Panning the scene view no longer redraws the whole scene

A middle-mouse pan used to run the full redraw on every frame. It
collected every object from the project, cleared and redrew every
shape, re-sorted all children and made Pixi re-upload every buffer,
although only the camera had moved. The user saw the frame rate drop
while panning.

- WorldViewport gets moveCamera(). When zoom and view size are
  unchanged it only moves the world and redraws the overlays drawn in
  screen pixels. collectFrame, the shape redraw and the re-sort drop
  out of a pan frame.
- Every full redraw remembers the box each object is culled by. A pan
  that moves an object across the edge of the view still takes the
  full redraw, so objects appear and vanish as before.
- Grid, selection outlines, rays and the container origin mark move
  into a shared drawOnScreen hook. It runs after every full redraw and
  after every pan. The parent links stay in afterItems because they
  are drawn in world units.
- Wheel zoom keeps the full redraw, because line widths follow the
  zoom. A cache for collectFrame was left out: it would save about
  1 ms and risk stale data.
- debugInfo() reports redraws and cameraMoves, and __gm gets a hook
  that forces a full redraw, so a check can compare against it.

Findings:
- Chrome already coalesces mouse moves to one per frame (500 moves
  gave 183 redraws in 189 frames). A throttle was tried and removed
  again, because its counter-check did not fail.
- A check in module 03 compared the whole gameInfo() object and broke
  on the new counters. It now compares camera, objects and rendering.
- The stall without ?vsync most likely comes from the desynchronized
  context in src/main.ts. It cannot be reproduced headless.

Tests:
- Measured on Jump and Run, main-thread time per frame, 3 runs of 240
  moves: pan 5.7-7.4 ms before, 3.8-4.8 ms after. Plain mouse moves
  stay at 2.1-2.4 ms. 208 of 240 moves took the fast path.
- ./check.sh: 141 files, 2080 tests, exit 0.
- GM_STEPS=1-16,29,42,43: 535 checks, 1 failed (the module 03 test
  above). After the fix GM_STEPS=1-5: all passed, 130 checks.
- 3 new e2e checks in 5d: 12 pan steps give 12 camera moves and 0
  full redraws, pixel rows after the pan match a fresh redraw, a box
  panned out of view and back is drawn again.
- Counter-checks: overlays not redrawn on pan gives "3 of 3 rows
  differ". Edge test disabled keeps the box visible with 0 redraws.
- Check total 1285 (1282 confirmed by CI task 229, plus 3).

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

tools/e2e/05-drawing.mjs

@@ -2,7 +2,7 @@ import { LANES, MAKE_OBJECT } from './lib/scaffold.mjs';
 
 /** Draw order: symbols always above sprites, `z` above hierarchy order. */
 export async function drawing(t) {
-  const { check, json, shot, click, locate, typeText, press, undo, mutate, select, object } = t;
+  const { check, json, shot, click, drag, locate, typeText, press, undo, mutate, select, object } = t;
   const orderOfCrates = () => json(`__gm.drawOrder().filter(id => id === 'o1' || id === 'o2')`);
 
   // 5a. Symbols stay on top: put the camera first in the hierarchy (drawn first) and a crate
@@ -103,4 +103,55 @@ export async function drawing(t) {
     scene.objects = scene.objects.filter((o) => !${JSON.stringify(ids)}.includes(o.id));
     p.assets = p.assets.filter((a) => !['s-box-a', 's-rb-a', 's-pt-a'].includes(a.id));
     __gm.lookAt(0, 0);`);
+
+  // 5d. A pan only moves the camera: no collect and no redraw of every shape per move. What it
+  //     leaves on screen – the crate, its outline, the grid – must be what a full redraw draws, and
+  //     an object panned back into view must be drawn again.
+  await select({ kind: 'object', holderId: 'scene1', objectId: 'o1' });
+  const vr = await json('__gm.viewportRect()');
+  const cx = Math.round(vr.x + vr.w / 2);
+  const cy = Math.round(vr.y + vr.h / 2);
+  const info = () => json('__gm.viewportInfo()');
+  const rows = () =>
+    json(`(() => {
+      const r = __gm.objectRect('o1');
+      const x = Math.round(r.x - r.w / 2 - 20);
+      return [r.y, r.y - r.h / 2 - 2, r.y + r.h / 2 + 2].map((y) => __gm.pixelRow(x, Math.round(y), Math.round(r.w + 40)).join());
+    })()`);
+  const sameAsRedraw = async () => {
+    const panned = await rows();
+    await json('(__gm.viewportRedraw(), true)');
+    const fresh = await rows();
+    return panned.filter((row, i) => row !== fresh[i]).length;
+  };
+  const before = await info();
+  await drag(cx, cy, cx + 36, cy + 24, { steps: 12, button: 'middle' });
+  const after = await info();
+  const moves = after.cameraMoves - before.cameraMoves;
+  const redraws = after.redraws - before.redraws;
+  check(
+    'a pan moves the camera without redrawing the scene',
+    moves >= 8 && redraws <= 4,
+    `${moves} camera moves, ${redraws} redraws in 12 steps`,
+  );
+  const offAfterPan = await sameAsRedraw();
+  check('a panned view draws what a full redraw draws', offAfterPan === 0, `${offAfterPan} of 3 rows differ`);
+  // Far enough that the crate's right edge passes the view's left one.
+  const crate = await json(`__gm.objectRect('o1')`);
+  const away = Math.round(crate.x + crate.w / 2 - vr.x + 20);
+  await drag(cx, cy, cx - away, cy, { steps: 12, button: 'middle' });
+  const gone = !(await json('__gm.drawOrder()')).includes('o1');
+  const back0 = await info();
+  // Pressed inside the view again: a press out over the panel would pan nothing.
+  await drag(cx, cy, cx + away, cy, { steps: 12, button: 'middle' });
+  const back = await info();
+  const shown = (await json('__gm.drawOrder()')).includes('o1');
+  const offAfterReturn = await sameAsRedraw();
+  check(
+    'an object panned out of view and back is drawn again',
+    gone && shown && back.redraws > back0.redraws && offAfterReturn === 0,
+    `gone=${gone} shown=${shown} redraws=${back.redraws - back0.redraws} rowsOff=${offAfterReturn}`,
+  );
+  await shot('15b-panned');
+  await mutate(`__gm.state.select(null); __gm.lookAt(0, 0)`);
 }