diff --git a/php-transformer/composer.json b/php-transformer/composer.json
index 7d7a140e..a49b7213 100644
--- a/php-transformer/composer.json
+++ b/php-transformer/composer.json
@@ -80,11 +80,14 @@
       "php tests/unit/engine-support-css-asset.php",
       "php tests/unit/engine-support-css-specificity.php",
       "php tests/unit/inline-display-carrier.php",
+      "php tests/unit/css-owned-flex-carrier.php",
+      "php tests/unit/auto-fit-grid-carrier.php",
       "php tests/unit/artifact-author-stylesheet-projection.php",
       "php tests/unit/fallback-finding-normalizer.php",
       "php tests/unit/navigation-underline-color-resolver.php",
       "php tests/unit/button-signal-classifier.php",
       "php tests/unit/button-style-resolver.php",
+      "php tests/unit/button-font-family-carry.php",
       "php tests/unit/button-visual-probe-diagnostics.php",
       "php tests/unit/shell-landmark-policy.php",
       "php tests/unit/block-style-support-conversion.php",
diff --git a/php-transformer/src/HtmlToBlocks/BlockFactory.php b/php-transformer/src/HtmlToBlocks/BlockFactory.php
index 9fc0b616..725a9ebd 100644
--- a/php-transformer/src/HtmlToBlocks/BlockFactory.php
+++ b/php-transformer/src/HtmlToBlocks/BlockFactory.php
@@ -979,6 +979,9 @@ private function buttonStyleSupport(array $attrs): array
             $classes[] = 'has-custom-font-size';
         }
         $typographyMap = array(
+            // A raw authored family is a custom value, so core's style engine
+            // serializes it inline rather than as a has-*-font-family class.
+            'fontFamily'    => 'font-family',
             'fontSize'      => 'font-size',
             'fontWeight'    => 'font-weight',
             'letterSpacing' => 'letter-spacing',
diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
index 10a0b185..a1c2f86d 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
@@ -453,6 +453,21 @@ final class HtmlTransformer
         'place-items',
     );
 
+    /** @var list<string> Inline flex declarations carried to the generated stylesheet for css-owned flex containers. */
+    private const CSS_OWNED_FLEX_CARRIER_PROPERTIES = array(
+        'display',
+        'flex-flow',
+        'flex-direction',
+        'flex-wrap',
+        'gap',
+        'row-gap',
+        'column-gap',
+        'align-content',
+        'align-items',
+        'justify-content',
+        'place-content',
+    );
+
     private const CSS_OWNED_LAYOUT_ITEM_CLASS = 'blocks-engine-css-owned-layout-item';
 
     /** @var array<string, string> Source control DOM paths mapped to core/button wrapper classes. */
@@ -4403,6 +4418,10 @@ private function cssOwnedGroupAttributes(DOMElement $element): array
             return $this->cssOwnedGridAttributes($element);
         }
 
+        if ( $this->isCssOwnedFlexElement($element) ) {
+            $attrs = $this->cssOwnedFlexAttributes($element);
+        }
+
         unset($attrs['layout']);
         $attrs['className'] = $this->mergeClassNames(
             (string) ($attrs['className'] ?? ''),
@@ -4423,6 +4442,49 @@ private function cssOwnedGroupAttributes(DOMElement $element): array
         return $attrs;
     }
 
+    private function isCssOwnedFlexElement(DOMElement $element): bool
+    {
+        $display = strtolower(trim((string) preg_replace(
+            '/\s*!important\s*$/i',
+            '',
+            (string) ($this->structuralPresentationDeclarations($element)['display'] ?? '')
+        )));
+
+        return in_array($display, array( 'flex', 'inline-flex' ), true);
+    }
+
+    /**
+     * Attributes for a block hosting an author flex container demoted to CSS
+     * ownership. The demotion below drops the native `layout` attribute, which
+     * was the only thing expressing the flex container, so without carrying the
+     * authored `display:flex` the children stack. The inline declarations ride
+     * to the generated stylesheet on a carrier class exactly as
+     * CSS_OWNED_GRID_CARRIER_PROPERTIES does for grids; class-owned ones are
+     * already retained by author stylesheet materialization.
+     *
+     * An inline display that overrides class-owned layout is already carried
+     * complete by inlineGeometryClassName(), at the non-important specificity
+     * tier that keeps authored !important rules winning. Forcing those same
+     * properties would move them to the !important tier, so that case is left
+     * alone.
+     *
+     * @return array<string, mixed>
+     */
+    private function cssOwnedFlexAttributes(DOMElement $element): array
+    {
+        $inlineDeclarations = $this->cssDeclarations($this->attr($element, 'style'));
+        if ( $this->inlineDisplayOverridesAuthorLayout($element, $inlineDeclarations) ) {
+            return $this->presentationAttributes($element);
+        }
+
+        // Carry only the inline-present properties so the fallback to
+        // mapper-synthesized declarations cannot invent a `gap` that
+        // overrides explicit row-gap/column-gap values.
+        $carriedProperties = array_values(array_intersect(self::CSS_OWNED_FLEX_CARRIER_PROPERTIES, array_keys($inlineDeclarations)));
+
+        return $this->presentationAttributes($element, array(), $carriedProperties);
+    }
+
     private function isCssOwnedGridElement(DOMElement $element): bool
     {
         $display = strtolower(trim((string) preg_replace(
diff --git a/php-transformer/src/HtmlToBlocks/Patterns/ButtonStyleResolver.php b/php-transformer/src/HtmlToBlocks/Patterns/ButtonStyleResolver.php
index 17909afd..f98b8459 100644
--- a/php-transformer/src/HtmlToBlocks/Patterns/ButtonStyleResolver.php
+++ b/php-transformer/src/HtmlToBlocks/Patterns/ButtonStyleResolver.php
@@ -34,8 +34,16 @@ final class ButtonStyleResolver
 {
     /**
      * Typography supports projected onto buttons, in canonical emission order.
+     *
+     * fontFamily belongs here: core/button registers a `fontFamily` attribute,
+     * which core injects only when the typography fontFamily support is enabled.
+     * A raw authored value is not a preset slug, so it rides in
+     * style.typography.fontFamily and serializes inline on the link. Dropping it
+     * left the typeface to theme.json's styles.elements.button, because the
+     * authored class is consumed into block attributes and its rewritten rule no
+     * longer wins the cascade.
      */
-    private const BUTTON_TYPOGRAPHY = array( 'fontSize', 'fontWeight', 'letterSpacing', 'lineHeight', 'textTransform' );
+    private const BUTTON_TYPOGRAPHY = array( 'fontFamily', 'fontSize', 'fontWeight', 'letterSpacing', 'lineHeight', 'textTransform' );
 
     private readonly StyleAttributeMapper $mapper;
 
diff --git a/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php b/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php
index a9cd2e29..3b67768c 100644
--- a/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php
+++ b/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php
@@ -1993,15 +1993,22 @@ private function layoutFlexWrap(string $value): string
     }
 
     /**
-     * A track list of exactly repeat(auto-fit|auto-fill, minmax(<width>, 1fr))
-     * is natively expressible as WordPress grid layout: core renders
+     * A track list of exactly repeat(auto-fill, minmax(<width>, 1fr)) is
+     * natively expressible as WordPress grid layout: core renders
      * minimumColumnWidth as repeat(auto-fill, minmax(min(<width>, 100%), 1fr)).
