Add Vitest test harness and first batch of logic tests

[fwextensions]

Summary

QuicKey has had no automated tests, in part because it drives interactive Chrome behavior that's hard to exercise headlessly. But almost all of the critical logic — the recent-tabs state machine, the storage migration/locking layer, and the worker↔popup control handoff — is plain code reachable with fakes. This adds a Vitest harness and a first batch of tests covering exactly those areas.

Notably, this batch reproduces three of the four bugs fixed this week as failing tests, so you can watch them go green as the fixes merge.

Harness (test/support/, test/setup.js, vitest.config.js)

• An in-memory chrome.* fake with real storage.local semantics (get(null)/get(key)/get(array)) and dispatchable event hubs.
• A navigator.locks fake with real FIFO queuing — a lock is held until its callback's promise settles, then the next waiter is granted on a microtask — so the storage mutex and the __control__ handoff can be driven deterministically.
• A faithful quickey-storage get/set stand-in that mirrors the real merge-and-save rule (a task returning undefined saves nothing — which is how the getAll no-op is observable).
• Setup that installs the globals the source reads (chrome, navigator, location, DEBUG) and stubs the analytics trackers (no GA network, no import-time await).
• Aliases mirror webpack.config.js (@/, lodash→lodont).

Two suites

Script	Runs	Status on this branch
npm test	test/unit/	green (29 tests)
npm run test:regression	test/regression/	4 failing, by design
npm run test:all	everything	29 pass / 4 fail

Green suite (test/unit/) — behavioral coverage that passes on dev: debounce semantics (including execute(waitForNext)), the recent-tabs add/remove/replace/toggle/updateAll state machine (recency order, penultimate insert, MaxTabsLength trim, URL→id remap on restart), and createStorage get/set, concurrent-write serialization under the lock, the migration chain, and reset-on-invalid.

Regression suite (test/regression/) — each test asserts the fixed behavior of a bug still present on dev, so it fails here and turns green once the fix lands:

Test	Documents	Fixed by
recent-tabs-getall	getAll() never persists refreshed recents (() => { tabsByID } is a no-op)	#139
abortable-promise-leak	abort listener leaked per AbortablePromise	#139
control-thenable	claimWhenAvailable awaits the task, so a promise-returning task holds the lock forever	#141
control-handoff	events arriving during the control gap are dropped, never replayed	#141

I verified the full loop locally: with the actual #139 and #141 branch changes applied, all four regression tests pass and the green suite stays green. test/README.md documents the convention — when a fix PR merges, move its now-passing regression test into test/unit/.

Follow-ups (not in this PR)

• The storage rewrite-skip optimization from Fix IPC memory leak and speed up service worker cold start #139 (don't re-save when the version is unchanged) isn't yet covered — it's a perf change rather than a correctness bug, and asserting it cleanly needs spying on the unawaited init writes. Worth adding to the storage suite later.
• There's no CI yet. A small GitHub Actions workflow running npm test on PRs would turn this green suite into an actual merge gate.

Testing

• npm test → 29 passed. npm run test:regression → 4 failed as designed (clean assertion/race failures, no import or harness errors).

🤖 Generated with Claude Code

https://claude.ai/code/session_01Hbx1WJrE7jYxhyvNZ2oLqK

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