fix(backup): stage SQLite snapshots beside output zip in pre-update path too

The pre-update / pre-migration backup path (_write_full_zip_backup) had the
same /tmp staging bug as run_backup: a small tmpfs at the default tempfile
location silently drops large *.db files from the archive. Route its SQLite
staging temp files to the output zip's directory as well, and add regression
tests (mutation-verified) for both staging paths.

Co-authored-by: liuhao1024 <sunsky.lau@gmail.com>

hermes_cli/backup.py

@@ -870,7 +870,13 @@ def _write_full_zip_backup(out_path: Path, hermes_root: Path) -> Optional[Path]:
             for abs_path, rel_path in files_to_add:
                 try:
                     if abs_path.suffix == ".db":
-                        with tempfile.NamedTemporaryFile(suffix=".db", delete=False) as tmp:
+                        # Stage the snapshot alongside the output zip so that the
+                        # temp file lives on the same filesystem.  The system
+                        # default (/tmp) may be a small tmpfs that cannot hold
+                        # large databases, causing silent backup incompleteness.
+                        with tempfile.NamedTemporaryFile(
+                            suffix=".db", delete=False, dir=str(out_path.parent)
+                        ) as tmp:
                             tmp_db = Path(tmp.name)
                         try:
                             if _safe_copy_db(abs_path, tmp_db):

tests/hermes_cli/test_backup.py

@@ -192,6 +192,66 @@ class TestBackup:
             # Skins
             assert "skins/cyber.yaml" in names
 
+    def test_db_snapshots_staged_beside_output_zip(self, tmp_path, monkeypatch):
+        """SQLite staging temp files must be created on the output zip's
+        filesystem (dir=out_path.parent), NOT the system /tmp default — a
+        small tmpfs there silently drops large DBs from the backup (#35376)."""
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        _make_hermes_tree(hermes_home)
+
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+        monkeypatch.setattr(Path, "home", lambda: tmp_path)
+
+        out_dir = tmp_path / "external-drive"
+        out_dir.mkdir()
+        out_zip = out_dir / "backup.zip"
+        args = Namespace(output=str(out_zip))
+
+        import hermes_cli.backup as backup_mod
+        staged_dirs = []
+        real_ntf = backup_mod.tempfile.NamedTemporaryFile
+
+        def _spy(*a, **kw):
+            staged_dirs.append(kw.get("dir"))
+            return real_ntf(*a, **kw)
+
+        monkeypatch.setattr(backup_mod.tempfile, "NamedTemporaryFile", _spy)
+        backup_mod.run_backup(args)
+
+        # At least one .db was staged, and every staging call targeted the
+        # output zip's directory rather than the system temp default.
+        assert staged_dirs, "no SQLite snapshot was staged"
+        assert all(d == str(out_dir) for d in staged_dirs), staged_dirs
+
+    def test_pre_update_db_snapshots_staged_beside_output_zip(self, tmp_path, monkeypatch):
+        """The pre-update/pre-migration zip path (_write_full_zip_backup) must
+        also stage SQLite snapshots beside its output zip, not in /tmp."""
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        _make_hermes_tree(hermes_home)
+
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+        monkeypatch.setattr(Path, "home", lambda: tmp_path)
+
+        out_zip = hermes_home / "backups" / "pre-update-test.zip"
+        out_zip.parent.mkdir(parents=True, exist_ok=True)
+
+        import hermes_cli.backup as backup_mod
+        staged_dirs = []
+        real_ntf = backup_mod.tempfile.NamedTemporaryFile
+
+        def _spy(*a, **kw):
+            staged_dirs.append(kw.get("dir"))
+            return real_ntf(*a, **kw)
+
+        monkeypatch.setattr(backup_mod.tempfile, "NamedTemporaryFile", _spy)
+        result = backup_mod._write_full_zip_backup(out_zip, hermes_home)
+
+        assert result is not None
+        assert staged_dirs, "no SQLite snapshot was staged"
+        assert all(d == str(out_zip.parent) for d in staged_dirs), staged_dirs
+
     def test_excludes_hermes_agent(self, tmp_path, monkeypatch):
         """Backup does NOT include hermes-agent/ directory."""
         hermes_home = tmp_path / ".hermes"