feat: reconcile legacy message identities

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a0230c-b06c-7641-808a-e191b6d1da49

hub_core/models/agent_message.py

@@ -1,7 +1,7 @@
 import uuid
 from datetime import datetime
 
-from sqlalchemy import DateTime, ForeignKey, String, Text, text
+from sqlalchemy import DateTime, ForeignKey, String, Text, func
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
@@ -32,7 +32,7 @@ class AgentMessage(Base):
     )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        server_default=text("now()"),
+        server_default=func.now(),
         nullable=False,
     )