backups: show timestamps in the site timezone

Backup timestamps read wrong because of two faults stacked, which is why it
looked like a single offset.

The API serialised naive ISO ("2026-08-07T12:00:00"), with nothing saying the
value was UTC. JavaScript's new Date() parses that as BROWSER-LOCAL, so every
timestamp shifted by the viewer's offset before any timezone formatting ran.
Every datetime this plugin stores is naive UTC, so the wire format now carries
a trailing Z.

The history view then formatted with toLocaleString(), i.e. the viewer's zone,
ignoring the site_timezone setting entirely. It now loads that setting and
formats through the shared formatInZone helper, matching NotificationsList.

The panel list label is built server-side with strftime, so a client cannot
correct it afterwards. It now converts to the site zone using the same Setting
lookup the notifications plugin uses - without that it showed UTC, four hours
out at West Jefferson.

Tests cover the wire format and that 16:30Z renders as 12:30 in
America/New_York.

plugins/backups/api/routes.py

@@ -12,6 +12,9 @@ because requiring the app server to mount the SFLD share would turn a
 permissions slip into an unexplained empty download.
 """
 
+from datetime import timezone
+from zoneinfo import ZoneInfo
+
 from flask import Blueprint, current_app, request, Response
 from flask_jwt_extended import jwt_required
 
@@ -22,15 +25,42 @@ from shopdb.api import (
 )
 
 from ..models import BackupRevision
+from ..models.backup import _utciso
 from ..services.registry import REGISTRY, getkind
 
 backups_bp = Blueprint('backups', __name__)
 
 
+_DEFAULTTZ = 'America/New_York'
+
+
+def _sitezone():
+    """Site-configured IANA zone (settings key site_timezone).
+
+    Same lookup the notifications plugin uses. A stored timestamp is UTC, so
+    anything rendered server-side has to be converted or it shows the wrong
+    wall clock for the site - four hours out at West Jefferson.
+    """
+    from shopdb.api import Setting
+    row = Setting.query.filter_by(key='site_timezone').first()
+    name = row.value if row and row.value else _DEFAULTTZ
+    try:
+        return ZoneInfo(name)
+    except Exception:
+        return ZoneInfo(_DEFAULTTZ)
+
+
 def _label(revision):
-    """Panel list title: kind-agnostic, readable at a glance."""
+    """Panel list title: kind-agnostic, readable at a glance.
+
+    Rendered in the SITE zone, not UTC: this string is baked server-side and
+    the client cannot correct it afterwards.
+    """
     when = revision.collectedat or revision.createdat
-    stamp = when.strftime('%Y-%m-%d %H:%M') if when else 'unknown time'
+    if not when:
+        return 'unknown time'
+    local = when.replace(tzinfo=timezone.utc).astimezone(_sitezone())
+    stamp = local.strftime('%Y-%m-%d %H:%M')
     if revision.sourcefilename:
         return '{} - {}'.format(stamp, revision.sourcefilename)
     return stamp
@@ -129,8 +159,7 @@ def asset_info(assetid):
         revision.payload, assetid,
         partmarkertypes=current_app.config.get('BACKUPS_PARTMARKER_TYPES'))
     data['backuprevisionid'] = revision.backuprevisionid
-    data['collectedat'] = (revision.collectedat.isoformat()
+    data['collectedat'] = _utciso(revision.collectedat)
-                           if revision.collectedat else None)
     return success_response(data)
 
 

plugins/backups/frontend/views/BackupHistory.vue

@@ -95,7 +95,8 @@
 <script setup>
 import { ref, onMounted } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
-import api from '@/api'
+import api, { settingsApi } from '@/api'
+import { formatInZone, DEFAULT_TZ } from '@/utils/datetime'
 
 const route = useRoute()
 const router = useRouter()
@@ -111,11 +112,13 @@ const diffs = ref({})
 const assetname = ref('')
 const loading = ref(true)
 const error = ref('')
+// Timestamps are stored UTC and must show in the SITE's zone, not the viewer's,
+// so a remote admin and someone at the bay read the same wall clock.
+const siteTimezone = ref(DEFAULT_TZ)
 
 function formatWhen(value) {
   if (!value) return 'unknown'
-  const d = new Date(value)
+  return formatInZone(value, siteTimezone.value, { second: '2-digit' }) || value
-  return isNaN(d) ? value : d.toLocaleString()
 }
 
 function display(value) {
@@ -124,6 +127,16 @@ function display(value) {
   return String(value)
 }
 
