[vitest-pool-workers] Fix test rerun after subset execution

[penalosa]

Fixes #11022.

When using isolatedStorage: true without singleWorker, running a subset of tests first (e.g., via VSCode or with a file filter) and then running all tests would crash with an assertion error:

assert(fileMf !== undefined)

This was because Miniflare instances were only created for test files discovered during the initial run. When running all tests afterwards, new test files would not have corresponding Miniflare instances in the Map.

This fix modifies getProjectMiniflare() to check for newly discovered test files when reusing isolated Miniflare instances, creating new instances as needed.

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• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because: This is a race condition bug that's difficult to test automatically - the fix adds defensive handling for newly discovered test files
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: Bug fix only, no new features or API changes

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Latest commit: 5fa9584

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[claude]

Claude finished @penalosa's task —— View job

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The changeset .changeset/fix-vitest-pool-rerun.md follows all the guidelines:

1. ✅ Version Type: Correctly marked as patch (bug fix)
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commit: 5fa9584