test(web): verify locale switches, cookies and hard reloads

[austinywang]

The locale switcher must keep the selected language, NEXT_LOCALE cookie, URL, metadata, document language/direction, and rendered headings consistent when returning to English. The implementation now on main writes the locale cookie before a full document navigation; this follow-up retains it and removes the conflicting older navigation attempts.

This PR expands the previous browser regression into four behavior tests:

• Korean, Japanese, and Arabic → English → the original locale → English, with a hard reload after every switch.
• English selection wins over a Korean Accept-Language preference, preserves query strings/fragments, and updates the cookie, title, heading, html lang, and rtl/ltr direction.
• A real client-side /ko → /ko/blog navigation followed by switching to English preserves /blog and its query/fragment across reload.

CMUX_WEB_TEST_BASE_URL lets the existing test:instant command run the same checks against a dev server or deployed preview. Default CI still builds and starts the production-style server.

Validation:

• CMUX_WEB_TEST_BASE_URL=http://localhost:4077 bun run test:instant locale-navigation — 4 passed.
• CMUX_WEB_TEST_BASE_URL=https://cmux.com bun run test:instant locale-navigation — 4 passed.
• bun run typecheck — passed.
• bun run lint -- e2e/instant/locale-navigation.instant.ts e2e/instant/marketing-navigation.instant.ts playwright.instant.config.ts — passed.
• Right-hand cmux browser verified Korean/Japanese/Arabic → English and English reload, including matching title, heading, selector, cookie, lang and direction.
• bun run test — 2,565 passed, 211 skipped; two unrelated existing vm-cmux-tui mount-supervisor timeout failures on this Mac (the isolated retry also hit supervisor timeouts).

Locale changes perform a full document load, trading preservation of transient page state for a single server-rendered locale. This behavior already exists on main; the final diff changes tests and their runner configuration only. All localized routes and catalogs are preserved; localization audit found no changed user-facing strings.

Closes #11979

Deployment note: Vercel previews for this branch are still queued in the shared team build queue (confirmed with Vercel CLI). The running local dev server is http://localhost:4077/ko. The final PR diff changes no production runtime files.

Summary by CodeRabbit

• Tests
  • Added end-to-end coverage for locale switching, including URL, content, metadata, language direction, cookies, query parameters, and fragments.
  • Added verification that locale changes persist across nested routes and page reloads.
  • Removed an existing marketing navigation test.
• Developer Experience
  • End-to-end tests can now target an externally running server through configuration, while retaining local server support by default.

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Project	Deployment	Actions	Updated
cmux166	Ready	Preview	Sep 5, 2026 4:57am UTC
cmux41	Ready	Preview	Sep 5, 2026 4:57am UTC

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ℹ️ Recent review info

⚙️ Run configuration

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Review profile: ASSERTIVE

Plan: Team

Run ID: df1661f4-5005-4f2d-b474-210877997128

📥 Commits

Reviewing files that changed from the base of the PR and between ff2c115 and db2458f.

📒 Files selected for processing (1)

• web/e2e/instant/locale-navigation.instant.ts

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📝 Walkthrough

Walkthrough

Adds Playwright coverage for locale switching, nested-route preservation, reload behavior, and locale metadata. Adds an environment-controlled mode for running tests against an external web server. Removes overlapping marketing navigation coverage.

Changes

Locale navigation regression coverage

Layer / File(s)	Summary
Locale navigation regression tests web/e2e/instant/locale-navigation.instant.ts, web/e2e/instant/marketing-navigation.instant.ts	The new tests verify locale content, metadata, cookies, URL query and fragment state, nested routes, and reload behavior. The overlapping marketing navigation test is removed.
External Playwright server targeting web/playwright.instant.config.ts	Playwright uses CMUX_WEB_TEST_BASE_URL when set and otherwise retains the local server configuration.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to ff2c1

This change adds locale-navigation regression coverage and optional preview-server test targeting. It covers the reported stale-content behavior across multiple locales and reloads, with no current merge-blocking risk identified.

🚥 Pre-merge checks | ✅ 14 | ❌ 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%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (14 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes address [#11979] by adding regression coverage for Korean, Japanese, and Arabic locale switches, repeated navigation, cookies, URLs, metadata, headings, document language and direction, cl…
Out of Scope Changes check	✅ Passed	The changes remain within the issue scope. The new regression tests, replacement of overlapping test coverage, and external-server configuration directly support locale-navigation validation.
Cmux Swift Actor Isolation	✅ Passed	PASS — The PR range contains no Swift changes. The full diff from the mainline parent changes only web TypeScript test/config files, and the two production commits modify only `web/app/[locale]/compon…
Cmux Swift Blocking Runtime	✅ Passed	The pull-request diff changes only TypeScript Playwright tests and configuration. git diff HEAD^ HEAD -- '*.swift' is empty, so the PR introduces no production Swift synchronization, blocking wait, …
Cmux Browser Automation Off-Main	✅ Passed	PASS. The PR diff changes only web/e2e/instant/*.instant.ts and web/playwright.instant.config.ts. It does not modify Sources/TerminalController.swift, ControlCommandExecutionPolicy.swift, or a…
Cmux Expensive Synchronous Load	✅ Passed	PASS. The locale PR changes are confined to web TypeScript tests/configuration and do not add or move a Swift agent-history load. The changed Swift diff contains no RestorableAgentSessionIndex, `Sha…
Cmux Cache Substitution Correctness	✅ Passed	PASS. The submitted diff adds and updates Playwright E2E tests and test-server configuration only. It does not replace an authoritative read with a cached value in a persistence, history, undo, or sna…
Cmux No Hacky Sleeps	✅ Passed	No explicit hacky sleep condition is introduced. The locale runtime changes use navigation, cookie assignment, and a locale-driven router.refresh() state effect; they do not use sleep, timers, fix…
Cmux Algorithmic Complexity	✅ Passed	PASS. The commit changes only Playwright E2E tests and web/playwright.instant.config.ts; it changes no production Swift, TypeScript, JavaScript, shell, or runtime code. The added loops cover three f…
Cmux Swift Concurrency	✅ Passed	The pull-request diff relative to its merged mainline parent changes only web TypeScript test/configuration files. It contains no Swift paths or Swift concurrency constructs. Therefore, the Swift-spec…
Cmux Swift @Concurrent	✅ Passed	PASS: The pull-request diff from the merged mainline parent changes only TypeScript E2E files and web/playwright.instant.config.ts. It contains no Swift paths, @concurrent annotations, or `nonisol…
Cmux Swift Package Boundaries	✅ Passed	The custom check is not triggered. The PR net diff against its mainline parent contains only three web files: the locale-navigation Playwright test, the marketing-navigation test, and the Playwright c…
Title check	✅ Passed	The title clearly describes the main change: testing locale switches, cookie behavior, and hard reloads.
Description check	✅ Passed	The description provides a detailed summary, rationale, testing results, deployment context, and known unrelated failures. It omits the template’s demo video, review trigger, and checklist sections, b…

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• Commit unit tests in branch issue-11979-language-switcher-followup

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