SRD Moving Through a Square: 'Any creature can move through a square
occupied by a creature three size categories larger than itself. A big
creature can move through a square occupied by a creature three size
categories smaller than it is. Creatures moving through squares occupied
by other creatures provoke attacks of opportunity from those creatures.'
- _can_pass_through: size ranks differ by >= 3 opens the through-gate
(_blocked_hostile) while _blocked/_cells_free keep the end-gate
('You can't end your movement in the same square as another creature
unless it is helpless').
- _check_enter_aoo wired into _walk_steps (move, explicit-destination
move, and run all commit steps there): the occupant strikes once per
fresh entry, capped by the per-round allowance; a dropped mover stops
the walk. S4c co-occupiable pairs (Tiny-or-smaller) keep no-AoO sharing.
- _has_free_descent generalized to a descending BFS so a walk can cross
a multi-cell Huge+ creature (one-step lookahead dead-ended inside).
- Golden transcript untouched (all 1480 tests green).
