MCP tasks with an unknown outcome are reported as unknown, and unservable input requests cancel the task

What

MCP servers are add-on programs that give Claude Code extra tools. Some of their tools start tasks that run on the server while Claude Code checks back for the result.

• When a task's result can never be learned, Claude now gets a "Task outcome unknown" notification instead of a plain failure. It tells the model not to claim the task finished or failed.
• New messages explain why a task was lost: unknown_to_server, expired and poll_failed, for example "the server refused to report on this task".
• When checking on a task returns error -32602, the error a server sends for invalid input, it is now treated as expired or unknown_to_server.
• If a task asks a question that this session cannot show, Claude Code now asks the server to cancel the task. Before, it could be left running on the server for a session that could show it. input_unservable is a new final outcome for this case.
• An interactive session that has a dialog now answers the task's question itself.
• The reason for a cancellation is recorded on the task.

Why

Claude no longer reports a lost or expired task as simply failed, and is told not to guess the outcome. Tasks that need an answer this session cannot give are cancelled rather than left waiting on the server.