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branderson 4130adfe58 docs: document Dotcom Arcade, streaming, proxy sign-in and saves

A new README for the combined project with setup from the Flashpoint
Ultimate torrent. New feature docs for streaming, proxy sign-in and
game saves; deployment, upgrade and streaming READMEs updated for the
single compose file; the project renamed throughout.

2026-10-13 19:31:06 -07:00

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Game Saves

Overview

Games keep their saves in the player's browser. For signed-in players, Dotcom Arcade also keeps them on their account, so a save made on one computer is there on the next, and the last 10 distinct saves of each game can be restored. Guests keep browser-only saves.

What a save is

A save is a snapshot of up to three kinds of browser storage:

Streamed games' files: what a streamed game wrote to its save directory. It's sent back from the streamer as it changes, and kept in the flashpoint-stream-saves IndexedDB database.
localStorage: Ruffle's Flash SharedObjects, and HTML5 games' localStorage.
IndexedDB: HTML5 games' databases, including Unity WebGL's /idbfs.

Games share the app's origin, so their keys can't tell which game wrote them. The app works it out by watching instead: whatever changes while a game is playing belongs to that game, and it remembers that for next time. The app's own storage is never included.

Sync

Before a game starts, the app compares the browser's save with the account's latest:

If they're the same, nothing happens.
If only one side changed since this browser last synced, that side wins.
If both changed, the newer one wins. The other is still kept as a backup.

While playing, changes are uploaded 10 seconds after they happen, when the player leaves the game, and when the tab closes.

Restoring

The Saves button under the game lists the account's backups with their times and sizes. Restoring one applies it and restarts the game. The save it replaced stays in the list.

Limits

Size: each snapshot is at most 10 MB.
History: the 10 newest distinct snapshots per user and game are kept.
Not covered: cookies set by HTML5 games.
No merging: when two browsers both changed a save, the newer one wins whole. Saves aren't combined.

API

Endpoints require a signed-in user with games.play:

Endpoint	Purpose
`GET /api/game-saves/:gameId`	Latest snapshot with its data, plus metadata for all backups
`GET /api/game-saves/:gameId/:id`	One snapshot with its data
`POST /api/game-saves/:gameId`	Upload `{data, hash, savedAt}`; a duplicate of the latest is a no-op

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