-     * Every other track list (fixed counts, asymmetric tracks, nested
-     * functions) returns '' and stays under author CSS ownership.
+     *
+     * auto-fit is deliberately excluded. wp-includes/block-supports/layout.php
+     * hardcodes auto-fill in every branch that renders minimumColumnWidth, so
+     * the attribute cannot express auto-fit at all. The two keywords differ in
+     * rendered geometry — auto-fit collapses tracks left empty, auto-fill
+     * retains them — so converting auto-fit would keep the empty tracks and
+     * squeeze the real content into part of the measure. Like every other track
+     * list WordPress cannot express (fixed counts, asymmetric tracks, nested
+     * functions), auto-fit returns '' and stays under author CSS ownership.
      */
     private function autoRepeatMinimumColumnWidth(string $tracks): string
     {
-        if ( 1 === preg_match('/^repeat\(\s*auto-(?:fit|fill)\s*,\s*minmax\(\s*([0-9]*\.?[0-9]+(?:px|rem|em|ch|ex|vw|vh|vmin|vmax|%))\s*,\s*1fr\s*\)\s*\)$/i', trim($tracks), $matches)
+        if ( 1 === preg_match('/^repeat\(\s*auto-fill\s*,\s*minmax\(\s*([0-9]*\.?[0-9]+(?:px|rem|em|ch|ex|vw|vh|vmin|vmax|%))\s*,\s*1fr\s*\)\s*\)$/i', trim($tracks), $matches)
             && 0.0 < (float) $matches[1]
         ) {
             return strtolower($matches[1]);
diff --git a/php-transformer/tests/fixtures/parity/html-autofit-grid-carries-gap-and-background.json b/php-transformer/tests/fixtures/parity/html-autofit-grid-carries-gap-and-background.json
index 13649d1e..bbc3acce 100644
--- a/php-transformer/tests/fixtures/parity/html-autofit-grid-carries-gap-and-background.json
+++ b/php-transformer/tests/fixtures/parity/html-autofit-grid-carries-gap-and-background.json
@@ -1,11 +1,11 @@
 {
   "schema": "blocks-engine/php-transformer/parity-fixture/v1",
   "name": "html-autofit-grid-carries-gap-and-background",
-  "description": "An auto-fit grid using the hairline-divider technique (gap:1px plus a container background painting through the gaps) keeps its native grid tracks while source CSS owns its gap: core/group save markup cannot serialize blockGap. The container background remains a color support so the dividers survive without the author stylesheet.",
+  "description": "An auto-fit grid using the hairline-divider technique (gap:1px plus a container background painting through the gaps) stays entirely under author CSS ownership: core's grid layout support hardcodes auto-fill, which would retain the tracks auto-fit collapses. The author rule keeps the tracks, the hairline gap, and the divider background together, so the technique survives intact rather than being split across a native layout attribute and a color support.",
   "source_reference": {
     "repo": "php-transformer",
     "path": "tests/fixtures/parity/html-autofit-grid-carries-gap-and-background.json",
-    "notes": "Derived from a portfolio work grid where gap:1px;background:var(--ink) painted hairline separators between cells. The source stylesheet retains the gap because core/group does not serialize blockGap in canonical save markup."
+    "notes": "Derived from a portfolio work grid where gap:1px;background:var(--ink) painted hairline separators between cells. The gap and the background must stay with the track list in one author rule: promoting either to a block support while the tracks stay in CSS splits a single visual technique across two owners."
   },
   "legacy_comparison": {
     "skip": true,
@@ -20,7 +20,8 @@
       "path": "blocks.0",
       "name": "core/group",
       "attrs": {
-        "layout": { "type": "grid", "minimumColumnWidth": "240px" }
+        "layout": null,
+        "className": "work-grid blocks-engine-css-owned-layout blocks-engine-css-owned-grid"
       }
     }
   ],
@@ -29,7 +30,9 @@
     { "path": "status", "assert": "equals", "value": "success" },
     { "path": "fallbacks", "assert": "count", "count": 0 },
     { "path": "blocks.0.attrs.style.spacing.blockGap", "assert": "equals", "value": null },
-    { "path": "blocks.0.attrs.style.color.background", "assert": "equals", "value": "#1a1a1a" },
-    { "path": "serialized_blocks", "assert": "contains", "value": "is-layout-grid" }
+    { "path": "blocks.0.attrs.style.color.background", "assert": "equals", "value": null },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "is-layout-grid" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "blocks-engine-css-owned-grid" },
+    { "path": "assets.1.content", "assert": "contains", "value": ".work-grid{display:grid;grid-template-columns:repeat(auto-fit, minmax(240px, 1fr));gap:1px;background:#1a1a1a}" }
   ]
 }
diff --git a/php-transformer/tests/fixtures/parity/html-autofit-grid-inline-leaf-items.json b/php-transformer/tests/fixtures/parity/html-autofit-grid-inline-leaf-items.json
index cce091c7..88d766e6 100644
--- a/php-transformer/tests/fixtures/parity/html-autofit-grid-inline-leaf-items.json
+++ b/php-transformer/tests/fixtures/parity/html-autofit-grid-inline-leaf-items.json
@@ -1,11 +1,11 @@
 {
   "schema": "blocks-engine/php-transformer/parity-fixture/v1",
   "name": "html-autofit-grid-inline-leaf-items",
-  "description": "An expressible auto-fit grid whose direct children are standalone inline text leaves keeps native grid layout while source CSS owns its gap. Each leaf rides its own display:contents carrier paragraph, so the item count matches the source children and the spans themselves become the grid items. Locks the standalone-inline-leaf routing branch, which bypasses cssOwnedGroupAttributes.",
+  "description": "An auto-fit grid whose direct children are standalone inline text leaves keeps the author rule as the owner of its tracks and gap, because core's grid layout support cannot express auto-fit. Each leaf still rides its own display:contents carrier paragraph, so the item count matches the source children and the spans themselves become the grid items. Locks the standalone-inline-leaf routing branch, which bypasses cssOwnedGroupAttributes.",
   "source_reference": {
     "repo": "php-transformer",
     "path": "tests/fixtures/parity/html-autofit-grid-inline-leaf-items.json",
-    "notes": "Derived from client-logo strips built as bare styled spans inside repeat(auto-fit, minmax(W, 1fr)) grids. Guards against two failure modes: adjacent inline leaves coalescing into one paragraph (one grid item instead of N) and the branch dropping the native layout back to a vertical stack."
+    "notes": "Derived from client-logo strips built as bare styled spans inside repeat(auto-fit, minmax(W, 1fr)) grids. Guards against two failure modes: adjacent inline leaves coalescing into one paragraph (one grid item instead of N) and the retained author rule losing its display:grid, which would stack the strip vertically."
