fix(mcp): write firebase-debug.log to ~/.firebase/ instead of cwd

[VishnuVardhanBR]

Problem

When the Firebase MCP server starts (via firebase mcp), it calls useFileLogger() unconditionally. useFileLogger() calls findAvailableLogFile() which writes firebase-debug.log to process.cwd(). This pollutes the user's project directory with an unrelated file on every MCP server startup — even in projects that have no Firebase configuration at all.

Fixes #9982.

Root Cause

In src/bin/mcp.ts:

process.env.IS_FIREBASE_MCP = "true";
useFileLogger(); // writes to process.cwd()/firebase-debug.log

And in src/logger.ts, findAvailableLogFile() hardcodes the log path to process.cwd():

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

Fix

Pass an explicit log file path to useFileLogger() when starting in MCP mode. The log is redirected to ~/.firebase/firebase-debug.log, which:

• Is already used by Firebase tooling for non-project data
• Keeps the user's working directory clean
• Requires no changes to logger.ts

const mcpLogDir = join(homedir(), ".firebase");
mkdirSync(mcpLogDir, { recursive: true });
useFileLogger(join(mcpLogDir, "firebase-debug.log"));

Testing

Manually verified by running npx firebase-tools mcp in a non-Firebase directory and confirming:

• No firebase-debug.log is created in the working directory
• ~/.firebase/firebase-debug.log is created with expected debug output

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where the Firebase MCP server would create a firebase-debug.log file directly in the current working directory upon startup, leading to unnecessary file clutter. The solution redirects this log file to the ~/.firebase/ directory, which is a standard location for Firebase tooling's non-project specific data, ensuring user project directories remain clean.

Highlights

• Log File Redirection: The Firebase MCP server's firebase-debug.log file is now written to ~/.firebase/firebase-debug.log instead of the current working directory, preventing pollution of user project folders.

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Changelog

• CHANGELOG.md
  • Fixed MCP server writing firebase-debug.log to the user's project directory; logs now go to ~/.firebase/firebase-debug.log instead. ([MCP] firebase-debug.log is created in user's working directory on every MCP server startup #9982)

Activity

• No human activity has been recorded on this pull request yet.

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[gemini-code-assist]

Code Review

This pull request correctly addresses the issue of firebase-debug.log being created in the user's current working directory by redirecting it to ~/.firebase/. The implementation is straightforward and effective. I've added a couple of suggestions to use asynchronous file system operations, which is a better practice within an async function context to avoid blocking the event loop.