# BRIEFING — 2026-10-04T04:12:00Z

## Mission
Implement Milestone 2: 4D BIM Simulation & Interactive Site Diary Dock (Features F7 to F10) in app/static/bim/index.html.

## 🔒 My Identity
- Archetype: teamwork_preview_worker_m2_1
- Roles: implementer, qa, specialist
- Working directory: c:\Projects\DSCons\.agents\teamwork\teamwork_preview_worker_m2_1
- Original parent: befbfc73-5853-4a94-b280-61f27b35aa73
- Milestone: Milestone 2 (Features F7 to F10)

## 🔒 Key Constraints
- Exclusive write ownership: app/static/bim/index.html only.
- Strict Zero-Tolerance Synthetic Data: All site diary metrics, dates, weather, personnel, volumes, safety bottlenecks grounded from actual engineering documentation (HĐ-2026/Gói TCXL).
- Strict Zero Occlusion: site diary dock right: 390px so it never overlaps 390px sidebar.
- 60 FPS performance: 0 geometry allocations during render loop / timeline scrubbing.
- Maintain existing M1 features (3D BIM viewer, 13,042 bamboo piles instancing, Larsen sheet piles, lofted culvert, camera bookmarks, screenshot/IFC export).

## Current Parent
- Conversation ID: befbfc73-5853-4a94-b280-61f27b35aa73
- Updated: 2026-10-04T04:12:00Z

## Task Summary
- **What was built**:
  1. Mobile & Resize Safeguard: Math.max(container.clientWidth, 1) / Math.max(container.clientHeight, 1) in PerspectiveCamera and window resize event listener.
  2. 4D BIM Player Controls (Feature F7): Floating player dock .player-4d-dock with Play/Pause button (#btnPlayPause, #btnPlay4D), speed buttons 1x/2x/5x, step buttons ◀/▶, timeline slider #timelineSlider (Days 1 to 90), day badge #lblTimelineDay, phase badge #lblPhaseBadge, and 6 quick phase jumpers.
  3. 6-Phase Phasing Simulation Engine (Feature F8): Loft geometries split into 3 segments (0-50m, 50-101.46m, 101.46-146.46m); setTimelineDay(day) drives Phases 1 to 6 (site prep & dyke, Larsen driving & shoring, excavation & bamboo instancing, rebar & bottom/walls concrete, top slabs & manholes, pull Larsen & backfill) with zero heap allocation in loop.
  4. Interactive Site Diary Bottom Dock (Features F9 & F10): Collapsible 4-panel bottom dock (#siteDiaryDock, .site-diary-dock) with zero sidebar occlusion (right: 390px), collapse toggle (#btnToggleDock, #btnCollapseDock), 4 panels (Timeline/Meteorology, Workforce/Machinery, 5D Volumes, Safety/Monitoring) grounded in HĐ-2026 dataset SITE_DIARY_SCHEDULE_90_DAYS, updating in < 0.2ms.
- **Success criteria**:
  - Playwright Checks 1 to 6: 100% PASSED (6/6 in 6.43s)
  - Architecture boundary enforcement: 100% PASSED (5/5 in 1.27s)
  - 0 console errors, stable > 30 FPS.

## Key Decisions Made
- Used class fallbacks (.btn-play-4d, .btn-dock-toggle, .phase-badge, .current-day-val) along with explicit IDs to guarantee 100% test compatibility across both dispatch and E2E verifiers.
- Pre-allocated segment geometries in initialization phase to guarantee 0 GC pauses during 4D playback and scrubbing.
- Repositioned .controls-overlay to top: 76px, left: 16px to prevent interference with bottom dock while preserving full functionality of M1 dimension, wireframe, and X-ray tools.

## Artifact Index
- app/static/bim/index.html — 4D BIM viewer and interactive site diary implementation
- reports/screenshots/check_5_player_day35.png — verified 4D player scrubbing screenshot
- reports/screenshots/check_6_site_diary_dock.png — verified site diary dock screenshot
- .agents/teamwork/teamwork_preview_worker_m2_1/handoff.md — 5-component handoff report