docs: session handoff + collision port mandate in memory

Session 2026-04-14 summary: rendering rebuild complete, movement
speed+jump+facing working, collision partially working but needs
full retail port.

Memory updated with explicit user feedback: no more patching
collision, must port from decompiled code faithfully per CLAUDE.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

memory/project_session_2026_04_14.md

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+# Session Handoff — 2026-04-14
+
+## What shipped this session
+
+### Rendering rebuild (5 steps, all complete)
+- Step 1: Instanced mesh rendering (DrawElementsInstanced, 800+ FPS)
+- Step 2: Terrain chunk batching (16×16 ACME-style chunks)
+- Step 3: AdjustPlanes lighting (ACME constants)
+- Step 4: EnvCell portal visibility (BFS, conditional depth clear)
+- Step 5: Animation already in instanced pipeline
+
+### Movement (Layer 1 — working)
+- Run speed from PlayerWeenie RunRate formula (Run skill 200 → 9.5 m/s)
+- Charged jump with proper physics arc + server packet (0xF61B)
+- Facing direction quaternion convention (AC heading via holtburger)
+- Jump apex velocity zeroing bug fixed (SmallVelocity threshold)
+- Airborne momentum preservation (no velocity replacement while jumping)
+
+### Collision (partially working — needs full rewrite)
+- ShadowObjectRegistry cell-based spatial index
+- PhysicsDataCache stores GfxObj BSP + Setup CylSphere + CellStruct BSP
+- BSPQuery with 6-path dispatcher (attempted but incomplete)
+- CylSphere collision for trees/rocks
+- SlideSphere crease-projection for wall sliding
+- Multiple bug fixes (broad-phase, push-out, corner stuck, safety margins)
+
+### Infrastructure
+- docs/bugs.md for tracking known issues
+- Movement completion design spec + implementation plan
+
+## What did NOT work
+
+The collision system was built by patching symptoms instead of porting
+the retail code faithfully. After ~10 iterations of fixes, it handles
+~60-70% of cases but still clips through some buildings, trees, and
+objects. The user explicitly requested a full retail port — no shortcuts.
+
+## Build/test state
+- `dotnet build`: green, 0 errors
+- `dotnet test`: 470 passed (361 core + 109 net), 0 failures
+- All commits on main
+
+## What to do next
+
+**PORT THE RETAIL COLLISION SYSTEM FROM SCRATCH.**
+
+The full plan is in `memory/project_collision_port.md`. The approach:
+
+1. Read the decompiled function (ground truth)
+2. Cross-reference ACE's C# (naming aid)  
+3. Write pseudocode
+4. Port line-by-line to C#
+5. When ACE and decompiled disagree, decompiled wins
+
+### Files to port (ACE → acdream):
+- `Sphere.cs` → sphere-vs-sphere collision dispatcher (FUN_005387c0)
+- `BSPTree.cs` → find_collisions 6-path dispatcher
+- `BSPNode.cs` / `BSPLeaf.cs` → BSP traversal with movement
+- `Polygon.cs` → pos_hits_sphere with FindTimeOfCollision
+- `Transition.cs` → FindTransitionalPosition, TransitionalInsert
+- `SpherePath.cs` → sphere state management
+- `LandCell.cs` → outdoor terrain collision
+- `EnvCell.cs` → indoor room collision
+- `ObjCell.cs` → object collision + cell enumeration
+
+### What to keep:
+- CollisionPrimitives.cs (9 functions, faithfully ported from decompiled)
+- PhysicsDataCache.cs (dat loading — correct)
+- ShadowObjectRegistry.cs (cell bucketing — correct concept)
+- PhysicsBody.cs, MotionInterpreter.cs, PlayerWeenie.cs (correct)
+
+### What to replace:
+- BSPQuery.cs — simplified, not retail-faithful
+- TransitionTypes.cs Transition methods — patched, not retail-faithful
+- PhysicsEngine.ResolveWithTransition — may need restructuring