perf: bound speech proxy synthesis

CHANGELOG.md

@@ -32,8 +32,9 @@ Follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) · versioned wi
 - **Docker Socket Isolation.** Compose deployments now place the host Docker socket behind a dedicated network proxy;
   the web container no longer mounts the socket or joins the host Docker group. The client retains direct Unix-socket
   compatibility for deployments that intentionally configure it.
-- **TTS Queue Bound.** Preview, style-variation, and seed-finder synthesis now share a two-slot process-local queue;
-  excess requests receive a retryable 429 after a bounded wait instead of creating unbounded worker threads.
+- **TTS Queue Bound.** Preview, style-variation, seed-finder, and OpenAI-compatible speech-proxy synthesis now share
+  a two-slot process-local queue; excess requests receive a retryable 429 after a bounded wait instead of creating
+  unbounded worker threads.
 - **STT Queue Bound.** Transcription and STT benchmark calls now share a single bounded process-local slot, preventing
   concurrent recognition requests from overcommitting the inference device.
 - **Visual Identity Versioning.** Consistent profile/reference results now carry the standardized v3 prompt marker,

TODO.md

@@ -121,8 +121,8 @@ the first block before investing in architecture or polish.
 - [ ] Prevent duplicate generation when a user clicks twice.
 - [ ] Centralize provider health checks and error handling.
 - [ ] Limit concurrency to 1–2 image generations, 1–2 voice generations, and 1 STT request per user. Consistent
-  portrait/reference rendering and preview/style/seed-finder synthesis are capped at two active jobs; extend the
-  cap to full speech-proxy paths; STT transcription and benchmarks are capped at one active job.
+  portrait/reference rendering, preview/style/seed-finder synthesis, and the OpenAI-compatible speech proxy are
+  capped at two active jobs; STT transcription and benchmarks are capped at one active job.
 - [ ] Use bounded server queues.
 
 ## P0 — Security

routes/tts.py

@@ -696,6 +696,8 @@ async def tts_preview(request: Request):
             )
         else:
             audio, media_type = await _bounded_tts_call(_preview_request_audio, text, voice, settings, instruct, backend)
+    except HTTPException:
+        raise
     except Exception as e:
         raise HTTPException(502, f"TTS error: {e}")
     audio, media_type, ext, duration_sec, clipped = _prepare_proxy_audio(audio, media_type, response_format)
@@ -733,6 +735,8 @@ async def tts_style_variation(request: Request):
     try:
         audio, media_type = await _bounded_tts_call(_preview_request_audio, text, source_voice, settings, instruct, backend)
         audio, media_type, _ext, duration, _clipped = _prepare_proxy_audio(audio, media_type, "wav")
+    except HTTPException:
+        raise
     except Exception as e:
         raise HTTPException(502, f"Style variation synthesis failed: {e}")
 
@@ -959,7 +963,9 @@ async def openai_speech_proxy(request: Request):
 
     if backend == "streaming" and not virtual and response_format == "wav" and not route_has_sounds and not route_has_speed:
         try:
-            resp = await asyncio.to_thread(_open_tts_stream_response, text, voice, settings, style_instruction)
+            resp = await _bounded_tts_call(_open_tts_stream_response, text, voice, settings, style_instruction)
+        except HTTPException:
+            raise
         except Exception as e:
             _routing_log_request(
                 request, status="error", app=request_app, requested_voice=original_voice,
@@ -996,43 +1002,45 @@ async def openai_speech_proxy(request: Request):
             instruct = str(preset.get("description", "")).strip()
             if not instruct:
                 raise RuntimeError(f"Virtual voice '{voice}' has no description")
-            audio, media_type = await asyncio.to_thread(
+            audio, media_type = await _bounded_tts_call(
                 _voice_design_request_audio,
                 instruct, text, str(preset.get("language", "Auto")), settings,
                 str(preset.get("gender", "")),
             )
         elif backend == "voice_design":
-            audio, media_type = await asyncio.to_thread(
+            audio, media_type = await _bounded_tts_call(
                 _voice_design_voice_request_audio,
                 voice, text, settings, style_instruction, str(data.get("language") or "Auto"),
             )
         elif backend == "streaming":
-            resp = await asyncio.to_thread(_open_tts_stream_response, text, voice, settings, style_instruction)
-            audio, media_type = await asyncio.to_thread(_read_tts_stream_response, resp)
+            resp = await _bounded_tts_call(_open_tts_stream_response, text, voice, settings, style_instruction)
+            audio, media_type = await _bounded_tts_call(_read_tts_stream_response, resp)
             if not audio:
                 raise RuntimeError("backend returned empty audio")
         elif backend == "nvidia_magpie":
-            audio, media_type = await asyncio.to_thread(
+            audio, media_type = await _bounded_tts_call(
                 _tts_request_audio, text, voice, settings, style_instruction,
                 _preview_backend_base_url(settings, "nvidia_magpie"),
                 settings.get("tts_api_key", ""), "nvidia_magpie", "nvidia_magpie",
             )
         elif backend in {"nvidia_zeroshot", "nvidia_flow"}:
-            audio, media_type = await asyncio.to_thread(
+            audio, media_type = await _bounded_tts_call(
                 _nvidia_clone_request_audio, text, voice, settings,
                 "flow" if backend == "nvidia_flow" else "zeroshot",
                 str(data.get("audio_prompt_transcript") or ""),
                 str(data.get("language") or ""),
             )
         elif backend == "fishspeech":
-            audio, media_type = await asyncio.to_thread(
+            audio, media_type = await _bounded_tts_call(
                 _fishspeech_request_audio, text, voice, settings,
                 style_instruction, str(data.get("language") or ""),
             )
         else:
-            audio, media_type = await asyncio.to_thread(
+            audio, media_type = await _bounded_tts_call(
                 _tts_request_audio, text, voice, settings, style_instruction,
             )
+    except HTTPException:
+        raise
     except Exception as e:
         _routing_log_request(
             request, status="error", app=request_app, requested_voice=original_voice,