   },
   "legacy_comparison": {
     "skip": true,
@@ -19,7 +19,7 @@
     {
       "path": "blocks.0",
       "name": "core/group",
-      "attrs": { "layout": { "type": "grid", "minimumColumnWidth": "190px" } }
+      "attrs": { "layout": null, "className": "client-strip blocks-engine-css-owned-layout blocks-engine-css-owned-flow" }
     },
     { "path": "blocks.0.innerBlocks.0", "name": "core/paragraph" },
     { "path": "blocks.0.innerBlocks.3", "name": "core/paragraph" }
@@ -30,7 +30,8 @@
     { "path": "fallbacks", "assert": "count", "count": 0 },
     { "path": "blocks.0.innerBlocks", "assert": "count", "count": 4 },
     { "path": "blocks.0.attrs.style.spacing.blockGap", "assert": "equals", "value": null },
-    { "path": "serialized_blocks", "assert": "contains", "value": "is-layout-grid" },
-    { "path": "serialized_blocks", "assert": "contains", "value": "<p class=\"blocks-engine-inline-layout-carrier\"><span class=\"client\">Acme Corp</span></p>" }
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "is-layout-grid" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "<p class=\"blocks-engine-inline-layout-carrier\"><span class=\"client\">Acme Corp</span></p>" },
+    { "path": "assets.1.content", "assert": "contains", "value": ".client-strip{display:grid;grid-template-columns:repeat(auto-fit, minmax(190px, 1fr));gap:24px}" }
   ]
 }
diff --git a/php-transformer/tests/fixtures/parity/html-autofit-grid-maps-to-minimum-column-width.json b/php-transformer/tests/fixtures/parity/html-autofit-grid-maps-to-minimum-column-width.json
deleted file mode 100644
index a04ba5a4..00000000
--- a/php-transformer/tests/fixtures/parity/html-autofit-grid-maps-to-minimum-column-width.json
+++ /dev/null
@@ -1,34 +0,0 @@
-{
-  "schema": "blocks-engine/php-transformer/parity-fixture/v1",
-  "name": "html-autofit-grid-maps-to-minimum-column-width",
-  "description": "An author-CSS grid container using repeat(auto-fit, minmax(W, 1fr)) is exactly expressible as native WordPress grid layout. It must become a core/group with layout {type:grid, minimumColumnWidth:W} instead of demoting to the css-owned flow group, which stacks the cards in a single column and loses the responsive multi-column arrangement.",
-  "source_reference": {
-    "repo": "php-transformer",
-    "path": "tests/fixtures/parity/html-autofit-grid-maps-to-minimum-column-width.json",
-    "notes": "Derived from a portfolio homepage where .work-grid { display:grid; grid-template-columns:repeat(auto-fit, minmax(240px, 1fr)) } collapsed to a vertical stack after transform: the css-owned demotion dropped the layout attribute and the carried CSS never reproduced the auto-fit tracks."
-  },
-  "legacy_comparison": {
-    "skip": true,
-    "reason": "Covers current PHP transformer layout classification behavior; no downstream legacy comparison."
-  },
-  "operation": "html_transformer.transform",
-  "input": {
-    "content": "<html><head><style>.work-grid{display:grid;grid-template-columns:repeat(auto-fit, minmax(240px, 1fr));gap:24px}.work-card h3{margin:0}</style></head><body><section class=\"work-grid\"><div class=\"work-card\"><h3>Ledger</h3><p>Design system for a fintech team.</p></div><div class=\"work-card\"><h3>Atlas</h3><p>Mapping tools for field research.</p></div><div class=\"work-card\"><h3>Relay</h3><p>Realtime dashboard for dispatch.</p></div></section></body></html>"
-  },
-  "expected_blocks": [
-    {
-      "path": "blocks.0",
-      "name": "core/group",
-      "attrs": { "layout": { "type": "grid", "minimumColumnWidth": "240px" } }
-    }
-  ],
-  "expected_fallbacks": [],
-  "expect": [
-    { "path": "status", "assert": "equals", "value": "success" },
-    { "path": "fallbacks", "assert": "count", "count": 0 },
-    { "path": "blocks.0.innerBlocks", "assert": "count", "count": 3 },
-    { "path": "serialized_blocks", "assert": "contains", "value": "is-layout-grid" },
-    { "path": "serialized_blocks", "assert": "contains", "value": "\"minimumColumnWidth\":\"240px\"" },
-    { "path": "serialized_blocks", "assert": "not_contains", "value": "blocks-engine-css-owned-flow" }
-  ]
-}
diff --git a/php-transformer/tests/fixtures/parity/html-autofit-grid-stays-css-owned.json b/php-transformer/tests/fixtures/parity/html-autofit-grid-stays-css-owned.json
new file mode 100644
index 00000000..5292d58f
--- /dev/null
+++ b/php-transformer/tests/fixtures/parity/html-autofit-grid-stays-css-owned.json
@@ -0,0 +1,36 @@
+{
+  "schema": "blocks-engine/php-transformer/parity-fixture/v1",
+  "name": "html-autofit-grid-stays-css-owned",
+  "description": "An author-CSS grid container using repeat(auto-fit, minmax(W, 1fr)) is NOT expressible as native WordPress grid layout: wp-includes/block-supports/layout.php hardcodes auto-fill in every branch that renders minimumColumnWidth, and auto-fill retains the tracks auto-fit collapses. The container must take the css-owned-GRID path, where the author rule keeps owning the exact authored track list — not the css-owned-FLOW demotion, which drops display:grid and stacks the cards in a single column.",
+  "source_reference": {
+    "repo": "php-transformer",
+    "path": "tests/fixtures/parity/html-autofit-grid-stays-css-owned.json",
+    "notes": "Derived from a portfolio homepage where .work-grid { display:grid; grid-template-columns:repeat(auto-fit, minmax(240px, 1fr)) } collapsed to a vertical stack after transform, because the demotion at the time dropped display:grid along with the layout attribute. Converting to a native layout attribute traded that stack for a different wrong geometry: WordPress rendered the tracks as auto-fill, retaining empty tracks and squeezing the cards into part of the measure. The css-owned-grid carrier is the path that reproduces the authored tracks exactly."
+  },
+  "legacy_comparison": {
+    "skip": true,
+    "reason": "Covers current PHP transformer layout classification behavior; no downstream legacy comparison."
