FC-concurrent-ptt-stream-budget-overspend.json

{
  "schema_version": 1,
  "id": "FC-concurrent-ptt-stream-budget-overspend",
  "violated_contract": "Concurrent /v2/voice-message/transcribe-stream sessions for the same uid must not each admit against the same remaining daily STT duration slice. Probe-only check_budget at connect plus force-record at end lets N sessions freeze identical remaining_ms and overspend the shared voice_duration budget after the fact.",
  "canonical_prevention": "Atomically reserve up to MAX_SESSION_DURATION_S at WS connect via try_reserve_session_budget (Lua force=2 consume-up-to). Cap mid-session audio to the reserved amount. On successful drain, settle_reserved_duration(reserved, actual); on terminal provider failure, refund the full reservation. Pin with fakeredis Lua tests that show probe+force overspend and reserve-up-to mutual exclusion.",
  "canonical_prevention_artifact": [
    "backend/tests/unit/test_voice_duration_limiter.py",
    "backend/tests/unit/test_desktop_transcribe.py"
  ],
  "evidence_prs": [],
  "scope_hints": [
    "backend/routers/chat.py",
    "backend/utils/voice_duration_limiter.py"
  ],
  "status": "open"
}