Stability checkpoint stable-v1.0.28 (UI) — Phase 4.2 wave continued: 11 TelemetryService tests covering all 4 log methods (debug/info/warn/error), Activity timeline integration on errors only, 500-event history cap, clear() scope, append-only chronological ordering. Cumulative UI Phase 4.2 across v1.0.23-28: 100 new UI tests across 8 specs. All 7 untested core UI services from start of session now covered: ActivityService, DeepLinkService, FeatureFlagService, PipelinesService, KeyboardService, Auth0BridgeService, TelemetryService. Post-merge main pipeline #390 SUCCESS.