bleed
+    path = tmp_path / "vocals.wav"
+    sf.write(path, audio.astype(np.float32), sr)
+    segments = [TranscriptSegment(0.0, 2.0, "one two")]
+    spans = REAL_UNTRANSCRIBED_SINGING(path, segments)
+    assert len(spans) == 1
+    assert spans[0][0] == pytest.approx(4.0, abs=0.1)
+    assert spans[0][1] == pytest.approx(9.0, abs=0.1)
+
+
+def test_lines_whisper_missed_are_aligned_in_the_untranscribed_singing(
+        tmp_path, monkeypatch):
+    lyrics = "one two three\nfour five six\nseven eight nine"
+    transcript = [{"start": 1.0, "end": 3.0, "text": "one two three"},
+                  {"start": 40.0, "end": 42.0, "text": "seven eight nine"}]
+    monkeypatch.setattr(align, "untranscribed_singing",
+                        lambda vocals, segments: [(20.0, 26.0)])
+    rows = run_align(tmp_path, monkeypatch, lyrics, transcript)
+    check_invariants(rows, lyrics)
+    middle = [r for r in rows if r["line_index"] == 1]
+    assert all(19.0 <= r["start"] and r["end"] <= 27.0 for r in middle)
+    meta = json.loads((tmp_path / "w" / "align_meta.json").read_text())
+    assert meta["dropped_lines"] == []
+
+
+def test_stars_bracket_each_line_and_take_no_words(tmp_path, monkeypatch):
+    lyrics = "one two\n...\nthree four"
+    transcript = [{"start": 0.0, "end": 10.0, "text": "one two three four"}]
+    seen = []
+
+    def spy(vocals_path, start, end, tokens, device):
+        seen.append(tokens)
+        # each star claims a long stretch, so a word given a star's span shows
+        spans = [(start + i, start + i + (5.0 if t == "*" else 0.5), 0.9)
+                 for i, t in enumerate(tokens)]
+        return spans
+
+    monkeypatch.setattr(align, "force_align_section", spy)
+    ctx = make_ctx(tmp_path, lyrics, transcript)
+    align.align_stage().run(ctx)
+    rows = json.loads((ctx.work / "alignment.json").read_text())
+    assert seen == [["*", "one", "two", "*", "three", "four", "*"]]
+    timed = [r for r in rows if r["word"] != "..."]
+    assert all(r["end"] - r["start"] == pytest.approx(0.5) for r in timed)
+    check_invariants(rows, lyrics)

tests/test_edits.py

@@ -0,0 +1,189 @@
+import json
+
+import pytest
+
+from songtrace import edits
+
+LYRICS = [["one", "two"], ["three", "four"], ["five", "six"]]
+
+
+def gen(start, line, pitch=0, dur=0.4, low=False, text="la"):
+    return {"start": start, "duration": dur, "pitch": pitch, "text": text,
+            "low_confidence": low, "line_index": line}
+
+
+def edited(*lines):
+    data = edits._empty(LYRICS)
+    for index, notes in lines:
+        edits.set_line(data, index, notes)
+    return data
+
+
+def note(start, pitch=5, dur=0.4, text="la", kind=":"):
+    return {"start": start, "duration": dur, "pitch": pitch, "text": text, "kind": kind}
+
+
+GENERATED = [gen(1.0, 0), gen(1.5, 0), gen(4.0, 1), gen(4.5, 1), gen(8.0, 2), gen(8.5, 2)]
+BREAKS = [3.0, 6.0]
+
+
+def test_no_edits_leaves_the_generated_song_alone():
+    assert edits.merge(GENERATED, BREAKS, edits._empty(LYRICS)) == (GENERATED, BREAKS)
+
+
+def test_an_edited_line_replaces_its_generated_notes():
+    notes, _ = edits.merge(GENERATED, BREAKS, edited(
+        (1, [note(4.2, pitch=7, kind="*"), note(4.8, pitch=9)])))
+    line1 = [n for n in notes if n["line_index"] == 1]
+    assert [(n["start"], n["pitch"], n["kind"]) for n in line1] == [
+        (4.2, 7, "*"), (4.8, 9, ":")]
+    assert not any(n["low_confidence"] for n in line1)
+    assert [n["line_index"] for n in notes] == [0, 0, 1, 1, 2, 2]
+
+
+def test_neighbours_give_way_to_an_edited_line():
+    # line 1 edited to run from 1.7s to 8.6s, over its neighbours' notes
+    notes, _ = edits.merge(GENERATED, BREAKS, edited(
+        (1, [note(1.7), note(8.2, dur=0.4)])))
+    by_line = {}
+    for n in notes:
+        by_line.setdefault(n["line_index"], []).append(
+            (round(n["start"], 2), round(n["start"] + n["duration"], 2)))
+    assert by_line[0] == [(1.0, 1.4), (1.5, 1.7)]     # cut back to end at 1.7s
+    assert by_line[2] == [(8.6, 8.9)]                 # 8.0 note gone, 8.5 starts at 8.6
+
+
+def test_breaks_beside_an_edited_line_move_and_the_rest_stay():
+    data = edited((2, [note(9.0), note(9.5)]))
+    _, breaks = edits.merge(GENERATED, BREAKS, data)
+    assert breaks[0] == 3.0                           # lines 0-1: generated
+    assert breaks[1] == pytest.approx((4.9 + 9.0) / 2)  # lines 1-2: re-centred
+
+
+def test_an_edit_follows_its_line_when_lines_are_added_above(tmp_path):
+    data = edited((1, [note(4.0)]))
+    edits.save(tmp_path, data)
+    moved = edits.load(tmp_path, [["zero"]] + LYRICS)
+    assert list(moved["lines"]) == ["2"] and moved["lines"]["2"]["line_index"] == 2
+    assert moved["stale"] == []
+    assert json.loads((tmp_path / edits.EDITS_FILE).read_text())["lyrics"][0] == ["zero"]
+
+
+def test_an_edit_whose_words_changed_is_set_aside(tmp_path):
+    edits.save(tmp_path, edited((1, [note(4.0)]), (2, [note(8.0)])))
+    changed = [LYRICS[0], ["three", "more"], LYRICS[2]]
+    data = edits.load(tmp_path, changed)
+    assert list(data["lines"]) == ["2"]
+    assert [s["words"] for s in data["stale"]] == [["three", "four"]]
+
+
+def test_validate_notes_checks_and_orders():
+    assert [n["start"] for n in edits.validate_notes([note(2.0), note(1.0)])] == [1.0, 2.0]
+    for bad in (note(1.0, kind="X"), note(1.0, dur=0), note(-1.0), note(1.0, text=" "),
+                {"start": 1.0}):
+        with pytest.raises(ValueError):
+            edits.validate_notes([bad])
+
+
+def test_saving_no_edits_removes_the_file(tmp_path):
+    edits.save(tmp_path, edited((0, [note(1.0)])))
+    data = edits.load(tmp_path, LYRICS)
+    edits.clear_line(data, 0)
+    edits.save(tmp_path, data)
+    assert not (tmp_path / edits.EDITS_FILE).exists()
+
+
+def _write_generated(work, notes, warnings):
+    (work / "notes_sec.json").write_text(json.dumps(
+        {"notes": notes, "breaks": BREAKS, "warnings": warnings}))
+
+
+def test_finalize_without_edits_passes_warnings_through(tmp_path):
+    _write_generated(tmp_path, GENERATED, ["anything at all"])
+    final = edits.finalize(tmp_path, LYRICS)
+    assert final["warnings"] == ["anything at all"]
+    assert final["edited_lines"] == [] and final["stale"] == []
+    assert json.loads((tmp_path / edits.FINAL_FILE).read_text()) == final
+
+
+def test_finalize_stops_reporting_a_line_the_user_fixed(tmp_path):
+    notes = [gen(1.0, 0), gen(4.0, 1, low=True), gen(8.0, 2)]
+    _write_generated(tmp_path, notes, ["1 low-confidence note near 0:04–0:04",
+                                       "missing lyrics near 0:20–0:25"])
+    edits.save(tmp_path, edited((1, [note(4.0)])))
+    final = edits.finalize(tmp_path, LYRICS)
+    assert final["warnings"] == ["missing lyrics near 0:20–0:25"]
+    assert final["edited_lines"] == [1]
+
+
+def test_finalize_reports_stale_edits(tmp_path):
+    _write_generated(tmp_path, GENERATED, [])
+    edits.save(tmp_path, edited((1, [note(4.0)])))
+    final = edits.finalize(tmp_path, [LYRICS[0], ["other"], LYRICS[2]])
+    assert final["warnings"] == ["1 edited line no longer matches the lyrics; "
+                                 "set aside in the editor"]
+
+
+def test_a_grid_set_in_the_editor_is_checked():
+    data = edits._empty(LYRICS)
+    edits.set_grid(data, "240.5", 1500)
+    assert data["grid"] == {"bpm": 240.5, "gap_ms": 1500.0}
+    for bpm, gap in ((0, 0), (-1, 0), (float("nan"), 0), (3000, 0), (300, -1), ("x", 0)):
+        with pytest.raises(ValueError):
+            edits.set_grid(data, bpm, gap)
+
+
+def test_a_grid_alone_keeps_the_edits_file_and_survives_new_lyrics(tmp_path):
+    data = edits._empty(LYRICS)
+    edits.set_grid(data, 300, 1000)
+    edits.save(tmp_path, data)
+    assert (tmp_path / edits.EDITS_FILE).exists()
+    loaded = edits.load(tmp_path, [["zero"]] + LYRICS)
+    assert loaded["grid"] == {"bpm": 300.0, "gap_ms": 1000.0}
+    assert edits.clear_grid(loaded) and not edits.clear_grid(loaded)
+    edits.save(tmp_path, loaded)
+    assert not (tmp_path / edits.EDITS_FILE).exists()
+
+
+def test_finalize_reports_the_grid(tmp_path):
+    _write_generated(tmp_path, GENERATED, [])
+    assert edits.finalize(tmp_path, LYRICS)["grid"] is None
+    data = edits._empty(LYRICS)
+    edits.set_grid(data, 300, 1000)
+    edits.save(tmp_path, data)
+    assert edits.finalize(tmp_path, LYRICS)["grid"] == {"bpm": 300.0, "gap_ms": 1000.0}
+
+
+def test_moved_breaks_are_checked():
+    data = edits._empty(LYRICS)
+    edits.set_breaks(data, {"1": 3.5, 2: "6.25"})
+    assert data["breaks"] == {"1": 3.5, "2": 6.25}
+    edits.set_breaks(data, {1: None})
+    assert data["breaks"] == {"2": 6.25}
+    for bad in ({0: 1.0}, {3: 1.0}, {"x": 1.0}, {1: -1}, {1: "soon"}, {1: float("inf")}):
+        with pytest.raises(ValueError):
+            edits.set_breaks(data, bad)
+
+
+def test_a_moved_break_stays_put_between_its_lines():
+    data = edits._empty(LYRICS)
+    edits.set_breaks(data, {1: 2.5})
+    notes, breaks = edits.merge(GENERATED, BREAKS, data)
+    assert notes == GENERATED                 # moving a break locks no notes
+    assert breaks == [2.5, 6.0]
+
+
+def test_a_moved_break_never_lands_inside_a_line():
+    data = edits._empty(LYRICS)
+    edits.set_breaks(data, {1: 1.0, 2: 9.0})  # into line 0's notes, past line 2's start
+    _, breaks = edits.merge(GENERATED, BREAKS, data)
+    assert breaks == [pytest.approx(1.9), 8.0]
+
+
+def test_moved_breaks_follow_their_lines_and_keep_the_file(tmp_path):
+    data = edits._empty(LYRICS)
+    edits.set_breaks(data, {1: 3.5, 2: 6.5})
+    edits.save(tmp_path, data)
+    assert (tmp_path / edits.EDITS_FILE).exists()
+    moved = edits.load(tmp_path, [["zero"], LYRICS[0], LYRICS[1], ["other"]])
+    assert moved["breaks"] == {"2": 3.5}      # line 2's words changed: its break goes

tests/test_grid.py

@@ -169,7 +169,7 @@ def test_grid_stage_writes_song_txt(tmp_path, monkeypatch):
     monkeypatch.setattr(grid_stage_mod.grid, "detect_bpm", lambda p: 120.0)
     ctx = make_ctx(work, language="English", genre="Pop", year=1999)
     stage = grid_stage_mod.grid_stage()
-    assert stage.outputs(ctx) == [work / "song.txt"]
+    assert stage.outputs(ctx) == [work / "song.txt", work / "notes_final.json"]
     stage.run(ctx)
     song = parse_ultrastar((work / "song.txt").read_text(encoding="utf-8"))
     assert [k for k, _ in song.headers] == [
@@ -222,7 +222,7 @@ def test_grid_stage_honours_zero_bpm_override(tmp_path, monkeypatch):
     monkeypatch.setattr(grid_stage_mod.grid, "detect_bpm", boom)
     captured = {}
 
