Each entity completion handler (wall/floor/door/bed/torch/workbench/crate
/tree/rock/big_rock/grave_slot) now calls World.clear_designation_at(tile)
so the orange/blue/etc. highlight overlay disappears with the job.
BigRock iterates its footprint to clear all four tiles.
World.designation_ctl is set during the scene boot wire-up; the helper
no-ops when the controller is absent (e.g. headless tests).
megaproxy
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