A creature stands idle after entering view, then jumps forward to catch up #272

Expected. A creature's movement looks continuous to a client in view of it, and it engages a player who enters aggro range promptly, not after a multi-second delay.

Actual (at 87109e3c). Two causes remain from the investigation that split this issue off #252 (a third, no spline replay on a CREATE mid-leg, is already fixed).

The Gateway sheds a queued motion flush under deep egress, and a later leg supersedes the pending one in the same per-viewer slot (world_view.rs#L1810-L1822). The latest leg still reaches the client, but late: the client plays it from receipt, while the server has already advanced the mover past start_micros, so the next leg snaps the client forward.

Proximity aggro also runs on an eight-tick sense cadence, about four seconds at the 500 ms creature tick, while chase runs every tick once engaged (ai.rs#L428-L435). A player walking into aggro range can wait up to four seconds before the creature reacts.

How it shows. A creature under load stands idle, then visibly jumps to its real position on the next leg. Separately, a creature can let a player stand in aggro range for several seconds before it notices.

Fix direction. Decide whether a shed flush may be re-sent with its true start_micros so the client catches up at normal speed instead of replaying from receipt, or whether shedding should stop entirely for creature legs. For the sense cadence, either shorten SENSE_EVERY_N_TICKS or add a cheap proximity check that runs every tick. Verify with the stock 1.12 acceptance recording from #252: engage from rest, stop right after approach, kite in a straight line, with no multi-second idle followed by a compressed catch-up.