Key what an empty timeline row shows on a double-click (#412)

A double-click into a timeline row without keys set the property's
default, while the field in the row header showed the value the target
actually holds. A sprite standing on x 40 got a key with 0, so the
first key moved it. The double-click now keys the value the row shows.

- trackHeld in src/core/model/animation.ts says what a row without keys
  holds. The field in the row header and SetAnimationKeyCommand both
  ask it, so they cannot drift apart again.
- A relative row still gets 0, a row with keys still takes the value of
  its curve at that frame, and a row whose target is gone still only
  gives a notice and no key.
- README and the wiki page Development name 2047 checks.

Tests:
- Unit animation: 87 green, 1 new. A sprite on x 40 with the override
  scale 2 gets keys with 40 and 2. Red with the old def.default.
- e2e 25 on melektaus-atx: ALL PASSED, 35 checks, 25i-ii new. The arm
  stands on x 40 and a double-click on frame 3 keys { frame: 3,
  value: 40 }.
- Gate on melektaus-atx: green, 304 files, 4703 tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -47,7 +47,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 2046 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 2047 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs

src/core/commands/animationCommands.ts

@@ -10,6 +10,7 @@ import {
   targetAssetOf,
   targetDefs,
   trackDef,
+  trackHeld,
   trackValueAt,
 } from '../model/animation';
 import type { AnimationAsset, AnimationKey, AnimationTrack, KeyInterpolation } from '../model/Asset';
@@ -215,7 +216,7 @@ export class SetTrackRelativeCommand extends TimelineCommand {
 /**
  * Sets the key at `frame`, replacing the value of one already there but keeping its interpolation.
  * Without a value it takes the value the row has at that frame – what a double click in the timeline
- * means – and on an empty row the property's default, which for a relative row is no offset at all.
+ * means – and on an empty row what the row's header shows: the object's value, or no offset when relative.
  */
 export class SetAnimationKeyCommand extends TimelineCommand {
   readonly label = 'Set key';
@@ -235,7 +236,7 @@ export class SetAnimationKeyCommand extends TimelineCommand {
     const def = trackDef(project, asset, track);
     if (!def) throw new CommandError('The row aims at something that is gone');
     const current = trackValueAt(track.keys, def.kind, this.frame, false, curveLookup(project));
-    const raw = this.value ?? current ?? (track.relative ? 0 : def.default);
+    const raw = this.value ?? current ?? trackHeld(project, asset, track);
     const key: AnimationKey = { frame: this.frame, value: coerceValue(def, raw) };
     const interpolation = track.keys.find((k) => k.frame === this.frame)?.interpolation;
     if (interpolation) key.interpolation = interpolation;

src/core/model/animation.ts

@@ -625,18 +625,27 @@ export function timelineLines(project: Project, animation: AnimationAsset): Time
     for (const track of rows) {
       const def = defs.find((d) => d.key === track.property);
       const label = def ? def.label : `${track.property} (missing)`;
-      const held = !aimed || !def ? 0 : track.relative ? 0 : heldBy(aimed, def);
+      lines.push({ kind: 'row', track, label, def, held: heldBy(aimed, def, track), depth });
-      lines.push({ kind: 'row', track, label, def, held, depth });
     }
   }
   return lines;
 }
 
-function heldBy(aimed: Aimed, def: PropertyDef): PropertyValue {
+function heldBy(
+  aimed: Aimed | undefined,
+  def: PropertyDef | undefined,
+  track: AnimationTrack,
+): PropertyValue {
+  if (!aimed || !def || track.relative) return 0;
   if (isPositionRow(aimed.asset.type, def.key)) return aimed.object?.position[def.key] ?? 0;
   return aimed.bag[def.key] ?? def.default;
 }
 
+/** What a row holds without keys (#412): the value its object has, no offset for a relative row. */
+export function trackHeld(project: Project, animation: AnimationAsset, track: AnimationTrack): PropertyValue {
+  return heldBy(aimedAt(project, animation, track.target), trackDef(project, animation, track), track);
+}
+
 /** What a row's header shows at `frame` (#408): the row's value there, else what it holds without keys. */
 export function lineValueAt(
   line: TimelineLine & { kind: 'row' },

tests/core/animation.test.ts

@@ -366,6 +366,23 @@ describe('editing the timeline', () => {
     expect(rowOf(walk, x).keys).toEqual(keys([0, 0]));
   });
 
+  it('starts an empty row at what its header shows, the value the object holds (#412)', () => {
+    const f = makeSpriteScene();
+    const a = place(f, f.spriteId, { x: 40, y: 0 });
+    f.stack.execute(new SetOverrideCommand(f.sceneId, a, 'scale', 2));
+    const walk = addAnimation(f, f.sceneId);
+    const x = addRow(f, walk, 'x', [], a);
+    const scale = addRow(f, walk, 'scale', [], a);
+    const shown = timelineLines(f.project, current(f, walk)).flatMap((l) =>
+      l.kind === 'row' ? [lineValueAt(l, 0)] : [],
+    );
+    f.stack.execute(new SetAnimationKeyCommand(walk.id, x, 0));
+    f.stack.execute(new SetAnimationKeyCommand(walk.id, scale, 0));
+    expect(shown).toEqual([40, 2]);
+    expect(rowOf(current(f, walk), x).keys).toEqual(keys([0, 40]));
+    expect(rowOf(current(f, walk), scale).keys).toEqual(keys([0, 2]));
+  });
+
   it('moves keys together; one landing on a key left behind replaces it, and undo brings both back', () => {
     const f = makeSpriteScene();
     const walk = addAnimation(f, f.spriteId);

tools/e2e/25-animation.mjs

@@ -478,6 +478,24 @@ export async function animation(t) {
     JSON.stringify({ whilePlaying, scrubbed }),
   );
 
+  // 25i-ii. A double click into a row without keys keys what its header showed (#412): the Arm
+  //         stands at x 40, not at the property's default 0.
+  await mutate(`
+    const p = __gm.state.project;
+    p.assets.find((a) => a.id === 'an-box').objects[0].position.x = 40;
+    p.assets.find((a) => a.id === 'an-walk').tracks = [{ id: 'an-r4', target: 'an-arm', property: 'x', keys: [] }];
+  `);
+  await sleep(150);
+  const shownX = (await json('__gm.animation.lines()')).find((l) => l.kind !== 'group')?.value;
+  const emptyCell = await json("__gm.animation.cellAt('an-r4', 3)");
+  await doubleClick(emptyCell.x, emptyCell.y);
+  const keyedX = (await walk()).tracks[0].keys;
+  check(
+    'a double click into an empty row keys the value its header showed – 40, not the default 0',
+    shownX === 40 && JSON.stringify(keyedX) === JSON.stringify([{ frame: 3, value: 40 }]),
+    JSON.stringify({ shownX, keyedX }),
+  );
+
   await mutate(`
     const p = __gm.state.project;
     p.assets = p.assets.filter((a) => !['an-walk', 'an-box', 'an-sprite'].includes(a.id));