Count clicks ourselves so double-clicks work at all

Pixi only fills `detail` on the `click` event it synthesises; on
`pointerdown` it is always 0, so every `e.detail === 2` branch was dead
code. Asset rows, hierarchy folding and select-all in text fields never
responded to a double-click.

A shared click counter in src/ui/clicks.ts replaces the three readings of
`e.detail`. A finished double-click ends the run, so two in a row count
2 and 2 rather than 3 and 4.

The harness could only send `clickCount: 1`, which is why no test caught
this: every "activate" check went through Enter. It can send real
double-clicks now, and five checks drive the three paths separately.

src/editor/debugHook.ts

@@ -181,6 +181,8 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     /** Rows the hierarchy shows – collapsed subtrees are not in here. */
     hierarchyOrder: () => hierarchy.rowOrder(),
     hierarchyChevron: (id: string) => hierarchy.chevronPosition(id),
+    /** Centre of a hierarchy row, clear of the chevron – for clicks that must hit the row itself. */
+    hierarchyRow: (id: string) => hierarchy.rowPosition(id),
     hierarchyRowColor: (id: string) => hierarchy.rowColor(id),
     hierarchyExpandAll: () => hierarchy.expandAll(),
     hierarchyCollapseAll: () => hierarchy.collapseAll(),

src/editor/panels/HierarchyPanel.ts

@@ -142,6 +142,11 @@ export class HierarchyPanel extends Panel {
     return this.list.chevronGlobal(id);
   }
 
+  /** Global centre of a row, away from its chevron (test hook). */
+  rowPosition(id: string): { x: number; y: number } | null {
+    return this.list.rowGlobal(id);
+  }
+
   expandAll(): void {
     for (const object of this.holder()?.objects ?? []) this.expanded.add(object.id);
     this.refresh();

src/ui/clicks.ts

@@ -0,0 +1,48 @@
+import type { FederatedPointerEvent } from 'pixi.js';
+
+/** Longest gap between two presses that still reads as one double-click. */
+const DOUBLE_MS = 400;
+/** How far the pointer may travel between them. */
+const SLOP = 6;
+
+interface LastPress {
+  key: unknown;
+  button: number;
+  time: number;
+  x: number;
+  y: number;
+  count: number;
+}
+
+let last: LastPress = { key: null, button: -1, time: 0, x: 0, y: 0, count: 0 };
+
+/**
+ * How often `key` was pressed in a row with the same button – 2 on a double-click. Pixi counts
+ * clicks only for the `click`/`pointertap` it synthesises and leaves `detail` at 0 on
+ * `pointerdown`, so a press handler reading `e.detail` never sees a second click.
+ *
+ * `key` identifies what was hit and should survive a rebuild of the widget it belongs to: list
+ * rows are thrown away and recreated whenever the list refreshes, which a selection – the first
+ * click – can trigger.
+ */
+export function pressCount(e: FederatedPointerEvent, key: unknown): number {
+  const gap = e.timeStamp - last.time;
+  const repeat =
+    key === last.key &&
+    e.button === last.button &&
+    gap >= 0 &&
+    gap <= DOUBLE_MS &&
+    Math.hypot(e.global.x - last.x, e.global.y - last.y) <= SLOP;
+  const count = repeat ? last.count + 1 : 1;
+  last = {
+    key,
+    button: e.button,
+    time: e.timeStamp,
+    x: e.global.x,
+    y: e.global.y,
+    // A finished double-click ends the run: folding a row open and shut again is two
+    // double-clicks, and the second must count as one rather than as clicks three and four.
+    count: count === 2 ? 0 : count,
+  };
+  return count;
+}

src/ui/widgets/ListView.ts

@@ -1,4 +1,5 @@
 import { type FederatedPointerEvent, Graphics, Text } from 'pixi.js';
+import { pressCount } from '../clicks';
 import { centreY } from '../math';
 import { Theme, textStyle } from '../Theme';
 import { type Size, Widget } from '../Widget';
@@ -223,7 +224,7 @@ export class ListView extends Widget {
       // being dragged into.
       if (!this.onDragOut && (!this.highlighted.has(item.id) || item.id === this.selectedId))
         this.select(item.id);
-      if (e.detail === 2) this.onActivate?.(item.id);
+      if (pressCount(e, item.id) === 2) this.onActivate?.(item.id);
       else if (this.onDrop || this.onDragOut) {
         this.drag = { id: item.id, startX: e.global.x, startY: e.global.y, active: false, spot: null };
       }

src/ui/widgets/TextField.ts

@@ -1,4 +1,5 @@
 import { CanvasTextMetrics, type FederatedPointerEvent, Graphics, Text } from 'pixi.js';
+import { pressCount } from '../clicks';
 import { drawControlBox } from '../draw';
 import type { TextEditTarget } from '../KeyboardBridge';
 import { centreY, clamp } from '../math';
@@ -101,11 +102,12 @@ export class TextField extends Widget implements TextEditTarget {
     if (e.button !== 0) return;
     e.stopPropagation();
     const index = this.indexAt(this.toLocal(e.global).x);
+    const presses = pressCount(e, this);
     if (!this.editing) {
       ui().focus.focus(this);
-      if (e.detail >= 2) this.selectAll();
+      if (presses >= 2) this.selectAll();
       else this.setSelection(index, index, true);
-    } else if (e.detail >= 2) {
+    } else if (presses >= 2) {
       this.selectAll();
     } else {
       this.setSelection(index, index, true);