Encode lazy-init invariants at the right site, not at read sites

Three spots had the same shape: a field starts None, a later method
populates it, a read site later reads it. Pyright can't track the
cross-method invariant. Rather than spray assertions at the read
sites, fix each site at the structural level:

- `FastAPIWebsocketInputTransport._monitor_websocket` now takes the
  session timeout as an argument. The task-creation site already
  guards on truthiness, so the call can pass the non-None value
  directly and the method's signature tells the truth.
- `FrameProcessorMetrics.task_manager` raises `RuntimeError` instead
  of asserting. Asserts are stripped under `python -O`; a real raise
  keeps the runtime safety net and still narrows the type for pyright.
- `SOXRStreamAudioResampler._maybe_initialize_sox_stream` returns the
  initialized stream. Callers use the return value and never touch
  the Optional `_soxr_stream` attribute, so narrowing stays inside
  the init method where the invariant is established.

pyrightconfig.json

@@ -2,8 +2,14 @@
   "typeCheckingMode": "basic",
   "pythonVersion": "3.11",
   "pythonPlatform": "All",
-  "include": ["scripts", "src/pipecat"],
-  "exclude": ["**/*_pb2.py", "**/__pycache__"],
+  "include": [
+    "scripts",
+    "src/pipecat"
+  ],
+  "exclude": [
+    "**/*_pb2.py",
+    "**/__pycache__"
+  ],
   "ignore": [
     "tests",
     "src/pipecat/adapters/base_llm_adapter.py",
@@ -23,7 +29,6 @@
     "src/pipecat/audio/filters/aic_filter.py",
     "src/pipecat/audio/filters/krisp_viva_filter.py",
     "src/pipecat/audio/filters/rnnoise_filter.py",
-    "src/pipecat/audio/resamplers/soxr_stream_resampler.py",
     "src/pipecat/audio/turn/smart_turn/local_smart_turn_v2.py",
     "src/pipecat/audio/turn/smart_turn/local_smart_turn_v3.py",
     "src/pipecat/audio/vad/silero.py",
@@ -35,7 +40,6 @@
     "src/pipecat/processors/frameworks/rtvi/processor.py",
     "src/pipecat/processors/frameworks/strands_agents.py",
     "src/pipecat/processors/gstreamer/pipeline_source.py",
-    "src/pipecat/processors/metrics/frame_processor_metrics.py",
     "src/pipecat/services/ai_service.py",
     "src/pipecat/services/anthropic/llm.py",
     "src/pipecat/services/assemblyai/stt.py",
@@ -130,9 +134,8 @@
     "src/pipecat/transports/smallwebrtc/transport.py",
     "src/pipecat/transports/tavus/transport.py",
     "src/pipecat/transports/websocket/client.py",
-    "src/pipecat/transports/websocket/fastapi.py",
     "src/pipecat/transports/websocket/server.py",
     "src/pipecat/transports/whatsapp/client.py"
   ],
   "reportMissingImports": false
-}
+}

src/pipecat/audio/resamplers/soxr_stream_resampler.py

@@ -68,7 +68,7 @@ class SOXRStreamAudioResampler(BaseAudioResampler):
                 self._soxr_stream.clear()
         self._last_resample_time = current_time
 
-    def _maybe_initialize_sox_stream(self, in_rate: int, out_rate: int):
+    def _maybe_initialize_sox_stream(self, in_rate: int, out_rate: int) -> "soxr.ResampleStream":
         if self._soxr_stream is None:
             self._initialize(in_rate, out_rate)
         else:
@@ -80,6 +80,9 @@ class SOXRStreamAudioResampler(BaseAudioResampler):
                 f"expected {self._in_rate}->{self._out_rate}, got {in_rate}->{out_rate}"
             )
 
+        assert self._soxr_stream is not None
+        return self._soxr_stream
+
     async def resample(self, audio: bytes, in_rate: int, out_rate: int) -> bytes:
         """Resample audio data using soxr.ResampleStream resampler library.
 
@@ -94,8 +97,8 @@ class SOXRStreamAudioResampler(BaseAudioResampler):
         if in_rate == out_rate:
             return audio
 
-        self._maybe_initialize_sox_stream(in_rate, out_rate)
+        stream = self._maybe_initialize_sox_stream(in_rate, out_rate)
         audio_data = np.frombuffer(audio, dtype=np.int16)
-        resampled_audio = self._soxr_stream.resample_chunk(audio_data)
+        resampled_audio = stream.resample_chunk(audio_data)
         result = resampled_audio.astype(np.int16).tobytes()
         return result

src/pipecat/processors/metrics/frame_processor_metrics.py

@@ -66,6 +66,8 @@ class FrameProcessorMetrics(BaseObject):
         Returns:
             The task manager instance for async operations.
         """
+        if self._task_manager is None:
+            raise RuntimeError("task_manager not set; call setup() first")
         return self._task_manager
 
     @property

src/pipecat/transports/websocket/fastapi.py

@@ -255,7 +255,9 @@ class FastAPIWebsocketInputTransport(BaseInputTransport):
         if self._params.serializer:
             await self._params.serializer.setup(frame)
         if not self._monitor_websocket_task and self._params.session_timeout:
-            self._monitor_websocket_task = self.create_task(self._monitor_websocket())
+            self._monitor_websocket_task = self.create_task(
+                self._monitor_websocket(self._params.session_timeout)
+            )
         await self._client.trigger_client_connected()
         await self.push_frame(ClientConnectedFrame())
         if not self._receive_task:
@@ -322,9 +324,9 @@ class FastAPIWebsocketInputTransport(BaseInputTransport):
         if not self._client.is_closing:
             await self._client.trigger_client_disconnected()
 
-    async def _monitor_websocket(self):
-        """Wait for self._params.session_timeout seconds, if the websocket is still open, trigger timeout event."""
-        await asyncio.sleep(self._params.session_timeout)
+    async def _monitor_websocket(self, timeout: int):
+        """Wait for ``timeout`` seconds, then trigger the client-timeout event if still open."""
+        await asyncio.sleep(timeout)
         await self._client.trigger_client_timeout()