Anchor generated attachments to assistant messages

Deliverables now inherit the active assistant draft message ID so clients can render them beside the reply that produced them.

plugin/pheby/adapter.py

@@ -379,11 +379,18 @@ class PhebyAdapter(BasePlatformAdapter):
         return SendResult(success=True, message_id=clarify_id)
 
     # ── deliverables (attachments) ───────────────────────────────────────
+    def _active_assistant_message_id(self, conversation_id: str) -> Optional[str]:
+        """Return the live assistant draft that a deliverable belongs beneath."""
+        draft = self._drafts.get(conversation_id)
+        message_id = draft.get("message_id") if isinstance(draft, dict) else None
+        return str(message_id) if message_id else None
+
     async def _register_and_broadcast(
         self,
         file_path: str,
         conversation_id: str,
         *,
+        message_id: Optional[str] = None,
         kind_hint: Optional[str] = None,
         filename: Optional[str] = None,
     ) -> Optional[Dict[str, Any]]:
@@ -392,7 +399,7 @@ class PhebyAdapter(BasePlatformAdapter):
         desc = await self._server.store.register_file(
             file_path,
             conversation_id=conversation_id,
-            message_id=None,
+            message_id=message_id or self._active_assistant_message_id(conversation_id),
             filename=filename,
             kind_hint=kind_hint,
         )