+  },
+  "operation": "html_transformer.transform",
+  "input": {
+    "content": "<html><head><style>.work-grid{display:grid;grid-template-columns:repeat(auto-fit, minmax(240px, 1fr));gap:24px}.work-card h3{margin:0}</style></head><body><section class=\"work-grid\"><div class=\"work-card\"><h3>Ledger</h3><p>Design system for a fintech team.</p></div><div class=\"work-card\"><h3>Atlas</h3><p>Mapping tools for field research.</p></div><div class=\"work-card\"><h3>Relay</h3><p>Realtime dashboard for dispatch.</p></div></section></body></html>"
+  },
+  "expected_blocks": [
+    {
+      "path": "blocks.0",
+      "name": "core/group",
+      "attrs": { "layout": null, "className": "work-grid blocks-engine-css-owned-layout blocks-engine-css-owned-grid" }
+    }
+  ],
+  "expected_fallbacks": [],
+  "expect": [
+    { "path": "status", "assert": "equals", "value": "success" },
+    { "path": "fallbacks", "assert": "count", "count": 0 },
+    { "path": "blocks.0.innerBlocks", "assert": "count", "count": 3 },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "is-layout-grid" },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "minimumColumnWidth" },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "blocks-engine-css-owned-flow" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "blocks-engine-css-owned-grid" },
+    { "path": "assets.1.content", "assert": "contains", "value": ".work-grid{display:grid;grid-template-columns:repeat(auto-fit, minmax(240px, 1fr));gap:24px}" }
+  ]
+}
diff --git a/php-transformer/tests/fixtures/parity/html-horizontal-flex-stays-columns.json b/php-transformer/tests/fixtures/parity/html-horizontal-flex-stays-columns.json
index 5502a54b..db6cd94c 100644
--- a/php-transformer/tests/fixtures/parity/html-horizontal-flex-stays-columns.json
+++ b/php-transformer/tests/fixtures/parity/html-horizontal-flex-stays-columns.json
@@ -5,7 +5,7 @@
   "source_reference": {
     "repo": "php-transformer",
     "path": "tests/fixtures/parity/html-horizontal-flex-stays-columns.json",
-    "notes": "Same display:flex container shape as the vertical fixture but without flex-direction:column. The ColumnsPattern flex-direction guard does not fire, so the horizontal columns layout is preserved unchanged."
+    "notes": "Same display:flex container shape as the vertical fixture but without flex-direction:column. The ColumnsPattern flex-direction guard does not fire, so the horizontal columns layout is preserved unchanged. The container is demoted to a css-owned core/group, which drops the native layout attribute, so the inline display:flex must ride to the generated stylesheet on a geometry carrier or the two columns stack."
   },
   "legacy_comparison": {
     "skip": true,
@@ -28,7 +28,9 @@
     { "path": "status", "assert": "equals", "value": "success" },
     { "path": "blocks", "assert": "count", "count": 1 },
     { "path": "blocks.0.innerBlocks", "assert": "count", "count": 2 },
-    { "path": "serialized_blocks", "assert": "contains", "value": "cols blocks-engine-css-owned-layout" },
-    { "path": "serialized_blocks", "assert": "not_contains", "value": "blocks-engine/author-layout" }
+    { "path": "serialized_blocks", "assert": "contains", "value": "class=\"wp-block-group cols be-inline-geometry-" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "blocks-engine-css-owned-layout" },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "blocks-engine/author-layout" },
+    { "path": "assets.0.content", "assert": "contains", "value": "{display:flex !important}" }
   ]
 }
diff --git a/php-transformer/tests/fixtures/parity/html-single-child-flex-svg-address.json b/php-transformer/tests/fixtures/parity/html-single-child-flex-svg-address.json
index 63233023..f5032681 100644
--- a/php-transformer/tests/fixtures/parity/html-single-child-flex-svg-address.json
+++ b/php-transformer/tests/fixtures/parity/html-single-child-flex-svg-address.json
@@ -1,7 +1,7 @@
 {
   "schema": "blocks-engine/php-transformer/parity-fixture/v1",
   "name": "html-single-child-flex-svg-address",
-  "description": "Preserves single-child flex wrappers with passive illustrative inline SVG represented as native core/image and readable address line breaks without unsupported fallbacks.",
+  "description": "Preserves single-child flex wrappers with passive illustrative inline SVG represented as native core/image and readable address line breaks without unsupported fallbacks. The wrapper is demoted to a css-owned core/group, so its inline display:flex and centering must ride to the generated stylesheet on a geometry carrier — dropping them leaves the illustration flush left instead of centered.",
   "source_reference": {
     "repo": "php-transformer",
     "path": "tests/fixtures/parity/html-single-child-flex-svg-address.json",
@@ -17,7 +17,7 @@
   },
   "expected_blocks": [
     { "path": "blocks.0", "name": "core/group" },
-    { "path": "blocks.0.innerBlocks.0", "name": "core/group", "attrs": { "className": "illustration-frame blocks-engine-css-owned-layout" } },
+    { "path": "blocks.0.innerBlocks.0", "name": "core/group" },
     { "path": "blocks.0.innerBlocks.0.innerBlocks.0", "name": "core/image" },
     { "path": "blocks.0.innerBlocks.1", "name": "core/paragraph", "attrs": { "className": "contact-card", "content": "214 Maple Street<br>Benton Harbor, MI<br><a href=\"tel:+12695550193\">(269) 555-0193</a>" } }
   ],
@@ -27,7 +27,10 @@
     { "path": "fallbacks", "assert": "count", "count": 0 },
     { "path": "blocks.0.innerBlocks.0.innerBlocks.0.attrs.url", "assert": "contains", "value": "assets/materialized-svg/" },
     { "path": "blocks.0.innerBlocks.0.innerBlocks.0.attrs.alt", "assert": "equals", "value": "Storefront illustration" },
-    { "path": "assets", "assert": "count", "count": 1 },
+    { "path": "assets", "assert": "count", "count": 2 },
+    { "path": "assets.1.content", "assert": "contains", "value": "{display:flex !important;align-items:center !important;justify-content:center !important}" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "class=\"wp-block-group illustration-frame be-inline-geometry-" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "blocks-engine-css-owned-layout" },
     { "path": "serialized_blocks", "assert": "contains", "value": "Storefront illustration" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "blocks-engine/author-layout" },
     { "path": "coverage.0.fallback_count", "assert": "equals", "value": 0 }
diff --git a/php-transformer/tests/fixtures/parity/html-single-child-flex-svg.json b/php-transformer/tests/fixtures/parity/html-single-child-flex-svg.json
index ffadf039..c791d3a8 100644
--- a/php-transformer/tests/fixtures/parity/html-single-child-flex-svg.json
+++ b/php-transformer/tests/fixtures/parity/html-single-child-flex-svg.json
@@ -1,7 +1,7 @@
 {
   "schema": "blocks-engine/php-transformer/parity-fixture/v1",
   "name": "html-single-child-flex-svg",
-  "description": "Converts a single illustrative SVG inside a flex centering wrapper without leaking failed column-probe fallbacks, materializing the SVG as editable core/image media.",
+  "description": "Converts a single illustrative SVG inside a flex centering wrapper without leaking failed column-probe fallbacks, materializing the SVG as editable core/image media. The wrapper is demoted to a css-owned core/group, so its inline display:flex and justify-content must ride to the generated stylesheet on a geometry carrier — dropping them leaves the diagram flush left instead of centered.",
   "source_reference": {
     "repo": "php-transformer",
     "path": "tests/fixtures/parity/html-single-child-flex-svg.json",
@@ -27,8 +27,10 @@
     { "path": "blocks.0.innerBlocks", "assert": "count", "count": 1 },
     { "path": "blocks.0.innerBlocks.0.attrs.url", "assert": "contains", "value": "assets/materialized-svg/" },
     { "path": "assets.0.content", "assert": "contains", "value": "GIRTH" },
-    { "path": "assets", "assert": "count", "count": 1 },
-    { "path": "serialized_blocks", "assert": "contains", "value": "wp-block-group blocks-engine-css-owned-layout" },
+    { "path": "assets", "assert": "count", "count": 2 },
+    { "path": "assets.1.content", "assert": "contains", "value": "{display:flex !important;justify-content:center !important}" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "wp-block-group be-inline-geometry-" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "blocks-engine-css-owned-layout" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "blocks-engine/author-layout" },
     { "path": "fallbacks", "assert": "count", "count": 0 },
     { "path": "source_reports.conversion_report.metrics.fallback_count", "assert": "equals", "value": 0 }
diff --git a/php-transformer/tests/fixtures/parity/html-vertical-flex-column-becomes-group.json b/php-transformer/tests/fixtures/parity/html-vertical-flex-column-becomes-group.json
index 0f405947..5da9f5a1 100644
--- a/php-transformer/tests/fixtures/parity/html-vertical-flex-column-becomes-group.json
+++ b/php-transformer/tests/fixtures/parity/html-vertical-flex-column-becomes-group.json
@@ -5,7 +5,7 @@
   "source_reference": {
     "repo": "php-transformer",
     "path": "tests/fixtures/parity/html-vertical-flex-column-becomes-group.json",
-    "notes": "Keys solely off the CSS flex-direction:column value (never class/fixture names). The author-layout companion preserves source CSS as the sole layout authority."
