fix: check AbortSignal in handleAutomaticTaskPolling to stop cancelled requests

.changeset/fix-automatic-task-polling-abort.md

@@ -0,0 +1,5 @@
+---
+'@modelcontextprotocol/server': patch
+---
+
+Check AbortSignal in handleAutomaticTaskPolling to stop cancelled requests from polling indefinitely. Previously, if a client cancelled a tools/call request during automatic task polling, the poll loop continued consuming server resources until the task completed or the process died.

packages/server/src/server/mcp.ts

@@ -326,6 +326,9 @@ export class McpServer {
         const pollInterval = task.pollInterval ?? 5000;
 
         while (task.status !== 'completed' && task.status !== 'failed' && task.status !== 'cancelled') {
+            if (ctx.mcpReq.signal.aborted) {
+                throw new ProtocolError(ProtocolErrorCode.InternalError, 'Request cancelled during task polling');
+            }
             await new Promise(resolve => setTimeout(resolve, pollInterval));
             const updatedTask = await ctx.task.store.getTask(taskId);
             if (!updatedTask) {