On Windows (Python 3.11–3.13), tests that spawn subprocesses occasionally time out in CI. The failures are inconsistent, affect different tests across runs, and usually indicate that a subprocess stalled during startup rather than that the test logic itself is broken.

What problem does it solve?

It lowers the frequency of spurious CI failures caused by:
backend auto-detection happening inside subprocesses,
contention around the shared font cache on Windows,
slower and less predictable subprocess startup compared to other platforms.
These issues currently cause otherwise valid PRs to fail CI.

Reasoning for this implementation

The change is applied in subprocess_run_helper, which is the common entry point for the affected tests. Inside the subprocess, the backend is set defensively to avoid auto-detection delays, the font cache is isolated to a temporary directory to prevent cross-process interference, and the timeout is relaxed on Windows only. A small amount of stderr logging is added to help diagnose any remaining stalls.
Linux and macOS behavior is unchanged.
Happy to add more details if needed !

PR checklist

• "closes[Bug]: Random timeout failures in CI #30851 " is in the body of the PR description tolink the related issue
• new and changed code istested
• Plotting related features are demonstrated in anexample
• New Features andAPI Changes are noted with adirective and release note
• Documentation complies withgeneral anddocstring guidelines