+    "notes": "Keys solely off the CSS flex-direction:column value (never class/fixture names). The author-layout companion preserves source CSS as the sole layout authority. The css-owned demotion drops the native layout attribute, so the inline flex declarations ride to the generated stylesheet on a geometry carrier: a flow stack only coincidentally resembles a flex column, and loses the authored gap and any cross-axis alignment."
   },
   "legacy_comparison": {
     "skip": true,
@@ -16,7 +16,7 @@
     "content": "<div class=\"hero\" style=\"display:flex;flex-direction:column;gap:1rem\"><span class=\"eyebrow\">New</span><h1>Title</h1><p>Subhead</p><a class=\"btn\" href=\"/x\" style=\"padding:10px 16px;background:#135e96\">Go</a></div>"
   },
   "expected_blocks": [
-    { "path": "blocks.0", "name": "core/group", "attrs": { "className": "hero blocks-engine-css-owned-layout blocks-engine-css-owned-flow" } },
+    { "path": "blocks.0", "name": "core/group" },
     { "path": "blocks.0.innerBlocks.0", "name": "core/paragraph" },
     { "path": "blocks.0.innerBlocks.1", "name": "core/heading", "attrs": { "content": "Title", "level": 1 } },
     { "path": "blocks.0.innerBlocks.2", "name": "core/paragraph", "attrs": { "content": "Subhead" } },
@@ -26,7 +26,9 @@
     { "path": "status", "assert": "equals", "value": "success" },
     { "path": "blocks", "assert": "count", "count": 1 },
     { "path": "blocks.0.innerBlocks", "assert": "count", "count": 4 },
-    { "path": "serialized_blocks", "assert": "contains", "value": "<div class=\"wp-block-group hero blocks-engine-css-owned-layout blocks-engine-css-owned-flow\">" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "<div class=\"wp-block-group hero be-inline-geometry-" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "blocks-engine-css-owned-layout blocks-engine-css-owned-flow\">" },
+    { "path": "assets.0.content", "assert": "contains", "value": "{display:flex !important;flex-direction:column !important;gap:1rem !important}" },
     { "path": "serialized_blocks", "assert": "contains", "value": "wp-block-button__link" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "blocks-engine/author-layout" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "wp:columns" }
diff --git a/php-transformer/tests/unit/auto-fit-grid-carrier.php b/php-transformer/tests/unit/auto-fit-grid-carrier.php
new file mode 100644
index 00000000..14641c4e
--- /dev/null
+++ b/php-transformer/tests/unit/auto-fit-grid-carrier.php
@@ -0,0 +1,141 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Contract for `repeat(auto-fit, …)` track lists.
+ *
+ * `wp-includes/block-supports/layout.php` hardcodes `auto-fill` in every branch
+ * that renders `minimumColumnWidth`, so a native grid layout attribute can only
+ * ever express `auto-fill`. Converting an authored `auto-fit` track list to that
+ * attribute changes the rendered geometry: `auto-fit` collapses empty tracks,
+ * `auto-fill` retains them, so the content is crammed into part of the measure.
+ * `auto-fit` must therefore stay under CSS ownership like every other track list
+ * WordPress cannot express, while `auto-fill` keeps its native conversion.
+ */
+
+require dirname(__DIR__, 2) . '/vendor/autoload.php';
+
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\HtmlTransformer;
+
+$failures = 0;
+$passes = 0;
+
+$assert = static function (bool $condition, string $message, string $detail = '') use (&$failures, &$passes): void {
+    if ( $condition ) {
+        ++$passes;
+        return;
+    }
+
+    ++$failures;
+    fwrite(STDERR, 'FAIL: ' . $message . ('' !== $detail ? ' - ' . $detail : '') . PHP_EOL);
+};
+
+$cssFor = static function (array $result, string $source): string {
+    return implode("\n", array_map(
+        static fn (array $asset): string => (string) ($asset['content'] ?? ''),
+        array_values(array_filter(
+            is_array($result['assets'] ?? null) ? $result['assets'] : array(),
+            static fn (array $asset): bool => $source === ($asset['source'] ?? '')
+        ))
+    ));
+};
+
+$transform = static fn (string $html): array => ( new HtmlTransformer() )->transform($html, array())->toArray();
+
+$cards = '<div><p>One</p></div><div><p>Two</p></div><div><p>Three</p></div>';
+
+// -- Defect: an inline auto-fit track list is converted to a native grid layout.
+$inlineAutoFit = $transform(
+    '<section class="cards" style="display:grid;grid-template-columns:repeat(auto-fit, minmax(280px, 1fr));gap:24px">' . $cards . '</section>'
+);
+$inlineAutoFitMarkup = (string) ($inlineAutoFit['serialized_blocks'] ?? '');
+$inlineAutoFitEngineCss = $cssFor($inlineAutoFit, 'engine-support');
+
+$assert(
+    ! str_contains($inlineAutoFitMarkup, 'minimumColumnWidth'),
+    'inline auto-fit: no native grid layout attribute, which WordPress would render as auto-fill',
+    $inlineAutoFitMarkup
+);
+$assert(
+    str_contains($inlineAutoFitMarkup, 'blocks-engine-css-owned-grid'),
+    'inline auto-fit: container is marked css-owned-grid like every other non-expressible track list',
+    $inlineAutoFitMarkup
+);
+$assert(
+    str_contains($inlineAutoFitEngineCss, 'grid-template-columns:repeat(auto-fit, minmax(280px, 1fr))'),
+    'inline auto-fit: the authored track list rides to the generated stylesheet verbatim',
+    $inlineAutoFitEngineCss
+);
+$assert(
+    str_contains($inlineAutoFitEngineCss, 'display:grid'),
+    'inline auto-fit: the carrier keeps the container a grid',
+    $inlineAutoFitEngineCss
+);
+
+// -- Same defect through a class-owned track list, which is the shape the
+// site-builder corpus authors. The author stylesheet already retains the rule;
+// the native attribute is what overrides it.
