Lay out a scroll container's content when the content changes

A short list opened after a long one drew all its rows stacked on one
point. The fault was not in the list tab: rebuild() handed the row stack
to setContent() while it was still empty, so the content was sized to
max(rows, viewport) = the viewport. The rows arrived after that, and for
a short list the same formula yields the same height, so resize() saw no
change and skipped layout(). A long list changes the height and never
showed it.

relayoutContent() now runs whenever the content changed, rather than
leaning on resize()'s change detection - that detection is the wrong
instrument for "the children moved".

The list tab was the only affected caller: the panels use ListView,
which positions its rows itself, and the inspector fills its body
before setContent.

Also drops the comma line under the list. Every section that can carry a
list supplies openList, so the comma fallback in fieldFactory was
unreachable; listToText/listFromText go with it. The list-value test now
covers coerceListItem through coerceValue instead, so the boolean
spelling stays guarded.

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

tools/e2e/21-list.mjs

@@ -52,7 +52,30 @@ export async function listTab(t) {
   info = await json('__gm.list.info()');
   check('undo takes just that item back', JSON.stringify(info.items) === '["30","11","44"]', info.items[1]);
 
-  // 4. Adding and removing whole items.
+  // 4. A short list opened after a long one. Its rows leave the content height pinned to the
+  // viewport, so a layout skipped on "same size" would stack them all at the top.
+  await mutate(`
+    const a = __gm.state.project.assets.find((x) => x.id === 'listy');
+    a.props.nums = Array.from({ length: 60 }, (_, i) => i);
+    __gm.state.preview();
+  `);
+  await sleep(250);
+  const longRows = [await json('__gm.list.fieldAt(0)'), await json('__gm.list.fieldAt(1)')];
+  check('a long list stacks its rows', longRows[0].y !== longRows[1].y, JSON.stringify(longRows));
+  await mutate(`
+    const a = __gm.state.project.assets.find((x) => x.id === 'listy');
+    a.props.nums = [30, 11, 44];
+    __gm.state.preview();
+  `);
+  await sleep(250);
+  const shortRows = [await json('__gm.list.fieldAt(0)'), await json('__gm.list.fieldAt(1)')];
+  check(
+    'and a short list after it still stacks its own',
+    shortRows[0].y !== shortRows[1].y,
+    JSON.stringify(shortRows),
+  );
+
+  // 5. Adding and removing whole items.
   await clickText('+ Item');
   await sleep(200);
   info = await json('__gm.list.info()');
@@ -61,7 +84,7 @@ export async function listTab(t) {
   check('undo removes it again', (await json('__gm.list.info()')).items.length === 3);
   await shot('03-rows');
 
-  // 5. Back on the scene tab the button carries the current count.
+  // 6. Back on the scene tab the button carries the current count.
   await mutate('__gm.state.openList(null)');
   await sleep(200);
   check('closing the list leaves the tab', (await json('__gm.tab()')) === 'scene');
@@ -72,7 +95,7 @@ export async function listTab(t) {
   await sleep(200);
   check('and the count follows the value', (await find('2 items')) !== null);
 
-  // 6. A list whose target is gone empties the tab rather than showing a stale one.
+  // 7. A list whose target is gone empties the tab rather than showing a stale one.
   await mutate("__gm.state.openList({ kind: 'asset', assetId: 'listy', key: 'nums' })");
   await sleep(200);
   check('a list can be opened from outside the inspector too', (await json('__gm.tab()')) === 'list');