# Grinding integration

## Current milestone: authored geometry, not playable grinding

The test course now owns seven named paths in `grind_world.rs`: two flat bars,
both half-pipe lips, and the three exposed platform edges. The downhill entrance
is not an edge, and triangle diagonals/transition tessellation are not splines.
Bar top centres and coping paths share the collision/render dimensions.
Climbing geometry from the other task is preserved.

`GrindGeometry` retains a relocatable Pegasus tSplineData blob. Its layout matches
the existing recomp's `owned/world/src/grind_spline.cpp`: 16-byte header,
32-byte rail records, 144-byte segments, signature `2C7017070007004A`, straight
segment delta at +0, origin at +48, inverse length at +64, bounds +80/+96,
length +112, cumulative length +116, and owner/previous/next +120/+124/+128.
IDs are stable host-authored integers, not guessed retail asset IDs.

This registry is not yet connected to contact acquisition or state selection.
Startup explicitly logs `native_acquisition=not_connected`. The game therefore
still treats the bars as ordinary collision geometry. Do not call this playable
grinding or replace the existing empty-edge providers with a proximity snap.

## Native integration audit

Evidence image: TU3 `default_82000000_011B0000.bin`, base `82000000`, SHA-256
`f4aa113eb541bfba03dbc108cf5ab43f58c965b20fa3b82f9c40938a0ad841c4`.
Community symbols plus generated PPC instruction comments were consulted.
The disposable IDA database's decompiler misdecodes some VMX128 operations;
its truncated pseudocode is not sufficient to port the nonempty branches.

- `82D8A828` GrindManager input update: constructs an AABB around processed
  position112 with half-extent1.2 (`821659F4`), unless byte2476 bit0 disables it.
- `82C1EAD8`: static asset/segment bounds collection, source order, maximum40;
  entries are48 bytes with endpoints and retained owner/flags. The final16
  bytes must not be invented as a surface normal.
- `82D875A8`: candidate acquisition/scoring. Dispatches truck/deck contact
  queries (`82C1FDC0`, `82C20130`, `82C1FB98`, `82C1F968`) before scoring. For
  example `82D89150` handles a two-truck candidate; it is not a nearest-rail
  angle classifier. Selection output has candidate byte384 in a416-byte record.
- `82C1E2C8` is now ported in core `physics/grind_contact.rs`: the exact
  segment/triangle leaf used by those truck/deck queries. It retains the
  zero-denominator rejection and closed0..1 bounds, unlike wheel probes with
  their endpoint tolerance. It does not itself accept a grind.
- `82D8AB08`: post-input manager publication precedes state selection.
- Native selector maps actual candidate grind type0..5 to states401,400,402,
  403,404,405. `player_state/selection.rs` currently publishes no candidate.
- Boardslide Enter `82D41100` calls shared grind entry `82D3F318`, then clears
  bytes240/241. Shared entry resets board controller settings, skeleton state
  and the grind manager; merely allowing state400 in transition.rs is unsafe.
- The active force/contact owner, output conditioner and graph attributes
  still need wiring. `player_state/publication.rs` currently uses default grind
  output; camera output has the same inactive assumption.
- Air acquisition also needs the nonempty trajectory path: `82D69F80`,
  `82D6A168`, `82D6A398`, `82D6A840` and GrindAirAdjust `82D712E0` onward.
  The clone's GRIND_CONTACT_SPEC explicitly leaves parts of this arbitration
  unresolved, so it cannot serve as a complete implementation.

Next implementation boundary: native endpoint/contact queries and candidate
record/scorer, then lifecycle/constraint/output integration as one coherent
vertical slice. Do not enable selector candidates before those owners exist.

Validation: build only; no gameplay or automated tests, per user instruction.

## 2026-09-07 collision and contact follow-up

The rail boxes were emitted with only ONE_SIDED. Native contact fixup82AD3130
rejects an edge-region contact when its convex bit is absent. Authored rail
faces now set the two perimeter-edge bits on each triangle and leave the
coplanar diagonal non-convex (0x60 /0xC0 for the existing triangle winding).
This change applies to rail/coping/support boxes only. Gameplay confirmation
is outstanding; a build does not establish that this explains every missed hit.

Core truck_contacts ports82C1FDC0's two local-board probe rectangles, using
TruckToWheel and DeckCenterToTruck, the -.02 start offset and -.20 depth,
first-triangle priority, strict squared-distance comparison and first-entry
tie retention. It remains a contact query, not an engagement decision.

Checked the task Research readable game recreation and its referenced
Skate3CustomEngineLayer/src/skate3_native_grind.cpp. That integration registers
splines in the original guest GrindData owner; it does not contain replacement
grind forces. Expand Skate 3 replay toolkit likewise supplies research and
capture infrastructure rather than a standalone grind controller.

The remaining native state/force and graph-attribute contracts are unresolved.
Do not advertise this build as grind-ready. Build log:
logs/grind-collision-build.log (successful,35 warnings); no tests executed.