Fix duplicate AP posts + stable object IDs

- Stable object ID per source (Post#123 always gets the same id)
  instead of deriving from activity UUID
- Dedup Update activities (Ghost fires duplicate webhooks)
- Use setdefault for object id in delivery handler

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

events/handlers/ap_delivery_handler.py

@@ -38,7 +38,8 @@ def _build_activity_json(activity: APActivity, actor: ActorProfile, domain: str)
         obj.setdefault("type", "Tombstone")
     else:
         # Create/Update: full object with attribution
-        obj["id"] = object_id
+        # Prefer stable id from object_data (set by try_publish), fall back to activity-derived
+        obj.setdefault("id", object_id)
         obj.setdefault("type", activity.object_type)
         obj.setdefault("attributedTo", actor_url)
         obj.setdefault("published", activity.published.isoformat() if activity.published else None)

services/federation_publish.py

@@ -8,6 +8,7 @@ which creates the APActivity in the same DB transaction.  AP delivery
 from __future__ import annotations
 
 import logging
+import os
 
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -48,14 +49,20 @@ async def try_publish(
     if existing:
         if activity_type == "Create" and existing.activity_type != "Delete":
             return  # already published (allow re-Create after Delete/unpublish)
+        if activity_type == "Update" and existing.activity_type == "Update":
+            return  # already updated (Ghost fires duplicate webhooks)
         if activity_type == "Delete" and existing.activity_type == "Delete":
             return  # already deleted
-    elif activity_type == "Delete":
+    elif activity_type in ("Delete", "Update"):
-        return  # never published, nothing to delete
+        return  # never published, nothing to delete/update
 
-    # Delete must reference the same object id Mastodon received in Create
+    # Stable object ID: same source always gets the same object id so
-    if activity_type == "Delete" and existing:
+    # Mastodon treats Create/Update/Delete as the same post.
-        object_data["id"] = existing.activity_id + "/object"
+    domain = os.getenv("AP_DOMAIN", "rose-ash.com")
+    object_data["id"] = (
+        f"https://{domain}/users/{actor.preferred_username}"
+        f"/objects/{source_type.lower()}/{source_id}"
+    )
 
     try:
         await services.federation.publish_activity(