Port retail's CTransition::check_other_cells (acclient_2013_pseudo_c.txt
:272717-272798) into Transition.FindEnvCollisions so the foot-sphere
sees walls in EVERY cell it overlaps, not just the one cell the player's
center is in. Closes the Holtburg inn vestibule wall walk-through
(cell 0xA9B40164 has only 4 polys; adjacent 0xA9B40157 has 23 walls
that are never queried today).
Architecture: new CellTransit.FindCellSet overload (preserves the
candidate HashSet that FindCellList currently discards), new private
Transition.CheckOtherCells method (direct port of the retail loop),
one wire-up in FindEnvCollisions between the existing primary-cell BSP
return and the synthesis fall-through. ~380 LOC total.
Out of scope: FindObjCollisions (already landblock-radius broadphased),
synthesis multi-cell search (A3's job), var_4c re-target (defer).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