-    def fake_to_ultrastar(notes, breaks, file_bpm, headers):
+    def fake_to_ultrastar(notes, breaks, file_bpm, headers, gap_ms=None):
         captured["bpm"] = file_bpm
         return to_ultrastar(notes, breaks, 240.0, headers)
 
@@ -257,3 +257,86 @@ def test_grid_stage_reports_no_notes_as_pipeline_error(tmp_path, monkeypatch):
 def test_grid_stage_registered():
     names = [s.name for s in all_stages()]
     assert names[-1] == "package" and names[-2] == "grid"
+
+
+def _regenerate(work, pitch):
+    """What a rebuild leaves: fresh notes for both lines, at `pitch`."""
+    (work / "notes_sec.json").write_text(json.dumps({
+        "notes": [{**note(1.0, 0.5, pitch, "one"), "line_index": 0},
+                  {**note(3.0, 0.5, pitch, "three"), "line_index": 1}],
+        "breaks": [2.0], "warnings": []}))
+
+
+def test_an_edited_line_survives_a_rebuild(tmp_path, monkeypatch):
+    from songtrace import edits
+    work = tmp_path / "w"
+    write_work(work)
+    monkeypatch.setattr(grid_stage_mod.grid, "detect_bpm", lambda p: 120.0)
+    ctx = make_ctx(work)
+    ctx.inp.lyrics_text = "one\nthree"
+    data = edits.load(work, [["one"], ["three"]])
+    edits.set_line(data, 1, [{"start": 3.2, "duration": 0.6, "pitch": 9,
+                              "text": "three", "kind": "*"}])
+    edits.save(work, data)
+    for regenerated_pitch in (0, 4):
+        _regenerate(work, regenerated_pitch)
+        grid_stage_mod.grid_stage().run(ctx)
+        song = parse_ultrastar((work / "song.txt").read_text(encoding="utf-8"))
+        notes = [n for n in song.body if isinstance(n, Note)]
+        assert [(n.kind, n.pitch, n.text) for n in notes] == [
+            (":", regenerated_pitch, "one"), ("*", 9, "three")]
+
+
+def test_rechart_replaces_the_notes_and_keeps_headers_and_tempo(tmp_path):
+    from songtrace.grid import rechart
+    from songtrace.ultrastar import serialize_ultrastar
+    txt = tmp_path / "song.txt"
+    txt.write_text(serialize_ultrastar(to_ultrastar(
+        [note(1.0, 0.5)], [], 300.0,
+        [("TITLE", "Song"), ("VIDEO", "Band - Song.mp4")])), encoding="utf-8")
+    rechart(txt, [{**note(2.0, 0.5, 7, "new"), "kind": "F"}], [])
+    song = parse_ultrastar(txt.read_text(encoding="utf-8"))
+    assert [k for k, _ in song.headers] == ["TITLE", "VIDEO", "BPM", "GAP"]
+    assert get_header(song, "BPM") == "300" and get_header(song, "GAP") == "2000"
+    assert [(n.kind, n.pitch, n.text) for n in song.body] == [("F", 7, "new")]
+
+
+def test_an_explicit_gap_sets_the_grid():
+    # 300 BPM: 0.05s beats; notes at 1.02s and 1.27s against GAP 1.0s
+    song = to_ultrastar([note(1.02, 0.1), note(1.27, 0.1)], [], 300.0, [], gap_ms=1000)
+    assert get_header(song, "GAP") == "1000"
+    assert [n.beat for n in song.body] == [0, 5]
+
+
+def test_a_gap_after_the_first_note_moves_back_by_whole_beats():
+    # GAP 1.13s is after the first note at 1.02s: back 3 beats to 0.98s, so
+    # the grid lines stay where they were set and the note is on beat 1
+    song = to_ultrastar([note(1.02, 0.1)], [], 300.0, [], gap_ms=1130)
+    assert get_header(song, "GAP") == "980"
+    assert song.body[0].beat == 1
+
+
+def test_the_grid_stage_uses_the_editors_grid_and_records_its_own(tmp_path, monkeypatch):
+    from songtrace import edits
+    work = tmp_path / "w"
+    write_work(work)
+    monkeypatch.setattr(grid_stage_mod.grid, "detect_bpm", lambda p: 120.0)
+    ctx = make_ctx(work)
+    data = edits.load(work, [["x"]])
+    edits.set_grid(data, 300.0, 900)
+    edits.save(work, data)
+    grid_stage_mod.grid_stage().run(ctx)
+    song = parse_ultrastar((work / "song.txt").read_text(encoding="utf-8"))
+    assert (get_header(song, "BPM"), get_header(song, "GAP")) == ("300", "900")
+    assert json.loads((work / "tempo.json").read_text()) == {"bpm": 240.0}
+
+
+def test_rechart_can_set_a_new_bpm_and_gap(tmp_path):
+    from songtrace.grid import rechart
+    from songtrace.ultrastar import serialize_ultrastar
+    txt = tmp_path / "song.txt"
+    txt.write_text(serialize_ultrastar(to_ultrastar([note(1.0, 0.5)], [], 240.0, [])),
+                   encoding="utf-8")
+    rechart(txt, [note(1.02, 0.1)], [], 300.0, 1000)
+    song = parse_ultrastar(txt.read_text(encoding="utf-8"))
+    assert (get_header(song, "BPM"), get_header(song, "GAP")) == ("300", "1000")

tests/test_models.py

@@ -0,0 +1,129 @@
+import sys
+import types
+
+import pytest
+
+from songtrace import models
+from songtrace.stages import align, pitch
+
+
+@pytest.fixture
+def isolated_callbacks(monkeypatch):
+    """release() with only the callbacks a test registers."""
+    monkeypatch.setattr(models, "_callbacks", [])
+    return models._callbacks
+
+
+def fake_torch(available=True, initialised=True, emptied=None, reserved=None):
+    """A torch whose allocator reports `reserved` bytes, then 0 once emptied."""
+    state = {"reserved": 4 * 2 ** 20 if reserved is None else reserved}
+
+    def empty_cache():
+        emptied.append(True)
+        state["reserved"] = 0
+
+    mod = types.ModuleType("torch")
+    mod.cuda = types.SimpleNamespace(
+        is_available=lambda: available,
+        is_initialized=lambda: initialised,
+        memory_reserved=lambda: state["reserved"],
+        empty_cache=empty_cache)
+    return mod
+
+
+def test_release_without_torch_or_callbacks_does_nothing(monkeypatch,
+                                                         isolated_callbacks):
+    monkeypatch.delitem(sys.modules, "torch", raising=False)
+    assert models.release() == 0
+
+
+def test_release_runs_every_registered_callback(isolated_callbacks):
+    called = []
+    models.on_release(lambda: called.append("a"))
+    models.on_release(lambda: called.append("b"))
+    models.release()
+    assert called == ["a", "b"]
+
+
+def test_on_release_returns_the_function_so_it_works_as_a_decorator():
+    def drop():
+        pass
+    assert models.on_release(drop) is drop
+    models._callbacks.remove(drop)
+
+
+def test_release_empties_the_allocator_when_cuda_is_in_use(monkeypatch,
+                                                           isolated_callbacks):
+    emptied = []
+    monkeypatch.setitem(sys.modules, "torch", fake_torch(emptied=emptied))
+    assert models.release() == 4 * 2 ** 20
+    assert emptied == [True]
+
+
+def test_release_leaves_the_allocator_alone_without_a_gpu(monkeypatch,
+                                                          isolated_callbacks):
+    emptied = []
+    monkeypatch.setitem(sys.modules, "torch",
+                        fake_torch(available=False, emptied=emptied))
+    assert models.release() == 0
+    assert emptied == []
+
+
+def test_release_does_not_initialise_cuda_just_to_clean_up(monkeypatch,
+                                                           isolated_callbacks):
+    """A run that never touched the GPU must not create a context on the way out."""
+    emptied = []
+    monkeypatch.setitem(sys.modules, "torch",
+                        fake_torch(initialised=False, emptied=emptied))
+    assert models.release() == 0
+    assert emptied == []
+
+
+def test_align_drops_its_cached_model():
+    align._model_cache["cuda"] = object()
+    align.unload_model()
+    assert align._model_cache == {}
+
+
+def test_align_registers_its_unload():
+    assert align.unload_model in models._callbacks
+
+
+def test_pitch_drops_the_model_torchcrepe_cached(monkeypatch):
+    torchcrepe = types.ModuleType("torchcrepe")
+
+    def infer():
+        pass
+
+    infer.model = object()
+    infer.capacity = "full"
+    torchcrepe.infer = infer
+    monkeypatch.setitem(sys.modules, "torchcrepe", torchcrepe)
+    pitch.unload_model()
+    assert not hasattr(infer, "model")
+    assert not hasattr(infer, "capacity")
+
+
+def test_pitch_unload_is_fine_when_torchcrepe_was_never_imported(monkeypatch):
+    monkeypatch.delitem(sys.modules, "torchcrepe", raising=False)
+    pitch.unload_model()
+
+
+def test_pitch_unload_is_fine_when_no_model_was_cached(monkeypatch):
+    torchcrepe = types.ModuleType("torchcrepe")
+    torchcrepe.infer = lambda: None
+    monkeypatch.setitem(sys.modules, "torchcrepe", torchcrepe)
+    pitch.unload_model()
+
+
+def test_pitch_registers_its_unload():
+    assert pitch.unload_model in models._callbacks
+
+
+def test_release_reports_nothing_freed_when_the_allocator_was_already_empty(
+        monkeypatch, isolated_callbacks):
+    emptied = []
+    monkeypatch.setitem(sys.modules, "torch",
+                        fake_torch(emptied=emptied, reserved=0))
+    assert models.release() == 0
+    assert emptied == [True]

