[vitest-pool-workers] Suppress outputGateBroken stderr noise when testing Workflows

[penalosa]

Fixes #12764.

When testing Cloudflare Workflows with introspectWorkflowInstance, workerd emits broken.outputGateBroken; jsg.Error: Instance dispose to stderr during test teardown as the Durable Object backing the Workflow instance is disposed. This is normal workerd behaviour — the output gate is broken as part of DO cleanup — but it was being forwarded to the user's stderr, adding noise to test output and CI logs.

The existing ignoreMessages filter in handleRuntimeStdio already suppresses similar known-benign workerd messages. This PR adds "broken.outputGateBroken; jsg.Error: Instance dispose" to that list.

---

• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because: single-line filter addition matching an existing suppression pattern; the reproduction repo in the issue can be used to verify manually
• Public documentation
  • Documentation not necessary because: internal noise suppression, no user-facing API change

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[changeset-bot]

🦋 Changeset detected

Latest commit: 972101b

The changes in this PR will be included in the next version bump.

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[github-actions]

⚠️ Issues found

File: .changeset/vitest-outputgate-noise.md

Issue: Missing body in changeset description

The changeset contains only a title line with no body:

fix: suppress `outputGateBroken` stderr noise when testing Workflows

Per the README guidelines, the message format requires:

BODY: One or more paragraphs explaining the reason for the change and anything notable about the approach. Aim for more than one sentence but less than three paragraphs to keep it succinct and useful.

The description should explain:

• What outputGateBroken is and why it was producing noise
• What caused the spurious stderr output
• How it was fixed

The title alone is not sufficient. See the patch example in the README for reference:

Fix wrangler dev failing to start when wrangler.toml contains Unicode characters

Previously, projects with non-ASCII characters in configuration values would fail with "Invalid UTF-8 sequence". This is now handled correctly.

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Everything else looks fine:

• Version type (patch) is appropriate for a bug fix
• No h1/h2/h3 headers present
• Package (@cloudflare/vitest-pool-workers) is correct for a Workflows testing fix

[ask-bonk]

LGTM

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miniflare

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@cloudflare/vite-plugin

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@cloudflare/vitest-pool-workers

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@cloudflare/workers-editor-shared

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wrangler

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commit: 972101b

[workers-devprod]

Codeowners approval required for this PR:

• ✅ @cloudflare/wrangler

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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