fix: retain demo sessions across seed resets

backend/app/api/deps.py

@@ -28,6 +28,16 @@ def get_current_user(request: Request, db: Session = Depends(get_db)) -> Current
     payload: SessionPayload | None = read_session_token(token) if token else None
     if payload is None or payload.role not in _VALID_ROLES:
         raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Not authenticated")
+    # Demo reset deliberately rebuilds the deterministic users table. Retaining the
+    # signed demo session until the reset endpoint clears its cookie keeps existing demo
+    # workflows stable; operational sessions are always checked against the live record.
+    if settings.mobilityops_demo_mode:
+        demo_role: Role = payload.role  # type: ignore[assignment]
+        return CurrentUser(
+            public_ref=payload.public_ref,
+            display_name=payload.display_name,
+            role=demo_role,
+        )
     user = db.get(User, payload.user_id)
     if (
         user is None