fix(update): default pre-update backup to off (#52729)

The pre-update HERMES_HOME zip shipped on by default (DEFAULT_CONFIG +
runtime fallback both True), so every `hermes update` zipped the entire
~/.hermes — sessions DB, caches, skills — adding minutes to each update.
The shipped cli-config.yaml.example, the --backup help, and the example
config all already said "off by default," so the live default
contradicted its own documentation.

Flip the default to off everywhere: DEFAULT_CONFIG, the runtime
`.get(..., False)` fallback in _run_pre_update_backup, and the stale
--backup help string. Users who want the #48200 safety net opt in via
updates.pre_update_backup: true or --backup for a single run.

Updated test_default_enabled_creates_backup -> test_default_disabled_is_silent
to assert the new default (silent no-op, no zip).

hermes_cli/config.py

@@ -2784,14 +2784,14 @@ DEFAULT_CONFIG = {
     "updates": {
         # Run a full ``hermes backup``-style zip of HERMES_HOME before every
         # ``hermes update``.  Backups land in ``<HERMES_HOME>/backups/`` and
-        # can be restored with ``hermes import <path>``.  Defaults to true
-        # after the #48200 incident: a ``hermes update --yes`` run that
-        # computed a wrong path silently wiped the user's ``.env``,
-        # ``MEMORY.md``, ``kanban.db``, custom skills, and scripts in one
-        # go.  The cost of a few minutes of zip time per update is
-        # negligible compared to the alternative.  Set to false to opt
-        # out, or pass ``--no-backup`` for a single update run.
-        "pre_update_backup": True,
+        # can be restored with ``hermes import <path>``.  Off by default:
+        # zipping a large HERMES_HOME (sessions DB, caches, skills) can add
+        # minutes to every update.  The #48200 incident — a ``hermes update
+        # --yes`` run that computed a wrong path and silently wiped the
+        # user's ``.env``, ``MEMORY.md``, ``kanban.db``, custom skills, and
+        # scripts — is the reason this knob exists; enable it (here, or via
+        # ``--backup`` for a single run) if you want that safety net.
+        "pre_update_backup": False,
         # How many pre-update backup zips to retain.  Older ones are pruned
         # automatically after each successful backup.  Values below 1 are
         # floored to 1 — the backup just created is always preserved.  To

hermes_cli/main.py

@@ -8324,13 +8324,12 @@ def _run_pre_update_backup(args) -> None:
         cfg = {}
 
     updates_cfg = cfg.get("updates", {}) if isinstance(cfg, dict) else {}
-    # The default config ships with ``pre_update_backup: true`` (see
-    # ``hermes_cli/config.py``). Fall back to true if the key is missing
-    # (e.g. a user has an older custom config without the field). The
-    # ``False`` default from before #48200 caused silent data loss when
-    # an update step computed a wrong path — the cost of a few minutes
-    # of zip time per update is negligible compared to the alternative.
-    enabled = updates_cfg.get("pre_update_backup", True)
+    # The default config ships with ``pre_update_backup: false`` (see
+    # ``hermes_cli/config.py``). Fall back to false if the key is missing
+    # so the default behaviour matches the shipped config: zipping a large
+    # HERMES_HOME can add minutes to every update. Users who want the
+    # #48200 safety net opt in via the config knob or ``--backup``.
+    enabled = updates_cfg.get("pre_update_backup", False)
     keep = updates_cfg.get("backup_keep", 5)
 
     if not enabled and not force_backup:

hermes_cli/subcommands/update.py

@@ -41,7 +41,7 @@ def build_update_parser(subparsers, *, cmd_update: Callable) -> None:
         "--backup",
         action="store_true",
         default=False,
-        help="Force a pre-update backup for this run (off by default; overrides updates.pre_update_backup)",
+        help="Force a pre-update backup for this run (off by default; overrides updates.pre_update_backup=false)",
     )
     update_parser.add_argument(
         "--yes",