Let a segmented row answer, and inset a list's dividers

Plan step 19, containment.md C-08, C-21, C-22 and C-16. The segmented
fill was declared unlayered, so it beat every state layer in
@layer components and a segmented row lit up for nothing: it now sits in
the layer, `:where()`d to weigh nothing, ahead of the state rules. Its
tone is `surface`, which is ListTokens' ItemSegmentedContainerColor, and
a keyboard-focused row morphs to the large corner like a pressed one.
`<x-list dividers>` draws ListTokens' 16dp-inset rule instead of a
full-bleed `divide-y`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

tests/Feature/Components/ListTest.php

@@ -5,8 +5,11 @@ it('draws a plain list, with dividers on request', function () {
         ->toContain('role="list"')
         ->toContain('aria-label="Files"')
         ->toContain('data-list="plain"')
-        ->toContain('divide-y divide-outline-variant')
-        ->toContain('role="listitem"');
+        ->toContain('data-dividers')
+        ->not->toContain('divide-y')
+        ->toContain('role="listitem"')
+        ->and((string) $this->blade('<x-list><x-list-item title="a.zip" /></x-list>'))->not->toContain('data-dividers')
+        ->and((string) $this->blade('<x-list segmented dividers><x-list-item title="a.zip" /></x-list>'))->not->toContain('data-dividers');
 });
 
 it('draws M3 Expressive\'s segmented list', function () {