tests/test_notes.py

@@ -4,7 +4,7 @@ import numpy as np
 import pytest
 from songtrace.config import Config
 from songtrace.notes import (
-    MIN_NOTE_SEC, TimedNote, build_notes, hz_to_ultrastar, segment_span,
+    MIN_NOTE_SEC, TimedNote, _warnings, build_notes, hz_to_ultrastar, segment_span,
     syllabify,
 )
 from songtrace.pipeline import Ctx, SongInput
@@ -78,7 +78,7 @@ def test_syllabify():
     assert syllabify("reminds", "English") == ["re", "minds"]
     assert syllabify("a", "English") == ["a"]
     assert syllabify("xyzzy", None) == ["xyzzy"]
-    assert syllabify("She's", "English") == ["She's"]
+    assert syllabify("It's", "English") == ["It's"]
 
 
 def test_syllabify_preserves_word_characters():
@@ -96,12 +96,12 @@ def test_syllabify_language_without_pyphen_dict_is_not_mishandled_as_english():
 def test_build_notes_basic_line():
     times, f0, conf = flat_pitch()
     rows = [
-        {"word": "She's", "start": 1.0, "end": 1.5, "score": 0.9, "line_index": 0},
+        {"word": "It's", "start": 1.0, "end": 1.5, "score": 0.9, "line_index": 0},
         {"word": "got", "start": 1.6, "end": 2.0, "score": 0.9, "line_index": 0},
         {"word": "Now", "start": 5.0, "end": 5.5, "score": 0.9, "line_index": 1},
     ]
     notes, breaks, warnings = build_notes(rows, times, f0, conf, "English")
-    assert notes[0].text == "She's"          # line-initial: no leading space
+    assert notes[0].text == "It's"          # line-initial: no leading space
     assert notes[1].text == " got"           # mid-line: leading space
     assert notes[2].text == "Now"            # new line: no leading space
     assert len(breaks) == 1 and 2.0 <= breaks[0] <= 5.0
@@ -127,11 +127,36 @@ def test_build_notes_unvoiced_word_flagged():
     assert warnings[0] == "1 low-confidence note near 0:01–0:01"
 
 
-def test_build_notes_low_score_word_flagged():
+def _scored_rows(scores, dur=0.4):
+    return [{"word": w, "start": 1.0 + i, "end": 1.0 + i + dur, "score": sc,
+             "line_index": 0}
+            for i, (w, sc) in enumerate(zip(["one", "two", "three", "four", "five"], scores))]
+
+
+def test_build_notes_flags_a_word_scoring_far_below_the_rest():
     times, f0, conf = flat_pitch()
-    rows = [{"word": "hey", "start": 1.0, "end": 1.4, "score": 0.1, "line_index": 0}]
-    notes, _, warnings = build_notes(rows, times, f0, conf, "English")
-    assert all(n.low_confidence for n in notes) and len(warnings) == 1
+    notes, _, warnings = build_notes(_scored_rows([0.4, 0.4, 0.05, 0.4, 0.4]),
+                                     times, f0, conf, "English")
+    assert [n.low_confidence for n in notes] == [False, False, True, False, False]
+    assert len(warnings) == 1
+
+
+def test_build_notes_judges_scores_against_the_song_not_a_fixed_cutoff():
+    # sung vocals score low throughout; uniformly low is not a reason to flag
+    times, f0, conf = flat_pitch()
+    notes, _, warnings = build_notes(_scored_rows([0.05] * 5), times, f0, conf, "English")
+    assert not any(n.low_confidence for n in notes) and warnings == []
+
+
+def test_build_notes_flags_words_too_short_or_too_long_to_be_sung():
+    times, f0, conf = flat_pitch()
+    for dur in (0.05, 3.5):
+        rows = _scored_rows([0.4] * 3)
+        rows[1]["end"] = rows[1]["start"] + dur
+        rows[2]["start"], rows[2]["end"] = rows[1]["end"] + 0.1, rows[1]["end"] + 0.5
+        notes, _, _ = build_notes(rows, times, f0, conf, "English")
+        # flat pitch: one note per word
+        assert [n.low_confidence for n in notes] == [False, True, False], dur
 
 
 def test_build_notes_unvoiced_word_inherits_previous_pitch():
@@ -278,7 +303,7 @@ def test_notes_stage_writes_json(tmp_path):
     times, f0, conf = flat_pitch()
     np.savez(work / "pitch.npz", times=times, f0=f0, conf=conf)
     (work / "alignment.json").write_text(json.dumps([
-        {"word": "She's", "start": 1.0, "end": 1.5, "score": 0.9, "line_index": 0},
+        {"word": "It's", "start": 1.0, "end": 1.5, "score": 0.9, "line_index": 0},
         {"word": "gone", "start": 3.0, "end": 3.5, "score": 0.9, "line_index": 1},
     ]))
     ctx = Ctx(inp=SongInput(title="T", artist="A", lyrics_text="x", language="English"),
@@ -287,7 +312,7 @@ def test_notes_stage_writes_json(tmp_path):
     assert stage.outputs(ctx) == [work / "notes_sec.json"]
     stage.run(ctx)
     data = json.loads((work / "notes_sec.json").read_text())
-    assert [n["text"] for n in data["notes"]] == ["She's", "gone"]
+    assert [n["text"] for n in data["notes"]] == ["It's", "gone"]
     assert data["breaks"] == [2.25]
     assert data["warnings"] == []
     assert TimedNote(**data["notes"][0]).pitch == 0
@@ -297,15 +322,19 @@ def test_notes_stage_registered():
     assert "notes" in [s.name for s in all_stages()]
 
 
-def test_build_notes_skips_notes_within_missing_span():
+def test_build_notes_keeps_matched_words_within_missing_span():
+    # A missing span covers whole Whisper segments, so it can hold matched
+    # lines alongside the unmatched singing; those lines must keep their notes.
     times, f0, conf = flat_pitch()
     rows = [
         {"word": "keep", "start": 1.0, "end": 1.4, "score": 0.9, "line_index": 0},
-        {"word": "skip", "start": 5.0, "end": 5.4, "score": 0.9, "line_index": 1},
+        {"word": "held", "start": 5.0, "end": 5.4, "score": 0.9, "line_index": 1},
     ]
-    notes, _, _ = build_notes(rows, times, f0, conf, "English",
-                              missing_spans=[(4.5, 6.0)])
-    assert [n.text for n in notes] == ["keep"]
+    notes, breaks, warnings = build_notes(rows, times, f0, conf, "English",
+                                          missing_spans=[(4.5, 6.0)])
+    assert [n.text for n in notes] == ["keep", "held"]
+    assert breaks == [(1.4 + 5.0) / 2]
+    assert warnings == ["missing lyrics near 0:04–0:06"]
 
 
 def test_warnings_report_dropped_lines():
@@ -325,25 +354,18 @@ def test_warnings_report_missing_spans():
     assert warnings == ["missing lyrics near 1:21–1:29"]
 
 
-def test_build_notes_skipped_row_mid_line_does_not_corrupt_spacing_or_breaks():
-    # "gone" falls inside a missing span and is skipped; "away" is the same
-    # line's next word and must still get its leading space, and the break
-    # before the next line must use the last *emitted* word's end (3.4, from
-    # "away"), not the skipped row's end (2.4).
-    times, f0, conf = flat_pitch()
-    rows = [
-        {"word": "keep", "start": 1.0, "end": 1.4, "score": 0.9, "line_index": 0},
-        {"word": "gone", "start": 2.0, "end": 2.4, "score": 0.9, "line_index": 0},
-        {"word": "away", "start": 3.0, "end": 3.4, "score": 0.9, "line_index": 0},
-        {"word": "next", "start": 5.0, "end": 5.4, "score": 0.9, "line_index": 1},
-    ]
-    notes, breaks, _ = build_notes(rows, times, f0, conf, "English",
-                                   missing_spans=[(1.9, 2.5)])
-    assert [n.text for n in notes] == ["keep", " away", "next"]
-    assert breaks == [(3.4 + 5.0) / 2]
-
 def test_notes_carry_line_index():
     times, f0, conf = flat_pitch()
     rows = [{"word": "hey", "start": 1.0, "end": 1.4, "score": 0.9, "line_index": 3}]
     notes, _, _ = build_notes(rows, times, f0, conf, "English")
     assert notes[0].line_index == 3
+
+
+def test_warnings_group_flagged_notes_close_together():
+    def note(start, low):
+        return TimedNote(start, 0.3, 0, "la", low, 0)
+    notes = [note(10.0, True), note(10.5, False), note(11.0, True),   # 0.7s apart
+             note(20.0, True)]                                       # far from both
+    assert _warnings(notes) == [
+        "2 low-confidence notes near 0:10–0:11",
+        "1 low-confidence note near 0:20–0:20"]

tests/test_package.py

@@ -49,19 +49,37 @@ def make_pipeline_inputs(tmp_path, cover=None):
     return inp, cfg
 
 
-def test_package_copies_compatible_video(tmp_path, monkeypatch):
-    monkeypatch.setattr(package, "ffmpeg", lambda *a: Path(a[-1]).write_bytes(b"m"))
+def test_package_remuxes_compatible_video_without_reencoding(tmp_path, monkeypatch):
+    calls = []
+    monkeypatch.setattr(package, "ffmpeg",
+                        lambda *a: (calls.append(a), Path(a[-1]).write_bytes(b"m")))
     monkeypatch.setattr(package, "ffprobe_codec", lambda p: ("webm", "vp9"))
     ctx = make_ctx(tmp_path, cover=make_cover(tmp_path))
     package.package_stage().run(ctx)
     out = tmp_path / "out" / "A - T"
     assert (out / "A - T.txt").exists()
     assert (out / "A - T.mp3").exists()
-    assert (out / "A - T.webm").read_bytes() == b"v"
+    assert (out / "A - T.webm").exists()
+    video_call = next(c for c in calls if c[-1].endswith("A - T.webm"))
+    assert "-c" in video_call and "copy" in video_call, "the video was re-encoded"
     img = Image.open(out / "A - T.jpg")
     assert img.width == img.height
 
