Walls you know are lies stand as ghosts

A wizard who has seen through an illusion no longer walks toward empty
air where the board shows a dashed ghost: the ray records the first
known-illusion edge it crosses without stopping, and the renderer
stands a wall there at one-fifth opacity, violet ripple running through
it, drawn over the sprites so bodies show through its breath. Untested
illusions get the same tell the board gives — a faint shimmer on their
solid face, maybe stone, maybe not — while a believed illusion stays
honest brick. The workshop rehearses it with ?illusion=H:2,8.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/web/src/fpv/raycast.ts

@@ -21,10 +21,14 @@ export interface Hit {
   /** The un-wrapped along-face coordinate: u plus the world cell it lies
    * in, so multi-cell surfaces (a long wall of fire) can read as one. */
   worldU: number;
-  /** The edge struck, for state the renderer dresses (jammed locks). */
+  /** The edge struck, for state the renderer dresses (jammed locks,
+   * untested illusions). */
   edge?: string;
   /** The eye reached this through a warp: haze it other-worldly. */
   warped?: boolean;
+  /** The first known-illusion edge the ray crossed before its solid hit:
+   * the eye passes, but a translucent ghost of a wall stands there. */
+  ghost?: { dist: number; u: number; worldU: number; axis: "x" | "y" };
 }
 
 export const SIDE_ANGLE: Record<Side, number> = { E: 0, S: Math.PI / 2, W: Math.PI, N: -Math.PI / 2 };
@@ -80,6 +84,7 @@ export function castRay(
   // a mouth re-enters at the paired mouth and marches on, its hits hazed.
   let baseDist = 0;
   let warped = false;
+  let ghost: Hit["ghost"];
   for (let traversal = 0; traversal < 3; traversal++) {
     const dx = Math.cos(angle);
     const dy = Math.sin(angle);
@@ -129,7 +134,7 @@ export function castRay(
         // A sliding door carries its texture with it: sample past the gap.
         return {
           dist: baseDist + b.t, kind: b.kind, u: Math.max(0, u - b.slide),
-          axis: b.axis, worldU: along, edge: b.edge, warped,
+          axis: b.axis, worldU: along, edge: b.edge, warped, ghost,
         };
       }
 
@@ -144,13 +149,17 @@ export function castRay(
       const u0 = along % 1;
       const texU = u0 < 0 ? u0 + 1 : u0;
 
+      const crossSide: Side = crossingX ? (stepX > 0 ? "E" : "W") : (stepY > 0 ? "S" : "N");
+      if (!ghost && view.knownIllusionEdges.includes(edgeKey({ x: cx, y: cy }, crossSide))) {
+        ghost = { dist: baseDist + dist, u: texU, worldU: along, axis };
+      }
       const offBoard = !view.board.cells[cellKey({ x: nx, y: ny })];
       if (offBoard) {
-        const side: Side = crossingX ? (stepX > 0 ? "E" : "W") : (stepY > 0 ? "S" : "N");
+        const side: Side = crossSide;
         const warp = view.board.warps.find(
           (w) => cellKey(w.from.cell) === cellKey({ x: cx, y: cy }) && w.from.side === side,
         );
-        if (!warp) return { dist: baseDist + dist, kind: "rim", u: texU, axis, worldU: along, warped };
+        if (!warp) return { dist: baseDist + dist, kind: "rim", u: texU, axis, worldU: along, warped, ghost };
         // Step through: re-enter at the paired mouth, heading inward, the
         // offset along the edge preserved (a wraparound keeps its lane).
         const exitHeading = SIDE_ANGLE[OPPOSITE[warp.to.side]];
@@ -167,14 +176,14 @@ export function castRay(
         break;
       }
       if (view.squareContents[cellKey({ x: nx, y: ny })]?.kind === "stone") {
-        return { dist: baseDist + dist, kind: "stone", u: texU, axis, worldU: along, warped };
+        return { dist: baseDist + dist, kind: "stone", u: texU, axis, worldU: along, warped, ghost };
       }
       cx = nx;
       cy = ny;
     }
     if (!warped || traversal === 2) break;
   }
-  return { dist: baseDist + 64, kind: "rim", u: 0, axis: "x", worldU: 0, warped };
+  return { dist: baseDist + 64, kind: "rim", u: 0, axis: "x", worldU: 0, warped, ghost };
 }
 
 /** Can a wizard's body (not just their eye) cross this edge? Workshop