diff --git a/lib/compute/crossday_pipeline.dart b/lib/compute/crossday_pipeline.dart
index e49f5ab87..2f923b638 100644
--- a/lib/compute/crossday_pipeline.dart
+++ b/lib/compute/crossday_pipeline.dart
@@ -24,7 +24,7 @@ import '../data/day_label.dart';
 // IO, no Flutter binding, so importing it does not compromise this file's
 // isolate safety. One grammar for "a required input was missing" across both
 // pipelines rather than a second one here.
-import 'onehz_pipeline.dart' show needInputNote;
+import 'onehz_pipeline.dart' show kSleepClockAnchorSec, needInputNote;
 
 /// Build the cross-day analytics bundle from a time-ordered (OLDEST FIRST) list
 /// of per-day records and the user profile.
@@ -34,6 +34,8 @@ import 'onehz_pipeline.dart' show needInputNote;
 ///    'resp_rate': num?, 'skin_temp_z': num?, 'skin_temp_adc': num?,
 ///    'skin_temp_family': String?, 'trimp': num?,
 ///    'onset_sec': int?, 'wake_sec': int?, 'tst_min': int?,
+///    'clock_shift_sec': int? (present only for a night recorded in another
+///      zone than the phone's current one — see [recordedClockShiftSec]),
 ///    'hypnogram': [{start,end,stage}]?}
 ///
 /// Returns a JSON-safe map of the latest/aggregate cross-day results. Every
@@ -209,7 +211,10 @@ Map<String, dynamic> buildCrossDayBundle(
     // LOCAL clock-hours [0,24). onset/wake are epoch SECONDS (UTC); `% 86400`
     // would give the UTC time-of-day, not the user's wall clock — convert via a
     // local DateTime so a UTC+5:30 user's 08:00 wake reads as 08:00, not 02:30.
-    final midH = _localTodMin(midSec.round()) / 60.0;
+    // …and on the clock the night was LIVED on, not the phone's current one:
+    // after a flight every past night would otherwise move by the zone change
+    // and chronotype/social jetlag would read the trip as a schedule shift.
+    final midH = _nightClockMin(midSec.round(), d) / 60.0;
     final free = _isFreeDay(d['date'] as String?);
     if (free) {
       freeMidH.add(midH);
@@ -482,9 +487,24 @@ Map<String, dynamic> buildCrossDayBundle(
           note: need.present ? needInputNote('tst_min') : need.note,
         );
   // typical wake clock-minute + efficiency from recent days (medians).
+  //
+  // The wake is read on the clock of the zone each night was LIVED in, not the
+  // phone's current zone. Converting the absolute instants with today's zone
+  // is what printed "Target bedtime 4:00 PM / Target wake 1:31 AM" to a user
+  // who had flown 7 h west: 08:31 wakes recorded at UTC+2 re-read as 01:31
+  // in the new zone, and the bedtime backed off them landed mid-afternoon.
+  //
+  // DESIGN: the targets are a LOCAL CLOCK schedule (wake ~07:45, bed ~23:30),
+  // carried into whatever zone the phone is in now — the social schedule moves
+  // with the traveller, the absolute instants do not. Nothing here models the
+  // body clock catching up across the trip; the median over up to 90 nights
+  // absorbs the first jet-lagged nights in the new zone, and as nights are
+  // lived there it simply keeps reading their local clock too. See
+  // [recordedClockShiftSec] for how a stored night's own clock is recovered.
   final wakeMins = <double>[
     for (final d in days)
-      if (d['wake_sec'] != null) _localTodMin((d['wake_sec'] as num).toInt()),
+      if (d['wake_sec'] != null)
+        _nightClockMin((d['wake_sec'] as num).toInt(), d),
   ];
   final effs = <double>[for (final d in days) ?_numOrNull(d['efficiency'])];
   final typicalWakeMin = _median(wakeMins);
@@ -741,6 +761,89 @@ double _localTodMin(int epochSec) {
   return t.hour * 60.0 + t.minute + t.second / 60.0;
 }
 
+/// Local minute-of-day [0,1440) of [epochSec] on the clock night [d] was LIVED
+/// on: [_localTodMin] moved by the record's `clock_shift_sec` (see
+/// [recordedClockShiftSec]). A record without one was recorded in the phone's
+/// current zone, or we cannot tell — and this IS [_localTodMin], to the second.