 
+@pytest.mark.parametrize("probe,name", [(("webm", "vp9"), "A - T.webm"),
+                                        (("avi", "mpeg4"), "A - T.mp4")])
+def test_package_strips_the_videos_audio_track(tmp_path, monkeypatch, probe, name):
+    """#MP3 is the song's audio; a video that keeps its own plays as an echo."""
+    calls = []
+    monkeypatch.setattr(package, "ffmpeg",
+                        lambda *a: (calls.append(a), Path(a[-1]).write_bytes(b"m")))
+    monkeypatch.setattr(package, "ffprobe_codec", lambda p: probe)
+    ctx = make_ctx(tmp_path, cover=make_cover(tmp_path))
+    package.package_stage().run(ctx)
+    video_call = next(c for c in calls if c[-1].endswith(name))
+    assert "-an" in video_call
+
+
 def test_package_reencodes_and_rewrites_video_header(tmp_path, monkeypatch):
     monkeypatch.setattr(package, "ffmpeg", lambda *a: Path(a[-1]).write_bytes(b"m"))
     monkeypatch.setattr(package, "ffprobe_codec", lambda p: ("avi", "mpeg4"))

tests/test_pipeline.py

@@ -53,3 +53,49 @@ def test_read_warnings_is_empty_without_a_notes_file(tmp_path):
 def test_read_warnings_reads_the_notes_file(tmp_path):
     (tmp_path / "notes_sec.json").write_text(json.dumps({"warnings": ["w1", "w2"]}))
     assert read_warnings(tmp_path) == ["w1", "w2"]
+
+def test_gpu_is_released_after_every_stage(tmp_path, monkeypatch):
+    """Not just at the end: a later stage may wait minutes on the Whisper server."""
+    from songtrace import models
+    cfg, inp, calls = make_cfg(tmp_path), make_inp(), []
+    monkeypatch.setattr(models, "release", lambda: calls.append("release"))
+    stages = [fake_stage("s1", calls), fake_stage("s2", calls)]
+    run_pipeline(inp, cfg, log=lambda m: None, stages=stages)
+    assert calls == ["s1", "release", "s2", "release"]
+
+def test_gpu_is_released_when_a_stage_fails(tmp_path, monkeypatch):
+    import pytest
+    from songtrace import models
+    from songtrace.pipeline import PipelineError
+    cfg, inp, calls = make_cfg(tmp_path), make_inp(), []
+    monkeypatch.setattr(models, "release", lambda: calls.append("release"))
+    def boom(ctx):
+        raise PipelineError("boom")
+    stages = [Stage(name="s1", outputs=lambda ctx: [ctx.work / "s1.done"], run=boom)]
+    with pytest.raises(PipelineError):
+        run_pipeline(inp, cfg, log=lambda m: None, stages=stages)
+    assert calls == ["release"]
+
+def test_a_cached_stage_does_not_pay_for_a_release(tmp_path, monkeypatch):
+    from songtrace import models
+    cfg, inp, calls = make_cfg(tmp_path), make_inp(), []
+    stages = [fake_stage("s1", calls)]
+    run_pipeline(inp, cfg, log=lambda m: None, stages=stages)
+    calls.clear()
+    monkeypatch.setattr(models, "release", lambda: calls.append("release"))
+    run_pipeline(inp, cfg, log=lambda m: None, stages=stages)
+    assert calls == []
+
+def test_a_release_that_freed_memory_is_reported_in_the_log(tmp_path, monkeypatch):
+    from songtrace import models
+    cfg, inp, lines = make_cfg(tmp_path), make_inp(), []
+    monkeypatch.setattr(models, "release", lambda: 512 * 2 ** 20)
+    run_pipeline(inp, cfg, log=lines.append, stages=[fake_stage("s1", [])])
+    assert "[s1] released 512 MiB of GPU memory" in lines
+
+def test_a_release_that_freed_nothing_stays_out_of_the_log(tmp_path, monkeypatch):
+    from songtrace import models
+    cfg, inp, lines = make_cfg(tmp_path), make_inp(), []
+    monkeypatch.setattr(models, "release", lambda: 0)
+    run_pipeline(inp, cfg, log=lines.append, stages=[fake_stage("s1", [])])
+    assert not any("released" in line for line in lines)

tests/test_pitch.py

@@ -17,3 +17,21 @@ def test_pitch_stage_writes_npz(tmp_path, monkeypatch):
     data = np.load(work / "pitch.npz")
     assert np.allclose(data["f0"], 220.0)
     assert data["times"].shape == data["conf"].shape
+
+
+def test_mute_silence_drops_bleed_but_keeps_quiet_singing():
+    # 60 frames of singing around -30 dB, one quiet sung frame at -50 dB, and
+    # 40 frames of bleed at -60 dB: only the bleed is more than 25 dB below
+    # the song's loud level.
+    loudness = np.array([-30.0] * 60 + [-50.0] + [-60.0] * 40)
+    conf = np.full_like(loudness, 0.8)
+    pitch.mute_silence(conf, loudness)
+    assert (conf[:61] == 0.8).all()
+    assert (conf[61:] == 0.0).all()
+
+
+def test_mute_silence_is_relative_to_the_songs_level():
+    loudness = np.array([-45.0] * 60 + [-75.0] * 40)
+    conf = np.full_like(loudness, 0.8)
+    pitch.mute_silence(conf, loudness)
+    assert (conf[:60] == 0.8).all() and (conf[60:] == 0.0).all()

tests/test_rebuild.py

@@ -5,7 +5,7 @@ import pytest
 
 from songtrace.config import Config
 from songtrace.pipeline import STAGE_ORDER, PipelineError, SongInput
-from songtrace.rebuild import (FIELD_STAGE, changed_fields, plan,
+from songtrace.rebuild import (FIELD_STAGE, changed_fields, earliest, plan,
                                    relocate_work, superseded_output)
 
 
@@ -124,3 +124,14 @@ def test_superseded_output_refuses_a_path_outside_the_output_root(tmp_path):
 def test_superseded_output_refuses_the_output_root_itself(tmp_path):
     root = tmp_path / "out"
     assert superseded_output(str(root), str(root / "A - T"), root) is None
+
+
+def test_earliest_picks_the_earlier_stage():
+    assert earliest("package", "separate") == "separate"
+    assert earliest("separate", "package") == "separate"
+
+
+def test_earliest_ignores_unset_stages():
+    assert earliest(None, "grid") == "grid"
+    assert earliest("grid", None) == "grid"
+    assert earliest(None, None) is None

tests/test_static_js.py

@@ -0,0 +1,15 @@
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+def test_static_js_unit_tests():
+    """The page's own logic, run under Node's test runner."""
+    node = shutil.which("node")
+    if node is None:
+        pytest.skip("node is not installed")
+    tests = sorted(str(p) for p in (Path(__file__).parent / "js").glob("*.test.mjs"))
+    proc = subprocess.run([node, "--test", *tests], capture_output=True, text=True)
+    assert proc.returncode == 0, proc.stdout + proc.stderr

tests/test_transcribe.py

@@ -1,6 +1,7 @@
 from songtrace.lyrics import normalize_lyrics
 from songtrace.whisper_client import TranscriptSegment
-from songtrace.stages.transcribe import classify_lyrics_match, lyrics_similarity, vocal_sections
+from songtrace.stages.transcribe import (classify_lyrics_match, lyrics_similarity,
+                                         recovered_spans, vocal_sections)
 
 def seg(s, e, t=""):
     return TranscriptSegment(start=s, end=e, text=t)
@@ -53,7 +54,7 @@ def test_classify_lyrics_match_keeps_partially_matched_lines():
 def test_classify_lyrics_match_scopes_missing_span_to_adlib_not_whole_section():
     # matched line and an unmatched ad-lib close enough together that
     # vocal_sections would merge them into one section; missing_spans must
-    # stay tight around the ad-lib so the matched line keeps its notes.
+    # stay tight around the ad-lib so the review marks the right place.
     ref = normalize_lyrics("it's one two three\nfour five six seven eight")
     segs = [seg(1, 4, "it's one two three four five six seven eight"),
             seg(6, 8, "completely unrelated ad lib")]
@@ -64,3 +65,31 @@ def test_classify_lyrics_match_scopes_missing_span_to_adlib_not_whole_section():
     assert missing == [(5.0, 9.0)]
     for a, b in missing:
         assert not (a <= 1.0 < b)        # matched line's start (1.0) untouched
+
+
+THREE_LINES = "one two three\nfour five six\nseven eight nine"
+
+
+def test_lines_whisper_missed_are_kept_when_singing_went_untranscribed():
+    ref = normalize_lyrics(THREE_LINES)
+    segs = [seg(0, 2, "one two three"), seg(20, 22, "seven eight nine")]
+    assert classify_lyrics_match(segs, ref)[0] == [1]
+    dropped, _ = classify_lyrics_match(segs, ref, unheard=[(8.0, 14.0)])
+    assert dropped == []
+
+
+def test_untranscribed_singing_elsewhere_does_not_keep_a_line():
+    ref = normalize_lyrics(THREE_LINES)
+    segs = [seg(0, 2, "one two three"), seg(20, 22, "seven eight nine")]
+    dropped, _ = classify_lyrics_match(segs, ref, unheard=[(30.0, 35.0)])
+    assert dropped == [1]
+
+
+def test_recovered_spans_are_the_singing_between_heard_neighbours():
+    ref = normalize_lyrics(THREE_LINES)
+    segs = [seg(10, 12, "four five six"), seg(20, 22, "seven eight nine")]
+    unheard = [(3.0, 9.0), (14.0, 18.0), (30.0, 35.0)]
+    # line 0 comes before anything heard, so only the singing before line 1
+    # can stand in for it; the other spans have no missing line around them
+    assert recovered_spans(segs, ref, unheard) == [(3.0, 9.0)]
+    assert classify_lyrics_match(segs, ref, unheard=unheard)[0] == []

tests/test_ultrastar.py

@@ -10,8 +10,8 @@ def load(name):
     return (FIXTURES / name).read_text(encoding="utf-8", errors="replace")
 
 def test_parse_headers_and_notes():
-    song = parse_ultrastar(load("sanctuary.txt"))
-    assert get_header(song, "artist") == "Utada Hikaru"
+    song = parse_ultrastar(load("chart_crlf.txt"))
+    assert get_header(song, "artist") == "Test Artist"
     assert parse_bpm(get_header(song, "BPM")) == 217.98
     first = song.body[0]
     assert first == Note(kind=":", beat=0, length=3, pitch=16, text="ah")
@@ -19,16 +19,16 @@ def test_parse_headers_and_notes():
     assert any(n.kind == "F" for n in song.body if isinstance(n, Note))
 
 def test_note_text_keeps_leading_space():
-    song = parse_ultrastar(load("sanctuary.txt"))
+    song = parse_ultrastar(load("chart_crlf.txt"))
     notes = [n for n in song.body if isinstance(n, Note)]
     assert notes[1].text == " ah"
 
 def test_negative_pitch():
-    song = parse_ultrastar(load("sweet_child.txt"))
+    song = parse_ultrastar(load("chart_latin1.txt"))
     assert any(n.pitch == -9 for n in song.body if isinstance(n, Note))
 
 def test_round_trip():
-    for name in ("sweet_child.txt", "sanctuary.txt"):
+    for name in ("chart_latin1.txt", "chart_crlf.txt"):
         song = parse_ultrastar(load(name))
         again = parse_ultrastar(serialize_ultrastar(song))
         assert again == song

tests/test_web.py

@@ -584,11 +584,19 @@ def _submit_body(html):
     return html[start:html.index("\n});\n", start)]
 
 
+def _listener_body(html, prefix):
+    start = html.index(prefix)
+    return html[start:html.index("\n});\n", start)]
+
+
 def _rebuild_flaws(html):
     """Ways rebuild mode could quietly stop working."""
     flaws, submit = [], _submit_body(html)
     if "rebuildOf ?" not in submit or "/rebuild" not in submit:
         flaws.append("the form always posts to /api/jobs, so edits create a new song")
+    if "form.reset()" in submit or "exitRebuild()" in submit:
+        flaws.append("a successful submission empties the form, so correcting "
+                     "or varying the song just sent means retyping it")
 
     actions = _fn_body(html, "renderActions")
     if not re.search(r"if \(.*dataset\.jobId === job\.id.*\) return;", actions):
@@ -596,9 +604,39 @@ def _rebuild_flaws(html):
     if '"failed"' not in actions or '"done"' not in actions:
         flaws.append("the action row does not key off the job status")
 
