A test that waits for a deadline somebody guessed is waiting for the wrong thing, so it waits for the editor (#93)

The suite spent 88% of its step time asleep: 564 s of steps, 496 s of
them in sleep(n) - fixed spans estimated by hand and then copied from
step to step. That is why it was slow, and why it flickered.

The signal is afterFrames(count, timeout) in ui/render.ts, exposed as
__gm.afterFrames(). It wakes the loop itself, because an editor that
draws nothing would never redeem a promise of a frame, and it gives up
after a timeout instead of hanging the run. settle() in the harness
waits two drawn frames (~32 ms) instead of 150-300 ms and falls back to
sleep(150) when the hook is missing (an old build): silently not
waiting would make every later check a coin toss.

Every action goes through it now - click, doubleClick, wheel, drag,
dragAsset, press, typeText, select, mutate, undo, redo - and with that
about 550 sleep() calls behind those actions became redundant, helpers
that are nothing but a mutate in a coat included. What a frame cannot
answer got its own condition instead: waitUntil(expr), play()/stop()
waiting on __gm.state.mode rather than on 300 ms, saved() for the
autosave (the two hand-written polling loops sampled at 300 ms for
something that arrives after a second), and showTab() as a real tool -
47 places called evaluate("__gm.showTab(...)") raw, and 24 of them
waited for nothing at all and read the old panel.

564 s -> 243 s of step time, the waiting share 88% -> 76%. Three kinds
of wait were kept, and each one bit when it was taken away: loading
bytes (textures, fonts), game time that a repaint cannot stand in for
(time scale, shader and particle clocks, the live values a running
graph carries), and the inertia the scroll step measures on purpose.

Two things the new speed uncovered, both real: 25-animation read the
frame menu unfiltered and had frozen an incomplete list (the CI failure
on c990dbc), and 33-render-on-change measured idleness while the
autosave of the step before was still painting - it waits for
saveStatus to leave dirty/saving now, so it measures that nothing
happens any more instead of that it waited long enough.

tools/e2e/13-frames.mjs

@@ -35,7 +35,7 @@ function nearestColour(sample) {
 }
 
 export async function frames(t) {
-  const { check, sleep, json, evaluate, shot, clickText, drag, press, undo, wheel } = t;
+  const { check, sleep, json, evaluate, shot, clickText, drag, press, undo, wheel, showTab } = t;
 
   // 13a. The tab exists and shows the texture the selection points at.
   await press('Escape');
@@ -43,7 +43,6 @@ export async function frames(t) {
   const texture = await json("(__gm.state.project.assets.find((a) => a.type === 'texture') ?? {}).id ?? ''");
   await evaluate(`__gm.state.select({ kind: 'asset', assetId: ${JSON.stringify(texture)} })`);
   await openTab(t, 'texture');
-  await sleep(400);
   check('the Texture tab opens', (await json('__gm.tab()')) === 'texture');
   check(
     'and shows the selected sheet',
@@ -84,7 +83,6 @@ export async function frames(t) {
 
   // 13c. It is one undo step, not one per pointer move.
   await undo();
-  await sleep(400);
   check(
     'undo removes the frame in one step',
     (await json(
@@ -92,7 +90,6 @@ export async function frames(t) {
     )) === 0,
   );
   await t.redo();
-  await sleep(400);
 
   // 13d. A sprite wearing the frame shows that part of the sheet and nothing else.
   await evaluate(`(() => {
@@ -101,7 +98,7 @@ export async function frames(t) {
     sprite.props.texture = ${JSON.stringify(frame.id)};
     __gm.state.preview();
   })()`);
-  await evaluate("__gm.showTab('scene')");
+  await showTab('scene');
   await sleep(900);
 
   const box = await json("__gm.objectRect('otex')");
@@ -128,8 +125,7 @@ export async function frames(t) {
     __gm.state.project.assets.find((a) => a.id === 'tex-sprite').props.color = 0xff00ff;
     __gm.state.preview();
   })()`);
-  await evaluate("__gm.showTab('texture')");
-  await sleep(400);
+  await showTab('texture');
   await clickText('Slice…');
   await sleep(500);
   const dialog = await json('__gm.overlayTexts()');
@@ -160,8 +156,7 @@ export async function frames(t) {
   // 13f. Zoomed in, the sheet is larger than the tab: nothing of it may be drawn next to the tab.
   //      The bug this guards against drew the checkerboard's base rectangle, the frame outlines
   //      and the name plates over the Assets panel, because only the picture itself was masked.
-  await evaluate("__gm.showTab('texture')");
-  await sleep(400);
+  await showTab('texture');
   const area = await json('__gm.texture.rect()');
   // Points on the panel left of the tab and on the tab row above it – both were painted over.
   const probes = [
@@ -198,10 +193,9 @@ export async function frames(t) {
     JSON.stringify(await json('__gm.textOverflows()')),
   );
   await clickText('Fit');
-  await sleep(400);
 
   // 13g. A sprite pointed at a frame slicing removed falls back to its colour.
-  await evaluate("__gm.showTab('scene')");
+  await showTab('scene');
   await sleep(700);
   if (box) {
     const fallback = await json(