Issue #269 — slope-stop capture and retail correction

Date: 2026-07-31 Status: implemented; user live gate passed Scope: landing-bounce follow-up, CTransition::validate_transition

Symptom

After the retail 5%-elasticity landing reflection was restored for #265, the character could retain too much downhill speed after landing on a walkable slope. The user described the residual as “slides too far on landing.”

ACDream live capture

ACDREAM_CAPTURE_PLAYER_QUANTA=<jsonl-path> records the local player's complete admitted object quantum without changing simulation order:

quantum start;
root/PositionManager composition;
pre- and post-UpdatePhysicsInternal;
transition result;
final collision-response commit.

The accepted repro contained 2,184 quanta. The clearest landing was:

Quantum	Event	Velocity
1740	final airborne quantum	`(-12.316, 8.187, -26.266)`
1741	slope collision, normal `(-0.236, 0.236, 0.943)`
1741 post-response	correct 5% reflect	`(-17.391, 13.262, -6.576)`
1742–1758	still Contact + OnWalkable, no new collision normal	velocity unchanged
1759+	contact relationship changes	friction finally begins decaying

The reflected velocity had dot(v, normal) = +1.0252: it pointed away from the slope. Retail calc_friction correctly skips while this value is at least 0.25, so friction was not the defect. ACDream was repeatedly restoring the remembered slope plane and re-grounding the body without performing retail's accompanying velocity stop.

Retail oracle

Named-retail:

CPhysicsObj::check_contact 0x0050F5B0
CPhysicsObj::get_object_info 0x00511CC0
CTransition::validate_transition 0x0050AA70
OBJECTINFO::kill_velocity 0x0050CFE0

The exact validate_transition order at 0x0050AAED–0x0050AB42 is:

enter only for a non-OK collision/adjusted/slid result;
if last_known_contact_plane_valid, call OBJECTINFO::kill_velocity;
test the current sphere center against the remembered plane using radius + 0.0002;
restore the contact plane only when still within that distance;
later, at 0x0050ACFF, overwrite last-known validity with final contact-plane validity.

OBJECTINFO::kill_velocity calls CPhysicsObj::set_velocity({0,0,0}, 0). ACDream had ported the proximity test and plane restore but omitted this call. It also allowed the last-known plane to re-ground clean accepted moves, although retail only consumes it in the non-OK recovery branch.

Correction

Transition.ValidateTransition now:

calls ObjectInfo.StopVelocity() before the remembered-plane proximity/restore test on a non-OK recovery;
performs that restore only in the retail branch;
overwrites last-known validity from final contact validity, so a clean move away cannot be re-grounded from stale memory.

The existing PhysicsEngine.ResolveWithTransition consumption of VelocityKilled applies the zero to the canonical PhysicsBody before the collision-response tail. The initial 5% landing reflection remains; only a following collision recovery performs the retail stop.

Gates

New focused pins:
- collision recovery with a remembered plane kills velocity;
- clean advance with a remembered plane neither kills nor re-grounds.
Full AcDream.Core.Tests: 4,107 passed / 2 skipped.
Full AcDream.Runtime.Tests: 439 passed.
AcDream.App Release build: 0 warnings / 0 errors.
Complete Release suite: 10,061 passed / 5 skipped / 0 failed.
User live gate: PASS — repeated slope jumps now settle correctly (“Perfect! Works great!”).

Diagnostic tools retained

tools/analyze_269_slope_stop_capture.py
tools/cdb/run-issue269-slope-stop.ps1
tools/cdb/issue269-slope-stop.cdb

The cdb runner refuses to attach unless the live retail executable matches the Sept 2013 named PDB. The locally installed 2015 retail executable does not match; the static named-retail decode above is therefore the retail oracle used for this correction.

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