Upstream: SDK requestStream() discards results for 'failed' tasks

[jirispilka]

Problem

The MCP SDK's requestStream() (@modelcontextprotocol/sdk/shared/protocol.js) only calls getTaskResult() for 'completed' tasks. For 'failed' tasks it yields a generic "Task X failed" error and discards the stored result entirely.

This forces us to store all task results as 'completed' even when they are errors — see res/task_status_workaround.md.

Three fixes needed in the SDK

1. Deliver results for 'failed' tasks

// Current:
if (task.status === 'failed') {
    yield { type: 'error', error: new McpError(ErrorCode.InternalError, `Task ${taskId} failed`) };
}

// Fix:
if (task.status === 'failed') {
    const result = await this.getTaskResult({ taskId }, resultSchema, options);
    yield { type: 'result', result };  // result has isError: true
}

2. Include statusMessage in the error (interim fix)

yield {
    type: 'error',
    error: new McpError(ErrorCode.InternalError, task.statusMessage || `Task ${taskId} failed`)
};

3. storeTaskResult() should accept an optional statusMessage

Our storeTaskResultWithMessage() calls updateTaskStatus('working', message) then storeTaskResult(status, result) — two non-atomic calls. The SDK should support this in one call.

Impact

Once fixed upstream, we can:

• Store errors as 'failed' (semantically correct)
• Remove the [error] prefix workaround from statusMessages
• Remove storeTaskResultWithMessage() helper

References

• res/task_status_workaround.md — full analysis
• fix: Set final statusMessage before storeTaskResult (#638) #680 — PR that introduced the workaround

[jancurn]

How about we report this to https://github.com/modelcontextprotocol/typescript-sdk/issues? I know people there, they might help us fix it

[jirispilka]

Raised an issue here: modelcontextprotocol/typescript-sdk#1922

I initially started with a PR, but couldn't keep Claude on a leash:

| stop the plan, since it is not minimal, we should raise an issue first!

You're right — I let scope creep. Beyond the 10-line code fix, I rewrote a test
(~150 lines), added a new test (~60 lines), and wrote two migration notes.
That's not minimal. Stopping now. Nothing has been committed — all changes are
on branch fix/tasks-failed-result-retrieval in the working tree.

[jancurn]

Cheers. Yeah imo it's better to just create the issue and have the team fix it with their agents - PRs are dead :) https://www.latent.space/p/ainews-rip-pull-requests-2005-2026

[jirispilka]

We are still waiting for typescript SDK release with this fix: modelcontextprotocol/typescript-sdk#1922, closing this issue for now, we are tracking it in the PR anyway