diff --git a/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php b/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php
index 54abfd09..9a9509d5 100644
--- a/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php
+++ b/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php
@@ -94,12 +94,38 @@ private function looksLikeColumnsContainer(DOMElement $element): bool
             return false;
         }
 
+        // A genuinely vertical flex container (display:flex with
+        // flex-direction: column / column-reverse) lays its children out in a
+        // vertical stack. Emitting core/columns would render them horizontally —
+        // the wrong direction. Decline here so the host transformer routes the
+        // element to a vertical core/group instead, preserving its classes and
+        // styles. Horizontal flex (row / row-reverse / default) and grid layouts
+        // are unaffected, so legitimate horizontal columns are never disturbed.
+        if ( $this->isVerticalFlexContainer($style) ) {
+            return false;
+        }
+
         return (bool) preg_match('/(?:^|[\s_-])columns?(?:$|[\s_-])/', $className)
             || ( $this->looksLikeSplitLayout($element) && 1 < $this->directElementChildCount($element) )
             || ( $this->looksLikeDocumentationLayout($element) && $this->hasSidebarAndContentChildren($element) )
             || preg_match('/(?:^|;)\s*(?:display\s*:\s*(?:inline-)?flex|grid-template-columns\s*:)/', $style);
     }
 
+    /**
+     * True when the resolved style declares a flex container whose main axis is
+     * vertical (flex-direction: column / column-reverse). flex-direction only has
+     * meaning on a flex container, so both display:flex and the column direction
+     * are required before redirecting away from horizontal columns.
+     */
+    private function isVerticalFlexContainer(string $style): bool
+    {
+        if ( ! preg_match('/(?:^|;)\s*display\s*:\s*(?:inline-)?flex\b/', $style) ) {
+            return false;
+        }
+
+        return (bool) preg_match('/(?:^|;)\s*flex-direction\s*:\s*column(?:-reverse)?\b/', $style);
+    }
+
     private function looksLikeSplitLayout(DOMElement $element): bool
     {
         $name = strtolower(trim($this->attr($element, 'class') . ' ' . $this->attr($element, 'id')));
diff --git a/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php b/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php
index ebf9dc56..3679d79e 100644
--- a/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php
+++ b/php-transformer/src/HtmlToBlocks/Style/StyleResolutionTrait.php
@@ -419,6 +419,18 @@ private function layoutAttribute(DOMElement $element, string $mergedStyle = ''):
 
