handleAutomaticTaskPolling ignores AbortSignal; cancelled requests poll indefinitely

Initial Checks

• Using the latest version of MCP TypeScript SDK
• Searched existing issues

Description

In packages/server/src/server/mcp.ts, handleAutomaticTaskPolling contains a while loop (lines 328-335) that polls a task store until completion. The loop never checks ctx.mcpReq.signal.aborted. If the client cancels the request, the poll loop continues consuming server resources indefinitely.

while (task.status !== 'completed' && task.status !== 'failed' && task.status !== 'cancelled') {
    await new Promise(resolve => setTimeout(resolve, pollInterval));
    const updatedTask = await ctx.task.store.getTask(taskId);
    // ...
}

The taskManager.ts implementation of the same pattern correctly checks the signal (line 856):

if (signal.aborted) {
    resolver(new ProtocolError(ProtocolErrorCode.InternalError, 'Task cancelled or completed'));
    break;
}

Impact

On multi-tenant servers, a single cancelled long-running tool leaks a polling loop per cancelled request. Over time this accumulates.

Suggested fix

while (task.status !== 'completed' && task.status !== 'failed' && task.status !== 'cancelled') {
    if (ctx.mcpReq.signal.aborted) {
        throw new ProtocolError(ProtocolErrorCode.RequestCancelled, 'Request cancelled during task polling');
    }
    await new Promise(resolve => setTimeout(resolve, pollInterval));
    // ...
}

Start in packages/server/src/server/mcp.ts at handleAutomaticTaskPolling and compare its polling loop with the signal check in taskManager.ts around line 856. Confirm that an aborted ctx.mcpReq.signal stops polling with the stated cancellation error, and verify that non-cancelled task polling still reaches completion or failure.