-    start = _fn_body(html, "startRebuild")
-    if "/input" not in start or "form.elements[" not in start:
+    load = _fn_body(html, "loadInputs")
+    if "/input" not in load or "form.elements[" not in load:
         flaws.append("rebuild mode does not prefill the form from the job's input")
+
+    select = _fn_body(html, "selectJob")
+    if "loadInputs(" not in select:
+        flaws.append("selecting a queue entry does not bring its inputs back up")
+    if "formDirty" not in select or "confirm(" not in select:
+        flaws.append("selecting a queue entry discards unsaved edits without asking")
+
+    if "if (rebuildOf === id) exitRebuild();" not in _fn_body(html, "deleteJob"):
+        flaws.append("deleting the loaded job leaves the form pointed at it")
+
+    # selecting a queue entry loads it, so the sidebar button is now the only
+    # way back to a blank form
+    create = _listener_body(html, 'createSong.addEventListener("click"')
+    if "exitRebuild()" not in create:
+        flaws.append("the queue's CREATE SONG button does not clear the form")
+    if "formDirty" not in create or "confirm(" not in create:
+        flaws.append("the queue's CREATE SONG button discards edits without asking")
+    if "clearDetail(" not in create:
+        flaws.append("CREATE SONG empties the form but leaves the previous "
+                     "song's review and player sitting under it")
+    if "composing" not in create or "composing" not in _fn_body(html, "refreshJobs"):
+        flaws.append("the blank page CREATE SONG made is selected back over by "
+                     "the next poll of the queue")
+
+    mode = _fn_body(html, "setFormMode")
+    if 'querySelector("details").open' not in mode:
+        flaws.append("prefilled genre/year/language/bpm stay hidden behind the "
+                     "closed Advanced summary, so they rebuild unseen")
+    if "submitButton.disabled" not in _fn_body(html, "setSubmitLock"):
+        flaws.append("the form lets you submit a rebuild the API will answer 409")
     return flaws
 
 
@@ -631,7 +669,7 @@ def test_rebuild_full_and_delete_controls_are_wired_up():
 
 def _empty_state_flaws(html):
     refresh = _fn_body(html, "refreshJobs")
-    if "clearDetail()" not in refresh:
+    if "clearDetail(" not in refresh:
         return ["refreshJobs never resets the panel when no job is selected"]
     return []
 
@@ -640,6 +678,54 @@ def test_review_panel_resets_when_no_job_is_selected():
     assert _empty_state_flaws(_index_html()) == []
 
 
+def _playback_flaws(html):
+    """Ways the review could stop tracking the media element."""
+    flaws = []
+    source = _fn_body(html, "setPlayerSource")
+    if "media/audio" not in source:
+        flaws.append("the player is not pointed at the job's packaged audio, "
+                     "which is the file the game plays and the notes track")
+    if "media/video" not in source:
+        flaws.append("the packaged video is never shown alongside the audio")
+
+    # the mp3 and the video carry the same recording; playing both is an echo
+    if not re.search(r"<video[^>]*\bmuted\b", html):
+        flaws.append("the background video is not muted, so its own audio "
+                     "plays on top of the mp3")
+    pump = _fn_body(html, "pumpPlayback")
+    if "slaveVideo(" not in pump:
+        flaws.append("the picture is never pulled back onto the audio clock, "
+                     "so it drifts out of sync over a long song")
+
+    if "requestAnimationFrame" not in _fn_body(html, "pumpPlayback"):
+        flaws.append("sync is not driven by the frame loop, so the playhead "
+                     "steps at timeupdate's ~4Hz instead of following the audio")
+
+    if "media.paused" not in _fn_body(html, "focusActive"):
+        flaws.append("the view is scrolled even while paused, fighting a reader "
+                     "who scrolled away to look at something else")
+
+    sync = _fn_body(html, "syncPlayback")
+    if "clearEntry(" not in sync:
+        flaws.append("the line the playhead left keeps its highlight")
+    clear = _fn_body(html, "clearEntry")
+    for name in ("review-word-sung", "review-word-active", "review-line-active"):
+        if name not in clear:
+            flaws.append(f"{name} is never taken off a line the playhead left")
+
+    # every branch that gives up on rendering a review has to unload the media
+    # too, or the previous song stays loaded and playable under the new one
+    render = _fn_body(html, "renderLyricsReview")
+    if render.count("resetPlayer()") < render.count("emptyNote("):
+        flaws.append("a review the page cannot render leaves the previous "
+                     "song's media loaded in the player")
+    return flaws
+
+
+def test_review_playback_tracks_the_media_element():
+    assert _playback_flaws(_index_html()) == []
+
+
 # each mutation is a plausible regression; the checker above must reject all of them
 MUTATIONS = [
     (_focus_flaws, "queue: card moved unconditionally",
@@ -672,9 +758,52 @@ MUTATIONS = [
      'if (!confirm("Delete this song? This removes all its files and cannot be undone.")) return;',
      ""),
     (_rebuild_full_and_delete_flaws, "rebuild-full: no longer offered on a done job",
-     '["edit", "rebuild-full", "delete"]', '["edit", "delete"]'),
+     '["rebuild-full", "delete"]', '["delete"]'),
+    (_rebuild_flaws, "prefill: selecting a queue entry no longer loads its inputs",
+     "  if (reload) await loadInputs(id, JOBS.find(j => j.id === id)?.status);\n", ""),
+    (_rebuild_flaws, "prefill: unsaved edits discarded without asking",
+     '  if (reload && formDirty && !confirm("Discard your unsaved edits to this form?")) return;\n',
+     ""),
+    (_rebuild_flaws, "prefill: deleting the loaded job leaves the form pointed at it",
+     "  if (rebuildOf === id) exitRebuild();\n", ""),
+    (_rebuild_flaws, "prefill: advanced fields stay hidden behind a closed summary",
+     'form.querySelector("details").open =', "const unusedAdvancedOpen ="),
+    (_rebuild_flaws, "prefill: an in-progress job can be submitted for rebuild anyway",
+     "submitButton.disabled = locked;", ""),
+    (_rebuild_flaws, "submit: a successful submission empties the form again",
+     "  rebuildOf = null;\n  formDirty = false;\n  setFormMode(null, null);\n  refreshJobs();",
+     "  exitRebuild();\n  refreshJobs();"),
+    (_rebuild_flaws, "create: the queue button no longer clears the form",
+     "  exitRebuild();\n  clearDetail(\"nothing selected\");\n", ""),
+    (_rebuild_flaws, "create: the review is left behind under a blank form",
+     '  clearDetail("nothing selected");\n', ""),
+    (_rebuild_flaws, "create: the next poll selects a song back into the blank page",
+     "  composing = true;\n", ""),
+    (_rebuild_flaws, "create: the queue button discards edits without asking",
+     '  if (formDirty && !confirm("Discard your unsaved edits to this form?")) return;\n  composing = true;',
+     "  composing = true;"),
+    (_playback_flaws, "playback: sync falls back to the timeupdate event's ~4Hz",
+     "syncFrame = media.paused ? null : requestAnimationFrame(pumpPlayback);",
+     "syncFrame = null;"),
+    (_playback_flaws, "playback: the view is scrolled even while paused",
+     "if (!activeEntry || media.paused) return;", "if (!activeEntry) return;"),
+    (_playback_flaws, "playback: the line the playhead left keeps its highlight",
+     "    if (activeEntry) clearEntry(activeEntry);\n", ""),
+    (_playback_flaws, "playback: a word stays lit after the playhead moves on",
+     'w.el.classList.remove("review-word-sung", "review-word-active");',
+     'w.el.classList.remove("review-word-sung");'),
+    (_playback_flaws, "playback: an unrenderable review leaves the old song loaded",
+     "    resetPlayer();\n", ""),
+    (_playback_flaws, "playback: the player is not pointed at the packaged audio",
+     'const src = available?.audio ? `/api/jobs/${job.id}/media/audio` : "";',
+     'const src = "";'),
+    (_playback_flaws, "playback: the background video plays its own audio too",
+     '<video id="player-video" muted playsinline',
+     '<video id="player-video" playsinline'),
+    (_playback_flaws, "playback: the picture is never re-synced to the audio",
+     "  slaveVideo(false);\n", ""),
     (_empty_state_flaws, "empty state: clearDetail no longer wired into refreshJobs",
-     "if (selectedId) refreshDetail();\n  else clearDetail();",
+     "if (selectedId) refreshDetail();\n  else clearDetail(composing ? \"nothing selected\" : undefined);",
      "if (selectedId) refreshDetail();"),
 ]
 
@@ -705,13 +834,13 @@ def test_narrow_stage_labels_stay_in_the_accessibility_tree():
 
 def test_rebuild_mode_reuses_the_one_form():
     html = _index_html()
-    assert html.count("<form") == 1
+    assert html.count('name="lyrics"') == 1    # one song form, not a rebuild copy
     assert _rebuild_flaws(html) == []
 
 
 def test_index_has_rebuild_hooks():
     html = _index_html()
-    for hook in ("review-actions", "review-lineage", "cancel-rebuild",
+    for hook in ("review-actions", "review-lineage", "create-song",
                  'data-keep="video"', 'data-keep="cover"'):
         assert hook in html, hook
 
@@ -1283,13 +1412,16 @@ def test_review_endpoint_groups_notes_by_line(tmp_path):
     wait_status(client, job_id, "done")
     body = client.get(f"/api/jobs/{job_id}/review").json()
     assert body["lines"] == [
-        {"index": 0, "text": "hi", "dropped": False,
-         "notes": [{"start": 1.0, "end": 1.4, "pitch": 0, "low_confidence": False}],
+        {"index": 0, "text": "hi", "dropped": False, "edited": False,
+         "notes": [{"start": 1.0, "end": 1.4, "pitch": 0, "low_confidence": False,
+                    "text": "hi", "kind": ":"}],
          "words": []},
-        {"index": 1, "text": "there", "dropped": False,
-         "notes": [{"start": 5.0, "end": 5.3, "pitch": 2, "low_confidence": True}],
+        {"index": 1, "text": "there", "dropped": False, "edited": False,
+         "notes": [{"start": 5.0, "end": 5.3, "pitch": 2, "low_confidence": True,
+                    "text": "there", "kind": ":"}],
+         "words": []},
+        {"index": 2, "text": "gone", "dropped": True, "edited": False, "notes": [],
          "words": []},
-        {"index": 2, "text": "gone", "dropped": True, "notes": [], "words": []},
     ]
     assert body["missing_spans"] == [{"start": 8.0, "end": 9.5}]
 
