fix(mcp): defer project detection from constructor to start()

[ajperel]

Description

FirebaseMcpServer previously ran void this.detectProjectSetup() in its constructor. In unit tests that instantiate FirebaseMcpServer without calling start(), the 2-second fallback timers all fired mid-suite and ran repo-wide glob scans against process.cwd(), blocking the event loop and causing flaky timeouts in downstream suites such as throttler.spec.ts.

This moves detectProjectSetup() from the constructor to start() so constructing a server in tests starts no background timers or filesystem scans. Availability specs also reuse a single server instance per suite.

Scenarios Tested

• Added unit tests verifying new FirebaseMcpServer({}) does not run project or feature detection until start() is called.
• Ran the 23-server reproduction spec and the full Mocha suite under --trace-gc, confirming 0 allocation storms and all unit tests passing.

Sample Commands

firebase mcp

[gemini-code-assist]

Code Review

This pull request modifies the Firebase MCP server to asynchronously detect and cache the availability of the local firebase CLI, resolving an issue where it always suggested the npx fallback. It also defers project setup detection from the constructor to the start method and adds corresponding unit tests. Feedback on these changes suggests adding a timeout to the spawned CLI version check to prevent potential hangs, extracting magic strings and numbers into static constants as per the style guide, and catching errors on the unawaited detectProjectSetup call to avoid unhandled promise rejections.

[gemini-code-assist]

Calling void this.detectProjectSetup() without awaiting or catching errors can lead to unhandled promise rejections if any of the underlying async operations (such as file system access or API calls) fail. This can crash the Node.js process or lead to silent failures. Let's catch and log any errors using this.logger.error.

    void this.detectProjectSetup().catch((err) => {
      this.logger.error(`Failed to detect project setup: ${err instanceof Error ? err.message : String(err)}`);
    });

[ajperel]

Pre-existing behavior unrelated to my test fix. Though maybe worth someone who works on MCP addressing.

[ajperel]

firebase-tools/src/mcp/index.ts

Line 333 in 332c571

const testCommand = crossSpawn.sync("firebase --version");

Note on line 333: crossSpawn.sync("firebase --version") passes --version inside the executable name instead of the args array, so it always fails with ENOENT and falls back to npx firebase-tools@latest. We left this out of this PR to keep it focused on the flaky test fix. (When fixed separately, it should also run asynchronously and be cached once per process so it does not add a synchronous CLI startup.)