Extract apply_skeleton_joints() as a pure module-level function that
copies prev_arr (or zeros) and writes a new array, never mutating the
old one. The TAG_SKELETON handler now stores the new array under the
state lock, so readers that captured a reference to the previous array
(multi.py shallow-copy + ArkitFuse.apply outside the lock) always see
a complete, consistent snapshot — eliminating the B4 tearing race.
6 new tests cover: shape, identity (is not), value preservation for
invalid joints, value application for valid joints, wrong-shape reset,
and no-mutation of prev_arr.
L'électron rare
8bc7acbd14