fix: redirect tracing logs from stdout to stderr#20
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The MCP stdio transport uses stdout exclusively for JSON-RPC messages. Tracing output on stdout is not valid JSON-RPC and causes parse errors on the client side (e.g. pydantic JSONRPCMessage validation failures), making tool calls silently return empty results. Redirect to stderr with `.with_writer(std::io::stderr)` so logs remain visible without interfering with the protocol stream.
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Problem
tracing_subscriber::fmt::init()writes logs to stdout by default. Whenproject-rag serveruns as an MCP stdio server, stdout is exclusively used for the JSON-RPC message stream. Log lines on stdout are not valid JSON-RPC and cause parse errors on the client side (e.g.JSONRPCMessagevalidation failures in Python MCP clients), making tool calls silently return empty results.Fix
Redirect tracing output to stderr with
.with_writer(std::io::stderr). Logs remain visible in the terminal without interfering with the MCP protocol stream.Test plan
project-rag servewithRUST_LOG=infoand confirm log lines appear on stderr, not stdout