[mikepitre]

Description

Second PR of the sync stack: main ← #9957 ← this PR ← #9956 ← #9962. Tests only. Adds an engine-agnostic behavioral test suite for the @clerk/expo JS <-> native client sync, so it can gate the upcoming replacement of the sync engine (native owns the device token, payload-free invalidations in both directions).

The suite lives in packages/expo/src/provider/__tests__/nativeClientSyncBehavior/ and asserts only user-observable outcomes: the JS signed-in state and active session, the native token and client view, request and refresh counts, the absence of signed-out emissions during session switches, and errors surfaced through the sync barrier. It is backed by:

• FakeClerkServer: one Frontend API shared by both SDKs, with clients keyed by device token.
• FakeNativeClerk: the native SDK's persisted token, its client view, and native-originated actions and change notifications.
• FakeClerk: a stand-in for the clerk-js instance returned by getClerkInstance, using the same surface the existing ClerkProvider tests mock. It talks to the fake Frontend API through the token cache it is built with, like createClerkInstance.
• currentEngineAdapter: renderWithNativeSync(scenario) for today's engine. It keeps today's native module contract (configure, getClientToken, syncClientStateFromJs, clerkNativeClientChanged payloads and sourceId tags) out of the tests. To run the suite against a new engine, only the export in index.ts needs to point at a new adapter.

Two behaviors the current engine does not meet yet are kept as it.fails under "known gaps in the current engine". They flip to it in #9956, which is the proof the new engine fixes them:

• JS starting with a stale device token replaces native's signed-in token, because configure adopts the JS bearer token.
• If JS and native rotate the device token at the same time, the two sides end up on different tokens.

The existing ClerkProvider.nativeClientSync and coordinator tests are unchanged.

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: tests

🤖 Generated with Claude Code

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🦋 Changeset detected

Latest commit: eae370c

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Project	Deployment	Actions	Updated
clerk-js-sandbox	Ready	Preview	Oct 20, 2026 4:02am UTC
swingset	Ready	Preview	Oct 20, 2026 4:02am UTC

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📒 Files selected for processing: 1

• packages/expo/src/provider/__tests__/nativeClientSyncBehavior/currentEngineAdapter.tsx

🔗 Linked repositories identified

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• 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-android (auto-detected)
• clerk/clerk-ios (auto-detected)

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📝 Walkthrough

Adds test support for Expo native client synchronization. The in-memory server and JavaScript and native client fakes model client, session, token, and request state. The harness configures the provider and native module, then exposes synchronization and lifecycle controls. Behavior tests cover sign-in, sign-out, session changes, token rotation, startup, synchronization barriers, refresh failures, and disabled synchronization. Two expected-failure tests cover stale JavaScript tokens and concurrent token rotations.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: ⚪ Minimal · up to 668dc

The test-harness change is mergeable after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 15 functions across 8 files.	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 identifies the addition of a behavioral native client synchronization test suite for Expo.
Description check		The description directly explains the new engine-agnostic native synchronization tests, their coverage, test fakes, adapter design, and known gaps.
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.

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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commit: eae370c

[github-actions]

API Changes Report

Generated by Break Check on 2026-10-20T04:03:54.724Z

Summary

Metric	Count
Packages analyzed	20
Packages with changes	0
🔴 Breaking changes	0
🟡 Non-breaking changes	0
🟢 Additions	0

No API Changes Detected

All packages have stable APIs with no detected changes.

---

Report generated by Break Check

_{Last ran on eae370c.}

[wobsoriano]

🧪 looks good!

pushed changes:

• suite now runs the real createClerkInstance
• removed the barrier tests, which covered an API with no production caller
• fake native module configures through configureWithOptions like real binaries do