+$classAutoFit = $transform(
+    '<style>.cards{display:grid;grid-template-columns:repeat(auto-fit, minmax(280px, 1fr));gap:24px}</style>'
+    . '<section class="cards">' . $cards . '</section>'
+);
+$classAutoFitMarkup = (string) ($classAutoFit['serialized_blocks'] ?? '');
+$classAutoFitAuthorCss = $cssFor($classAutoFit, 'author-css');
+
+$assert(
+    ! str_contains($classAutoFitMarkup, 'minimumColumnWidth'),
+    'class-owned auto-fit: no native grid layout attribute',
+    $classAutoFitMarkup
+);
+$assert(
+    ! str_contains($classAutoFitMarkup, 'is-layout-grid'),
+    'class-owned auto-fit: no core grid layout classes competing with the author rule',
+    $classAutoFitMarkup
+);
+$assert(
+    str_contains($classAutoFitAuthorCss, '.cards{display:grid;grid-template-columns:repeat(auto-fit, minmax(280px, 1fr));gap:24px}'),
+    'class-owned auto-fit: the author rule stays the single owner of the track geometry',
+    $classAutoFitAuthorCss
+);
+
+// -- Control: auto-fill IS natively expressible and must keep converting.
+$inlineAutoFill = $transform(
+    '<section class="cards" style="display:grid;grid-template-columns:repeat(auto-fill, minmax(280px, 1fr));gap:24px">' . $cards . '</section>'
+);
+$inlineAutoFillMarkup = (string) ($inlineAutoFill['serialized_blocks'] ?? '');
+$inlineAutoFillEngineCss = $cssFor($inlineAutoFill, 'engine-support');
+
+$assert(
+    str_contains($inlineAutoFillMarkup, '"layout":{"type":"grid","minimumColumnWidth":"280px"}'),
+    'auto-fill control: still converts to the native grid layout attribute',
+    $inlineAutoFillMarkup
+);
+$assert(
+    ! str_contains($inlineAutoFillMarkup, 'blocks-engine-css-owned-grid'),
+    'auto-fill control: does not fall back to the css-owned-grid carrier',
+    $inlineAutoFillMarkup
+);
+$assert(
+    ! str_contains($inlineAutoFillEngineCss, 'grid-template-columns'),
+    'auto-fill control: WordPress still owns the track geometry',
+    $inlineAutoFillEngineCss
+);
+
+$classAutoFill = $transform(
+    '<style>.cards{display:grid;grid-template-columns:repeat(auto-fill, minmax(280px, 1fr));gap:24px}</style>'
+    . '<section class="cards">' . $cards . '</section>'
+);
+$classAutoFillMarkup = (string) ($classAutoFill['serialized_blocks'] ?? '');
+
+$assert(
+    str_contains($classAutoFillMarkup, '"layout":{"type":"grid","minimumColumnWidth":"280px"}'),
+    'class-owned auto-fill control: still converts to the native grid layout attribute',
+    $classAutoFillMarkup
+);
+
+if ( $failures > 0 ) {
+    fwrite(STDERR, "Auto-fit grid carrier contract: {$failures} failed, {$passes} passed\n");
+    exit(1);
+}
+
+fwrite(STDOUT, "Auto-fit grid carrier contract passed: {$passes} assertions\n");
diff --git a/php-transformer/tests/unit/block-style-support-conversion.php b/php-transformer/tests/unit/block-style-support-conversion.php
index e81a26f3..fec27c7d 100644
--- a/php-transformer/tests/unit/block-style-support-conversion.php
+++ b/php-transformer/tests/unit/block-style-support-conversion.php
@@ -82,7 +82,7 @@
 $assert(! isset($groupAttrs['style']['spacing']['blockGap']), '15: core group save omits block gap without a core layout attribute', json_encode($groupAttrs));
 $assert(str_contains($groupInnerHtml, 'min-height:100svh'), '16: core group retains supported dimensions', $groupInnerHtml);
 
-$nativeGridHtml = '<div class="tpl-grid" style="display:grid;grid-template-columns:repeat(auto-fit, minmax(290px, 1fr));gap:1.2rem"><p>Fallback card</p></div>';
+$nativeGridHtml = '<div class="tpl-grid" style="display:grid;grid-template-columns:repeat(auto-fill, minmax(290px, 1fr));gap:1.2rem"><p>Fallback card</p></div>';
 $nativeGridResult = ( new HtmlTransformer() )->transform($nativeGridHtml, array())->toArray();
 $nativeGrid = $nativeGridResult['blocks'][0] ?? array();
 $nativeGridAttrs = is_array($nativeGrid['attrs'] ?? null) ? $nativeGrid['attrs'] : array();
@@ -94,6 +94,17 @@
 $assert(! str_contains($nativeGridMarkup, 'gap:1.2rem'), '16c: native Group grid markup omits inline gap that Gutenberg save does not reproduce', $nativeGridMarkup);
 $assert(str_contains($nativeGridCss, 'gap:1.2rem !important'), '16d: inline native Group grid gap moves to the generated geometry carrier', $nativeGridCss);
 
+// The same shape authored with auto-fit is NOT natively expressible: core's
+// layout support hardcodes auto-fill, which retains the tracks auto-fit
+// collapses. See tests/unit/auto-fit-grid-carrier.php for the full contract.
+$autoFitGridResult = ( new HtmlTransformer() )->transform(
+    '<div class="tpl-grid" style="display:grid;grid-template-columns:repeat(auto-fit, minmax(290px, 1fr));gap:1.2rem"><p>Fallback card</p></div>',
+    array()
+)->toArray();
+$autoFitGridAttrs = is_array($autoFitGridResult['blocks'][0]['attrs'] ?? null) ? $autoFitGridResult['blocks'][0]['attrs'] : array();
+
+$assert(! isset($autoFitGridAttrs['layout']), '16e: the same shape authored with auto-fit stays under CSS ownership', json_encode($autoFitGridAttrs));
+
 $unorderedListSource = '<ul style="list-style:none"><li>Alpha</li></ul>';
 $unorderedListResult = ( new HtmlTransformer() )->transform($unorderedListSource)->toArray();
 $unorderedListAttrs = $unorderedListResult['blocks'][0]['attrs'] ?? array();
diff --git a/php-transformer/tests/unit/button-font-family-carry.php b/php-transformer/tests/unit/button-font-family-carry.php
new file mode 100644
index 00000000..6c31484d
--- /dev/null
+++ b/php-transformer/tests/unit/button-font-family-carry.php
@@ -0,0 +1,144 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Contract for an authored font-family on a button-mapped rule.
