feat: deferred 1a items - menu_rev lock, lit_mcp_guides filter, warnings, schedule guard precision

Task 14 (rulings P17/P18, Q10):
- lit/menu-get returns menu_rev (Rev::ofMenu over id, parent, position,
  title, url, object, object_id); lit/menu-set-items requires it, refuses
  a stale one with rev_mismatch (hint: lit/menu-get) and returns the new
  menu_rev. Errors::revMismatch takes an optional message/hint.
- GuideRepository: filter lit_mcp_guides adds/overrides topics; invalid
  topic names and non-string content are ignored, files stay the default.
- lit/post-trash names front page, posts page and linking menus in the
  confirmation and as warnings; lit/menu-assign-location needs confirm
  to remove an assigned menu and names it; lit/post-schedule warns that
  a private entry becomes public; Divi hints no longer point to
  non-existing lit-divi-* tools.
- PostGuard::missedSchedule: 60 s publish window, zero GMT date falls
  back to get_gmt_from_date(post_date); post-schedule refuses dates
  within that window.
- write_failed after a clean rollback that keeps a revision/backup says
  "Die Aenderung wurde nicht gespeichert (... bleibt erhalten)" via the
  new state parameter (Errors::writeFailed / WriteFailed rolledBackState).
- wp-basis-smoke: menu_rev flow, unassign confirm, trash/menu and
  private-schedule warnings.

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

src/Guides/GuideRepository.php

@@ -5,19 +5,55 @@ declare(strict_types=1);
 namespace LIT\MCP\Guides;
 
 /**
- * Reads guide markdown files from one directory. Topic names are restricted to
- * lowercase slugs, so no path outside the directory can ever be read.
+ * Guide topics: markdown files from one directory (the default), extended or overridden
+ * by the site via the filter `lit_mcp_guides` (spec §9.2), which returns
+ * array<string topic, string markdown>. Topic names are restricted to lowercase slugs,
+ * so no path outside the directory can ever be read; filter entries with another name or
+ * a non-string content are ignored. Filtered content is site-owned and returned as-is.
  */
 final class GuideRepository
 {
     private const TOPIC_PATTERN = '/^[a-z0-9]+(?:-[a-z0-9]+)*$/';
 
+    /** @var array<string, string>|null Filtered topics, read once per instance (= request). */
+    private ?array $filtered = null;
+
     public function __construct(private string $directory)
     {
     }
 
     /** @return list<string> */
     public function topics(): array
+    {
+        $topics = array_unique(array_merge($this->fileTopics(), array_keys($this->filtered())));
+        sort($topics);
+
+        return array_values($topics);
+    }
+
+    public function get(string $topic): ?string
+    {
+        if (! self::isTopic($topic)) {
+            return null;
+        }
+
+        $filtered = $this->filtered();
+        if (array_key_exists($topic, $filtered)) {
+            return $filtered[$topic];
+        }
+
+        if (! in_array($topic, $this->fileTopics(), true)) {
+            return null;
+        }
+
+        // phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
+        $content = file_get_contents($this->directory . '/' . $topic . '.md');
+
+        return $content === false ? null : $content;
+    }
+
+    /** @return list<string> */
+    private function fileTopics(): array
     {
         $files = glob($this->directory . '/*.md');
         if ($files === false) {
@@ -27,25 +63,34 @@ final class GuideRepository
         $topics = [];
         foreach ($files as $file) {
             $topic = basename($file, '.md');
-            if (preg_match(self::TOPIC_PATTERN, $topic) === 1) {
+            if (self::isTopic($topic)) {
                 $topics[] = $topic;
             }
         }
-        sort($topics);
 
         return $topics;
     }
 
-    public function get(string $topic): ?string
+    /** @return array<string, string> */
+    private function filtered(): array
     {
-        if (preg_match(self::TOPIC_PATTERN, $topic) !== 1 || ! in_array($topic, $this->topics(), true)) {
-            return null;
+        if ($this->filtered !== null) {
+            return $this->filtered;
         }
 
-        $path = $this->directory . '/' . $topic . '.md';
-        // phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
-        $content = file_get_contents($path);
+        $guides = apply_filters('lit_mcp_guides', []);
+        $this->filtered = [];
+        foreach (is_array($guides) ? $guides : [] as $topic => $markdown) {
+            if (is_string($topic) && self::isTopic($topic) && is_string($markdown)) {
+                $this->filtered[$topic] = $markdown;
+            }
+        }
 
-        return $content === false ? null : $content;
+        return $this->filtered;
+    }
+
+    private static function isTopic(string $topic): bool
+    {
+        return preg_match(self::TOPIC_PATTERN, $topic) === 1;
     }
 }