feat(sessions): drop empty sessions on CLI exit and session rotation

Port from google-gemini/gemini-cli#27770: starting the CLI and
immediately quitting (or rotating with /new, /clear) left an empty
untitled session row behind. These ghost rows pile up in /resume,
`hermes sessions list`, and the in-chat recent-sessions browser.

- SessionDB.delete_session_if_empty(): transactional check-and-delete
  that only removes rows with no messages, no title, and no child
  sessions (delegate subagent parents are preserved). Also removes
  on-disk transcript files via the existing _remove_session_files.
- HermesCLI._discard_session_if_empty(): thin wrapper, wired into the
  cli_close shutdown path and the new_session() rotation path.
  Skipped when /exit --delete already handles removal.

Unlike the one-shot prune_empty_ghost_sessions migration (TUI-only,
24h-old rows), this prevents new ghost rows from accumulating at the
moment they would be created.

cli.py

@@ -5821,6 +5821,29 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin):
         except Exception:
             pass
 
+    def _discard_session_if_empty(self, session_id: Optional[str]) -> bool:
+        """Drop a just-ended session row when it never gained content.
+
+        Starting the CLI and immediately quitting (or rotating with /new,
+        /clear) used to leave an empty untitled row behind that clutters
+        ``/resume`` and ``hermes sessions list``. Delegates the
+        check-and-delete to ``SessionDB.delete_session_if_empty``, which
+        only removes rows with no messages, no title, and no child
+        sessions. Ported from google-gemini/gemini-cli#27770.
+        """
+        if not self._session_db or not session_id:
+            return False
+        try:
+            from hermes_constants import get_hermes_home as _ghh
+            return self._session_db.delete_session_if_empty(
+                session_id, sessions_dir=_ghh() / "sessions"
+            )
+        except Exception:
+            logger.debug(
+                "Could not prune empty session %s", session_id, exc_info=True
+            )
+            return False
+
     def new_session(self, silent=False, title=None):
         """Start a fresh session with a new session ID and cleared agent state."""
         if self.agent and self.conversation_history:
@@ -5837,6 +5860,9 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin):
                 self._session_db.end_session(old_session_id, "new_session")
             except Exception:
                 pass
+            # Don't let immediately-rotated empty sessions pile up in
+            # /resume and `hermes sessions list` (gemini-cli#27770 port).
+            self._discard_session_if_empty(old_session_id)
 
         self.session_start = datetime.now()
         timestamp_str = self.session_start.strftime("%Y%m%d_%H%M%S")
@@ -13074,6 +13100,15 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin):
                     self._session_db.end_session(self.agent.session_id, "cli_close")
                 except (Exception, KeyboardInterrupt) as e:
                     logger.debug("Could not close session in DB: %s", e)
+                # Started-and-immediately-quit sessions never gained content;
+                # drop the empty row so /resume and `hermes sessions list`
+                # stay clean (gemini-cli#27770 port). No-op for resumed or
+                # titled sessions and anything with messages or children.
+                if not getattr(self, '_delete_session_on_exit', False):
+                    try:
+                        self._discard_session_if_empty(self.agent.session_id)
+                    except (Exception, KeyboardInterrupt) as e:
+                        logger.debug("Could not prune empty session: %s", e)
                 # /exit --delete: also remove the current session's transcripts
                 # and SQLite history. Ported from google-gemini/gemini-cli#19332.
                 if getattr(self, '_delete_session_on_exit', False):