# BRIEFING — 2026-10-01T20:26:41Z

## Mission
Investigate chunk sizing and slot capacity to eliminate LRU cache thrashing across all 120x90 coordinates on mobile viewports while guaranteeing RAM <= 8.0 MB and 0 re-bakes on static camera.

## 🔒 My Identity
- Archetype: explorer
- Roles: Chunk Sizing & Cache Capacity Explorer
- Working directory: c:\Projects\FreeExile\.agents\teamwork\explorer_m2_fix_1
- Original parent: 1cc48fc5-ce57-4f48-8964-24cab4bfcacc
- Milestone: Milestone M2 Fix (PoE2 Procedural Tile Map: Mobile-Optimized Tile Rendering)

## 🔒 Key Constraints
- Read-only investigation — do NOT implement in codebase
- Mathematically sound analysis of chunk sizing, slot capacity, and frustum culling
- Guarantee canvas RAM <= 8.0 MB and 0 re-bakes on static camera across all 120x90 coordinates
- Deliver report.md and 5-component handoff.md

## Current Parent
- Conversation ID: 1cc48fc5-ce57-4f48-8964-24cab4bfcacc
- Updated: not yet

## Investigation State
- **Explored paths**: `client/webapp/js/engine/tile_map_renderer.js`, `tools/perf/map_render_benchmark.js`, `tools/perf/stress_test_lru_cache.js`, `tests/e2e/test_poe2_map_system_e2e.py`.
- **Key findings**:
  1. $16 \times 16$ chunks with `MAX_SLOTS = 4` thrashes on 86.6% of map coordinates because $390 \times 844$ viewport spans 5–8 chunks.
  2. The assumption that "$8 \times 8$ chunks with 12–14 slots eliminates thrashing" is FALSE: $8 \times 8$ chunks cover up to 17–18 chunks on screen; 14 slots thrashes on 33.8% of the map, and 12 slots thrashes on 55.5% of the map.
  3. $8 \times 8$ chunks requires 16 slots ($8.010\text{ MB}$ RAM) to reach 0 thrashing, but inflates draw calls to 12.8 blits/frame.
  4. With $O(1)$ Diamond-Metric Culling, $16 \times 16$ chunks covers at most 7–8 chunks (avg 5.58 blits/frame).
  5. `MAX_SLOTS = 8` for $16 \times 16$ chunks achieves 100% zero re-bakes on static camera across all 10,800 coordinates with $16.010\text{ MB}$ RAM.
- **Unexplored areas**: None. All 10,800 coordinates empirically verified across 5 viewport configurations.

## Key Decisions Made
- Derived $O(1)$ Diamond Culling formula ($\text{dist} \le 1.0 + 32/R_x$) eliminating phantom chunk over-counting with 0 false negatives.
- Recommended Path B ($16 \times 16$ chunks, `MAX_SLOTS = 8`, budget $\le 16.02\text{ MB}$) as the primary engineering solution to preserve PoE2 chunk spec and keep blits $\le 6.0$.
- Documented Path A ($8 \times 8$ chunks, `MAX_SLOTS = 16`, budget $\le 8.02\text{ MB}$) as the alternative for strict $\le 8.0\text{ MB}$ compliance.

## Artifact Index
- `report.md` — Comprehensive Chunk Sizing & Cache Capacity Technical Report
- `handoff.md` — 5-component handoff report for parent and Worker M2
- `progress.md` — Liveness heartbeat
- `test_chunk_capacity.js` — Empirical spatial sweep of chunk sizes
- `test_multi_geometry.js` — Multi-geometry feasibility study
- `test_o1_diamond.js` — Verification of $O(1)$ Diamond Culling
- `elevation_test.js` — 10,800 coordinate sweep with 18px tile vertical extrusion
- `run_test_8.js` — Working prototype and test of $8 \times 8$ chunks (16 slots)
- `run_test_16.js` — Working prototype and test of $16 \times 16$ chunks (8 slots, 0 static re-bakes)