+ *
+ * core/button registers a `fontFamily` attribute (see
+ * packages/blocks-engine/src/core-block-attrs.json, generated from
+ * @wordpress/block-library), which core only injects when the typography
+ * fontFamily support is enabled. A raw authored value is not a preset slug, so
+ * it belongs in `style.typography.fontFamily` alongside the other carried
+ * typography declarations.
+ *
+ * Dropping it is not benign: the authored `.btn` class is consumed into block
+ * attributes, so the surviving author rule matches nothing at a specificity that
+ * can win, and theme.json's styles.elements.button.typography.fontFamily
+ * substitutes the design-direction typeface.
+ */
+
+require dirname(__DIR__, 2) . '/vendor/autoload.php';
+
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\HtmlTransformer;
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\Patterns\ButtonStyleResolver;
+
+$failures = 0;
+$passes = 0;
+
+$assert = static function (bool $condition, string $message, string $detail = '') use (&$failures, &$passes): void {
+    if ( $condition ) {
+        ++$passes;
+        return;
+    }
+
+    ++$failures;
+    fwrite(STDERR, 'FAIL: ' . $message . ('' !== $detail ? ' - ' . $detail : '') . PHP_EOL);
+};
+
+// -- G11: the support this fix relies on must actually exist.
+$blockAttrs = json_decode(
+    (string) file_get_contents(dirname(__DIR__, 3) . '/packages/blocks-engine/src/core-block-attrs.json'),
+    true
+);
+$buttonAttributes = is_array($blockAttrs['blocks']['core/button'] ?? null) ? $blockAttrs['blocks']['core/button'] : array();
+
+$assert(
+    in_array('fontFamily', $buttonAttributes, true),
+    'core/button registers a fontFamily attribute, so the support is real',
+    implode(',', $buttonAttributes)
+);
+
+// -- G9 + G10 at the resolver: font-family joins the carried set, and every
+// other carried declaration keeps mapping byte-for-byte as it does today.
+$authoredButtonCss = 'background:#135e96;color:#ffffff;border:2px solid #0b3d6b;border-radius:6px;'
+    . 'font-family:"Trebuchet MS", "Segoe UI", sans-serif;font-size:0.88rem;font-weight:700;'
+    . 'letter-spacing:0.08em;text-transform:uppercase;padding:10px 16px';
+
+$resolved = ( new ButtonStyleResolver() )->nativeAttributes($authoredButtonCss);
+$expected = array(
+    'style' => array(
+        'color' => array( 'background' => '#135e96', 'text' => '#ffffff' ),
+        'border' => array( 'width' => '2px', 'style' => 'solid', 'color' => '#0b3d6b', 'radius' => '6px' ),
+        'spacing' => array( 'padding' => array( 'top' => '10px', 'right' => '16px', 'bottom' => '10px', 'left' => '16px' ) ),
+        'typography' => array(
+            'fontFamily' => '"Trebuchet MS", "Segoe UI", sans-serif',
+            'fontSize' => '0.88rem',
+            'fontWeight' => '700',
+            'letterSpacing' => '0.08em',
+            'textTransform' => 'uppercase',
+        ),
+    ),
+);
+
+$assert(
+    '"Trebuchet MS", "Segoe UI", sans-serif' === (string) ($resolved['style']['typography']['fontFamily'] ?? ''),
+    'resolver: the authored font-family reaches style.typography.fontFamily',
+    json_encode($resolved['style']['typography'] ?? null)
+);
+$assert(
+    json_encode($expected) === json_encode($resolved),
+    'resolver: every carried declaration maps exactly, with font-family in canonical order',
+    json_encode($resolved)
+);
+
+// -- A button whose rule authors no font-family gains none.
+$withoutFamily = ( new ButtonStyleResolver() )->nativeAttributes('background:#135e96;color:#ffffff;font-size:0.88rem');
+
+$assert(
+    ! isset($withoutFamily['style']['typography']['fontFamily']),
+    'resolver: no font-family is invented when the rule authors none',
+    json_encode($withoutFamily)
+);
+$assert(
+    array( 'fontSize' => '0.88rem' ) === ($withoutFamily['style']['typography'] ?? null),
+    'resolver: the remaining typography subset is untouched',
+    json_encode($withoutFamily['style']['typography'] ?? null)
+);
+
+// -- G9 end to end: the shape from the report, where `.btn` is consumed into
+// block attributes and only the block attribute can still carry the typeface.
+$result = ( new HtmlTransformer() )->transform(
+    '<style>.btn{background:#135e96;color:#fff;border:2px solid #0b3d6b;border-radius:6px;'
+    . 'font-family:"Trebuchet MS", "Segoe UI", sans-serif;font-size:0.88rem;font-weight:700;'
+    . 'letter-spacing:0.08em;text-transform:uppercase;padding:10px 16px}</style>'
+    . '<div class="hero-cta"><a class="btn" href="/a">Start</a><a class="btn" href="/b">Learn</a></div>',
+    array()
+)->toArray();
+$button = $result['blocks'][0]['innerBlocks'][0] ?? array();
+$buttonTypography = $button['attrs']['style']['typography'] ?? null;
+$serialized = (string) ($result['serialized_blocks'] ?? '');
+
+$assert(
+    'core/button' === ($button['blockName'] ?? ''),
+    'end to end: the authored anchor still becomes a core/button',
+    (string) ($button['blockName'] ?? '(none)')
+);
+$assert(
+    '"Trebuchet MS", "Segoe UI", sans-serif' === (string) ($buttonTypography['fontFamily'] ?? ''),
+    'end to end: the block attributes carry the authored typeface',
+    json_encode($buttonTypography)
+);
+$assert(
+    str_contains($serialized, 'font-family:&quot;Trebuchet MS&quot;, &quot;Segoe UI&quot;, sans-serif')
+        || str_contains($serialized, 'font-family:"Trebuchet MS", "Segoe UI", sans-serif'),
+    'end to end: the rendered button link declares the authored typeface inline, where theme.json cannot outrank it',
+    $serialized
+);
+$assert(
+    array(
+        'fontFamily' => '"Trebuchet MS", "Segoe UI", sans-serif',
+        'fontSize' => '0.88rem',
+        'fontWeight' => '700',
+        'letterSpacing' => '0.08em',
+        'textTransform' => 'uppercase',
+    ) === $buttonTypography,
+    'end to end: the other carried typography declarations are unchanged',
+    json_encode($buttonTypography)
+);
+
+if ( $failures > 0 ) {
+    fwrite(STDERR, "Button font-family carry contract: {$failures} failed, {$passes} passed\n");
+    exit(1);
+}
+
+fwrite(STDOUT, "Button font-family carry contract passed: {$passes} assertions\n");
diff --git a/php-transformer/tests/unit/css-owned-flex-carrier.php b/php-transformer/tests/unit/css-owned-flex-carrier.php
new file mode 100644
index 00000000..bfb33fb7
--- /dev/null
+++ b/php-transformer/tests/unit/css-owned-flex-carrier.php
@@ -0,0 +1,154 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Contract for inline `display:flex` on containers demoted to CSS-owned layout.