         $style = strtolower('' !== trim($mergedStyle) ? $mergedStyle : $this->attr($element, 'style'));
         if ( preg_match('/(?:^|;)\s*display\s*:\s*(inline-)?flex\b/', $style) ) {
+            // flex-direction: column / column-reverse is a vertical main axis. A
+            // core/group flex layout defaults to a horizontal Row, so the
+            // orientation must be made explicit or the children render
+            // side-by-side instead of stacked. Row / row-reverse / default flex
+            // keeps the implicit horizontal orientation.
+            if ( preg_match('/(?:^|;)\s*flex-direction\s*:\s*column(?:-reverse)?\b/', $style) ) {
+                return array(
+                    'type'        => 'flex',
+                    'orientation' => 'vertical',
+                );
+            }
+
             return array( 'type' => 'flex' );
         }
         if ( preg_match('/(?:^|;)\s*display\s*:\s*(inline-)?grid\b/', $style) ) {
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
new file mode 100644
index 00000000..a41510a6
--- /dev/null
+++ b/php-transformer/tests/fixtures/parity/html-horizontal-flex-stays-columns.json
@@ -0,0 +1,33 @@
+{
+  "schema": "blocks-engine/php-transformer/parity-fixture/v1",
+  "name": "html-horizontal-flex-stays-columns",
+  "description": "A flex container with the default (row) main axis is a genuine horizontal layout, so it stays a core/columns block. Guards that the flex-direction:column redirect never disturbs legitimate horizontal column layouts.",
+  "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."
+  },
+  "legacy_comparison": {
+    "skip": true,
+    "reason": "Covers current PHP transformer columns recognizer behavior; no downstream legacy comparison."
+  },
+  "operation": "html_transformer.transform",
+  "input": {
+    "content": "<div class=\"cols\" style=\"display:flex\"><div class=\"c\"><h2>A</h2><p>one</p></div><div class=\"c\"><h2>B</h2><p>two</p></div></div>"
+  },
+  "expected_blocks": [
+    { "path": "blocks.0", "name": "core/columns", "attrs": { "className": "cols", "layout": { "type": "flex" } } },
+    { "path": "blocks.0.innerBlocks.0", "name": "core/column", "attrs": { "className": "c" } },
+    { "path": "blocks.0.innerBlocks.0.innerBlocks.0", "name": "core/heading", "attrs": { "content": "A", "level": 2 } },
+    { "path": "blocks.0.innerBlocks.0.innerBlocks.1", "name": "core/paragraph", "attrs": { "content": "one" } },
+    { "path": "blocks.0.innerBlocks.1", "name": "core/column", "attrs": { "className": "c" } },
+    { "path": "blocks.0.innerBlocks.1.innerBlocks.0", "name": "core/heading", "attrs": { "content": "B", "level": 2 } },
+    { "path": "blocks.0.innerBlocks.1.innerBlocks.1", "name": "core/paragraph", "attrs": { "content": "two" } }
+  ],
+  "expect": [
+    { "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": "<!-- wp:columns {\"className\":\"cols\",\"layout\":{\"type\":\"flex\"}}" }
+  ]
+}
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
new file mode 100644
index 00000000..bb0c8352
--- /dev/null
+++ b/php-transformer/tests/fixtures/parity/html-vertical-flex-column-becomes-group.json
@@ -0,0 +1,33 @@
+{
+  "schema": "blocks-engine/php-transformer/parity-fixture/v1",
+  "name": "html-vertical-flex-column-becomes-group",
+  "description": "A flex container with flex-direction:column is a vertical stack, so it converts to a vertical core/group (layout type flex, orientation vertical) rather than a horizontal core/columns. This is the regression guard for layout_direction_misrecognition :: columns_from_vertical_flex — a hero stack (eyebrow, title, subhead, buttons) must render stacked, not side-by-side.",
+  "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). ColumnsPattern declines vertical flex so the host routes to core/group, and layoutAttribute emits an explicit orientation:vertical so the flex group stacks instead of defaulting to a horizontal Row."
+  },
+  "legacy_comparison": {
+    "skip": true,
+    "reason": "Covers current PHP transformer flex-direction-aware layout behavior; no downstream legacy comparison."
+  },
+  "operation": "html_transformer.transform",
+  "input": {
+    "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\">Go</a></div>"
+  },
+  "expected_blocks": [
+    { "path": "blocks.0", "name": "core/group", "attrs": { "className": "hero", "layout": { "type": "flex", "orientation": "vertical" } } },
+    { "path": "blocks.0.innerBlocks.0", "name": "core/paragraph", "attrs": { "content": "New", "className": "eyebrow" } },
+    { "path": "blocks.0.innerBlocks.1", "name": "core/heading", "attrs": { "content": "Title", "level": 1 } },
+    { "path": "blocks.0.innerBlocks.2", "name": "core/paragraph", "attrs": { "content": "Subhead" } },
+    { "path": "blocks.0.innerBlocks.3", "name": "core/buttons" },
+    { "path": "blocks.0.innerBlocks.3.innerBlocks.0", "name": "core/button", "attrs": { "className": "btn", "text": "Go", "url": "/x" } }
+  ],
+  "expect": [
+    { "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": "<!-- wp:group {\"className\":\"hero\",\"layout\":{\"type\":\"flex\",\"orientation\":\"vertical\"}}" },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "wp:columns" }
+  ]
+}
diff --git a/php-transformer/tests/unit/corpus-detectors.php b/php-transformer/tests/unit/corpus-detectors.php
index 56df1bd4..c4d2d868 100644
--- a/php-transformer/tests/unit/corpus-detectors.php
+++ b/php-transformer/tests/unit/corpus-detectors.php
@@ -159,18 +159,16 @@
 $assert(2 === count($diagSvg), '3d: inline-svg fallback diagnostics route into svg_content_lost', 'got ' . count($diagSvg));
 
