fix: prevent in-process callback failures from breaking calls

src/mcp/shared/direct_dispatcher.py

@@ -90,7 +90,10 @@ async def send_raw_request(
 
     async def progress(self, progress: float, total: float | None = None, message: str | None = None) -> None:
         if self._on_progress is not None:
-            await self._on_progress(progress, total, message)
+            try:
+                await self._on_progress(progress, total, message)
+            except Exception:
+                logger.exception("progress callback raised")
 
 
 class DirectDispatcher:
@@ -301,7 +304,10 @@ async def _dispatch_notify(self, method: str, params: Mapping[str, Any] | None)
             return
         assert self._on_notify is not None
         dctx = self._make_context()
-        await self._on_notify(dctx, method, params)
+        try:
+            await self._on_notify(dctx, method, params)
+        except Exception:
+            logger.exception("notification handler for %r raised", method)
 
 
 def create_direct_dispatcher_pair(

tests/shared/test_dispatcher.py

@@ -216,6 +216,43 @@ async def on_progress(progress: float, total: float | None, message: str | None)
     assert received == [(0.5, 1.0, "halfway")]
 
 
+@pytest.mark.anyio
+async def test_progress_callback_exception_does_not_fail_request(
+    pair_factory: PairFactory, caplog: pytest.LogCaptureFixture
+) -> None:
+    async def on_progress(progress: float, total: float | None, message: str | None) -> None:
+        raise RuntimeError("progress callback failed")
+
+    async def server_on_request(
+        ctx: DispatchContext[TransportContext], method: str, params: Mapping[str, Any] | None
+    ) -> dict[str, Any]:
+        await ctx.progress(0.5)
+        return {"ok": True}
+
+    async with running_pair(pair_factory, server_on_request=server_on_request) as (client, *_):
+        with anyio.fail_after(5):
+            result = await client.send_raw_request("tools/call", None, {"on_progress": on_progress})
+    assert result == {"ok": True}
+    assert "progress callback raised" in caplog.text
+
+
+@pytest.mark.anyio
+async def test_notification_handler_exception_does_not_reach_sender(
+    pair_factory: PairFactory, caplog: pytest.LogCaptureFixture
+) -> None:
+    called = anyio.Event()
+
+    async def on_notify(ctx: DispatchContext[TransportContext], method: str, params: Mapping[str, Any] | None) -> None:
+        called.set()
+        raise RuntimeError("notification handler failed")
+
+    async with running_pair(pair_factory, server_on_notify=on_notify) as (client, *_):
+        with anyio.fail_after(5):
+            await client.notify("notifications/message", None)
+            await called.wait()
+    assert "notification handler for 'notifications/message' raised" in caplog.text
+
+
 @pytest.mark.anyio
 async def test_ctx_progress_is_noop_when_caller_supplied_no_callback(pair_factory: PairFactory):
     async def server_on_request(