Revert incidental comment change in write_updated_conversation_state

Restore the original M1 comment; the rewrite was a side-effect of the
is_durable_observer_parent extraction.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: cephalonaut

app/src/ai/agent/conversation.rs

@@ -3476,7 +3476,7 @@ impl AIConversation {
         &mut self,
         ctx: &mut ModelContext<BlocklistAIHistoryModel>,
     ) {
-        // Shared-session views remain ephemeral.
+        // We should not persist non-local conversations (e.g. shared sessions).
         if self.is_viewing_shared_session {
             return;
         }