feat(like): send Like activity for AP objects, bookmark for regular URLs

When the `like-of` URL serves ActivityPub content (detected via content
negotiation with Accept: application/activity+json), deliver a proper
`Like { actor, object, to: Public }` activity to followers.

For likes of regular (non-AP) URLs, fall through to the existing
bookmark-style `Create(Note)` behaviour (🔖 content with #bookmark tag).

- Add `isApUrl()` async helper (3 s timeout, fails silently)
- Make `jf2ToAS2Activity` async; add Like detection before repost block
- Update all four call sites in federation-setup.js and index.js

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

index.js

@@ -583,7 +583,7 @@ export default class ActivityPubEndpoint {
             }
           }
 
-          const activity = jf2ToAS2Activity(
+          const activity = await jf2ToAS2Activity(
             properties,
             actorUrl,
             self._publicationUrl,

lib/federation-setup.js

@@ -560,7 +560,7 @@ function setupFeatured(federation, mountPath, handle, collections, publicationUr
         });
         if (!post) continue;
         const actorUrl = ctx.getActorUri(identifier).href;
-        const activity = jf2ToAS2Activity(
+        const activity = await jf2ToAS2Activity(
           post.properties,
           actorUrl,
           publicationUrl,
@@ -637,19 +637,21 @@ function setupOutbox(federation, mountPath, handle, collections) {
           .toArray();
 
         const { jf2ToAS2Activity } = await import("./jf2-to-as2.js");
-        const items = posts
-          .map((post) => {
-            try {
-              return jf2ToAS2Activity(
-                post.properties,
-                ctx.getActorUri(identifier).href,
-                collections._publicationUrl,
-              );
-            } catch {
-              return null;
-            }
-          })
-          .filter(Boolean);
+        const items = (
+          await Promise.all(
+            posts.map(async (post) => {
+              try {
+                return await jf2ToAS2Activity(
+                  post.properties,
+                  ctx.getActorUri(identifier).href,
+                  collections._publicationUrl,
+                );
+              } catch {
+                return null;
+              }
+            }),
+          )
+        ).filter(Boolean);
 
         return {
           items,
@@ -687,7 +689,7 @@ function setupObjectDispatchers(federation, mountPath, handle, collections, publ
     // Soft-deleted posts should not be dereferenceable
     if (post.properties?.deleted) return null;
     const actorUrl = ctx.getActorUri(handle).href;
-    const activity = jf2ToAS2Activity(post.properties, actorUrl, publicationUrl);
+    const activity = await jf2ToAS2Activity(post.properties, actorUrl, publicationUrl);
     // Only Create activities wrap Note/Article objects
     if (!(activity instanceof Create)) return null;
     return await activity.getObject();

lib/jf2-to-as2.js

@@ -14,6 +14,7 @@ import {
   Create,
   Hashtag,
   Image,
+  Like,
   Mention,
   Note,
   Video,
@@ -79,6 +80,30 @@ function linkifyMentions(html, resolvedMentions) {
   return html;
 }
 
+// ---------------------------------------------------------------------------
+// ActivityPub URL detection
+// ---------------------------------------------------------------------------
+
+/**
+ * Check whether a URL serves ActivityPub content by doing a quick content
+ * negotiation request. Returns true if the server responds with an AP
+ * media type (application/activity+json or application/ld+json).
+ * Fails silently — any network/timeout error returns false.
+ */
+async function isApUrl(url) {
+  try {
+    const res = await fetch(url, {
+      headers: { Accept: "application/activity+json, application/ld+json" },
+      redirect: "follow",
+      signal: AbortSignal.timeout(3000),
+    });
+    const ct = res.headers.get("content-type") || "";
+    return ct.includes("activity+json") || ct.includes("ld+json");
+  } catch {
+    return false;
+  }
+}
+
 // ---------------------------------------------------------------------------
 // Plain JSON-LD (content negotiation on individual post URLs)
 // ---------------------------------------------------------------------------
@@ -239,13 +264,24 @@ export function jf2ToActivityStreams(properties, actorUrl, publicationUrl, optio
  * @param {object} [options] - Optional settings
  * @param {string} [options.replyToActorUrl] - Original post author's actor URL (for reply addressing)
  * @param {string} [options.replyToActorHandle] - Original post author's handle (for Mention tag)
- * @returns {import("@fedify/fedify").Activity | null}
+ * @returns {Promise<import("@fedify/fedify").Activity | null>}
  */
-export function jf2ToAS2Activity(properties, actorUrl, publicationUrl, options = {}) {
+export async function jf2ToAS2Activity(properties, actorUrl, publicationUrl, options = {}) {
   const postType = properties["post-type"];
   const actorUri = new URL(actorUrl);
 
-  // Likes are delivered as bookmarks — fall through to bookmark handling below
+  // Likes of ActivityPub objects are sent as a proper Like activity.
+  // Likes of regular URLs fall through to bookmark-style Create(Note) below.
+  if (postType === "like") {
+    const likeOfUrl = properties["like-of"];
+    if (likeOfUrl && (await isApUrl(likeOfUrl))) {
+      return new Like({
+        actor: actorUri,
+        object: new URL(likeOfUrl),
+        to: new URL("https://www.w3.org/ns/activitystreams#Public"),
+      });
+    }
+  }
 
   // Reposts are always public — upstream @rmdes addressing
   if (postType === "repost") {