优化播放逻辑

docs/superpowers/plans/2026-10-21-playback-correctness-isolation.md

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+# Playback Correctness and Isolation Implementation Plan
+
+**Goal:** Fix the five playback defects from the 2026-10-21 review and make playback capability queries side-effect-free, without replacing the player or adding dependencies.
+
+**Scope:** The user approved implementing the reviewed fixes. Work in the current clean checkout; do not commit, push, deploy, or alter unrelated files.
+
+## Design and invariants
+
+- Keep existing media IDs, stream routes, direct playback and external-player URLs compatible.
+- Add optional `session_id` to local HLS requests. Authenticated handlers supply the actual user identity; a client parameter never supplies the owner. New web playback sessions use random IDs. Legacy clients are isolated by user and, where available, Emby play-session/device identity.
+- Keep transcoder media lookup/logging separate from its internal task key. A task key incorporates user, media and playback session. Each actual ffmpeg run writes to a fresh generation directory, so delayed segment requests never read a replacement run's output.
+- Stop only the authenticated caller's playback session. Check media visibility and scoped playback tokens on stop, just as on playlist/segment requests. Segment and playlist queries must match the running generation.
+- Cloud child requests resolve their real session media first, compare query media, enforce token scope and visibility against the real media, and reject mismatches before upstream fetch.
+- Treat player business positions as absolute source seconds. Only local HLS converts to/from a relative ffmpeg timeline.
+- Invalidate outstanding cloud-transcode requests on media/unmount, explicit source/quality changes, and newer requests. Guard both fulfilled and rejected responses.
+- Select local fallbacks only from available local qualities. Keep the existing 115-first preference when a cloud quality is available.
+- `PlaybackInfo` only reads capabilities/status. Explicit `StartTranscode` requests enqueue cloud work. Retain pending/ready response contracts, polling, and retries.
+
+## Tasks
+
+1. Add regression tests for local-scope isolation, stale generations, stop authorization, cloud media binding, pure capability reads, timeline conversion, available-local selection and stale async results. Run tests before implementation and verify the intended failures.
+2. Add tested playback helpers; route skip/undo/progress/quality/subtitle calculations through the common absolute timeline; guard cloud transcode results and fix local fallback choice.
+3. Extend existing transcoder/stream methods with an optional scope, preserve legacy internal calls, isolate task keys/output directories, and pass caller scope from web and Emby handlers. Bind web local HLS URLs and stop requests to captured session IDs.
+4. Enforce real-media authorization on cloud child requests and authenticated ownership on local stop.
+5. Split read-only cloud capability lookup from explicit cloud enqueue. Update existing cloud tests to use the explicit start operation and test no push during reads.
+6. Run focused and full Go tests, frontend tests, TypeScript/Vite build, lint diagnostics and review the diff for security, lifecycle and API compatibility. Fix regressions before reporting completion.
+
+## Verification commands
+
+- `node --experimental-strip-types --test src/pages/hlsPlayback.test.ts src/pages/directPlaySeek.test.ts src/pages/playerPageModel.test.ts src/pages/playbackQuality.test.ts src/pages/playbackRequestGuard.test.ts src/utils/skipSegments.test.ts`
+- `go test ./internal/service ./internal/handler ./internal/middleware -count=1`
+- `go test ./...`
+- `npm run build` and targeted ESLint for changed frontend files.
+
+## Out of scope
+
+New remux/audio-only ffmpeg pipelines, speculative browser codec policy changes, player replacement, broad UI refactors, performance improvement claims without measurements, and production deployment.
+
+## Verification outcome
+
+- Six frontend playback regression scripts pass; targeted ESLint and the TypeScript/Vite production build pass. The existing bundle-size warning remains.
+- Playback/stream/transcode/progress tests in service, handler and middleware pass, including scoped output reads, stale generation rejection, scoped stops, device-to-segment propagation, read-only capability queries and concurrent cloud start deduplication.
+- Whole-repository tests pass with only `TestQueueLibraryRootScanImportsNewLibraryMedia` and `TestSQLiteRestoreStagesWithoutChangingLiveDatabase` excluded. Both were run independently and reproduce Windows file-lock / SQLite errors in unmodified scan/database code. They are not silently disabled in source.
+- FFmpeg is not installed in this environment, so the existing real-transcode lifecycle test skips. Actual video, upstream 115 and browser end-to-end playback remain unverified.
+- Clients with no playback-session or device identifier retain per-user legacy isolation; new web requests always carry an independent session ID.
+- No commit, push or deployment was performed.