fix: prevent handle inheritance in subprocess to resolve stdio deadlock

[gitrishiom]

Description

This PR addresses the remaining Windows deadlock issue over stdio transport.

While PR #151 successfully moved client initialization to a background thread to prevent main-thread blocking, the underlying OS-level collision still persists: on Windows, the subprocess.Popen call spawned by google.auth.default() defaults to stdin=None. This causes the child process (e.g., gcloud) to inherit the parent's stdin handle. Because the parent's stdin is actively bound to the ProactorEventLoop (Overlapped I/O) managing the MCP stdio transport, this shared reference corrupts the pipe state, resulting in a hard crash ([WinError 6] The handle is invalid and ValueError: I/O operation on closed pipe).

To resolve this without altering the core initialization architecture or removing gcloud feature parity for Windows users, this fix introduces a prevent_stdio_inheritance context manager. It temporarily patches subprocess.Popen to enforce stdin=subprocess.DEVNULL during the google.auth.default() call. This isolates the standard file handles, preventing destructive inheritance while allowing gcloud to successfully fetch credentials.

Changes

• Wrapped google.auth.default() in analytics_mcp/tools/client.py with a prevent_stdio_inheritance context manager.
• Ensures 100% feature parity for developers relying on Application Default Credentials via gcloud.
• Verified locally on Windows 11 using a stdio integration harness. The server no longer hangs on initialization.
• Formatted with black and wrapped to the 80-character limit required by nox.

Resolves #134

[selutions]

docs/tutorials/48-intent-based-authorization.md

[matt-landers]

This will go out with the 0.6.0 release next week.

[gitrishiom]

This will go out with the 0.6.0 release next week.

Thanks. Good to hear the PR is accepted & merged into main. All the best.

[Gavin-Attard-120feet]

@matt-landers does this also resolve #156 ?