User-reported recurrence of "legs stutter and lose sync". Live [sync] showed
advSum/legSum drifting 5->92 during walk-up churn, then locking. Reproduced
headlessly (BT_FORCE_OSC throttle feathering + BT_FORCE_TURN + the new
per-frame BT_SYNC_LOG probe) and root-caused in two parts:
- SEED: the bring-up turn-in-place trigger arms only the LEG channel, so the
walk re-entry lands one frame apart -> a persistent clip phase offset.
- AMPLIFIER: with offset clips the two end-of-clip callbacks fire on different
frames; a demand change landing between them picks DIFFERENT next states
(one channel winds down, the other keeps walking) -> opposite-phase churn
(observed bs=6 ls=7 -- body on walk-R, leg on walk-L).
Under v4 (display+travel = BODY) the out-of-phase LEG pose showed through on
every frame the body didn't write joints (Standing/wind-down) = the visible
stutter/pop.
DISASM GROUND TRUTH (neither Advance fn has a static decomp caller; found by
byte-scanning the CODE section for e8 calls):
- master perf (0x4a9b5c gap) -> AdvanceLegAnimation @0x4aa399 (air @0x4aa388)
-> -dist/dt into localVelocity (+0x1cc): the LEG drives LOCAL travel and
(writing last) the displayed pose;
- IntegrateMotion (0x4ab1c8, body advance @0x4ab312, caller FUN_004ab430 =
the projected-origin updater) -> -dist/dt into projectedVelocity (+0x2a0):
the BODY is the dead-reckoning PROJECTOR -- locally invisible.
v4's reading of FUN_004ab430 as the travel source was wrong.
FIX: advance body FIRST (projection; its writes get overwritten), leg LAST
(displayed pose); travel = legAdv under the two-channel split. Display ==
travel through the LEG by construction -- body-channel drift can no longer
become visible, structurally (not by input-symmetry luck).
Verified: trn+feathering repro clean; straight drive locked (adv==proj);
solo goto=enemy kill chain intact; MP 2-node drive-to-range cross-pod kill
intact (241 hits, DESTROYED); no crashes. KB corrected (locomotion.md roles
+ P3_LOCOMOTION.md v5 entry). New gated instruments: BT_SYNC_LOG,
BT_FORCE_OSC.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