+async function loadTimezone() {
+  try {
+    const response = await settingsApi.get('site_timezone')
+    const value = response?.data?.data?.value
+    if (value) siteTimezone.value = value
+  } catch (e) {
+    // Keep the default zone; a missing setting must not blank the page.
+  }
+}
+
 async function load() {
   loading.value = true
   error.value = ''
@@ -183,7 +196,10 @@ async function download(rev, fmt) {
   URL.revokeObjectURL(link.href)
 }
 
-onMounted(load)
+onMounted(async () => {
+  await loadTimezone()
+  await load()
+})
 </script>
 
 <style scoped>

plugins/backups/models/backup.py

@@ -27,6 +27,15 @@ from datetime import datetime
 from shopdb.api import db
 
 
+def _utciso(value):
+    """Naive-UTC datetime -> ISO string marked as UTC, or None.
+
+    Every datetime this plugin stores is naive UTC. Serialising it without the
+    Z leaves the receiver to guess, and JavaScript guesses browser-local.
+    """
+    return value.isoformat() + 'Z' if value else None
+
+
 class BackupRevision(db.Model):
     """A single point-in-time configuration snapshot of an asset."""
 
@@ -123,8 +132,13 @@ class BackupRevision(db.Model):
             # download <machinenumber>.reg without a second round trip.
             'assetnumber': self.asset.assetnumber if self.asset else None,
             'sourcehostname': self.sourcehostname,
-            'collectedat': self.collectedat.isoformat() if self.collectedat else None,
+            # Both columns hold NAIVE UTC (see collectedat above), so the wire
-            'createdat': self.createdat.isoformat() if self.createdat else None,
+            # format says so with a trailing Z. Without it JavaScript's
+            # `new Date('2026-08-07T12:00:00')` parses the string as
+            # BROWSER-LOCAL and the timestamp silently shifts by the viewer's
+            # offset before any site-timezone formatting is applied.
+            'collectedat': _utciso(self.collectedat),
+            'createdat': _utciso(self.createdat),
         }
         if includepayload:
             data['payloadjson'] = self.payload

tests/test_plugins/test_backups.py

@@ -669,3 +669,44 @@ def test_a_kind_that_sets_emptytext_still_gets_it():
 
 def test_base_kind_defaults_to_hiding_when_empty():
     assert registry.BackupKind.emptytext is None
+
+
+# =============================================================================
+# Timestamp wire format
+# =============================================================================
+
+def test_timestamps_are_serialised_as_utc(bk_app, bk_plugin):
+    """Naive ISO is parsed as BROWSER-LOCAL by JavaScript, silently shifting
+    every timestamp by the viewer's offset before any site-timezone formatting
+    runs. The wire format has to say the value is UTC."""
+    from plugins.backups.models import BackupRevision
+    with bk_app.app_context():
+        result = bk_plugin.apply_collector_payload(
+            _payload(collectedat='2026-08-07T12:00:00Z'))
+        revision = _db.session.get(BackupRevision, result['backuprevisionid'])
+        data = revision.to_dict()
+        assert data['collectedat'].endswith('Z')
+        assert data['createdat'].endswith('Z')
+        # 12:00Z stored naive-UTC, so it round-trips as the same wall clock.
+        assert data['collectedat'].startswith('2026-08-07T12:00:00')
+
+
+def test_utciso_helper_passes_none_through():
+    from plugins.backups.models.backup import _utciso
+    assert _utciso(None) is None
+
+
+def test_panel_label_is_rendered_in_the_site_zone(bk_app, bk_plugin):
+    """The label is baked server-side, so the client cannot correct it later.
+    A UTC afternoon is the morning of the same day at West Jefferson."""
+    from shopdb.core.models import Setting
+    from plugins.backups.models import BackupRevision
+    from plugins.backups.api.routes import _label
+    with bk_app.app_context():
+        _db.session.add(Setting(key='site_timezone', value='America/New_York'))
+        _db.session.commit()
+        result = bk_plugin.apply_collector_payload(
+            _payload(collectedat='2026-08-07T16:30:00Z'))
+        revision = _db.session.get(BackupRevision, result['backuprevisionid'])
+        # 16:30 UTC on 2026-08-07 is 12:30 EDT.
+        assert '12:30' in _label(revision)