User repro (100%): turn in place, push forward before the turn stops -> the gait
skips/stutters + visibly reduced bob; standstill starts always clean. Three-layer
fix, user-verified:
1) THE DISPLAY BUG (the actual visible artifact): v5's "body advances first with
mj=1, leg overwrites last, so body drift can't show" was FALSE. Whenever the two
gait channels phase-split, the BODY channel's out-of-phase joint writes leaked
into the rendered skeleton (rhythmic leg skips, averaged-down bob) while every
leg-channel trace read clean -- the leg DATA was fine, the RENDERED pose wasn't
the leg's. v6: AdvanceBodyAnimation(dt, mj=0) -- the body still advances +
projects for replication (records/cycle speeds unchanged) but no longer touches
the skeleton. One writer, structurally; matches the binary's own observable
("body phase drift is locally INVISIBLE in the binary"). BT_BODY_MJ=1 = old A/B.
2) THE SPLIT SEED: the bring-up trn trigger armed only the LEG channel, so a
turn-in-place entry guaranteed the channels re-entered walk frames apart and the
walk cycles ran permanently out of phase. Lockstep: the Standing trn entry arms
BOTH channels the same frame (body case-4 twin added, same rate/keying), gated on
both Standing. The authentic dispatcher (un-decompiled master-perf gap 0x4a9b5c-
0x4ab188, the sole reader of turnDemand/turnCapable) armed both -- the body's
case-4 machinery is dead code otherwise [T1].
3) THE POSE-MATCH INVARIANT: the engine has NO pose blending; transitions avoid
pops purely by authored pose-matched boundaries. The old trn exits cut the pivot
clip MID-STEP (legFrm 7->1 teleport). Now: entry gated on near-zero speed
(turn-IN-place); on forward command the pivot FAST-FORWARDS to completion (x4)
and the authentic finish callback lands Standing at the stand pose -> the normal
pose-matched stand->walk runs. Decompiled reverse abort kept; the standSpeed
mid-clip abort subsumed (it WAS the pose cut). [T3: 0.25*standSpeed threshold +
4x rate stand in for the gap's constants.]
Harness: BT_FORCE_TURN now reaches gBTDrive.turn (was silently inert for the
gait), BT_WALK_DELAY=<s> holds forced throttle then ramps (the turn-first repro),
BT_GAIT_TRACE=1 per-frame gait trace. Regressions: standstill start, turn-entry,
pure pivot loops, run cycle -- all clean, bob full amplitude (1.33/1.32).
KB: locomotion.md v6 section + trn reconstruction + symptom-family closure.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
