Concurrency controls for projects

Clear and concise description of the problem

With over 20 projects using browser mode, it seems our CI is running into some resource exhaustion issues. It looks like vitest starts a dev server for each project and a browser tab for each project. We already reduce concurrency per project, but it does seem to start all projects simultaneously. Causing a lot more concurrency than we intend. We already optimized by using a single browser instance.

Suggested solution

Hard to say with my limited knowledge of vitest architecture. But if we could have a single pool across all projects and control concurrency globally, that would be ideal. Otherwise a way to specify concurrency for running the projects. e.g. only 4 projects may run simultaneously.

Alternative

Wrapping vitest with an orchestrator that runs only X projects simultaneously, but it complicates things around test output, coverage, projects filtering...

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

Start by reviewing the linked CircleCI run and how Vitest launches browser-mode projects, dev servers, and tabs. Define a global project concurrency control that preserves test output, coverage, and project filtering; the work is done when projects share the intended limit without resource exhaustion.