Guest switch dispatch pre-marked its dedup key and fired-and-forgot, so
any failure (fetch error, reload busy with an auto-advance, navigation
race with the host exiting) silently stranded the guest on the old media.
A CurrentPlaybackDispatcher now marks a key handled only after the sink
reports success against the committed identity, with a serialized
in-flight slot, timeout, and generation reset; the reconciler re-offers
unattached media on every host heartbeat, making the heartbeat the retry
channel. Fetches that outlive their dispatch are re-validated against the
current snapshot so a stale switch can't override the live one.
hostExitedPlayer now rides the controller's ordered message queue with
host authentication instead of racing state handling in the provider.
Replaces the imperative play/pause/seek/positionSync message soup with a
single host-authored PlaybackState (seq-ordered, anchor-extrapolated,
phase machine: loading/waitingForPeers/paused/playing) that doubles as
the heartbeat, plus guest status reports and host-applied control
requests. Fixes the guest seek-back loop while the host loads (readiness
was keyed on a pre-load !buffering snapshot and heartbeats broadcast
frozen positions), adds real group buffering coordination (stall grace,
scheduled simultaneous resumes, 15s safety timeout), rate-nudge drift
correction with passthrough-aware seek fallback, session-scoped message
handling (no lost messages during episode-switch detach gaps), and an
expected-state ledger replacing the racy remote-action flag.
edde746