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>

tests/ui/scroll-container.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from 'vitest';
+import { ScrollContainer, Spacer, VStack } from '../../src/ui';
+
+/** Row tops after a layout; an unlaid-out stack leaves every child at 0. */
+const tops = (stack: VStack) => stack.children.map((c) => c.y);
+
+describe('a scroll container told its content changed', () => {
+  it('lays out rows that leave the height pinned to the viewport', () => {
+    const scroll = new ScrollContainer();
+    scroll.resize(200, 300);
+    const rows = new VStack();
+    // The list tab hands over the stack before filling it, so the empty content is measured first
+    // and pinned to the viewport height.
+    scroll.setContent(rows);
+    rows.add(new Spacer(20));
+    rows.add(new Spacer(20));
+    rows.add(new Spacer(20));
+
+    // 60 < 300, so the content keeps the height it already had: `resize` alone would see no
+    // change and skip the layout, leaving all three rows stacked at the top.
+    scroll.relayoutContent();
+    expect(tops(rows)).toEqual([0, 20, 40]);
+  });
+
+  it('still lays out rows that make the content taller than the viewport', () => {
+    const scroll = new ScrollContainer();
+    scroll.resize(200, 50);
+    const rows = new VStack();
+    scroll.setContent(rows);
+    rows.add(new Spacer(20));
+    rows.add(new Spacer(20));
+    rows.add(new Spacer(20));
+
+    scroll.relayoutContent();
+    expect(tops(rows)).toEqual([0, 20, 40]);
+    expect(scroll.maxScroll).toBe(10);
+  });
+});