Transcription: config-driven OpenAI-compatible STT with OpenAI fallback (server-26#297, server-26#83)

STT_PROVIDER=auto picks Groq whisper-large-v3-turbo only when GROQ_API_KEY is
set (else OpenAI, unchanged); compat covers any OpenAI-compatible server via
STT_BASE_URL/STT_API_KEY. A failed primary falls back to OpenAI STT_MODEL on
the same downloaded audio; the fallback reports to its own ai_health tier so
a dead primary stays red. The non-OpenAI provider gets a token-budgeted
glossary prompt (area places, local_knowledge, vocabulary; never ten-codes),
guarded by a narrow prompt-echo check. A per-30s-window zlib compression
check (Whisper's 2.4) adds a noise gate that survives correction being off
(#83, partial). Call docs record stt_provider/model/audio_seconds/confidence.
The sweep hold-back counts the fallback attempt. gate_chatter added to
chatter_classifier (used by transcription to skip correction when
CHATTER_GATE_ENABLED). GROQ_API_KEY templated with default ''.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-c2-core/tests/test_ai_flag_gating.py

@@ -219,15 +219,21 @@ async def test_transcript_correction_is_skipped_when_its_flag_is_off():
          patch.object(transcription, "fstore") as fs, \
          patch.object(transcription, "ai_health") as health, \
          patch.object(transcription, "transcript_correction") as tc, \
-         patch("asyncio.to_thread", AsyncMock(return_value=("units respond", [], False))):
+         patch.object(transcription.settings, "openai_api_key", "k"), \
+         patch.object(transcription.settings, "groq_api_key", None), \
+         patch.object(transcription, "_download", lambda uri: "/nonexistent.mp3"), \
+         patch.object(transcription, "_sync_transcribe_file", lambda *a, **k: {
+             "text": "units respond to the fire on Main Street", "segments": [],
+             "degenerate": False, "duration": 3.0, "confidence": None}):
         fs.doc_set = AsyncMock()
         health.report_healthy = AsyncMock()
         health.report_failure = AsyncMock()
         tc.correct = AsyncMock()
-        await transcription.transcribe_call(
+        text, _ = await transcription.transcribe_call(
             "call-1", "gs://bucket/call-1.mp3", "PD Dispatch", system_id="sys-1"
         )
 
+    assert text == "units respond to the fire on Main Street", "the transcript must still be produced"
     tc.correct.assert_not_awaited()