Accept a nil Serve error in TestGoneClientStopsQueuedCalls (#240)

On Linux the test's input reached EOF before the failed write
cancelled the session, so Serve returned nil after the cancelled call
finished, which is correct. The test now accepts nil or
context.Canceled; what it checks is that Serve returns promptly.

Refs #240

Co-Authored-By: Claude Opus 5.5 <[email protected]>

Author: TMHSDigital

internal/mcp/mcp_test.go

@@ -365,8 +365,10 @@ func TestGoneClientStopsQueuedCalls(t *testing.T) {
 	go func() { done <- (&Server{Tools: []Tool{block}}).Serve(context.Background(), in, brokenWriter{}) }()
 	select {
 	case err := <-done:
-		if !errors.Is(err, context.Canceled) {
-			t.Errorf("Serve returned %v, want context.Canceled from the failed write", err)
+		// nil when the input's end is read before the failed write cancels
+		// the session; either way the queued call did not run on.
+		if err != nil && !errors.Is(err, context.Canceled) {
+			t.Errorf("Serve returned %v, want nil or context.Canceled", err)
 		}
 	case <-time.After(5 * time.Second):
 		t.Fatal("Serve kept running queued calls after its client was gone")