Capture bisect (docs/research/2026-07-30-265-capture-bisect.md, mined
from artifacts/matrix-session2-resolve.jsonl records 3415-3434) traced
#265's lost roof slides / permanent landing freeze and #166's missing
downhill sled to a pre-existing (2026-07-20, ten days before Campaign P
- not a regression) mechanism in PlayerMovementController.cs's grounded
quantum block: it hand-zeroed Velocity.X/Y to exactly zero every tick
once OnWalkable whenever animation root motion drives the walk (the
production graphical local-player path), discarding any residual
horizontal momentum a fall left on the body before calc_friction
(AP-7/AD-55, already correctly ported) or PhysicsBody.
UpdatePhysicsInternal's Euler integrator ever got a chance to act on it.
Two changes:
1. PhysicsEngine.cs now syncs body.GroundNormal (the vector
calc_friction dots velocity against, per retail
CPhysicsObj::calc_friction 0x0050ee70's `contact_plane.Normal` read)
from the committed ContactPlane.Normal at the same commit point that
already publishes ContactPlane. GroundNormal had zero production
writers before this and silently defaulted to Vector3.UnitZ forever
- even surviving velocity would have been tested against a fake
flat-ground normal on any real slope. Core-level, so player, remote,
ordinary, and projectile movers all benefit uniformly.
2. PlayerMovementController.cs's grounded block no longer reconstructs
Velocity at all for the animation-root-motion case (only the
headless/test-controller get_state_velocity fallback still does,
unchanged). Root motion continues to fully own commanded locomotion;
this only stops destroying whatever Velocity already holds, letting
it compose with root motion through the same ResolveWithTransition
sweep exactly as retail's CPhysicsObj::UpdatePositionInternal
composes both channels.
Symptom (a), the uphill-jump bounce, traces to a SEPARATE, byte-exact
(re-verified against acclient_2013_pseudo_c.txt:282647-282760),
already-closed retail mechanism (AD-25, PhysicsObjUpdate.
HandleAllCollisions's shouldReflect gate) - confirmed orthogonal to this
fix, not addressed here (see the research doc's as-fixed addendum §9.5).
Issue265SteepSlopeCaptureBisectTests.cs gains a composed harness
(ReplayRealRoofLandingComposed) mirroring PlayerMovementController.cs's
per-tick composition against Core types only, proving: the old model
reproduces the mined freeze exactly; the new model survives the landing
and slides continuously (the real captured geometry glides at constant
velocity per retail's own dot>=0.25 early-return - AP-7); a synthetic
dot<0.25 case shows genuine exponential decay via calc_friction; and a
synthetic uphill-bounce case proves the fix changes nothing about
HandleAllCollisions's reflection decision.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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