handleAutomaticTaskPolling ignores AbortSignal; cancelled requests poll indefinitely

[blackwell-systems]

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));
    // ...
}