# Movement & Collision Conformance Crib

## Phase

Active phase: **L.2 - Movement & Collision Conformance**.

Plan: `docs/plans/2026-04-29-movement-collision-conformance.md`.

Roadmap: `docs/plans/2026-04-11-roadmap.md`.

## One-Sentence Framing

B.3 shipped the MVP resolver foundation; L.2 is the holistic conformance
program for physics, collision, buildings, edge/wall sliding, cell ownership,
movement packets, and server correction.

## Active Movement Spine

```text
InputDispatcher / PlayerMovementController
  -> MotionInterpreter + local body prediction
  -> PhysicsEngine.ResolveWithTransition
  -> TransitionTypes + BSPQuery + ShadowObjectRegistry
  -> ResolveResult contact/cell state
  -> MoveToState / AutonomousPosition outbound messages
  -> WorldSession server echo or correction diagnostics
```

## Lane Ownership

- L.2a: truth probes, diagnostics, fixture capture.
- L.2b: movement wire/contact truth, cell id on packets, correction handling.
- L.2c: transition parity, edge-slide, cliff-slide, precipice-slide,
  `NegPolyHit`.
- L.2d: `CSphere` / `CCylSphere`, live entity shapes, building object identity.
- L.2e: outdoor seams, `CELLARRAY`, `find_cell_list`, adjacent-cell checks,
  `cell_bsp`, building entry/exit boundaries.
- L.2f: real-DAT fixtures and live retail-observer conformance.

## Non-Negotiables

- Grep named retail before changing AC-specific physics or movement behavior.
- Do not treat ACE accepting a position as proof of retail collision parity.
- Do not reintroduce rewrite-from-zero collision guidance. Continue the partial
  retail port by L.2 lanes.
- G.3 dungeon/portal delivery waits on L.2e for trustworthy cell/building
  ownership.
- L.1 animation work must coordinate with L.2 when root motion or observer
  movement changes the predicted body path.

## Shipped Slices

- 2026-04-29: L.2a/L.2b first diagnostic slice. `ACDREAM_DUMP_MOVE_TRUTH=1`
  logs `move-truth OUT` for outbound `MoveToState` / `AutonomousPosition` and
  `move-truth ECHO` for player `UpdatePosition` echoes, including local/server
  delta. `GameWindow` now passes explicit grounded/airborne contact bytes from
  `MovementResult.IsOnGround` to both movement packet builders.
- 2026-04-29: L.2e first cell-ownership fix. `ResolveWithTransition` refreshes
  outdoor cell ownership from world position during the sphere sweep, so 24m
  outdoor seams update low cell ids and full-cell callers crossing landblock
  seams get the destination landblock prefix plus the correct outdoor low cell.
- 2026-04-30: L.2c edge-slide plumbing. User live-tested wall-adjacent slide as
  acceptable. Local player and remote dead-reckoning now pass retail-default
  `ObjectInfoState.EdgeSlide`; `ACDREAM_DUMP_EDGE_SLIDE=1` logs failed
  step-down edge cases so the next slice can distinguish missing walkable
  polygon context from cliff-slide/NegPolyHit gaps.