Real request logged after the last fix (MediaSourceId in the query
string) shipped: still a 400, now Emby's own "Value cannot be null.
(Parameter 'key')" - a bare .NET Dictionary null-key exception, not
the earlier problem (MediaSourceId was present and well-formed in the
logged request).
This exact message already burned this app once before, in
CatalogService.negotiateStreamTarget's hand-built fallback URL (see
its own long-standing TODO(verify) comment) - diagnosed there as Emby
indexing some internal state by a parameter the request hadn't
supplied. PlaySessionId is the standout remaining candidate: it's how
Emby/Jellyfin clients normally correlate a progress report with the
specific playback/transcode session it belongs to, and evidently
Emby's real Progress handler keys a lookup on it even though the
OpenAPI spec doesn't mark it required.
Fixed the same way MediaSourceId was: CatalogService
.negotiateStreamTarget already reads info.PlaySessionId from the same
PlaybackInfo response (it already used it in the hand-built fallback
URL) - its return type just needed to surface it too. PartyStreamService
now caches it alongside mediaSourceId and exposes both together from
one accessor, getCachedPlaybackIds(partyId), replacing the
round-1 getCachedMediaSourceId. PlaystateService.reportProgress and
index.ts's sweep both thread it through.
Not independently confirmed against a real server yet (no safe way to
fire a real, state-mutating test call without one) - flagged in
docs/architecture.md the same way every other real-server-dependent
guess in this app is, but grounded in this app's own prior confirmed
diagnosis of the identical error message rather than a fresh guess.
Updated catalogService.test's negotiateStreamTarget assertions to
cover playSessionId in both return branches, partyStreamService.test's
mocks/assertions for the new {mediaSourceId, playSessionId} cache
shape, and playstateService.test's request-shape and logging
assertions for the extra PlaySessionId param. Full typecheck/test/build
green (96/96 tests). docs/architecture.md and README.md updated.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Nicolas
8718175bae