[Test Improver] Add unit tests for wm store (window manager)

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Goal and Rationale

Add unit tests for shell/store/wm.ts — the Vuex store powering the window manager panel (tabs, positions, pinning, dimensions). This store has zero existing test coverage despite containing complex, conditional logic for:

• Tab deduplication and default-value injection on addTab
• Position fallback from localStorage (pin key) when no position is supplied
• Forced-BOTTOM pinning when lockedPositions is set
• Multi-tab active-state reconciliation on switchTab and closeTab
• localStorage persistence for panel dimensions and pin preferences
• Guard-throw semantics on both open and close actions

Approach

Direct mutation/getter/action calls against a plain state object — no full Vuex store needed, matching the pattern used in cookies.test.ts and catalog.test.ts.

window.localStorage is replaced with a per-test in-memory mock (same pattern as dynamic-content/__tests__/index.test.ts) so setItem/getItem calls can be asserted without touching disk state.

Layout const-enum values are referenced as their underlying string literals ('default', 'home') to avoid isolatedModules const-enum inlining issues at test time.

Coverage Impact

Metric	Before	After (wm.ts only)
wm.ts — statements	0 %	~100 %
wm.ts — branches	0 %	~95 %
wm.ts — functions	0 %	100 %

58 new tests, zero pre-existing tests modified.

Trade-offs

• Tests call mutations/getters directly rather than through createStore. This is intentional: it keeps tests fast, focused, and free of Vuex plumbing noise. The store module's logic is self-contained.
• The state() factory's localStorage.getItem calls are exercised by the localStorage mock — no special initialisation tricks required.

Reproducibility

# Run just this test file
YARN_IGNORE_ENGINES=true NODE_OPTIONS=--max_old_space_size=8192 yarn test:ci --testPathPattern="shell/store/__tests__/wm.test.ts"

# Run the full suite
yarn test:ci

Test Status

✅ 58 / 58 tests pass
✅ ESLint clean (--max-warnings 0)
✅ No pre-existing tests broken

Warning

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