refactor: DiviSaver writes content through one guarded writeContent() (M4)

writeContent($postId, $content, ?$before) holds the kses window plus
wp_update_post(wp_slash([ID, post_content]), true); save() passes the restore
point capture as $before, so the window still holds exactly RevisionPoint::
capture() and wp_update_post() (S37), saveNew() and the restore() rollback use it
without. refusal() turns WP_Error / 0 into the message ("returned 0" as before)
for save() and saveNew(); restore() keeps its own RuntimeException text. The
class docblock (the M-5 window description) is unchanged.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Integrations/Divi/Pages/DiviSaver.php

@@ -68,20 +68,19 @@ class DiviSaver
         $revisionId = null;
 
         try {
-            $result = $this->withoutKses(static function () use ($postId, $content, &$revisionId): int|WP_Error {
+            // Ruling S37: the restore point is captured inside the same kses window.
+            $result = $this->writeContent($postId, $content, static function () use ($postId, &$revisionId): void {
                 $revisionId = RevisionPoint::capture($postId);
-
-                return wp_update_post(wp_slash(['ID' => $postId, 'post_content' => $content]), true);
             });
         } catch (Throwable $e) {
             $this->restore($postId, (string) $post->post_content, $revisionId, $e);
         }
 
-        if ($result instanceof WP_Error || $result === 0) {
+        $refusal = self::refusal($result);
-            $message = $result instanceof WP_Error ? $result->get_error_message() : 'returned 0';
+        if ($refusal !== null) {
             throw WriteFailed::rolledBack(
                 self::REASON,
-                detail: sprintf('wp_update_post(%d) refused: %s', $postId, $message),
+                detail: sprintf('wp_update_post(%d) refused: %s', $postId, $refusal),
                 state: self::keeping($revisionId),
                 postId: $postId,
                 revisionId: $revisionId
@@ -129,12 +128,9 @@ class DiviSaver
      */
     public function saveNew(int $postId, string $content): array
     {
-        $result = $this->withoutKses(
+        $refusal = self::refusal($this->writeContent($postId, $content));
-            static fn (): int|WP_Error => wp_update_post(wp_slash(['ID' => $postId, 'post_content' => $content]), true)
+        if ($refusal !== null) {
-        );
+            throw new RuntimeException(sprintf('wp_update_post(%d) refused the Divi layout: %s', $postId, $refusal));
-        if ($result instanceof WP_Error || $result === 0) {
-            $message = $result instanceof WP_Error ? $result->get_error_message() : 'returned 0';
-            throw new RuntimeException(sprintf('wp_update_post(%d) refused the Divi layout: %s', $postId, $message));
         }
 
         DiviFlags::set($postId);
@@ -144,6 +140,34 @@ class DiviSaver
         return $stored instanceof WP_Post && (string) $stored->post_content !== $content ? [self::CHANGED_ON_SAVE] : [];
     }
 
+    /**
+     * The one guarded content write: wp_update_post() (wp_slash, status unchanged) of $content in
+     * the kses window. $before runs first inside the same window – save() captures the restore
+     * point there (ruling S37); nothing else ever runs in it (see the class docblock).
+     *
+     * @param (callable(): void)|null $before
+     */
+    private function writeContent(int $postId, string $content, ?callable $before = null): int|WP_Error
+    {
+        return $this->withoutKses(static function () use ($postId, $content, $before): int|WP_Error {
+            if ($before !== null) {
+                $before();
+            }
+
+            return wp_update_post(wp_slash(['ID' => $postId, 'post_content' => $content]), true);
+        });
+    }
+
+    /** Why wp_update_post() refused ($result WP_Error or 0), null when it saved. */
+    private static function refusal(int|WP_Error $result): ?string
+    {
+        if ($result instanceof WP_Error) {
+            return $result->get_error_message();
+        }
+
+        return $result === 0 ? 'returned 0' : null;
+    }
+
     /**
      * Runs $write with kses' filters off for users without unfiltered_html (D7); restored in
      * finally, right when $write returns or throws.
@@ -174,11 +198,7 @@ class DiviSaver
         $failures = Rollback::attempt(function () use ($postId, $before): void {
             PostGuard::assertNoMissedSchedule($postId, 'restoring would publish a missed schedule');
 
-            $restored = $this->withoutKses(
+            if (self::refusal($this->writeContent($postId, $before)) !== null) {
-                static fn (): int|WP_Error
-                    => wp_update_post(wp_slash(['ID' => $postId, 'post_content' => $before]), true)
-            );
-            if ($restored instanceof WP_Error || $restored === 0) {
                 throw new RuntimeException('previous content could not be written back');
             }
         });