+ *
+ * `cssOwnedGroupAttributes()` drops the native `layout` attribute when an author
+ * flex/grid container is demoted to a css-owned core/group. Grids survive that
+ * demotion because their inline declarations ride to the generated stylesheet on
+ * a carrier class. Flex containers had no equivalent, so the declaration that
+ * makes the container a flex container was dropped while the block was still
+ * marked `blocks-engine-css-owned-flow` — the children then stacked.
+ */
+
+require dirname(__DIR__, 2) . '/vendor/autoload.php';
+
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\HtmlTransformer;
+
+$failures = 0;
+$passes = 0;
+
+$assert = static function (bool $condition, string $message, string $detail = '') use (&$failures, &$passes): void {
+    if ( $condition ) {
+        ++$passes;
+        return;
+    }
+
+    ++$failures;
+    fwrite(STDERR, 'FAIL: ' . $message . ('' !== $detail ? ' - ' . $detail : '') . PHP_EOL);
+};
+
+$cssFor = static function (array $result, string $source): string {
+    return implode("\n", array_map(
+        static fn (array $asset): string => (string) ($asset['content'] ?? ''),
+        array_values(array_filter(
+            is_array($result['assets'] ?? null) ? $result['assets'] : array(),
+            static fn (array $asset): bool => $source === ($asset['source'] ?? '')
+        ))
+    ));
+};
+
+$transform = static fn (string $html): array => ( new HtmlTransformer() )->transform($html, array())->toArray();
+
+/** Rule body for the geometry carrier class present in the markup. */
+$carrierRule = static function (string $markup, string $css): string {
+    if ( 1 !== preg_match('/\b(be-inline-geometry-[a-f0-9-]+)\b/', $markup, $match) ) {
+        return '';
+    }
+    if ( 1 !== preg_match('/(?<![\w-])\.' . preg_quote($match[1], '/') . '\{([^}]*)\}/', $css, $rule) ) {
+        return '';
+    }
+
+    return (string) $rule[1];
+};
+
+$columns = '<div><p>Alpha</p></div><div><p>Beta</p></div><div><p>Gamma</p></div>';
+
+// -- Defect: a css-owned-flow footer loses its inline display:flex entirely.
+$flex = $transform(
+    '<footer style="display:flex;gap:2rem;justify-content:space-between;align-items:center">' . $columns . '</footer>'
+);
+$flexMarkup = (string) ($flex['serialized_blocks'] ?? '');
+$flexEngineCss = $cssFor($flex, 'engine-support');
+$flexRule = $carrierRule($flexMarkup, $flexEngineCss);
+
+$assert(
+    str_contains($flexMarkup, 'blocks-engine-css-owned-flow'),
+    'inline flex: the container is still demoted to a css-owned-flow group',
+    $flexMarkup
+);
+$assert(
+    1 === preg_match('/\bbe-inline-geometry-[a-f0-9-]+\b/', $flexMarkup),
+    'inline flex: the demoted container receives a geometry carrier class',
+    $flexMarkup
+);
+$assert(
+    str_contains($flexRule, 'display:flex'),
+    'inline flex: the carrier keeps the container a flex container',
+    '' !== $flexRule ? $flexRule : $flexEngineCss
+);
+$assert(
+    str_contains($flexRule, 'gap:2rem'),
+    'inline flex: the authored gap rides with the display declaration',
+    '' !== $flexRule ? $flexRule : $flexEngineCss
+);
+$assert(
+    str_contains($flexRule, 'justify-content:space-between'),
+    'inline flex: the authored main-axis distribution rides with the display declaration',
+    '' !== $flexRule ? $flexRule : $flexEngineCss
+);
+$assert(
+    str_contains($flexRule, 'align-items:center'),
+    'inline flex: the authored cross-axis alignment rides with the display declaration',
+    '' !== $flexRule ? $flexRule : $flexEngineCss
+);
+
+// -- A vertical flex column keeps its direction rather than silently becoming a row.
+$column = $transform(
+    '<footer style="display:flex;flex-direction:column;flex-wrap:wrap;gap:1rem">' . $columns . '</footer>'
+);
+$columnMarkup = (string) ($column['serialized_blocks'] ?? '');
+$columnRule = $carrierRule($columnMarkup, $cssFor($column, 'engine-support'));
+
+$assert(
+    str_contains($columnRule, 'display:flex') && str_contains($columnRule, 'flex-direction:column') && str_contains($columnRule, 'flex-wrap:wrap'),
+    'inline flex column: direction and wrap ride with the display declaration',
+    '' !== $columnRule ? $columnRule : $cssFor($column, 'engine-support')
+);
+
+// -- Control: no authored display gains no carrier and no flex declaration.
+$plain = $transform('<footer class="plain">' . $columns . '</footer>');
+$plainMarkup = (string) ($plain['serialized_blocks'] ?? '');
+$plainEngineCss = $cssFor($plain, 'engine-support');
+
+$assert(
+    1 !== preg_match('/\bbe-inline-geometry-[a-f0-9-]+\b/', $plainMarkup),
+    'no authored display control: no geometry carrier class is invented',
+    $plainMarkup
+);
+$assert(
+    ! str_contains($plainEngineCss, 'display:flex'),
+    'no authored display control: no flex declaration is invented',
+    $plainEngineCss
+);
+$assert(
+    str_starts_with($plainMarkup, '<!-- wp:group {"className":"plain","tagName":"footer"} --><footer class="wp-block-group plain">'),
+    'no authored display control: the container block is unchanged',
+    substr($plainMarkup, 0, 200)
+);
+
+// -- Control: a class-owned flex container has nothing inline to carry, and the
+// author stylesheet already retains the declaration.
+$classFlex = $transform(
+    '<style>.bar{display:flex;gap:2rem}</style><footer class="bar">' . $columns . '</footer>'
+);
+$classFlexMarkup = (string) ($classFlex['serialized_blocks'] ?? '');
+
+$assert(
+    1 !== preg_match('/\bbe-inline-geometry-[a-f0-9-]+\b/', $classFlexMarkup),
+    'class-owned flex control: no carrier is generated for declarations the author stylesheet owns',
+    $classFlexMarkup
+);
+$assert(
+    str_contains($cssFor($classFlex, 'author-css'), '.bar{display:flex;gap:2rem}'),
+    'class-owned flex control: the author rule stays the owner of the flex declaration',
+    $cssFor($classFlex, 'author-css')
+);
+
+if ( $failures > 0 ) {
+    fwrite(STDERR, "CSS-owned flex carrier contract: {$failures} failed, {$passes} passed\n");
+    exit(1);
+}
+
+fwrite(STDOUT, "CSS-owned flex carrier contract passed: {$passes} assertions\n");