AIService: handle StartFrame/EndFrame/CancelFrame exceptions

If AIService subclasses implement start()/stop()/cancel() and exception are not
handled, execution will not continue and therefore the originator frames will
not be pushed. This would cause the pipeline to not be started (i.e. StartFrame
would not be pushed downstream) or stopped properly.

src/pipecat/services/ai_service.py

@@ -148,11 +148,11 @@ class AIService(FrameProcessor):
         await super().process_frame(frame, direction)
 
         if isinstance(frame, StartFrame):
-            await self.start(frame)
-        elif isinstance(frame, CancelFrame):
-            await self.cancel(frame)
+            await self._start(frame)
         elif isinstance(frame, EndFrame):
-            await self.stop(frame)
+            await self._stop(frame)
+        elif isinstance(frame, CancelFrame):
+            await self._cancel(frame)
 
     async def process_generator(self, generator: AsyncGenerator[Frame | None, None]):
         """Process frames from an async generator.
@@ -169,3 +169,21 @@ class AIService(FrameProcessor):
                     await self.push_error_frame(f)
                 else:
                     await self.push_frame(f)
+
+    async def _start(self, frame: StartFrame):
+        try:
+            await self.start(frame)
+        except Exception as e:
+            logger.error(f"{self}: exception processing {frame}: {e}")
+
+    async def _stop(self, frame: EndFrame):
+        try:
+            await self.stop(frame)
+        except Exception as e:
+            logger.error(f"{self}: exception processing {frame}: {e}")
+
+    async def _cancel(self, frame: CancelFrame):
+        try:
+            await self.cancel(frame)
+        except Exception as e:
+            logger.error(f"{self}: exception processing {frame}: {e}")