Routes are walked without re-checking collision #22

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opened 2026-07-27 22:31:57 +00:00 by sickday · 0 comments

sickday commented

2026-07-27 22:31:57 +00:00

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A route is computed once, when the click is handled, and then walked without
being looked at again. World.step_player/2 takes the tiles from
World.Movement.stride/3 and consults only World.MovementAuthority.claim/4,
which is entity occupancy — never terrain.

So anything that changes the world between the click and the last step is not
noticed. A door closed behind a player mid-walk, a loc added by a script, a
region whose diffs were replayed — the player walks through it. audit_walk/3
will log stepped through collision and nothing will stop it.

Today the only thing that mutates collision at runtime is a door swap, so the
window is small and the consequence is one tile. It gets wider with every
feature that adds or removes a loc.

Shape of a fix

Validate each tile in the stride against World.Collision.step?/2 before
claiming it, and drop the rest of the path when one fails. That is the same
predicate the route was built with, so it costs two map reads per step and can
only reject steps that have genuinely become illegal.

A route is computed once, when the click is handled, and then walked without being looked at again. `World.step_player/2` takes the tiles from `World.Movement.stride/3` and consults only `World.MovementAuthority.claim/4`, which is entity occupancy — never terrain. So anything that changes the world between the click and the last step is not noticed. A door closed behind a player mid-walk, a loc added by a script, a region whose diffs were replayed — the player walks through it. `audit_walk/3` will log `stepped through collision` and nothing will stop it. Today the only thing that mutates collision at runtime is a door swap, so the window is small and the consequence is one tile. It gets wider with every feature that adds or removes a loc. ### Shape of a fix Validate each tile in the stride against `World.Collision.step?/2` before claiming it, and drop the rest of the path when one fails. That is the same predicate the route was built with, so it costs two map reads per step and can only reject steps that have genuinely become illegal.

sickday referenced this issue from a commit

2026-07-28 00:31:19 +00:00

fix(world): re-check collision while a route is walked, not only when found

sickday referenced this issue from a pull request that will close it,

2026-07-28 00:32:13 +00:00

fix/reach-and-movement-integrity #28

sickday closed this issue

2026-07-28 00:32:21 +00:00