fix: detect own posts in Mastodon API status serialization

Own posts in ap_timeline have author.url set to the publication URL
(site root like "https://rmendes.net/") with no /@handle or /users/handle
pattern. extractUsername("/") returns "" which falls back to "unknown".

Fix: set module-level local identity (publicationUrl + handle) at plugin
init via setLocalIdentity(). serializeStatus() compares item.author.url
against the publication URL and passes isLocal:true + handle to
serializeAccount() when they match.

This is zero-cost for callers — no signature changes needed at the 20+
serializeStatus() call sites.

index.js

@@ -2,6 +2,7 @@ import express from "express";
 
 import { setupFederation, buildPersonActor } from "./lib/federation-setup.js";
 import { createMastodonRouter } from "./lib/mastodon/router.js";
+import { setLocalIdentity } from "./lib/mastodon/entities/status.js";
 import { initRedisCache } from "./lib/redis-cache.js";
 import { lookupWithSecurity } from "./lib/lookup-helpers.js";
 import {
@@ -1492,6 +1493,9 @@ export default class ActivityPubEndpoint {
       routesPublic: this.contentNegotiationRoutes,
     });
 
+    // Set local identity for own-post detection in status serialization
+    setLocalIdentity(this._publicationUrl, this.options.actor?.handle || "user");
+
     // Mastodon Client API — virtual endpoint at root
     // Mastodon-compatible clients (Phanpy, Elk, etc.) expect /api/v1/*,
     // /api/v2/*, /oauth/* at the domain root, not under /activitypub.

lib/mastodon/entities/status.js

@@ -16,6 +16,21 @@
 import { serializeAccount } from "./account.js";
 import { sanitizeHtml } from "./sanitize.js";
 
+// Module-level defaults set once at startup via setLocalIdentity()
+let _localPublicationUrl = "";
+let _localHandle = "";
+
+/**
+ * Set the local identity for own-post detection.
+ * Called once during plugin init.
+ * @param {string} publicationUrl - e.g. "https://rmendes.net/"
+ * @param {string} handle - e.g. "rick"
+ */
+export function setLocalIdentity(publicationUrl, handle) {
+  _localPublicationUrl = publicationUrl;
+  _localHandle = handle;
+}
+
 /**
  * Serialize an ap_timeline document as a Mastodon Status entity.
  *
@@ -207,7 +222,11 @@ export function serializeStatus(item, { baseUrl, favouritedIds, rebloggedIds, bo
     reblog: null,
     application: null,
     account: item.author
-      ? serializeAccount(item.author, { baseUrl })
+      ? serializeAccount(item.author, {
+          baseUrl,
+          isLocal: !!(_localPublicationUrl && item.author.url === _localPublicationUrl),
+          handle: _localHandle,
+        })
       : null,
     media_attachments: mediaAttachments,
     mentions,