[MCP] firebase-debug.log is created in user's working directory on every MCP server startup

[cathandnya]

[REQUIRED] Environment info

firebase-tools: 15.1.0 (via Claude Code Firebase plugin)

Platform: macOS (Darwin 25.3.0)

[REQUIRED] Test case

Install the Firebase plugin for Claude Code (which runs npx firebase-tools mcp --dir . as an MCP server). Open any project directory and use any Firebase MCP tool.

[REQUIRED] Steps to reproduce

1. Install the official Firebase plugin for Claude Code
2. Open a terminal in any project directory (e.g. an iOS project with no Firebase config)
3. Start a Claude Code session — the Firebase MCP server starts automatically
4. Invoke any Firebase MCP tool (e.g. firebase_get_environment)
5. Check the working directory

[REQUIRED] Expected behavior

The MCP server should not create firebase-debug.log in the user's working directory. When running as an MCP server, debug logs should either:

• Be written to a well-known location (e.g. ~/.firebase/logs/), or
• Be suppressed by default unless explicitly enabled, or
• Be configurable via an environment variable (e.g. FIREBASE_DEBUG_LOG_FILE)

[REQUIRED] Actual behavior

A firebase-debug.log file is created in process.cwd() every time the MCP server starts. This pollutes the user's project directory with an unrelated file.

The root cause is in src/logger.ts — findAvailableLogFile() hardcodes the log path to the current working directory:

const logFilename = path.join(process.cwd(), c);

This behavior makes sense for interactive CLI usage, but is problematic for MCP server mode where the server runs in the background and the user did not explicitly invoke a Firebase command.