anomalyco / anomalyco/opencode
Local MCP requests time out when stderr pipe fills
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Since Aug 31, 2026.
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Description
Description
Verbose local MCP output eventually causes a 60-second timeout. OpenCode creates the local transport with stderr: "pipe" but does not consume the SDK stream. On Linux Desktop 1.18.23, the child was observed blocked in write(2) with a full stderr send queue, preventing the request from completing.
Plugins
None required.
OpenCode version
1.18.23
Steps to reproduce
- Start a local MCP fixture that writes 1 MiB to stderr before returning a tool result and waits for
drain. - Connect it as a local MCP server.
- Invoke the tool.
- Observe the request time out after 60 seconds because the child blocks writing stderr.
Expected: OpenCode drains the local MCP stderr stream and the tool returns.
Actual: the child blocks on stderr and the tool times out.
Screenshot and/or share link
Not applicable; deterministic regression fixture available.
Operating System
Linux Desktop
Terminal
Not applicable
Related context
Prior automatically closed reports/PRs #12229, #16449, and #37634 are related context; this report adds direct process evidence and a deterministic regression.
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Assessment
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