@@ -1358,3 +1490,587 @@ def test_review_missing_when_pipeline_never_wrote_notes(tmp_path):
     client, _ = make_client(tmp_path, ok_runner)
     job_id = make_done_job(client)
     assert client.get(f"/api/jobs/{job_id}/review").status_code == 404
+
+
+# --- review playback -------------------------------------------------------
+
+MEDIA_FILES = {"A - T.mp3": b"ID3audio", "A - T.mp4": b"\0\0\0\x18ftypvideo",
+               "A - T.jpg": b"\xff\xd8cover"}
+MEDIA_HEADERS = [("TITLE", "T"), ("ARTIST", "A"), ("MP3", "A - T.mp3"),
+                 ("COVER", "A - T.jpg"), ("VIDEO", "A - T.mp4")]
+
+
+def media_runner_factory(files=None, headers=None, write_txt=True):
+    """A run that leaves behind a song folder, the way package does."""
+    def runner(inp, cfg, log=print, force_from=None, stages=None):
+        slug = song_slug(inp)
+        out = cfg.output_dir / slug
+        out.mkdir(parents=True, exist_ok=True)
+        for name, body in (MEDIA_FILES if files is None else files).items():
+            (out / name).write_bytes(body)
+        if write_txt:
+            rows = [f"#{k}:{v}" for k, v in
+                    (MEDIA_HEADERS if headers is None else headers)]
+            (out / f"{slug}.txt").write_text("\n".join(rows) + "\n: 0 4 0 la\nE\n",
+                                             encoding="utf-8")
+        return PipelineResult(output_dir=out)
+    return runner
+
+
+def test_media_serves_the_files_the_song_txt_names(tmp_path):
+    client, _ = make_client(tmp_path, media_runner_factory())
+    job_id = make_done_job(client)
+    for kind, name in (("audio", "A - T.mp3"), ("video", "A - T.mp4"),
+                       ("cover", "A - T.jpg")):
+        resp = client.get(f"/api/jobs/{job_id}/media/{kind}")
+        assert resp.status_code == 200, kind
+        assert resp.content == MEDIA_FILES[name], kind
+
+
+def test_media_serves_whatever_the_header_was_rewritten_to(tmp_path):
+    """package transcodes to .mp4 and rewrites #VIDEO; the extension is not fixed."""
+    files = {**MEDIA_FILES, "A - T.webm": b"transcoded"}
+    headers = [(k, "A - T.webm" if k == "VIDEO" else v) for k, v in MEDIA_HEADERS]
+    client, _ = make_client(tmp_path, media_runner_factory(files, headers))
+    job_id = make_done_job(client)
+    assert client.get(f"/api/jobs/{job_id}/media/video").content == b"transcoded"
+
+
+def test_media_supports_range_requests(tmp_path):
+    """Without 206 the browser cannot seek, which is the point of the player."""
+    client, _ = make_client(tmp_path, media_runner_factory())
+    job_id = make_done_job(client)
+    resp = client.get(f"/api/jobs/{job_id}/media/video", headers={"Range": "bytes=0-3"})
+    assert resp.status_code == 206
+    assert resp.headers["content-range"] == f"bytes 0-3/{len(MEDIA_FILES['A - T.mp4'])}"
+    assert resp.content == MEDIA_FILES["A - T.mp4"][:4]
+
+
+def test_media_of_an_unknown_kind_is_404(tmp_path):
+    client, _ = make_client(tmp_path, media_runner_factory())
+    job_id = make_done_job(client)
+    assert client.get(f"/api/jobs/{job_id}/media/instrumental").status_code == 404
+
+
+def test_media_refuses_a_header_pointing_outside_the_song_folder(tmp_path):
+    secret = tmp_path / "secret.txt"
+    secret.write_text("not yours")
+    headers = [(k, "../../secret.txt" if k == "MP3" else v) for k, v in MEDIA_HEADERS]
+    client, _ = make_client(tmp_path, media_runner_factory(headers=headers))
+    job_id = make_done_job(client)
+    assert client.get(f"/api/jobs/{job_id}/media/audio").status_code == 404
+
+
+def test_media_refuses_an_absolute_header_path(tmp_path):
+    secret = tmp_path / "secret.txt"
+    secret.write_text("not yours")
+    headers = [(k, str(secret) if k == "MP3" else v) for k, v in MEDIA_HEADERS]
+    client, _ = make_client(tmp_path, media_runner_factory(headers=headers))
+    job_id = make_done_job(client)
+    assert client.get(f"/api/jobs/{job_id}/media/audio").status_code == 404
+
+
+def test_media_404s_when_the_named_file_is_missing(tmp_path):
+    client, _ = make_client(tmp_path, media_runner_factory(files={}))
+    job_id = make_done_job(client)
+    assert client.get(f"/api/jobs/{job_id}/media/audio").status_code == 404
+
+
+def test_media_404s_when_the_header_was_dropped(tmp_path):
+    """package strips #COVER when there is no usable cover image."""
+    headers = [(k, v) for k, v in MEDIA_HEADERS if k != "COVER"]
+    client, _ = make_client(tmp_path, media_runner_factory(headers=headers))
+    job_id = make_done_job(client)
+    assert client.get(f"/api/jobs/{job_id}/media/cover").status_code == 404
+    assert client.get(f"/api/jobs/{job_id}/media/audio").status_code == 200
+
+
+def test_media_404s_when_there_is_no_song_txt(tmp_path):
+    client, _ = make_client(tmp_path, media_runner_factory(write_txt=False))
+    job_id = make_done_job(client)
+    assert client.get(f"/api/jobs/{job_id}/media/audio").status_code == 404
+
+
+def test_media_of_a_failed_job_is_404(tmp_path):
+    def bad_runner(*a, **kw):
+        raise PipelineError("boom")
+    client, _ = make_client(tmp_path, bad_runner)
+    job_id = client.post("/api/jobs", data={
+        "title": "T", "artist": "A", "lyrics": "x", "youtube_url": "http://y"}).json()["id"]
+    wait_status(client, job_id, "failed")
+    assert client.get(f"/api/jobs/{job_id}/media/audio").status_code == 404
+
+
+def test_media_of_a_running_job_is_409(tmp_path):
+    release = threading.Event()
+
+    def blocking(inp, cfg, log=print, force_from=None, stages=None):
+        release.wait(5)
+        return PipelineResult(output_dir=cfg.output_dir / "X")
+
+    client, _ = make_client(tmp_path, blocking)
+    job_id = client.post("/api/jobs", data={
+        "title": "T", "artist": "A", "lyrics": "x", "youtube_url": "http://y"}).json()["id"]
+    try:
+        wait_status(client, job_id, "running")
+        assert client.get(f"/api/jobs/{job_id}/media/audio").status_code == 409
+    finally:
+        release.set()
+    wait_status(client, job_id, "done")
+
+
+def test_media_of_an_unknown_job_is_404(tmp_path):
+    client, _ = make_client(tmp_path, media_runner_factory())
+    assert client.get("/api/jobs/nope/media/audio").status_code == 404
+
+
+def test_review_reports_which_media_the_player_can_load(tmp_path):
+    notes = [{"start": 1.0, "duration": 0.4, "pitch": 0, "text": "hi",
+              "low_confidence": False, "line_index": 0}]
+    review = review_runner_factory(notes)
+    media = media_runner_factory(headers=[(k, v) for k, v in MEDIA_HEADERS
+                                          if k != "COVER"])
+
+    def runner(inp, cfg, **kw):
+        media(inp, cfg, **kw)
+        return review(inp, cfg, **kw)
+
+    client, _ = make_client(tmp_path, runner)
+    job_id = make_done_job(client, lyrics="hi")
+    body = client.get(f"/api/jobs/{job_id}/review").json()
+    assert body["media"] == {"audio": True, "video": True, "cover": False}
+
+
+# --- restarting a rebuild from a chosen stage ------------------------------
+
+def force_from_runner_factory(seen):
+    def runner(inp, cfg, log=print, force_from=None, stages=None):
+        seen.append(force_from)
+        out = cfg.output_dir / song_slug(inp)
+        out.mkdir(parents=True, exist_ok=True)
+        return PipelineResult(output_dir=out)
+    return runner
+
+
+def rebuild_with(client, job_id, **extra):
+    data = {"title": "T", "artist": "A", "lyrics": "x", "youtube_url": "http://y"}
+    data.update(extra)
+    return client.post(f"/api/jobs/{job_id}/rebuild", data=data)
+
+
+def test_rebuild_without_edits_restarts_from_the_stage_asked_for(tmp_path):
+    """The point of the control: a change in songtrace invalidates no field."""
+    seen = []
+    client, _ = make_client(tmp_path, force_from_runner_factory(seen))
+    parent = make_done_job(client)
+    resp = rebuild_with(client, parent, force_from="package")
+    assert resp.status_code == 201
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[-1] == "package"
+
+
+def test_rebuild_without_a_stage_still_plans_from_the_edit(tmp_path):
+    seen = []
+    client, _ = make_client(tmp_path, force_from_runner_factory(seen))
+    parent = make_done_job(client)
+    resp = rebuild_with(client, parent, lyrics="different words")
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[-1] == "align"
+
+
+def test_an_edit_wins_when_it_invalidates_more_than_the_stage_asked_for(tmp_path):
+    """A choice may widen what is redone, never narrow it below correctness."""
+    seen = []
+    client, _ = make_client(tmp_path, force_from_runner_factory(seen))
+    parent = make_done_job(client)
+    resp = rebuild_with(client, parent, lyrics="different words",
+                        force_from="package")
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[-1] == "align"
+
+
+def test_the_stage_asked_for_wins_when_it_is_earlier_than_the_edit(tmp_path):
+    seen = []
+    client, _ = make_client(tmp_path, force_from_runner_factory(seen))
+    parent = make_done_job(client)
+    resp = rebuild_with(client, parent, title="Renamed", force_from="separate")
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[-1] == "separate"
+
+
+def test_rebuild_rejects_a_stage_that_is_not_in_the_pipeline(tmp_path):
+    client, _ = make_client(tmp_path, ok_runner)
+    parent = make_done_job(client)
+    resp = rebuild_with(client, parent, force_from="deechoing")
+    assert resp.status_code == 400
+    assert "deechoing" in resp.json()["detail"]
+
+
+def test_a_blank_stage_is_the_same_as_not_asking(tmp_path):
+    seen = []
+    client, _ = make_client(tmp_path, force_from_runner_factory(seen))
+    parent = make_done_job(client)
+    resp = rebuild_with(client, parent, force_from="")
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[-1] is None
+
+
+def test_rebuild_from_scratch_still_restarts_at_the_first_stage(tmp_path):
+    seen = []
+    client, _ = make_client(tmp_path, force_from_runner_factory(seen))
+    parent = make_done_job(client)
+    resp = client.post(f"/api/jobs/{parent}/rebuild-full")
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[-1] == STAGE_ORDER[0]
+
+
+def test_the_restart_control_offers_every_stage():
+    html = _index_html()
+    assert 'name="force_from"' in html
+    stages = _fn_body(html, "loadStages")
+    assert "force_from" in stages and "STAGES.map" in stages
+    mode = _fn_body(html, "setFormMode")
+    assert "restart-field" in mode, "the control is shown outside rebuild mode"
+
+
+def test_a_textareas_crlf_does_not_read_as_a_lyrics_edit(tmp_path):
+    """Browsers submit textareas with CRLF; the stored lyrics use LF."""
+    seen = []
+    client, _ = make_client(tmp_path, force_from_runner_factory(seen))
+    parent = make_done_job(client, lyrics="one\ntwo")
+    resp = rebuild_with(client, parent, lyrics="one\r\ntwo")
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[-1] is None, "the rebuild redid the alignment for nothing"
+    body = client.get(f"/api/jobs/{resp.json()['id']}/input").json()
+    assert body["lyrics"] == "one\ntwo"
+
+
+def test_submitting_crlf_lyrics_stores_them_with_lf(tmp_path):
+    client, _ = make_client(tmp_path, ok_runner)
+    job_id = make_done_job(client, lyrics="one\r\ntwo")
+    assert client.get(f"/api/jobs/{job_id}/input").json()["lyrics"] == "one\ntwo"
+
+
+def test_rebuild_all_rebuilds_every_song_from_the_stage(tmp_path):
+    seen = []
+    client, _ = make_client(tmp_path, capture_runner_factory(seen))
+    first = make_done_job(client, title="One")
+    second = make_done_job(client, title="Two")
+    resp = client.post("/api/rebuild-all", data={"force_from": "pitch"})
+    assert resp.status_code == 201
+    body = resp.json()
+    assert len(body["ids"]) == 2 and body["skipped"] == []
+    jobs = [wait_status(client, i, "done") for i in body["ids"]]
+    assert {j["rebuilt_from"] for j in jobs} == {first, second}
+    assert [s["force_from"] for s in seen[2:]] == ["pitch", "pitch"]
+    by_title = lambda runs: sorted((r["inp"] for r in runs), key=lambda i: i.title)
+    assert by_title(seen[2:]) == by_title(seen[:2])
+
+
+def test_rebuild_all_skips_jobs_that_were_already_rebuilt(tmp_path):
+    client, _ = make_client(tmp_path, capture_runner_factory([]))
+    parent = make_done_job(client)
+    renamed = client.post(f"/api/jobs/{parent}/rebuild",
+                          data=rebuild_form(title="Renamed")).json()["id"]
+    wait_status(client, renamed, "done")
+    body = client.post("/api/rebuild-all", data={"force_from": "notes"}).json()
+    assert len(body["ids"]) == 1
+    job = wait_status(client, body["ids"][0], "done")
+    assert job["rebuilt_from"] == renamed
+
+
+def test_rebuild_all_takes_the_latest_job_for_a_song(tmp_path):
+    client, _ = make_client(tmp_path, capture_runner_factory([]))
+    make_done_job(client)
+    latest = make_done_job(client)
+    body = client.post("/api/rebuild-all", data={"force_from": "grid"}).json()
+    assert len(body["ids"]) == 1
+    assert wait_status(client, body["ids"][0], "done")["rebuilt_from"] == latest
+
+
+def test_rebuild_all_skips_songs_in_progress(tmp_path):
+    gate = threading.Event()
+
+    def blocking_runner(inp, cfg, log=print, force_from=None, stages=None):
+        gate.wait(timeout=5)
