LC3 frame-cadence replay oracle

Run with:

npm run test:replay-lc3-frame-timing

This is a Linux x86_64-only, loopback-only test harness. It requires the locked lc3py==1.1.3 backend environment and rejects unsupported hosts rather than skipping. A test-owned lc3.Encoder produces three inert in-memory 30-byte / 10 ms frames. The harness runs the production listen admission format check and codec normalizer, the real ListenReceiver LC3 decoder, and the real ParakeetWebSocketSocket against a local fake upstream.

The oracle proves that those frames decode to three 320-byte PCM frames and flush one 960-byte STT message after frame three. When the fake upstream closes, a fourth queued frame produces no second STT message or reconnect; the listen client gets one bounded terminal status and closes with 1011. A test-only decoder-bypass mutant is required to fail the same decoded-size and flush-index checks.

The emitted evidence is structural only: labels/order, byte-count buckets, counts, close/retry enums, 10ms_frame / 30ms_flush timing buckets, hashes of static metadata, and a coarse local deadline. It never emits, logs, hashes, or persists audio bytes, audio-derived values, transcript text, IDs, headers, credentials, provider bodies, or payload hashes. A default-deny egress guard allows only the in-process loopback upstream.

Residual gaps: this does not qualify Flutter, Friend Pendant, device behavior, multi-channel LC3, malformed or variable-length LC3 policy, provider quality, real scheduling/finalization/reconnect timing, capture corpora, or production network/release behavior. Existing Listen/Pusher and Sync/Cloud Tasks gauntlets remain unchanged.