Asset panel: double-click opens the tab, single click only selects (#71)

One rule for every asset type: a click on an asset row selects it, a
double-click (or Enter, or creating it via +) opens its tab. Selection
alone still switches tabs only for nodes, frames and template objects.

- state.openAsset(id) = select + 'open' event; the editor maps the asset
  type to its tab via TAB_OF_ASSET. The two special clauses for state
  machine and shader assets in the selection handler are gone.
- Creating via + and importing a texture from the picker open the tab;
  paste/drop of an image only selects.
- 3 unit tests (event order, re-open of a selected asset, selection never
  fires open), 14 e2e checks in step 4.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tools/e2e/04-assets.mjs

@@ -88,12 +88,15 @@ export async function assets(t) {
     `__gm.state.project.assets.push({ id: 'scene2', type: 'scene', name: 'Level 2', props: { backgroundColor: 0x22252c }, objects: [] })`,
   );
   const secondScene = await json("__gm.assetRow('scene2')");
+  await evaluate("__gm.showTab('graph')");
+  await sleep(150);
   await doubleClick(secondScene.x, secondScene.y);
   check(
     'double-clicking a scene asset makes it the active scene',
     (await json('__gm.state.project.activeSceneId')) === 'scene2',
     await json('__gm.state.project.activeSceneId'),
   );
+  check('and opens the Scene tab', (await json('__gm.tab()')) === 'scene', await json('__gm.tab()'));
   const firstScene = await json("__gm.assetRow('scene1')");
   await doubleClick(firstScene.x, firstScene.y);
   check(
@@ -103,6 +106,72 @@ export async function assets(t) {
   );
   await mutate(`__gm.state.project.assets = __gm.state.project.assets.filter((a) => a.id !== 'scene2')`);
 
+  // 4d′. Opening an asset: a click on its row only selects, a double-click opens the tab it
+  //      lives in – every type that has one. The fixture lacks four of them; they go in through
+  //      the model, empty.
+  await mutate(`__gm.state.project.assets.push(
+    { id: 'sm-open', type: 'statemachine', name: 'Machine', props: {}, graph: { nodes: [], edges: [] } },
+    { id: 'tex-open', type: 'texture', name: 'Sheet', props: {}, file: '', width: 0, height: 0, frames: [] },
+    { id: 'anim-open', type: 'animation', name: 'Walk', props: {}, frames: [] },
+    { id: 'box-open', type: 'container', name: 'Box', props: {}, objects: [] },
+  )`);
+  const openable = [
+    ['mover', 'graph', '__gm.graph.current()'],
+    ['sm-open', 'statemachine', '__gm.stateMachine.current()'],
+    ['adjust-colors', 'shader', '__gm.shader.current()'],
+    ['tex-open', 'texture', '__gm.texture.current()'],
+    ['anim-open', 'animation', '__gm.animation.current().assetId'],
+    ['box-open', 'container', '__gm.container.current()'],
+  ];
+  for (const [id, tab, shown] of openable) {
+    await evaluate("__gm.showTab('scene')");
+    await sleep(150);
+    const row = await json(`__gm.assetRow(${JSON.stringify(id)})`);
+    await click(row.x, row.y);
+    await sleep(500); // past the double-click window, so the next press starts a fresh pair
+    const clicked = {
+      tab: await json('__gm.tab()'),
+      selected: (await json('__gm.state.selection'))?.assetId,
+    };
+    check(
+      `a click on the ${tab} asset selects it and leaves the Scene tab alone`,
+      clicked.tab === 'scene' && clicked.selected === id,
+      JSON.stringify(clicked),
+    );
+    await doubleClick(row.x, row.y);
+    await sleep(300);
+    const opened = { tab: await json('__gm.tab()'), shown: await json(shown) };
+    check(
+      `a double-click opens the ${tab} tab on it`,
+      opened.tab === tab && opened.shown === id,
+      JSON.stringify(opened),
+    );
+  }
+  // Enter goes the same way (`onActivate`), but only once the list holds keyboard focus, which a
+  // click does not give it – so it is not driven here.
+  await evaluate("__gm.showTab('scene')");
+  await sleep(150);
+  await clickText('+');
+  await sleep(200);
+  const entry = await evaluate(`__gm.locate('Behavior', true)`);
+  await click(entry.x, entry.y);
+  await sleep(400);
+  const created = await json(
+    "(__gm.state.project.assets.find((a) => a.type === 'behavior' && !['mover', 'spawner'].includes(a.id)) ?? {}).id ?? ''",
+  );
+  const fresh = { created, tab: await json('__gm.tab()'), shown: await json('__gm.graph.current()') };
+  check(
+    'creating an asset through + opens its tab on the new one',
+    Boolean(created) && fresh.tab === 'graph' && fresh.shown === created,
+    JSON.stringify(fresh),
+  );
+  await undo();
+  await mutate(
+    `__gm.state.project.assets = __gm.state.project.assets.filter((a) => !['sm-open', 'tex-open', 'anim-open', 'box-open'].includes(a.id))`,
+  );
+  await evaluate("__gm.showTab('scene')");
+  await sleep(150);
+
   // 4e. Asset defaults: the Crate deviates in height (60 against the schema's 100) and colour,
   //     so two rows carry a reset. Rows run Enabled, Width, Height, Color, Texture, so height's
   //     reset is the first on screen and colour's the last.