world: per-file heat map — persistent touch-count residual (V4)

Files that see repeated touches decay back to visual silence within a
couple of seconds because `n.heat` decays at 0.5/sec. Hard to tell a
hot-spot file (touched 20 times over a run) from a virgin one; both
look the same at rest.

Adds a monotonically-increasing per-node `touchCount` on the engine
and a log-scaled residual on the render that never decays. Files
climbing the touch count grow subtly, tint whiter, and pull more
emissive — even at heat=0.

- GNode gains `touchCount`, initialized 0 on ensureNode and on the
  ROOT sentinel.
- onTouch bumps `touchCount` only for `file:` prefix nodes so
  landmarks + structural orbs don't accumulate a hot halo just because
  agents converge on them.
- WorldCanvas node loop computes `residual = min(0.7, log(1+count)/log(50))`
  and adds it into radius, whiten-lerp, and emissiveIntensity.

Feel: hot files stay softly-warm indefinitely (residual stops climbing
around ~50 touches). Cold files stay cold. Live activity still dominates
via the transient `heat` bump; residual is the ghost trail.

frontend/src/components/world/WorldCanvas.tsx

@@ -695,14 +695,16 @@ export function WorldCanvas({ roots, selectedId, onSelect, expanded, onToggleExp
           nodeMeshes.set(n.id, m);
           gourceGroup.add(m);
         }
-        const r = n.r * (1 + n.heat * 0.4);
+        // touchCount → log-scaled residual heat that never decays.
+        const residual = Math.min(0.7, Math.log(1 + (n.touchCount ?? 0)) / Math.log(50));
+        const r = n.r * (1 + n.heat * 0.4 + residual * 0.15);
         m.position.set(n.x, n.y, 0);
         m.scale.set(r, r, r);
         const mat = m.material as THREE.MeshStandardMaterial;
-        col.set(n.color).lerp(white, n.heat * 0.6);
+        col.set(n.color).lerp(white, n.heat * 0.6 + residual * 0.35);
         mat.color.copy(col);
         mat.emissive.copy(col);
-        mat.emissiveIntensity = 0.35 + n.heat * 0.6;
+        mat.emissiveIntensity = 0.35 + n.heat * 0.6 + residual * 0.4;
         mat.opacity = n.alpha;
         mat.transparent = n.alpha < 0.99; // solid when present; only fades on appear/disappear
         let g = nodeGlows.get(n.id);

frontend/src/components/world/engine.ts

@@ -28,6 +28,11 @@ export interface GNode {
   alpha: number; // fade in/out (world nodes)
   lastSeen: number;
   fixed?: boolean;
+  /** Cumulative touch count (per session). Grows monotonically on every
+   * world.touch that lands here. Used by the render to compute a
+   * persistent "heat map" tint so files touched many times stay visibly
+   * warmer than virgin files even at heat=0. */
+  touchCount: number;
 }
 
 export interface GPawn {
@@ -144,6 +149,7 @@ export class WorldEngine {
       alpha: 1,
       lastSeen: 0,
       fixed: true,
+      touchCount: 0,
     });
   }
 
@@ -189,6 +195,7 @@ export class WorldEngine {
         burst: 0,
         alpha: 1,
         lastSeen: this.now,
+        touchCount: 0,
       };
       this.nodes.set(id, n);
     }
@@ -291,6 +298,14 @@ export class WorldEngine {
     // permanent hot spot regardless of intent.
     node.heat = Math.min(1, node.heat + w * 0.6);
     node.burst = Math.max(node.burst, w); // file ops (weight 1) → explosive burst
+    // Persistent per-file heat map — tracks TOTAL touches so hot files
+    // stay visibly warmer even after `heat` decays (see the render's
+    // touchCount → residual emissive intensity in WorldCanvas). We only
+    // count file: touches; landmarks and structural nodes shouldn't
+    // accumulate a "hot" halo just because agents converge on them.
+    if (e.nodeId.startsWith("file:")) {
+      node.touchCount = (node.touchCount ?? 0) + 1;
+    }
     // activity type → signal colour: file=coral, tool=cyan, run=green,
     // repo=sky-blue, loop=amber
     if (e.nodeId.startsWith("tool:")) p.fireColor = w >= 0.9 ? "#ff6f61" : "#5ec8d8";