The BT keyframe-animation player embedded in the Mech as legAnimation/
bodyAnimation. Struct field layout (from BT411's binary-offset map), default
ctor, dtor, and Init(Mech*) reconstructed and compile-verified; Init is
ctor-time (Mech ctor calls legAnimation.Init(this)/bodyAnimation.Init(this)) so
it's real (binds owner + caches owner->GetJointSubsystem()). The per-frame gait
engine (SelectSequence/Advance/Reset) is staged with Fail bodies -- it fires
only once the mech is ticking, past the current ctor frontier.
BT stage 23 ok; full tree still links clean. Evidence + real/staged split in
SEQCTL.NOTES.md.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>