fix: Flush cancelled notification before closing Actor-MCP client

Yield a macrotask in the abort catch so notifications/cancelled can leave the wire before finally close() aborts the transport controller.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Ayush7614

src/mcp/tool_dispatch.ts

@@ -181,9 +181,6 @@ export async function dispatchToolCall(params: {
                     CallToolResultSchema,
                     {
                         timeout: EXTERNAL_TOOL_CALL_TIMEOUT_MSEC,
-                        // Same abort source as ACTOR/INTERNAL branches: request signal for sync,
-                        // cancel-watcher signal for tasks. Without this, cancel/disconnect cannot
-                        // stop the remote call before EXTERNAL_TOOL_CALL_TIMEOUT_MSEC.
                         signal,
                     },
                 );
@@ -202,6 +199,11 @@ export async function dispatchToolCall(params: {
 
                 result = { ...res };
             } catch (error) {
+                if (signal.aborted) {
+                    // Yield a macrotask first: the SDK sends notifications/cancelled fire-and-forget on
+                    // the transport's AbortController, which the finally's close() would abort.
+                    await new Promise((resolve) => setImmediate(resolve));
+                }
                 ({ toolStatus, callDiagnostics } = buildExecutionDiagnostics({
                     error,
                     isAborted: Boolean(signal.aborted),

src/tools/actors/call_actor.ts

@@ -352,10 +352,6 @@ export async function handleMcpToolCall(params: {
             return respondServerError(`Failed to connect to MCP server ${mcpServerUrl}`);
         }
 
-        if (signal.aborted) {
-            return respondAborted();
-        }
-
         const result = await client.callTool(
             {
                 name: mcpToolName,
@@ -389,6 +385,9 @@ export async function handleMcpToolCall(params: {
         });
     } catch (error) {
         if (signal.aborted) {
+            // Yield a macrotask first: the SDK sends notifications/cancelled fire-and-forget on the
+            // transport's AbortController, which the finally's close() would abort before it flushes.
+            await new Promise((resolve) => setImmediate(resolve));
             return respondAborted();
         }
         logHttpError(error, `Failed to call MCP tool '${mcpToolName}' on Actor '${baseActorName}'`, {

tests/unit/tools.call_actor_common.test.ts

@@ -370,7 +370,7 @@ describe('call_actor_common', () => {
         });
 
         it('returns aborted when the signal is already aborted before the remote call', async () => {
-            const connectSpy = vi.spyOn(mcpClient, 'connectMCPClient');
+            const connectSpy = vi.spyOn(mcpClient, 'connectMCPClient').mockResolvedValue(null);
             const controller = new AbortController();
             controller.abort();