+        return PipelineResult(output_dir=cfg.output_dir / song_slug(inp))
+
+    client, _ = make_client(tmp_path, blocking_runner)
+    try:
+        busy = client.post("/api/jobs", data={
+            "title": "T", "artist": "A", "lyrics": "x", "youtube_url": "http://y"}).json()["id"]
+        body = client.post("/api/rebuild-all", data={"force_from": "pitch"}).json()
+        assert body == {"ids": [], "skipped": [{"id": busy, "reason": "still in progress"}]}
+    finally:
+        gate.set()
+
+
+def test_rebuild_all_from_acquire_skips_a_song_whose_upload_is_gone(tmp_path):
+    client, _ = make_client(tmp_path, capture_runner_factory([]))
+    job_id = client.post("/api/jobs", data={"title": "T", "artist": "A", "lyrics": "x"},
+                         files={"video": ("v.mp4", io.BytesIO(b"data"), "video/mp4")}
+                         ).json()["id"]
+    wait_status(client, job_id, "done")
+    shutil.rmtree(tmp_path / "work" / "uploads", ignore_errors=True)
+    body = client.post("/api/rebuild-all", data={"force_from": "acquire"}).json()
+    assert body["ids"] == []
+    assert body["skipped"][0]["id"] == job_id
+    assert "upload" in body["skipped"][0]["reason"]
+
+
+def test_rebuild_all_rejects_an_unknown_stage(tmp_path):
+    client, _ = make_client(tmp_path, ok_runner)
+    make_done_job(client)
+    assert client.post("/api/rebuild-all", data={"force_from": "nope"}).status_code == 400
+    assert client.post("/api/rebuild-all", data={}).status_code == 422
+
+
+def test_rebuild_all_lists_the_current_job_of_each_song(tmp_path):
+    client, _ = make_client(tmp_path, capture_runner_factory([]))
+    one = make_done_job(client, title="One")
+    two = make_done_job(client, title="Two")
+    rerun = client.post(f"/api/jobs/{one}/rerun").json()["id"]
+    wait_status(client, rerun, "done")
+    songs = client.get("/api/rebuild-all").json()
+    assert [(s["id"], s["title"], s["rebuilt_from"]) for s in songs] == [
+        (rerun, "One", one), (two, "Two", None)]
+    assert all(s["status"] == "done" and s["finished_at"] for s in songs)
+
+
+def test_rebuild_all_rebuilds_only_the_songs_selected(tmp_path):
+    client, _ = make_client(tmp_path, capture_runner_factory([]))
+    make_done_job(client, title="One")
+    two = make_done_job(client, title="Two")
+    resp = client.post("/api/rebuild-all", data={"force_from": "pitch", "ids": [two]})
+    body = resp.json()
+    assert len(body["ids"]) == 1 and body["skipped"] == []
+    assert wait_status(client, body["ids"][0], "done")["rebuilt_from"] == two
+
+
+def test_rebuild_all_reports_a_selected_job_that_was_since_rebuilt(tmp_path):
+    client, _ = make_client(tmp_path, capture_runner_factory([]))
+    old = make_done_job(client)
+    rerun = client.post(f"/api/jobs/{old}/rerun").json()["id"]
+    wait_status(client, rerun, "done")
+    body = client.post("/api/rebuild-all", data={"force_from": "pitch", "ids": [old]}).json()
+    assert body == {"ids": [], "skipped": [
+        {"id": old, "reason": "no longer the current job for its song"}]}
+
+
+def test_a_job_is_only_reported_finished_once_it_has_finished(tmp_path, monkeypatch):
+    """Done must mean done: a slow upload cleanup used to show a 'done' job
+    with its upload still there and no finished_at."""
+    from songtrace import web
+    real_cleanup = web._cleanup_uploads
+
+    def slow_cleanup(*args):
+        time.sleep(0.3)
+        real_cleanup(*args)
+
+    monkeypatch.setattr(web, "_cleanup_uploads", slow_cleanup)
+    client, cfg = make_client(tmp_path, ok_runner)
+    job_id = client.post("/api/jobs", data={"title": "T", "artist": "A", "lyrics": "x"},
+                         files={"video": ("v.mp4", io.BytesIO(b"data"), "video/mp4")}
+                         ).json()["id"]
+    job = wait_status(client, job_id, "done")
+    assert job["finished_at"] is not None
+    assert not (cfg.work_dir / "uploads" / job_id / "v.mp4").exists()
+
+
+def chart_runner(inp, cfg, log=print, force_from=None, stages=None):
+    """Leaves what a real build does for the editor: generated notes and a
+    chart in the work dir, and the packaged chart."""
+    from songtrace.grid import to_ultrastar
+    from songtrace.ultrastar import serialize_ultrastar
+    work = cfg.work_dir / song_slug(inp)
+    work.mkdir(parents=True, exist_ok=True)
+    notes = [{"start": 1.0, "duration": 0.5, "pitch": 0, "text": "one",
+              "low_confidence": False, "line_index": 0},
+             {"start": 3.0, "duration": 0.5, "pitch": 2, "text": "three",
+              "low_confidence": True, "line_index": 1}]
+    warnings = ["1 low-confidence note near 0:03–0:03"]
+    (work / "notes_sec.json").write_text(json.dumps(
+        {"notes": notes, "breaks": [2.0], "warnings": warnings}))
+    chart = serialize_ultrastar(to_ultrastar(notes, [2.0], 300.0, [("TITLE", inp.title)]))
+    (work / "song.txt").write_text(chart, encoding="utf-8")
+    out = cfg.output_dir / song_slug(inp)
+    out.mkdir(parents=True, exist_ok=True)
+    (out / f"{song_slug(inp)}.txt").write_text(chart, encoding="utf-8")
+    return PipelineResult(output_dir=out, warnings=warnings)
+
+
+def make_charted_job(client, lyrics="one\nthree"):
+    job_id = client.post("/api/jobs", data={
+        "title": "T", "artist": "A", "lyrics": lyrics, "youtube_url": "http://y"}).json()["id"]
+    wait_status(client, job_id, "done")
+    return job_id
+
+
+EDIT = {"notes": [{"start": 3.1, "duration": 0.5, "pitch": 9, "text": "three",
+                   "kind": "*"}]}
+
+
+def test_saving_a_line_rewrites_both_charts(tmp_path):
+    from songtrace.ultrastar import Note, parse_ultrastar
+    client, cfg = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    resp = client.put(f"/api/jobs/{job_id}/lines/1", json=EDIT)
+    assert resp.status_code == 200
+    line = resp.json()["lines"][1]
+    assert line["edited"] and line["notes"][0]["kind"] == "*" and line["notes"][0]["pitch"] == 9
+    assert resp.json()["grid"] == {"bpm": 300.0, "gap_ms": 1000.0}
+    for txt in (cfg.work_dir / "A - T" / "song.txt", cfg.output_dir / "A - T" / "A - T.txt"):
+        notes = [n for n in parse_ultrastar(txt.read_text(encoding="utf-8")).body
+                 if isinstance(n, Note)]
+        assert [(n.kind, n.pitch) for n in notes] == [(":", 0), ("*", 9)], txt
+    # the fixed line was the one being warned about
+    assert client.get(f"/api/jobs/{job_id}").json()["warnings"] == []
+
+
+def test_reverting_a_line_returns_it_to_the_generated_notes(tmp_path):
+    client, _ = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    client.put(f"/api/jobs/{job_id}/lines/1", json=EDIT)
+    resp = client.delete(f"/api/jobs/{job_id}/lines/1")
+    assert resp.status_code == 200
+    line = resp.json()["lines"][1]
+    assert not line["edited"] and line["notes"][0]["pitch"] == 2
+    assert client.delete(f"/api/jobs/{job_id}/lines/1").status_code == 404
+
+
+def test_line_edits_are_checked(tmp_path):
+    client, _ = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    assert client.put(f"/api/jobs/{job_id}/lines/5", json=EDIT).status_code == 404
+    bad = {"notes": [{**EDIT["notes"][0], "kind": "X"}]}
+    assert client.put(f"/api/jobs/{job_id}/lines/1", json=bad).status_code == 400
+    assert client.put(f"/api/jobs/{job_id}/lines/1", json={"x": 1}).status_code == 400
+
+
+def test_a_song_cannot_be_edited_while_it_is_being_rebuilt(tmp_path):
+    gate = threading.Event()
+
+    def runner(inp, cfg, log=print, force_from=None, stages=None):
+        if force_from:
+            gate.wait(timeout=5)
+        return chart_runner(inp, cfg)
+
+    client, _ = make_client(tmp_path, runner)
+    try:
+        job_id = make_charted_job(client)
+        client.post(f"/api/jobs/{job_id}/rebuild-full")
+        assert client.put(f"/api/jobs/{job_id}/lines/1", json=EDIT).status_code == 409
+    finally:
+        gate.set()
+
+
+def test_a_stale_edit_can_be_discarded(tmp_path):
+    from songtrace import edits
+    client, cfg = make_client(tmp_path, chart_runner)
+    first = make_charted_job(client)
+    client.put(f"/api/jobs/{first}/lines/1", json=EDIT)
+    # the same song again with that line's words changed
+    second = make_charted_job(client, lyrics="one\nthree more")
+    work = cfg.work_dir / "A - T"
+    assert len(edits.load(work, [["one"], ["three", "more"]])["stale"]) == 1
+    resp = client.delete(f"/api/jobs/{second}/stale/0")
+    assert resp.status_code == 200 and resp.json()["stale"] == []
+    assert not (work / edits.EDITS_FILE).exists()
+    assert client.delete(f"/api/jobs/{second}/stale/0").status_code == 404
+
+
+def test_pitch_curve_is_in_note_semitones_with_gaps_where_unvoiced(tmp_path):
+    import numpy as np
+
+    def runner(inp, cfg, log=print, force_from=None, stages=None):
+        result = chart_runner(inp, cfg)
+        times = np.arange(0, 0.1, 0.01)
+        f0 = np.array([440.0] * 4 + [261.63] * 4 + [0.0] * 2)   # A4, C4, nothing
+        conf = np.array([0.9] * 4 + [0.9, 0.9, 0.1, 0.1] + [0.9] * 2)
+        np.savez(cfg.work_dir / song_slug(inp) / "pitch.npz", times=times, f0=f0, conf=conf)
+        return result
+
+    client, _ = make_client(tmp_path, runner)
+    job_id = make_charted_job(client)
+    body = client.get(f"/api/jobs/{job_id}/pitch").json()
+    assert body["start"] == 0.0 and body["step"] == pytest.approx(0.02)
+    assert body["pitch"][:2] == [9.0, 9.0]                  # A4 is 9 above C4
+    assert body["pitch"][2] == pytest.approx(0.0, abs=0.01)  # C4
+    assert body["pitch"][3:] == [None, None]                # unsure, then silent
+
+
+def test_pitch_curve_is_404_without_a_pitch_track(tmp_path):
+    client, _ = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    assert client.get(f"/api/jobs/{job_id}/pitch").status_code == 404
+
+
+def _chart_header(path, key):
+    from songtrace.ultrastar import get_header, parse_ultrastar
+    return get_header(parse_ultrastar(path.read_text(encoding="utf-8")), key)
+
+
+def test_setting_the_grid_recharts_and_survives_line_saves(tmp_path):
+    client, cfg = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    resp = client.put(f"/api/jobs/{job_id}/grid", json={"bpm": 240, "gap_ms": 900})
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["grid"] == {"bpm": 240.0, "gap_ms": 900.0} and body["grid_edited"]
+    packaged = cfg.output_dir / "A - T" / "A - T.txt"
+    assert (_chart_header(packaged, "BPM"), _chart_header(packaged, "GAP")) == ("240", "900")
+    client.put(f"/api/jobs/{job_id}/lines/1", json=EDIT)
+    assert (_chart_header(packaged, "BPM"), _chart_header(packaged, "GAP")) == ("240", "900")
+
+
+def test_resetting_the_grid_returns_to_the_pipelines_tempo(tmp_path):
+    client, cfg = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    (cfg.work_dir / "A - T" / "tempo.json").write_text(json.dumps({"bpm": 300.0}))
+    client.put(f"/api/jobs/{job_id}/grid", json={"bpm": 240, "gap_ms": 900})
+    resp = client.delete(f"/api/jobs/{job_id}/grid")
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["grid"] == {"bpm": 300.0, "gap_ms": 1000.0}   # GAP back at the first note
+    assert not body["grid_edited"] and body["auto_bpm"] == 300.0
+    assert client.delete(f"/api/jobs/{job_id}/grid").status_code == 404
+
+
+def test_a_bad_grid_is_refused(tmp_path):
+    client, _ = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    for body in ({"bpm": 0, "gap_ms": 0}, {"bpm": 300, "gap_ms": -5}, {"bpm": "x"}, {}):
+        assert client.put(f"/api/jobs/{job_id}/grid", json=body).status_code == 400
+
+
+def test_reset_on_a_song_built_before_tempo_was_recorded_restores_its_bpm(tmp_path):
+    client, _ = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)   # charted at 300 BPM, no tempo.json
+    client.put(f"/api/jobs/{job_id}/grid", json={"bpm": 240, "gap_ms": 900})
+    body = client.delete(f"/api/jobs/{job_id}/grid").json()
+    assert body["grid"]["bpm"] == 300.0 and body["auto_bpm"] == 300.0
+
+
+def test_moving_a_break_recharts_and_is_reported(tmp_path):
+    from songtrace.ultrastar import LineBreak, parse_ultrastar
+    client, cfg = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    assert client.get(f"/api/jobs/{job_id}/review").json()["breaks"] == [
+        {"line": 1, "time": 2.0, "moved": False}]
+    resp = client.put(f"/api/jobs/{job_id}/breaks", json={"1": 2.8})
+    assert resp.status_code == 200
+    assert resp.json()["breaks"] == [{"line": 1, "time": 2.8, "moved": True}]
+    assert not any(line["edited"] for line in resp.json()["lines"])
+    packaged = cfg.output_dir / "A - T" / "A - T.txt"
+    body = parse_ultrastar(packaged.read_text(encoding="utf-8")).body
+    # 300 BPM: 0.05s beats from GAP 1.0s, so 2.8s is beat 36
+    assert [b.beat for b in body if isinstance(b, LineBreak)] == [36]
+    back = client.put(f"/api/jobs/{job_id}/breaks", json={"1": None}).json()
+    assert back["breaks"] == [{"line": 1, "time": 2.0, "moved": False}]
+
+
+def test_a_bad_break_is_refused(tmp_path):
+    client, _ = make_client(tmp_path, chart_runner)
+    job_id = make_charted_job(client)
+    for body in ({"0": 1.0}, {"9": 1.0}, {"1": -2}, {"1": "x"}):
+        assert client.put(f"/api/jobs/{job_id}/breaks", json=body).status_code == 400

