p_ceilng: T_MoveCeiling direction-gate divergence from C

[sunsided]

Context

T_MoveCeiling in room/src/doom/p_ceilng.rs is the per-tic ceiling mover.

C behavior

The C original uses a switch(direction) with three branches:

• case 0: stasis — no-op
• case 1: moving up — calls T_MovePlane, handles pastdest/crushed for upward completion
• case -1: moving down — calls T_MovePlane, handles pastdest/crushed for downward completion

The pastdest and crushed reactions are gated on direction so they only fire when moving in the matching direction.

Rust behavior

The Rust port passes direction to T_MovePlane correctly but the match-arm reactions for pastdest/crushed may not be properly gated on the current direction, potentially causing spurious firing when direction == 0 (stasis).

Impact

Ceiling movers in stasis could erroneously trigger sound/state-change logic.

Location

room/src/doom/p_ceilng.rs — T_MoveCeiling

Flagged with // FIXME: in the source.