Skip a font face named in a comment when trimming the fallback

Found while doing plan step 46: withoutFontFace() searched the raw
bundle, so the `@font-face` that foundation/base.css's and
error-page.css's header comments mention read as the rule. Each cut from
inside its comment to the end of the next block and left the comment
open, so the no-build fallback lost base.css's html rule and icon.css's
rules. The search and the brace count now read Stylesheets::mask(), and
only tokens/font.css's real block leaves.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/Support/ErrorPage.php

@@ -137,24 +137,29 @@ class ErrorPage
     /**
      * `$css` with every `@font-face` block dropped, wherever it sits: not a search for the block's
      * text (fragile the moment a comment or a value is reworded) but a structural read — find
-     * `@font-face` outside nothing else looks at here, then remove the balanced `{ … }` that
-     * follows it, brace for brace, however the block itself is written. `tokens/font.css`'s is the
-     * only one the bundle carries, and it is also the bundle's only relative `url()` (button.css,
-     * icon.css, shape.css and the rest reference nothing on disk), so this removal is also what
-     * leaves the fallback with no `url()` to a font the fallback cannot serve. The typeface itself
+     * `@font-face` outside comments and strings, then remove the balanced `{ … }` that follows it,
+     * brace for brace, however the block itself is written. Both reads go through
+     * `Stylesheets::mask()`, because the bundle's comments name the rule too (foundation/base.css's
+     * and error-page.css's headers): read as the rule, such a mention cut from inside its comment to
+     * the end of the next balanced block, leaving the comment open over the rules after it —
+     * base.css's `html` rule and icon.css's rules left the fallback that way. `tokens/font.css`'s
+     * block is the only one the bundle carries, and it is also the bundle's only relative `url()`
+     * (button.css, icon.css, shape.css and the rest reference nothing on disk), so this removal is
+     * also what leaves the fallback with no `url()` to a font it cannot serve. The typeface itself
      * degrades on its own: `--md-ref-typeface-brand` (tokens/type.css) lists `ui-sans-serif`,
      * `system-ui` and `sans-serif` right after the brand name, so with no `@font-face` to resolve
      * it the browser skips straight to that system stack — nothing here has to name one.
      */
     protected static function withoutFontFace(string $css): string
     {
+        $masked = Stylesheets::mask($css);
         $result = '';
         $offset = 0;
         $length = strlen($css);
 
-        while (($start = stripos($css, '@font-face', $offset)) !== false) {
+        while (($start = stripos($masked, '@font-face', $offset)) !== false) {
             $result .= substr($css, $offset, $start - $offset);
-            $open = strpos($css, '{', $start);
+            $open = strpos($masked, '{', $start);
 
             if ($open === false) {
                 $offset = $start + strlen('@font-face');
@@ -166,7 +171,7 @@ class ErrorPage
             $i = $open + 1;
 
             while ($i < $length && $depth > 0) {
-                $depth += match ($css[$i]) {
+                $depth += match ($masked[$i]) {
                     '{' => 1,
                     '}' => -1,
                     default => 0,

src/Support/Stylesheets.php

@@ -230,9 +230,10 @@ final class Stylesheets
     /**
      * `$css` with every comment and quoted string blinded to spaces (newlines kept), same length —
      * so a search on it for `@import` or `url(` never matches one written inside a comment or a
-     * string, while every offset still lines up with `$css` itself.
+     * string, while every offset still lines up with `$css` itself. Public for
+     * `ErrorPage::withoutFontFace()`, which searches a bundle for `@font-face` the same way.
      */
-    private static function mask(string $css): string
+    public static function mask(string $css): string
     {
         $masked = $css;
         $length = strlen($css);

tests/Feature/ErrorPagesTest.php

@@ -406,3 +406,25 @@ it('inlines beside a build the error layout\'s bundle, which holds no font face,
         ->not->toMatch('/\burl\(/i')
         ->toContain('@layer material.reset, material.tokens, material.base, material.layout, material.components, material.text, material.visibility;');
 });
+
+/**
+ * The bundle's comments name `@font-face` too (foundation/base.css's and error-page.css's headers).
+ * Read as the rule, each mention cut from inside its comment to the end of the next balanced block
+ * and left the comment open, so base.css's `html` rule and icon.css's rules went missing from the
+ * fallback. Only the real block may leave: what remains is the bundle, rule for rule, without it.
+ */
+it('drops only the real font face from the fallback, not the rules after a comment that names one', function () {
+    $files = [
+        realpath(__DIR__.'/../../resources/css/foundation.css'),
+        realpath(__DIR__.'/../../resources/css/components/error-page.css'),
+    ];
+    $withoutComments = fn (string $css): string => (string) preg_replace('~/\*.*?\*/~s', '', $css);
+    $bundle = Stylesheets::bundle($files);
+
+    expect(substr_count($withoutComments($bundle), '@font-face'))->toBe(1)
+        ->and(substr_count($bundle, '@font-face'))->toBeGreaterThan(1)
+        ->and($withoutComments((string) ErrorPage::fallbackStyles()))
+        ->toStartWith($withoutComments((string) preg_replace('/@font-face\s*\{[^{}]*\}/', '', $bundle)))
+        ->toMatch('/html \{\s*background-color: var\(--md-sys-color-surface\);/')
+        ->toContain('[data-md-icon] {');
+});