Wait past LayoutTest's FAB spring before measuring, fix its safe-area math

Three FAB position tests chained ->assertScript() off a bare
$page->script(), which returns the script's value, not the page.
Fixing that surfaced a real settling issue: layoutPage() opens wider
than the 599/600px these tests probe before resize() narrows it, so
the FAB's inset-block-end (a spatial spring, scaffold.css) is still
animating in from the wider default margin when the page first
reports ready. Any baseline captured then is mid-flight, not the
resting value, so both tests now wait past the spring before taking
one. The safe-area test's inline-end (right) assertion also assumed
its margin and the safe area add together; the CSS is
max(margin, safe-right), an alternative to the margin, not additive
with it, unlike the bottom edge (plan step 36, navigation group).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

tests/Browser/LayoutTest.php

@@ -462,11 +462,18 @@ it('drops the bar\'s own height from the FAB\'s offset once hide-bar-on-scroll s
         </x-scaffold>
         BLADE;
 
-    $page = layoutPage($body, 599, 800);
+    // The window opens wider than 599 before resize() narrows it (layoutPage()), so the FAB's own
+    // spatial-spring transition is still settling from the wider margin when the page first
+    // reports ready; wait it out before the baseline below or it captures a mid-flight value.
+    $page = layoutPage($body, 599, 800)->wait(0.6);
     $shown = (int) $page->script(layoutRect(SCAFFOLD_FAB, 'bottom'));
 
-    $page->script('window.scrollTo(0, 400)')
+    $page->script('window.scrollTo(0, 400)');
-        ->assertScript("document.querySelector('[data-md-navigation-bar]').hasAttribute('data-md-hidden')")
+
+    $page->assertScript("document.querySelector('[data-md-navigation-bar]').hasAttribute('data-md-hidden')")
+        // The FAB's inset-block-end is a spatial spring (scaffold.css), so its move down is not
+        // done the instant the bar's data-md-hidden attribute flips; wait past it before measuring.
+        ->wait(0.6)
         // The bar's own 64px is what --material-bottom-bar drops once the bar has slid off, so the
         // FAB moves down by exactly that much (navigation-bar.css, layout/scaffold.css).
         ->assertScript(layoutRect(SCAFFOLD_FAB, 'bottom')." === {$shown} + 64")
@@ -487,14 +494,24 @@ it('clears a safe area an application sets on the FAB\'s inline-end and bottom e
         </x-scaffold>
         BLADE;
 
-    $page = layoutPage($body, 599, 800);
+    // The window opens wider than 599 before resize() narrows it (layoutPage()), so the FAB's
+    // margin (and with it inset-block-end, a spatial spring) is still settling from the wider
+    // default when the page first reports ready; wait it out before either baseline below.
+    $page = layoutPage($body, 599, 800)->wait(0.6);
     $right = (int) $page->script('window.innerWidth - '.layoutRect(SCAFFOLD_FAB, 'right'));
     $bottom = (int) $page->script('window.innerHeight - '.layoutRect(SCAFFOLD_FAB, 'bottom'));
 
-    $page->script("document.documentElement.style.setProperty('--material-safe-right', '20px')")
+    // inset-inline-end (right) has no transition of its own, so this one applies at once. It is
-        ->assertScript('window.innerWidth - '.layoutRect(SCAFFOLD_FAB, 'right')." === {$right} + 20");
+    // max(margin, safe-right) — an alternative to the margin, not additive with it — unlike the
+    // bottom edge below, which always adds its margin on top of the greater of the two.
+    $page->script("document.documentElement.style.setProperty('--material-safe-right', '20px')");
 
-    $page->script("document.documentElement.style.setProperty('--material-safe-bottom', '30px')")
+    $page->assertScript('window.innerWidth - '.layoutRect(SCAFFOLD_FAB, 'right')." === Math.max({$right}, 20)");
+
+    // inset-block-end (bottom) is the spatial spring scaffold.css transitions; wait past it.
+    $page->script("document.documentElement.style.setProperty('--material-safe-bottom', '30px')");
+
+    $page->wait(0.6)
         ->assertScript('window.innerHeight - '.layoutRect(SCAFFOLD_FAB, 'bottom')." === {$bottom} + 30")
         ->assertNoJavaScriptErrors();
 });