Tighten catch filter: only catch OCE when tcs.Task has already completed, preventing masking of transport errors like connection closure

Copilot · stephentoub · Copilot · commit bd41d2b0e833 · 2026-02-24T20:15:54.000Z
Co-authored-by: stephentoub &lt;2642209+stephentoub@users.noreply.github.com&gt;
diff --git a/src/ModelContextProtocol.Core/McpSessionHandler.cs b/src/ModelContextProtocol.Core/McpSessionHandler.cs
@@ -544,8 +544,10 @@ public async Task<JsonRpcResponse> SendRequestAsync(JsonRpcRequest request, Canc
             {
                 await sendTask.ConfigureAwait(false);
             }
-            catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
+            catch (OperationCanceledException) when (tcs.Task.IsCompleted && !cancellationToken.IsCancellationRequested)
             {
+                // The response arrived via a concurrent channel (e.g., background GET SSE stream),
+                // which cancelled the transport send. Proceed to retrieve the already-completed response.
             }
             finally
             {

Original file line number	Diff line number	Diff line change
`@@ -544,8 +544,10 @@ public async Task<JsonRpcResponse> SendRequestAsync(JsonRpcRequest request, Canc`
`544`	`544`	`{`
`545`	`545`	`await sendTask.ConfigureAwait(false);`
`546`	`546`	`}`
`547`		`- catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)`
	`547`	`+ catch (OperationCanceledException) when (tcs.Task.IsCompleted && !cancellationToken.IsCancellationRequested)`
`548`	`548`	`{`
	`549`	`+ // The response arrived via a concurrent channel (e.g., background GET SSE stream),`
	`550`	`+ // which cancelled the transport send. Proceed to retrieve the already-completed response.`
`549`	`551`	`}`
`550`	`552`	`finally`
`551`	`553`	`{`