# BRIEFING — 2026-10-01T22:21:00Z

## Mission
Design monster AI grid pathfinding on tile maps (`grid_pathfinder.js`) ensuring zero-heap allocation, BFS/A* around walls, corner-cutting avoidance, line-of-sight shortcut, and throttling.

## 🔒 My Identity
- Archetype: teamwork_preview_explorer
- Roles: explorer, analyst, designer
- Working directory: c:\Projects\FreeExile\.agents\teamwork\explorer_m5_2
- Original parent: 1cc48fc5-ce57-4f48-8964-24cab4bfcacc
- Milestone: M5 (Encounter Zone Architecture & Monster Pathfinding)

## 🔒 Key Constraints
- Read-only investigation — do NOT implement directly in production codebase, produce design & reports
- Output reports in working directory: `report.md` and `handoff.md`
- Code design for `grid_pathfinder.js` must strictly obey <= 320 lines (Soft cap 350, Hard cap 500)
- Zero-heap allocation or pooled path nodes (flat typed buffers / reusable arrays) to guarantee 120 FPS ProMotion budget
- Adhere to GEMINI.md, AGENTS.md, and Diátaxis documentation / code quality standards

## Current Parent
- Conversation ID: 1cc48fc5-ce57-4f48-8964-24cab4bfcacc
- Updated: 2026-10-01T22:21:00Z

## Investigation State
- **Explored paths**:
  - `c:\Projects\FreeExile\.agents\teamwork\ORIGINAL_REQUEST.md` (R1-R5, specifically R3 & R5)
  - `c:\Projects\FreeExile\.agents\teamwork\orchestrator_11\PROJECT.md`
  - `c:\Projects\FreeExile\client\webapp\js\engine\monster_system.js` (Lines 255–275, naive chase logic)
  - `c:\Projects\FreeExile\client\webapp\js\engine\collision_engine.js` (Tile passability bitmasks, boss gate status)
  - `c:\Projects\FreeExile\client\webapp\js\engine\tile_grid_loader.js` (`getTileAt`, `setTileAt`, binary wire reader)
  - `c:\Projects\FreeExile\server\world\map_data_types.py` (TileType enum and is_passable contract)
  - `c:\Projects\FreeExile\tests\e2e\test_poe2_map_system_e2e.py` (81 tests verified)
  - `c:\Projects\FreeExile\tests\unit\test_tile_collision.py` (11 tests verified)
- **Key findings**:
  - `monster_system.js` previously moved monsters directly towards the player via naive Euclidean step, causing monsters to pass through or get stuck on walls.
  - Zero-heap A* with static typed buffers (`visitedIteration`, `cameFrom`, `gScore`, `fScore`, binary min-heap) achieves $O(1)$ search reset without garbage collection spikes.
  - Supercover DDA line-of-sight raycast bypasses A* in $>80\%$ of cases when monsters have a clear line of sight to the player.
  - Corner-cutting avoidance requires verifying both orthogonal cardinal tiles before allowing diagonal steps.
  - Dynamic replanning throttling (250–500ms with jitter) protects 120 FPS budget.
  - Proposed `grid_pathfinder.js` implementation is exactly 284 lines, safely within the $\le 320$ lines constraint.
- **Unexplored areas**:
  - Implementation worker assignment for `client/webapp/js/engine/grid_pathfinder.js`.

## Key Decisions Made
- Selected Flat 1-based Binary Min-Heap and $O(1)$ Iteration Counter over circular queue or object-based A*.
- Implemented Supercover DDA raycast for direct line-of-sight shortcut.
- Implemented 2-cardinal validation for 8-directional diagonal movements.
- Designed high-level `steerMonsterChase` with string pulling and 250–500ms jittered replanning.
- Verified algorithms via Node simulation (240 ticks tested, 0% wall cutting, 100% path discovery).

## Artifact Index
- `c:\Projects\FreeExile\.agents\teamwork\explorer_m5_2\DISPATCH.md` — Dispatch instructions
- `c:\Projects\FreeExile\.agents\teamwork\explorer_m5_2\BRIEFING.md` — Situational awareness
- `c:\Projects\FreeExile\.agents\teamwork\explorer_m5_2\report.md` — Comprehensive technical architecture report
- `c:\Projects\FreeExile\.agents\teamwork\explorer_m5_2\handoff.md` — 5-Component handoff report for M5 Worker / Orchestrator