Fix stdio MCP server: redirect logging to stderr to prevent protocol corruption

[Copilot]

Problem

The stdio MCP server was failing with "Failed to parse initialize response from stdio MCP server" errors because log messages were being written to stdout, corrupting the JSON-RPC protocol stream.

In stdio transport mode, stdout must be reserved exclusively for MCP JSON-RPC messages, but the logging system was mixing log entries with protocol messages:

{"timestamp":"2025-09-27T04:08:40.326088Z","level":"INFO",...}  # Log message
{"jsonrpc":"2.0","method":"protocol","params":{"version":"2025-06-18"}}  # Protocol message
{"timestamp":"2025-09-27T04:08:40.326364Z","level":"INFO",...}  # Another log message

This caused MCP clients to fail parsing responses, breaking the initialization handshake.

Solution

Modified the logging system to redirect all log output to stderr in stdio mode while preserving stdout logging for web/websocket modes:

1. Enhanced init_logging function to accept a use_stderr parameter that controls output destination
2. Updated main.rs to use stderr logging specifically for stdio transport mode
3. Maintained backward compatibility for web and websocket modes which can safely log to stdout

After Fix

The stdio transport now produces clean JSON-RPC protocol messages on stdout:

{"jsonrpc":"2.0","method":"protocol","params":{"version":"2025-06-18"}}
{"jsonrpc":"2.0","id":1,"result":{"capabilities":{"tools":{},"resources":{...}},"protocolVersion":"2025-06-18","serverInfo":{"name":"solana-mcp-server","version":"1.1.1"}}}

All log messages are properly redirected to stderr, ensuring MCP clients can successfully parse initialize responses and complete the handshake.

Testing

• All unit tests pass
• MCP initialization test passes
• Manual validation confirms clean JSON-RPC protocol stream on stdout
• Verified proper log redirection to stderr in stdio mode

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Failed to parse initialize response from stdio MCP server</issue_title>
<issue_description>➜ osvm-cli git:(copilot/fix-61ce1f52-d43c-4fc5-8502-1813e5b2f744) ✗ ./target/release/osvm mcp tools solana-mcp-server
🔄 Fetching tools from MCP server 'solana-mcp-server'...
❌ Failed to fetch tools from MCP server 'solana-mcp-server': Failed to parse initialize response from stdio MCP server
➜ osvm-cli git:(copilot/fix-61ce1f52-d43c-4fc5-8502-1813e5b2f744) ✗ </issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #39

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[devloai]

Unable to perform a code review. You have run out of credits 😔
Please upgrade your plan or buy additional credits from the subscription page.