fix #11030: create branch session before ending original session

/branch marked the original session as ended with end_reason='branched'
BEFORE creating the new session. If create_session() failed, the original
session was left in an inconsistent state (ended but still active).

Now creates the new session first, and only ends the original on success.

Fixes NousResearch/hermes-agent#11030

cli.py

@@ -4263,13 +4263,8 @@ class HermesCLI:
         # Save the current session's state before branching
         parent_session_id = self.session_id
 
-        # End the old session
-        try:
-            self._session_db.end_session(self.session_id, "branched")
-        except Exception:
-            pass
-
-        # Create the new session with parent link
+        # Create the new session with parent link BEFORE ending the old one
+        # (so if creation fails, the original session remains active)
         try:
             self._session_db.create_session(
                 session_id=new_session_id,
@@ -4285,6 +4280,12 @@ class HermesCLI:
             _cprint(f"  Failed to create branch session: {e}")
             return
 
+        # Only end the old session after the new one is successfully created
+        try:
+            self._session_db.end_session(self.session_id, "branched")
+        except Exception:
+            pass
+
         # Copy conversation history to the new session
         for msg in self.conversation_history:
             try: