The discriminating user report: peer motion was smooth under the autonomous
harness but skipped when driven by KEYBOARD -- even pure walking / pure spinning.
The harness pins throttle/turn constant; the keyboard SWEEPS the throttle lever
every frame of a key-hold (mech4 sLever integrator), so mapper->speedDemand
changes every frame, and the speed-deadband gate (authentic exact !=) fires a
type-2 speed record EVERY FRAME for the whole accel/decel. The base reader
Simulation::ReadUpdateRecord stamps lastUpdate=Now() on EVERY record (flagged
'HACK - should be based upon message->timeStamp' in the 1995 source) -- so each
type-2 SHRINKS the peer reckoner's projection span (nextUpdate-lastUpdate)
without refreshing updateOrigin: the position target jumps backward toward the
stale origin, the next pose record yanks it forward -> target oscillation every
frame during any input sweep. Matches the session-long 'worst on accel/decel'.
FIX (mech.cpp Mech::ReadUpdateRecord): non-pose records (2,3,5,6,7,8) preserve
lastUpdate around the base call (keeping the real payload, simulationState).
Pose (0) and resync (4) keep their authentic clock behavior. BT_T2_CLOCK
restores the old stamping for A/B.
REPRO HARNESS (mechmppr.cpp): BT_FORCE_SWEEP=<period> triangle-sweeps the forced
throttle 0.2..0.9 -- a type-2 record per frame, the keyboard-skip repro the
constant-throttle harness could never produce.
Verified A/B, autonomous circle+sweep (the keyboard regime):
old clock: worst frame spike 10.4x avg, path/net ratio 1.069 (backtracking)
guarded: worst 4.6x, ratio 1.0022 (no backtracking)
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
