Enemy wall respect (collision + LOS)

name: Enemy wall respect overview: Harden enemy wall collision and line-of-sight by using the wall grid as the single source of truth (matching LOS), fixing corner-cutting in grid LOS, and adding spawn/move validation so enemies cannot see through or walk through walls. todos:

• id: supercover-los

content: "GridCollision2D: supercover LOS + clearanceRadius; add unit tests" status: completed

• id: enemy-grid-move

content: "EnemySystem: grid-only TryMove, OverlapsWall post-check, thick LOS for chase/melee" status: completed

• id: spawn-validate

content: Filter enemy spawns with OverlapsWall at EnemyRadius status: completed isProject: false

Current state

`EnemySystem.cs` already gates chase/melee/shots with GridCollision2D.HasLineOfSight and moves via GridPhysicsMovement (BVH) when `DoomLiteGame` passes _physicsWorld.

That split is the likely gap:

BVH meshes from `RoomMeshBuilder` should align with the grid, but axis-separated sphere sweeps can slide differently than circle-vs-cell `TryMove`. LOS uses thin Bresenham lines, which can cut corners in 2-wide corridors (see through / shoot through wall tips).

flowchart LR
  subgraph today [Today]
    GridLOS[Grid LOS]
    BvhMove[BVH TryMove]
  end
  subgraph target [Target]
    GridLOS2[Grid LOS thick]
    GridMove[Grid TryMove]
  end
  GridLOS --> GridLOS2
  BvhMove --> GridMove

1. Grid-only enemy movement

In `EnemySystem.TryMoveEnemy`:

• Always use GridCollision2D.TryMove(level.Walls, ...) (drop BVH branch for enemies).
• After move, reject if GridCollision2D.OverlapsWall(level.Walls, next, EnemyRadius, CellSize) — return previous position (safety net for spawn overlap or numeric edge cases).
• Remove physicsWorld from TryMoveEnemy signature; keep it on Update only if needed elsewhere, or remove from Update if unused.

Player keeps BVH movement unchanged.

2. Stronger grid LOS (novolis-math)

In `GridCollision2D.cs`:

a) Supercover line traversal — replace thin Bresenham with a line walk that visits every grid cell the segment touches (fixes diagonal corner peek).

b) Optional clearance — overload or parameter:

public static bool HasLineOfSight(
    DenseGrid<byte> map, Vector2 from, Vector2 to,
    float cellSize = 1f, float clearanceRadius = 0f)

When clearanceRadius > 0, any blocked cell within that radius of the supercover path returns false (accounts for enemy/player body width in 2-cell halls).

Tests in `GridCollision2DTests.cs`:

• Diagonal past L-corner stays blocked (existing test, may need tightening).
• New: thin gap between two wall cells — thin LOS false, thick clearance false.
• New: open 2-cell-wide corridor — LOS true with clearance < 1 cell.

3. Enemy LOS call sites

In `EnemySystem.cs`:

Chase only when HasLineOfSight(..., clearance); melee same.

4. Safe enemy spawn

In `MazeGenerator.PlaceEnemies` or `EnemySystem.Reset`:

• Skip / don't place if GridCollision2D.OverlapsWall(walls, cellCenterXZ, EnemyRadius, CellSize).
• Ensures enemies start in valid floor, not on wall edges after 2-wide rasterize.

5. Files touched

No changes to maze layout or minimap.

Verification

dotnet test novolis-math/tests/Novolis.Math.Geometry.Tests
dotnet build novolis-dogfooding/apps/DoomLite3D/DoomLite3D.csproj
dotnet run --project novolis-dogfooding/apps/DoomLite3D/DoomLite3D.csproj

Manual: enemy behind wall does not move or melee; cannot be shot through wall; around corners no peeking; enemies do not slide through wall corners in 2-wide halls.