modelcontextprotocol / modelcontextprotocol/servers
Claude Desktop: tool_result POST fails with side_channel_waiting_key_absent (Filesystem connector appears broken)
Open
Nobody has claimed this yet.
bug
- Dominant language
- TypeScript
- Stars
- 90.5k
- Forks
- 11.7k
- Avg merge
- 2d 2h
- Merged PRs (30d)
- 5
Description
- Error: side_channel_waiting_key_absent on endpoint tool_result
- Request ID from your log: req_011CdG5CtZqaXRHAgjaShMu1
- Timestamp: 2026-07-21 16:30:35 UTC
- What happened: Filesystem tool call completed locally, POST of result back to claude.ai returned 404 with that error code, causing the connector to appear broken
- App version: 1.24012.1, macOS Tahoe 26.5.1
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the Filesystem tool call with Claude Desktop 1.24012.1 and inspect the POST to the tool_result endpoint using request ID req_011CdG5CtZqaXRHAgjaShMu1. Compare the local tool completion with the 404 side_channel_waiting_key_absent response; done means the result POST succeeds or the responsible component and required fix are identified.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- backend-api-design
- Issue type
- Bug
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Quiet
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100