fix: robust mastodon dedup with MutationObserver + URL normalization

- MutationObserver set up before fetching so webmention NEW cards added after
  the dedup pass are also removed immediately (race condition fix)
- Normalize /@handle and /users/handle URL variants to same form before
  comparing — covers Mastodon instances that use either format
- Add wm-owner-reply-slot div + Reply link to bsky/mastodon Alpine cards
  to match build-time webmention card structure

_includes/components/webmentions.njk

@@ -228,8 +228,12 @@
               </div>
               <div class="text-surface-700 dark:text-surface-300 prose dark:prose-invert prose-sm max-w-none"
                    x-text="reply.text"></div>
+              <a :href="reply.url"
+                 class="wm-reply-btn hidden text-xs text-primary-600 dark:text-primary-400 hover:underline mt-2"
+                 target="_blank" rel="noopener">Reply on Bluesky</a>
             </div>
           </div>
+          <div class="wm-owner-reply-slot ml-13 mt-2"></div>
         </li>
       </template>
       {% endif %}
@@ -258,8 +262,12 @@
               </div>
               <div class="text-surface-700 dark:text-surface-300 prose dark:prose-invert prose-sm max-w-none"
                    x-html="reply.content"></div>
+              <a :href="reply.url"
+                 class="wm-reply-btn hidden text-xs text-primary-600 dark:text-primary-400 hover:underline mt-2"
+                 target="_blank" rel="noopener">Reply on Mastodon</a>
             </div>
           </div>
+          <div class="wm-owner-reply-slot ml-13 mt-2"></div>
         </li>
       </template>
       {% endif %}

js/social-threads.js

@@ -8,7 +8,34 @@ document.addEventListener("alpine:init", () => {
     mastodonReplies: [],
     loading: true,
 
+    // Normalized mastodon author URLs for dedup — populated after _fetchMastodon
+    _mastodonAuthorNormed: new Set(),
+
+    // Normalize /@handle and /users/handle to the same form for URL comparison
+    _normalizeActorUrl(url) {
+      return (url || "").replace(/\/(users\/|@)/, "/").replace(/\/$/, "").toLowerCase();
+    },
+
     async init() {
+      // Watch for webmention cards added AFTER our dedup pass (race condition with webmentions.js)
+      const repliesList = this.$el.querySelector("ul");
+      if (repliesList) {
+        const observer = new MutationObserver((mutations) => {
+          for (const m of mutations) {
+            for (const node of m.addedNodes) {
+              if (node.nodeType === 1 && node.dataset.authorUrl) {
+                if (this._mastodonAuthorNormed.has(this._normalizeActorUrl(node.dataset.authorUrl))) {
+                  node.remove();
+                }
+              }
+            }
+          }
+        });
+        observer.observe(repliesList, { childList: true });
+        // Disconnect after page is hidden — observer is no longer needed
+        document.addEventListener("visibilitychange", () => observer.disconnect(), { once: true });
+      }
+
       const tasks = [];
       if (bskyUrl) tasks.push(this._fetchBsky(bskyUrl));
       if (mastodonInstance && apIdentity) tasks.push(this._fetchMastodon(postUrl, mastodonInstance, apIdentity));
@@ -98,11 +125,13 @@ document.addEventListener("alpine:init", () => {
           favourites: s.favourites_count || 0,
         }));
 
-        // Remove webmention cards (build-time or client-fetched) that duplicate mastodon replies.
-        // Webmention cards have data-author-url; Alpine x-for cards do not.
-        const mastodonAuthorUrls = new Set(this.mastodonReplies.map((r) => r.author.url));
+        // Build normalized author URL set for dedup (covers /@handle and /users/handle variants)
+        this._mastodonAuthorNormed = new Set(
+          this.mastodonReplies.map((r) => this._normalizeActorUrl(r.author.url))
+        );
+        // Remove webmention cards (build-time or NEW) that duplicate mastodon replies
         document.querySelectorAll(".webmention-replies li[data-author-url]").forEach((li) => {
-          if (mastodonAuthorUrls.has(li.dataset.authorUrl)) li.remove();
+          if (this._mastodonAuthorNormed.has(this._normalizeActorUrl(li.dataset.authorUrl))) li.remove();
         });
       } catch {
         // fail silently