Fog lit by rays: shadows cut through tiles, and walls stay visible

The fog asked one question per tile -- can I see its centre? -- and drew or
skipped the whole tile on the answer. Every shadow was a staircase, tiles
snapped in and out as you walked, and a wall beside you vanished whenever
its centre happened to sit behind its neighbour.

Visibility casts rays from the eye instead: a fixed sweep, plus two aimed
either side of every wall corner, which is what makes each shadow edge a
straight line rather than a smear between rays. The view now draws terrain
and actors first and then darkness over whatever the rays did not reach,
so a shadow runs straight through a tile and an enemy rounding a corner
appears a slice at a time. Bullets are a child node and are still drawn
over the dark; telegraphs are drawn after it, as they must be.

"A bit less strict" is three specific things. A wall face you can see is
lit 26 units in, measured perpendicular to the face; shadows end in a
short fade rather than a line; and sight fades over its last 64 units
rather than stopping at a circle. Still hard fog -- nothing remembered.

The first version measured that depth along the ray, and a screenshot
caught what no test had: a wall you look along got a sliver, so the wall
beside you in a tunnel looked missing -- the old fog's own complaint.
Perpendicular depth fixes it, and light stops the instant a ray steps
back into the open, so it never rounds a corner, never reaches the far
side of a one-tile wall, and never leaves a stepped wall through its
other face. Two tiles touching only at a corner are closed.

About half a millisecond a frame. Measured against the old fog in the
same scene: hub 68 fps against 62, dungeon 240 against 240. The hub's
own low rate predates this.

MapGrid gains a revision counter so the corner list is rebuilt only when
the map changes or the eye crosses a tile. screenshot.tscn now captures a
dungeon, a tunnel and the tunnel with F1's overlay, which draws where
each ray stopped -- and makes SHOT_DIR rather than failing every capture
when it does not exist.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -48,8 +48,10 @@ This project deliberately does not, for four reasons:
 The trade is that there is no physics engine, so collision is hand-written.
 Since Stage 1 that means a tile grid ([MapGrid](../src/sim/map_grid.gd)):
 circle-vs-tile for actors, a point test for bullets, and Bresenham line of sight
-shared by fog and aggro. Actor-vs-actor hits stay circle-vs-circle, which is the
-genre convention anyway.
+for aggro. Actor-vs-actor hits stay circle-vs-circle, which is the genre
+convention anyway. The client's fog no longer shares that line test: it casts
+exact rays through the same grid ([Visibility](../src/view/visibility.gd)), so
+shadows cut through tiles rather than snapping to them.
 
 That was the right call rather than a compromise: the same grid answers
 collision, sight, and per-peer interest management as array lookups. On arbitrary
@@ -186,7 +188,8 @@ nothing from `net`, `view` or `ui`, and never touches `Net`.**
 
 | File | Role |
 | --- | --- |
-| `src/view/world_view.gd` | Everything that is not a bullet. Fog, actors, loot, telegraphs. |
+| `src/view/world_view.gd` | Everything that is not a bullet. Fog, actors, loot, telegraphs. Draw order is the fog's mechanism: everything it may hide, then the darkness, then what it must not. |
+| `src/view/visibility.gd` | The fog's geometry: rays from the eye, wall corners, the shadow mesh. Pure, so `test_visibility.gd` asks it which points are lit. |
 | `src/view/bullet_renderer.gd` | The bullet field: one MultiMesh per bullet kind. |
 | `src/view/art.gd` | Every atlas rect and sound path, in one table. |
 | `src/view/ui_theme.gd` | The control theme, built in code from the UI pack. |