feat: lit/divi-insert and lit/divi-update

All-or-nothing at ability level (S39), duplicate ids refused (S14),
set and attrs on the same path refused (S38), invalid_attr_path error.

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

src/Integrations/Divi/Compose/Composer.php

@@ -116,6 +116,7 @@ final class Composer
             }
         }
 
+        $this->overlaps($block->shortName(), $change, $field);
         $attrs = $this->presetAndAttrs($block->name(), $attrs, $change, $field);
         if (array_key_exists('label', $change)) {
             $attrs = $change['label'] === null || $change['label'] === ''
@@ -126,6 +127,39 @@ final class Composer
         return ['attrs' => $attrs, 'errors' => $this->errors, 'invalid_paths' => $this->invalidPaths];
     }
 
+    /**
+     * Ruling S38: one change may not reach the same attribute path through "set" and "attrs" –
+     * composite values are replaced whole per breakpoint, so combining them would silently lose
+     * sub-keys. Paths overlap when equal or when one lies below the other.
+     *
+     * @param array<array-key, mixed> $change
+     */
+    private function overlaps(string $type, array $change, string $field): void
+    {
+        $set = $change['set'] ?? null;
+        $full = $change['attrs'] ?? null;
+        if (! is_array($set) || ! is_array($full) || $set === [] || $full === []) {
+            return;
+        }
+
+        $short = $this->shortform->paths($type, array_map('strval', array_keys($set)));
+        foreach (array_keys($full) as $path) {
+            $path = (string) $path;
+            foreach ($short as $name => $shortPath) {
+                if (
+                    $path === $shortPath || str_starts_with($path, $shortPath . '.')
+                    || str_starts_with($shortPath, $path . '.')
+                ) {
+                    $this->errors[$field . '.attrs.' . $path] = sprintf(
+                        'derselbe Attributpfad wird auch über set.%s geändert; bitte als zwei Änderungen senden',
+                        $name
+                    );
+                    break;
+                }
+            }
+        }
+    }
+
     /** Admin label for a new module: "<Abschnitt> – <Modultitel>" or the title alone. */
     public function autoLabel(string $name, string $context): string
     {

src/Integrations/Divi/Compose/ShortformWriter.php

@@ -72,6 +72,25 @@ final class ShortformWriter
         return ['attrs' => $attrs, 'errors' => $errors];
     }
 
+    /**
+     * Attribute paths the given short-form fields of $type write to (unknown fields left out).
+     *
+     * @param list<string> $names Field names.
+     * @return array<string, string> Field => attribute path.
+     */
+    public function paths(string $type, array $names): array
+    {
+        $fields = $this->modules === null ? ShortformMap::fields($type) : ($this->modules[$type] ?? []);
+        $paths = [];
+        foreach ($names as $name) {
+            if (isset($fields[$name]['path'])) {
+                $paths[$name] = (string) $fields[$name]['path'];
+            }
+        }
+
+        return $paths;
+    }
+
     /**
      * The short-form color check (ruling S13; Task 3 reuses it for background_color): a
      * placeholder or reference that is a color reference, or a plain CSS color – checked