test(mosaic): give each feature test its own fake FAPI host

[alexcarpenter]

Description

Mosaic feature tests share one MSW worker and, until now, one fake FAPI host. Each test creates a new Clerk that is never torn down, so a request a previous test's Clerk sends late (an in-flight fetch, a debounced search) can be matched by the next test's handlers. That is how organization-profile-requests.feature.test.tsx failed in this run: a holdRequests hold counted a members request left over from the previous test.

Each test now gets its own FAPI host. The setup file switches the host before every test, the publishable key is built from it, and a permanent fallback handler answers requests to any older host with a network error. A late request from a previous test fails instead of reaching the current test's handlers, and never goes to the real network. The unhandled-request check only looks at the current host.

fake-fapi-isolation.feature.test.tsx leaves a request in flight, and schedules one after the test ends, then checks the next test's handlers don't see either.

Checklist

• pnpm test runs as expected.
• pnpm build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🐛 Bug fix
• 🌟 New feature
• 🔨 Breaking change
• 📖 Refactoring / dependency upgrade / documentation
• other: test infrastructure

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Project	Deployment	Actions	Updated
clerk-js-sandbox	Ready	Preview	Oct 9, 2026 9:00pm UTC
swingset	Ready	Preview	Oct 9, 2026 9:00pm UTC

[changeset-bot]

🦋 Changeset detected

Latest commit: b8fa912

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

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository YAML (base), Organization UI (inherited)
• Review profile: ASSERTIVE
• Plan: Team
• Run ID: e9fa38c3-d4a6-426b-97d0-460941df7e34

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📥 Commits

Reviewing files that changed from the base of the PR and between 23b1e0d and b8fa912.

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📒 Files selected for processing (6)

• .changeset/isolate-mosaic-fake-fapi.md
• packages/mosaic/docs/testing.md
• packages/mosaic/src/__tests__/feature/fake-fapi-isolation.feature.test.tsx
• packages/mosaic/src/__tests__/feature/fake-fapi.ts
• packages/mosaic/src/__tests__/feature/render.tsx
• packages/mosaic/vitest.setup.browser.mts

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🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• clerk/clerk_go (manual)
• clerk/dashboard (manual)
• clerk/accounts (manual)
• clerk/backoffice (manual)
• clerk/clerk (manual)
• clerk/clerk-docs (manual)
• clerk/cloudflare-workers (manual)
• clerk/clerk-ios (auto-detected)
• clerk/clerk-android (auto-detected)
• clerk/cli (auto-detected)

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📝 Walkthrough

Walkthrough

The fake FAPI now uses a numbered host that changes before each browser test. Its worker allows requests to the current host and returns a network error for requests to other hosts. New tests cover in-flight and delayed requests crossing test boundaries. The testing documentation describes this behavior and retains the existing cleanup and failure checks.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~12 minutes

Suggested reviewers: ephem

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Merge Risk: ⚪ Minimal · up to b8fa9

No actionable merge-blocking issue is established; the change is ready for normal checks.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 4 files. (2 skipped: 2 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: assigning each Mosaic feature test its own fake FAPI host.
Description check		The description directly explains the test-isolation problem, the per-test host solution, the fallback handler, and the added coverage.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 4 files. (2 skipped: 2 unsupported.)

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✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Commit to this branch
• Create a new PR

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commit: b8fa912