docs(theme): record deterministic state evidence

2026-08-09 18:37:52 +02:00
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+# UX-002 deterministic theme state
+
+Updated: 2026-08-09
+
+Status: `IMPLEMENTED — NOT VERIFIED`. Automated, build and local browser checks pass. Production and authenticated multi-user browser checks remain.
+
+## Confirmed root cause
+
+The theme preference was keyed by the last `authUserKey`, but login completion emitted the general authentication event before `/auth/me` stored the new user key. `Shell` then stored that key with event emission disabled. Theme state therefore continued using the anonymous preference until a refresh, when the user key was already present and the page appeared to switch theme randomly. Logout had a similar asynchronous boundary.
+
+Theme changes also keyed `CssVarsProvider` and captured `themeMode` in the router memo. A preference change remounted the provider and recreated the router, risking loss of in-page state even though the URL did not intentionally change. MUI also retained its own default local-storage mode, creating another potential source of truth.
+
+## Implemented contract
+
+- Preference resolution is explicit user key, then anonymous preference for a user without a saved choice, then the documented `System` default.
+- Explicit Light and Dark ignore operating-system changes. Only System resolves through the current media query.
+- Auth user-key changes have a dedicated event. It updates theme state without re-running authentication requests or creating an event loop.
+- Relevant `storage` events update another tab without writing back. Unrelated storage events are ignored.
+- MUI mode is changed in place through its color-scheme context with its private persistence disabled. The app/router tree is not keyed or recreated by theme changes.
+- A Next `beforeInteractive` bootstrap applies the same user/anonymous/System resolution before client application paint.
+- Settings tabs are scrollable at narrow widths; this removes the mobile overflow discovered during the required theme browser pass.
+
+No backend, database, dependency, entitlement or production configuration changed.
+
+## Verification
+
+- Focused deterministic theme suite: 6/6.
+- Full frontend: 48/48 suites and 172/172 tests.
+- Production frontend build/TypeScript and `git diff --check`: pass.
+- Browser: explicit Light persisted across Settings → Dashboard navigation and refresh; explicit Dark switched without navigation; System selected the browser's dark preference; a second tab inherited Dark and changing it to Light updated the first tab without reload.
+- Browser widths: 375, 768 and 1440; document width did not exceed the viewport after the tabs correction. Light 375/768 and Dark 1440 evidence is retained.
+- Browser console warnings/errors after the final interactive pass: none. Development HMR emitted transient module-update messages while source files were being edited; they were not present in the captured tab diagnostics and the clean production build passes.
+
+## Remaining gates
+
+- Authenticated User A/User B scoped preference switching was proven at the storage/event unit boundary but not with two live browser accounts because no isolated API authentication environment was running.
+- A real operating-system preference-change event was tested at the resolver/provider boundary, not by changing the host OS during browser automation.
+- Production deployment/browser smoke is not authorized/configured.
+
+## Evidence
+
+- Screenshots: `docs/audits/evidence/ux-002/`
+- Commands/results: `docs/audits/verification-log.md` V-111–V-113
+- Tests: `job-tracker-ui/src/theme-state.test.tsx`
+- Implementation commit: `11734ee`
+
+## Rollback
+
+Revert `11734ee`. No data migration is required; existing `themeMode:<user>` and `themeMode:anon` values remain compatible. Reversion restores the prior delayed-login theme and provider/router remount behavior.