[Erry91]

What this changes

Walls block light (gap 16, the alpha blocker that could make a corridor around a corner look lit).

• luxpath-geom: Wall is an opaque vertical panel on a plan segment, between two heights.
  • Wall::blocks(from, to) tests a sight line against it.
  • Points and luminaires within 1 mm of a wall's face are not hidden by it.
  • Grazing a wall's end counts as blocked.
• luxpath-calc: illuminance_with_walls; illuminance keeps its signature (no walls).
• Scenes:
  • [[wall]] with a path polyline, height_m and an optional floor_m; doorways are gaps.
  • Documented in docs/scene-format.md.
• luxpath check states how many wall pieces block light, and that furniture and doors do not.
• Examples now have their walls. The corridor's route minimum drops from 1.45 lx to 0.60 lx (max/min from 2.0:1 to 4.8:1) once light no longer passes through the corner.
• Gap 16 narrowed to "luminaires are points"; it is no longer an alpha blocker.

How you verified it

• cargo xtask ci, natively and in the local Linux container, including timing:

  • without walls, 55 ms;
  • with 36 walls, about 90 ms (new budget 500 ms).

  Merged on the local checks (hosted CI unavailable).

• Hand-checked cases:

  • behind a wall: 0 lx;
  • in front of it: the unobstructed 1000 · 2.5 / 7.25^1.5;
  • over a low wall, crossed at z = 1.25 m: blocked only when the wall reaches that height.

• Watched it fail: with wall blocking disabled, the calc and rules tests go red.

Life safety (AGENTS.md §2)

• Removes a known wrong pass; the remaining approximations (point luminaires, no furniture) are printed as assumptions

Never panic (AGENTS.md §3)

• NaN, parallel and degenerate sight lines tested; wall heights validated

Provenance (AGENTS.md §1)

• Nothing from a standard

Records

• parity/features.toml, docs/scene-format.md, docs/gaps.md, docs/status.md, ROADMAP.md log