diff --git a/apps/server/src/schema.sql b/apps/server/src/schema.sql
index ef62af4..a573e94 100644
--- a/apps/server/src/schema.sql
+++ b/apps/server/src/schema.sql
@@ -57,3 +57,12 @@ CREATE TABLE IF NOT EXISTS session_panes (
   UNIQUE (session_id, position)
 );
 CREATE INDEX IF NOT EXISTS idx_session_panes_session ON session_panes (session_id);
+
+-- Backfill: ensure every session has at least one pane (default Chat).
+-- Idempotent: skipped on subsequent runs because session_panes rows already exist.
+INSERT INTO session_panes (session_id, position, kind, state)
+SELECT s.id, 0, 'chat', '{}'::jsonb
+FROM sessions s
+WHERE NOT EXISTS (
+  SELECT 1 FROM session_panes p WHERE p.session_id = s.id
+);