fix: lazy session creation — defer DB row until first message (#18370)

Prevents ghost sessions from accumulating in state.db when the TUI/web
dashboard is opened and closed without sending a message.

Changes:
- run_agent.py: Add _ensure_db_session() gate method, called at
  run_conversation() entry. Remove eager create_session() from __init__.
  Handle compression rotation flag correctly.
- tui_gateway/server.py: Remove eager db.create_session() in
  _start_agent_build(). Add post-first-message pending_title re-apply.
- hermes_state.py: Extract _insert_session_row() shared helper (DRY).
  Add prune_empty_ghost_sessions() for one-time migration.
- cli.py: One-time ghost session prune on startup. Fix _pending_title
  to call _ensure_db_session() before set_session_title().
- hermes_cli/main.py: Guard TUI exit summary on message_count > 0.
- tests: Update test_860_dedup to call _ensure_db_session() before
  direct _flush_messages_to_session_db() calls.

Closes: ghost session clutter in hermes sessions list and web dashboard.

cli.py

@@ -934,6 +934,20 @@ def _run_state_db_auto_maintenance(session_db) -> None:
     try:
         from hermes_cli.config import load_config as _load_full_config
         from hermes_constants import get_hermes_home as _get_hermes_home
+        _hermes_home_maint = _get_hermes_home()
+
+        # One-time prune of empty TUI ghost sessions.
+        try:
+            if not session_db.get_meta("ghost_session_prune_v1"):
+                pruned = session_db.prune_empty_ghost_sessions(
+                    sessions_dir=_hermes_home_maint / "sessions"
+                )
+                session_db.set_meta("ghost_session_prune_v1", "1")
+                if pruned:
+                    logger.info("Pruned %d empty TUI ghost sessions", pruned)
+        except Exception as _prune_exc:
+            logger.debug("Ghost session prune skipped: %s", _prune_exc)
+
         cfg = (_load_full_config().get("sessions") or {})
         if not cfg.get("auto_prune", False):
             return
@@ -941,7 +955,7 @@ def _run_state_db_auto_maintenance(session_db) -> None:
             retention_days=int(cfg.get("retention_days", 90)),
             min_interval_hours=int(cfg.get("min_interval_hours", 24)),
             vacuum=bool(cfg.get("vacuum_after_prune", True)),
-            sessions_dir=_get_hermes_home() / "sessions",
+            sessions_dir=_hermes_home_maint / "sessions",
         )
     except Exception as exc:
         logger.debug("state.db auto-maintenance skipped: %s", exc)
@@ -3618,14 +3632,18 @@ class HermesCLI:
                 tuple(runtime.get("args") or ()),
             )
 
-            if self._pending_title and self._session_db:
+            # Force-create DB row on /title intent, then apply title.
+            if self._pending_title and self._session_db and self.agent:
                 try:
-                    self._session_db.set_session_title(self.session_id, self._pending_title)
-                    _cprint(f"  Session title applied: {self._pending_title}")
-                    self._pending_title = None
+                    self.agent._ensure_db_session()
+                    if self.agent._session_db_created:
+                        self._session_db.set_session_title(self.session_id, self._pending_title)
+                        _cprint(f"  Session title applied: {self._pending_title}")
+                        self._pending_title = None
+                    # else: row creation failed transiently — keep _pending_title for retry
                 except (ValueError, Exception) as e:
                     _cprint(f"  Could not apply pending title: {e}")
-                    self._pending_title = None
+                    # Keep _pending_title so it can be retried after row creation succeeds
             return True
         except Exception as e:
             ChatConsole().print(f"[bold red]Failed to initialize agent: {e}[/]")
@@ -4953,6 +4971,7 @@ class HermesCLI:
 
             if self._session_db:
                 try:
+                    self.agent._session_db_created = False
                     self._session_db.create_session(
                         session_id=self.session_id,
                         source=os.environ.get("HERMES_SESSION_SOURCE", "cli"),
@@ -4962,6 +4981,7 @@ class HermesCLI:
                             "reasoning_config": self.reasoning_config,
                         },
                     )
+                    self.agent._session_db_created = True
                 except Exception:
                     pass
             # Notify memory providers that session_id rotated to a fresh