test(e2e): Add integration tests for Fastify

[tmilewski]

Description

• Add end-to-end integration tests for @clerk/fastify covering basic auth flows and frontend API proxy mode
• Add a new fastify-vite test template app with Fastify server + Vite client, using Express as a bridge to serve the Vite frontend
• Add proxy-specific tests including a handshake redirect test that verifies x-forwarded-* headers are used to derive the public origin instead of localhost
• Register the new fastify suite in CI and add a test:integration:fastify script

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:

Summary by CodeRabbit

• New Features

  • Added Fastify framework support with Vite integration for full-stack applications with Clerk authentication.

• Tests

  • Added integration tests for Fastify covering authentication and proxy scenarios.
  • Expanded CI coverage to include Fastify and additional frameworks in the test matrix.

[changeset-bot]

🦋 Changeset detected

Latest commit: 688887a

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

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Project	Deployment	Actions	Updated (UTC)
clerk-js-sandbox	Ready	Preview, Comment	Mar 13, 2026 2:32am

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commit: 688887a

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository YAML (base), Organization UI (inherited)

Review profile: ASSERTIVE

Plan: Pro

Run ID: 4ce25e54-07d3-4260-a8bc-b813bae78769

📥 Commits

Reviewing files that changed from the base of the PR and between d32bf2c and 688887a.

📒 Files selected for processing (16)

• .changeset/three-cameras-decide.md
• .github/workflows/ci.yml
• integration/presets/fastify.ts
• integration/presets/index.ts
• integration/presets/longRunningApps.ts
• integration/templates/fastify-vite/index.html
• integration/templates/fastify-vite/package.json
• integration/templates/fastify-vite/src/client/main.ts
• integration/templates/fastify-vite/src/client/tsconfig.json
• integration/templates/fastify-vite/src/client/vite-env.d.ts
• integration/templates/fastify-vite/src/server/main.ts
• integration/templates/fastify-vite/tsconfig.json
• integration/templates/index.ts
• integration/tests/fastify/basic.test.ts
• integration/tests/fastify/proxy.test.ts
• package.json

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📝 Walkthrough

Walkthrough

This change introduces Fastify as a new supported application framework for integration testing. It adds a Fastify preset configuration, a complete Fastify + Vite template with Clerk authentication wiring on both client and server sides, and comprehensive integration tests covering authenticated and unauthenticated access as well as frontend API proxy behavior. The CI workflow is updated to include Fastify in the integration-tests matrix, and a new npm script is added for running Fastify-specific integration tests.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: adding integration tests for Fastify. It accurately reflects the primary objective of the PR, which is to introduce end-to-end testing for Fastify with a new test template app and test cases.

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📝 Coding Plan

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[wobsoriano]

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