tests/test_ytdlp.py

@@ -0,0 +1,139 @@
+import os
+import time
+
+import pytest
+
+from songtrace import ytdlp
+from songtrace.config import Config
+from songtrace.ytdlp import YtDlp, YtDlpError
+
+
+def fake_package(path, version="2026.09.01", body=""):
+    """A stand-in yt_dlp that answers --version and otherwise runs `body`."""
+    pkg = path / "yt_dlp"
+    pkg.mkdir(parents=True)
+    (pkg / "__init__.py").touch()
+    (pkg / "__main__.py").write_text(
+        "import sys\n"
+        f"if '--version' in sys.argv: print({version!r}); sys.exit()\n"
+        + body)
+    return path
+
+
+@pytest.fixture
+def cache(tmp_path, monkeypatch):
+    monkeypatch.setenv("XDG_CACHE_HOME", str(tmp_path / "cache"))
+    monkeypatch.setattr(ytdlp, "bundled", lambda: YtDlp("2026.8.19"))
+    return ytdlp.cache_dir()
+
+
+@pytest.fixture
+def pypi(monkeypatch):
+    """Stubs PyPI and pip: `latest` is the newest release, `installs` logs pip."""
+    state = {"latest": "2026.9.1", "installs": []}
+    monkeypatch.setattr(ytdlp, "_latest_release", lambda: state["latest"])
+    def pip_install(target, version):
+        state["installs"].append(version)
+        fake_package(target, version)
+    monkeypatch.setattr(ytdlp, "_pip_install", pip_install)
+    return state
+
+
+def cfg(version="auto"):
+    return Config(whisper_url="http://x/v1", ytdlp_version=version)
+
+
+def test_run_uses_the_install_on_its_path_and_logs_its_output(tmp_path):
+    path = fake_package(tmp_path, body="print('[youtube] hello', sys.argv[1:])\n")
+    logged = []
+    YtDlp("2026.09.01", path).run(["--", "https://yt/x"], logged.append)
+    assert logged == ["[youtube] hello ['--ignore-config', '--', 'https://yt/x']"]
+
+
+def test_run_raises_the_error_line(tmp_path):
+    path = fake_package(tmp_path, body=(
+        "print('ERROR: HTTP Error 403: Forbidden', file=sys.stderr)\n"
+        "print('trailing noise')\nsys.exit(1)\n"))
+    with pytest.raises(YtDlpError, match="^ERROR: HTTP Error 403"):
+        YtDlp("2026.09.01", path).run([], lambda m: None)
+
+
+def test_run_flags_a_usage_error_as_incompatible(tmp_path):
+    path = fake_package(tmp_path, body=(
+        "print('error: no such option: --retries', file=sys.stderr)\n"
+        "sys.exit(2)\n"))
+    with pytest.raises(YtDlpError, match="2026.09.01 rejected.*--retries"):
+        YtDlp("2026.09.01", path).run([], lambda m: None)
+
+
+def test_auto_installs_a_newer_release_and_tries_it_first(cache, pypi):
+    found = ytdlp.candidates(cfg(), lambda m: None)
+    assert [y.version for y in found] == ["2026.9.1", "2026.8.19"]
+    assert found[0].path == cache / "2026.9.1"
+    assert not [p for p in cache.iterdir() if p.name.startswith(".tmp-")]
+
+
+def test_auto_checks_pypi_once_a_day(cache, pypi):
+    ytdlp.candidates(cfg(), lambda m: None)
+    pypi["latest"] = "2026.10.1"
+    found = ytdlp.candidates(cfg(), lambda m: None)
+    assert found[0].version == "2026.9.1"
+    found = ytdlp.candidates(cfg(), lambda m: None, refresh=True)
+    assert found[0].version == "2026.10.1"
+    assert not (cache / "2026.9.1").exists()
+    old = time.time() - ytdlp.CHECK_INTERVAL - 1
+    os.utime(cache / ".checked", (old, old))
+    pypi["latest"] = "2026.11.1"
+    assert ytdlp.candidates(cfg(), lambda m: None)[0].version == "2026.11.1"
+
+
+def test_auto_uses_only_bundled_when_it_is_newest(cache, pypi):
+    pypi["latest"] = "2026.8.19"
+    assert [y.version for y in ytdlp.candidates(cfg(), lambda m: None)] == [
+        "2026.8.19"]
+    assert pypi["installs"] == []
+
+
+def test_auto_survives_pypi_being_unreachable(cache, pypi, monkeypatch):
+    ytdlp.candidates(cfg(), lambda m: None)
+    def down():
+        raise OSError("network unreachable")
+    monkeypatch.setattr(ytdlp, "_latest_release", down)
+    logged = []
+    found = ytdlp.candidates(cfg(), logged.append, refresh=True)
+    assert [y.version for y in found] == ["2026.9.1", "2026.8.19"]
+    assert any("network unreachable" in m for m in logged)
+
+
+def test_an_install_that_fails_its_check_is_discarded(cache, pypi, monkeypatch):
+    monkeypatch.setattr(ytdlp, "_pip_install",
+                        lambda target, v: fake_package(target, "2026.1.1"))
+    logged = []
+    assert [y.version for y in ytdlp.candidates(cfg(), logged.append)] == [
+        "2026.8.19"]
+    assert any("failed its check" in m for m in logged)
+    assert list(cache.iterdir()) == [cache / ".checked"]
+
+
+def test_bundled_never_touches_pypi(cache, pypi):
+    pypi["latest"] = None
+    assert [y.version for y in ytdlp.candidates(cfg("bundled"), print)] == [
+        "2026.8.19"]
+    assert not cache.exists()
+
+
+def test_pin_installs_that_release_even_if_older(cache, pypi):
+    found = ytdlp.candidates(cfg("2026.07.01"), lambda m: None)
+    assert [y.version for y in found] == ["2026.07.01", "2026.8.19"]
+    assert pypi["installs"] == ["2026.07.01"]
+
+
+def test_pin_matching_bundled_installs_nothing(cache, pypi):
+    found = ytdlp.candidates(cfg("2026.08.19"), lambda m: None)
+    assert [y.version for y in found] == ["2026.8.19"]
+    assert pypi["installs"] == []
+
+
+def test_pin_must_be_a_release_number(cache, pypi):
+    with pytest.raises(YtDlpError, match="ytdlp_version"):
+        ytdlp.candidates(cfg("latest; rm -rf /"), lambda m: None)