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/app/internal/ai_clients.py

@@ -34,6 +34,24 @@ def openai_client(timeout: Optional[float] = None):
     )
 
 
+def stt_client(api_key: Optional[str], base_url: Optional[str] = None):
+    """
+    Synchronous client for an OpenAI-compatible transcription endpoint
+    (server-26#297) -- OpenAI itself, Groq, or a self-hosted server. Same
+    timeout/retry limits as every other client here, with STT's own timeout.
+    """
+    from openai import OpenAI
+    kwargs = {}
+    if base_url:
+        kwargs["base_url"] = base_url
+    return OpenAI(
+        api_key=api_key,
+        timeout=settings.stt_timeout_seconds,
+        max_retries=settings.openai_max_retries,
+        **kwargs,
+    )
+
+
 def async_openai_client(timeout: Optional[float] = None):
     """Async OpenAI client, same limits as openai_client()."""
     from openai import AsyncOpenAI