Claude Code 2.1.288: MCP calls that ran twice, and paid Sume calls

Claude Code 2.1.288 (Oct 2) fixed MCP tool calls that sometimes ran twice when the remote result was over 16 MB or could not be parsed. A paid Sume call that runs twice would be two renders if the key differs, which is why paid and write MCP calls require an idempotency_key.

What was fixed?

From the changelog: MCP tool calls sometimes running twice when a remote result was over 16 MB or unparsable. The fix is in the client, so keep the version current in CI.

What does the key do on Sume?

The MCP docs describe idempotency_key as a stable key for transport and dedup, required on write and paid tools. It is not human approval. A repeat with the same key is meant to return the original job rather than start another.

How do you choose a key?

Tie it to the task, not the attempt:

• Good: a hash of the campaign id, scene number and prompt.
• Bad: a timestamp or random value made on each retry. It defeats the dedup.
• Keep the key in the log with the job id, so a replay can reuse it.

Is the cap also repeated?

Send max_spend_usd on each call; a second run is then bounded too. For bursts, check generation_admission_preview first. See MCP tools and gates.