fix: stop MCP server stderr from corrupting the TUI - #237
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rmcp's child-process builder defaults stderr to Stdio::inherit(), so a chatty MCP server (e.g. codebase-memory-mcp) writes its debug logs straight to the user's terminal, painting over the alt-screen TUI. Pipe the child's stderr instead and drain it into tracing (which logs to the log file, not the terminal), server-prefixed at debug level. Draining also prevents a verbose server from deadlocking on a full pipe buffer.
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Summary
A chatty MCP server (e.g.
codebase-memory-mcp) floods the terminal with its debug logs and breaks the TUI display.Root cause
TokioChildProcess's builder defaults the child's stderr toStdio::inherit(), so anything an MCP server writes to stderr goes straight to the user's terminal and paints over the alt-screen TUI. (stdoutis the JSON-RPC protocol channel and is unaffected.)Fix
Spawn command-transport MCP servers with
stderr: Stdio::piped()and drain the pipe intotracing(debug level, prefixed with the server name), which writes to zerostack's log file instead of the terminal. Draining also keeps a very verbose server from deadlocking on a full pipe buffer, and preserves diagnostics for MCP troubleshooting.Verification
cargo test(715 passed),cargo test --no-default-features(600),cargo clippy --all-featuresand--no-default-featureswith-D warnings— all clean.