workspace-server/internal/handlers/mcp_test.go

@@ -280,6 +280,62 @@ func TestMCPHandler_DelegateTaskAsync_RoutesThroughPlatformA2AProxy(t *testing.T
 	}
 }
 
+// TestMCPHandler_DelegateTaskAsync_MarshalFailureDoesNotCallProxy proves the
+// extracted #1933 fix: when the A2A body fails to marshal, the detached
+// goroutine returns early and never calls proxyA2ARequest with a nil/empty
+// body. Before the fix the goroutine logged the error and fell through,
+// dispatching a malformed A2A request.
+func TestMCPHandler_DelegateTaskAsync_MarshalFailureDoesNotCallProxy(t *testing.T) {
+	h, mock := newMCPHandler(t)
+	callerID := "11111111-1111-1111-1111-111111111111"
+	targetID := "22222222-2222-2222-2222-222222222222"
+	parentID := "33333333-3333-3333-3333-333333333333"
+
+	expectCanCommunicateSiblings(mock, callerID, targetID, parentID)
+	mock.ExpectExec(`(?s)INSERT INTO activity_logs.*'delegation'.*'delegate'`).
+		WithArgs(callerID, callerID, targetID, "Delegating to "+targetID, sqlmock.AnyArg(), "pending").
+		WillReturnResult(sqlmock.NewResult(1, 1))
+	mock.ExpectExec(`UPDATE activity_logs`).
+		WithArgs("dispatched", "", callerID, sqlmock.AnyArg()).
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	// Force the (otherwise near-impossible) marshal failure for the A2A body.
+	origMarshal := marshalA2ABody
+	marshalA2ABody = func(any) ([]byte, error) {
+		return nil, errors.New("forced marshal failure")
+	}
+	t.Cleanup(func() { marshalA2ABody = origMarshal })
+
+	proxyCalled := make(chan struct{}, 1)
+	h.a2aProxy = func(ctx context.Context, workspaceID string, body []byte, proxyCallerID string, logActivity bool) (int, []byte, error) {
+		proxyCalled <- struct{}{}
+		return 200, []byte(`{}`), nil
+	}
+
+	out, err := h.toolDelegateTaskAsync(context.Background(), callerID, map[string]interface{}{
+		"workspace_id": targetID,
+		"task":         "async work",
+	})
+	if err != nil {
+		t.Fatalf("delegate_task_async returned error: %v", err)
+	}
+	if !strings.Contains(out, `"status":"dispatched"`) {
+		t.Fatalf("delegate_task_async response = %s", out)
+	}
+
+	// Wait for the detached goroutine to finish, then assert the proxy was
+	// never reached because of the early return on marshal failure.
+	waitGlobalAsyncForTest()
+	select {
+	case <-proxyCalled:
+		t.Fatal("proxyA2ARequest was called after marshal failure; expected early return")
+	default:
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Fatalf("unmet expectations: %v", err)
+	}
+}
+
 // ─────────────────────────────────────────────────────────────────────────────
 // notifications/initialized
 // ─────────────────────────────────────────────────────────────────────────────

workspace-server/internal/handlers/mcp_tools.go

@@ -20,6 +20,11 @@ import (
 	"github.com/google/uuid"
 )
 
+// marshalA2ABody marshals the JSON-RPC body for an async A2A dispatch.
+// Indirected through a package var so tests can force the (otherwise
+// near-impossible) marshal-failure path and assert the early return.
+var marshalA2ABody = json.Marshal
+
 // insertMCPDelegationRow writes a delegation activity row so the canvas
 // Agent Comms tab can show the task text for MCP-initiated delegations.
 // Mirrors insertDelegationRow (delegation.go) for the MCP tool path.
@@ -269,7 +274,7 @@ func (h *MCPHandler) toolDelegateTaskAsync(ctx context.Context, callerID string,
 		bgCtx, cancel := context.WithTimeout(context.Background(), mcpAsyncCallTimeout)
 		defer cancel()
 
-		a2aBody, marshalErr := json.Marshal(map[string]interface{}{
+		a2aBody, marshalErr := marshalA2ABody(map[string]interface{}{
 			"jsonrpc": "2.0",
 			"id":      delegationID,
 			"method":  "message/send",
@@ -283,6 +288,9 @@ func (h *MCPHandler) toolDelegateTaskAsync(ctx context.Context, callerID string,
 		})
 		if marshalErr != nil {
 			log.Printf("toolDelegateTask %s: json.Marshal a2aBody failed: %v", delegationID, marshalErr)
+			// Bail out: proceeding would call proxyA2ARequest with a
+			// nil/empty body, dispatching a malformed A2A request.
+			return
 		}
 
 		status, _, err := h.proxyA2ARequest(bgCtx, targetID, a2aBody, callerID, true)