 // ---------------------------------------------------------------------------
-// 4. Layout-direction misrecognition: a vertical flex container that converts to
-//    core/columns flags columns_from_vertical_flex; horizontal flex does not.
+// 4. Layout-direction misrecognition: the detector flags a vertical flex
+//    container that converts to core/columns; horizontal flex does not. The
+//    verifier is stubbed here so the detector logic is exercised independently
+//    of the live transformer (whose vertical-flex routing is asserted in 4e).
 // ---------------------------------------------------------------------------
 $verticalFlex = '<div style="display:flex; flex-direction:column; gap:1rem; max-width:760px;">'
     . '<p>One</p><p>Two</p><p>Three</p></div>';
 $layout = CorpusDetectors::layoutDirectionMisrecognition(
     $verticalFlex,
-    static function (string $fragment): bool {
-        $blocks = ( new HtmlTransformer() )->transform($fragment, array())->toArray()['blocks'] ?? array();
-
-        return is_array($blocks[0] ?? null) && 'core/columns' === ($blocks[0]['blockName'] ?? '');
-    }
+    static fn (string $fragment): bool => true
 );
 $assert(1 === count($layout), '4: a vertical-flex container that becomes core/columns is flagged', 'got ' . count($layout));
 $assert(
@@ -195,6 +193,41 @@ static function (string $fragment): bool {
 );
 $assert(0 === count($vetoed), '4d: a vertical-flex candidate that does not become columns is vetoed', 'got ' . count($vetoed));
 
+// 4e. Regression guard for the fix: the live transformer must route a vertical
+//     flex container (display:flex; flex-direction:column) to a vertical
+//     core/group, not a horizontal core/columns. With the real transformer as
+//     the verifier the detector therefore finds nothing.
+$verticalBlocks = ( new HtmlTransformer() )->transform($verticalFlex, array())->toArray()['blocks'] ?? array();
+$assert(
+    'core/group' === ($verticalBlocks[0]['blockName'] ?? ''),
+    '4e: live transformer emits core/group for a vertical flex container',
+    (string) ($verticalBlocks[0]['blockName'] ?? '(none)')
+);
+$assert(
+    'vertical' === ($verticalBlocks[0]['attrs']['layout']['orientation'] ?? ''),
+    '4e: the vertical flex group carries an explicit vertical flex orientation',
+    (string) ($verticalBlocks[0]['attrs']['layout']['orientation'] ?? '(none)')
+);
+$liveLayout = CorpusDetectors::layoutDirectionMisrecognition(
+    $verticalFlex,
+    static function (string $fragment): bool {
+        $blocks = ( new HtmlTransformer() )->transform($fragment, array())->toArray()['blocks'] ?? array();
+
+        return is_array($blocks[0] ?? null) && 'core/columns' === ($blocks[0]['blockName'] ?? '');
+    }
+);
+$assert(0 === count($liveLayout), '4e: detector reports no misrecognition once the transformer stacks the flex column vertically', 'got ' . count($liveLayout));
+
+// 4f. Horizontal flex still becomes core/columns — the fix must not disturb
+//     legitimate horizontal column layouts.
+$horizontalColumns = '<div style="display:flex; gap:1rem;"><div><h2>A</h2><p>one</p></div><div><h2>B</h2><p>two</p></div></div>';
+$horizontalBlocks = ( new HtmlTransformer() )->transform($horizontalColumns, array())->toArray()['blocks'] ?? array();
+$assert(
+    'core/columns' === ($horizontalBlocks[0]['blockName'] ?? ''),
+    '4f: live transformer keeps horizontal flex as core/columns',
+    (string) ($horizontalBlocks[0]['blockName'] ?? '(none)')
+);
+
 // ---------------------------------------------------------------------------
 // 5. Severity ranking and cluster keys.
 // ---------------------------------------------------------------------------