test: close coverage gaps found in final branch review

- add test_rebuild_inherits_the_parents_cover: covers the cover_path
  inheritance mechanism in the rebuild endpoint (Task 2's upload-retention
  design relied on it, but nothing exercised it)
- tighten test_lineage_marker_survives_in_the_accessibility_tree to assert
  the literal " rebuilt" screen-reader text, not just that rebuilt_from
  is referenced somewhere in paintCard
- normalize submit's youtube_url/genre/language the same way rebuild does,
  for symmetry, plus a pinning test
- pin acquire's stage outputs to [meta.json, audio.wav] in test_acquire.py,
  since web.py's _require_source hardcodes those same filenames

src/karaoke_maker/web.py

@@ -194,6 +194,8 @@ def create_app(cfg: Config, runner=run_pipeline) -> FastAPI:
                       language: str | None = Form(None), bpm: float | None = Form(None),
                       video: UploadFile | None = File(None),
                       cover: UploadFile | None = File(None)):
+        youtube_url, genre, language = (youtube_url or None, genre or None,
+                                        language or None)
         has_video = bool(video and video.filename)
         if bool(youtube_url) == has_video:
             raise HTTPException(400, "provide exactly one of youtube_url / video")

tests/test_acquire.py

@@ -38,6 +38,12 @@ def test_youtube(tmp_path, monkeypatch):
     assert meta["video_file"] == "source_video.webm"
     assert meta["thumbnail"] == "source_video.jpg"
 
+def test_outputs_are_meta_and_audio(tmp_path):
+    """_require_source in web.py hardcodes these filenames; pin them here."""
+    ctx = make_ctx(tmp_path, youtube_url="https://yt/x")
+    outputs = acquire.acquire_stage().outputs(ctx)
+    assert [p.name for p in outputs] == ["meta.json", "audio.wav"]
+
 def test_requires_exactly_one_source(tmp_path):
     import pytest
     from karaoke_maker.pipeline import PipelineError

tests/test_web.py

@@ -52,6 +52,16 @@ def test_failure_reported(tmp_path):
     assert job["error"] == "boom"
 
 
+def test_submit_normalises_a_blank_genre_to_none(tmp_path):
+    seen = []
+    client, _ = make_client(tmp_path, capture_runner_factory(seen))
+    resp = client.post("/api/jobs", data={
+        "title": "T", "artist": "A", "lyrics": "x",
+        "youtube_url": "http://y", "genre": ""})
+    wait_status(client, resp.json()["id"], "done")
+    assert seen[0]["inp"].genre is None
+
+
 def test_requires_one_source(tmp_path):
     client, _ = make_client(tmp_path, ok_runner)
     resp = client.post("/api/jobs", data={"title": "T", "artist": "A", "lyrics": "x"})
@@ -599,6 +609,7 @@ def test_lineage_marker_survives_in_the_accessibility_tree():
     html = _index_html()
     body = _fn_body(html, "paintCard")
     assert "rebuilt_from" in body
+    assert '" rebuilt"' in body
     assert '"sr-only"' in _fn_body(html, "jobCard")
 
 
@@ -815,6 +826,20 @@ def test_rebuild_inherits_the_parents_source(tmp_path):
     assert seen[1]["inp"].video_path == seen[0]["inp"].video_path
 
 
+def test_rebuild_inherits_the_parents_cover(tmp_path):
+    seen = []
+    client, _ = make_client(tmp_path, capture_runner_factory(seen))
+    resp = client.post("/api/jobs", data={"title": "T", "artist": "A", "lyrics": "x",
+                                          "youtube_url": "http://y"},
+                        files={"cover": ("c.jpg", io.BytesIO(b"img"), "image/jpeg")})
+    parent = resp.json()["id"]
+    wait_status(client, parent, "done")
+    child = client.post(f"/api/jobs/{parent}/rebuild",
+                        data=rebuild_form(year="1998")).json()["id"]
+    wait_status(client, child, "done")
+    assert seen[1]["inp"].cover_path == seen[0]["inp"].cover_path
+
+
 def test_rebuild_rejects_a_missing_upload_that_would_be_needed(tmp_path):
     client, _ = make_client(tmp_path, ok_runner)
     resp = client.post("/api/jobs", data={"title": "T", "artist": "A", "lyrics": "x"},