+double _nightClockMin(int epochSec, Map<String, dynamic> d) {
+  final shift = d['clock_shift_sec'];
+  final shiftMin = shift is num && shift.isFinite ? shift / 60.0 : 0.0;
+  return (_localTodMin(epochSec) + shiftMin) % 1440.0;
+}
+
+/// How far a stored night's OWN local clock sits from the phone's CURRENT
+/// zone, in seconds [0,86400) — 0 when it was recorded in this zone, or when
+/// we cannot tell. Called by the record builder
+/// (`DerivationEngine.crossDayInputRecord`), which writes it as
+/// `clock_shift_sec` only when it is non-zero.
+///
+/// WHY THIS EXISTS. `onset_sec`/`wake_sec` are absolute instants. The only way
+/// to put one on a wall clock is a zone, and `DateTime` only knows the phone's
+/// CURRENT zone: after a trip it converts every past night with the new zone's
+/// rules (DST-correct for the new zone, but the user was never there). The
+/// zone they were in is not stored on the day row — but the per-day pipeline
+/// wrote `sleep_onset_sec` (onehz_pipeline's `sleepClockOffsetSec`): the
+/// onset's LOCAL clock position, frozen at derive time in the zone the phone
+/// was in then ([onsetClockSec], signed seconds either side of
+/// [kSleepClockAnchorSec]). Comparing that frozen clock with the same instant
+/// re-read in today's zone yields the frame shift, which then applies to every
+/// other instant of that night (wake, mid-sleep).
+///
+/// SNAPPED TO 15 MIN, because every real UTC offset is a multiple of 15 min
+/// and the two clocks are the same instant read twice — any residue is
+/// rounding, never a zone.
+///
+/// LIMITS, stated rather than hidden:
+///   - A night without the frozen clock (derived before SLP-09 started writing
+///     it, mid-August 2026) reads in the current zone, as it always did. Those
+///     age out of the 90-night window.
+///   - A night first derived AFTER the trip (synced only once there) froze
+///     the new zone's clock and reads in it. A RE-derive keeps the clock the
+///     stored row already had ([storedNightClockShiftSec]), so "Re-analyze
+///     data" or a version bump does not move a pre-trip night.
+///   - A DST change inside the night itself is applied with the CURRENT zone's
+///     rules at the wake instant: off by at most an hour, twice a year, for a
+///     traveller only (the shift is 0 at home).
+int recordedClockShiftSec({
+  required num? onsetSec,
+  required num? onsetClockSec,
+}) {
+  if (onsetSec == null || onsetClockSec == null || !onsetClockSec.isFinite) {
+    return 0;
+  }
+  final recordedSecOfDay =
+      (onsetClockSec.round() + kSleepClockAnchorSec) % 86400;
+  final nowFrameSecOfDay = (_localTodMin(onsetSec.toInt()) * 60).round();
+  final raw = (recordedSecOfDay - nowFrameSecOfDay) % 86400;
+  return ((raw / 900).round() * 900) % 86400;
+}
+
+/// [recordedClockShiftSec] of a stored `day_result` payload: its sleep onset
+/// instant against the `sleep_onset_sec` clock it froze. 0 when either is
+/// missing.
+int storedNightClockShiftSec(Map<String, dynamic>? payload) {
+  final sleep = payload?['sleep'];
+  final win = sleep is Map ? sleep['window'] : null;
+  final val = win is Map ? win['value'] : null;
+  final onsetMs = val is Map ? val['onset_ms'] : null;
+  final scalars = payload?['scalars'];
+  final clock = scalars is Map ? scalars['sleep_onset_sec'] : null;
+  return recordedClockShiftSec(
+    onsetSec: onsetMs is num ? (onsetMs / 1000).round() : null,
+    onsetClockSec: clock is num ? clock : null,
+  );
+}
+
+/// A frozen sleep clock (signed seconds either side of
+/// [kSleepClockAnchorSec], as `sleepClockOffsetSec` writes it) moved by
+/// [shiftSec] and wrapped back into (-12 h, +12 h]. Null stays null.
+double? shiftRecordedClockSec(num? clockSec, int shiftSec) {
+  if (clockSec == null || !clockSec.isFinite) return null;
+  var v = (clockSec + shiftSec) % 86400;
+  if (v > 43200) v -= 86400;
+  return v.toDouble();
+}
+
 double? _mean(List<double> xs) {
   if (xs.isEmpty) return null;
   var s = 0.0;
diff --git a/lib/compute/derivation_engine.dart b/lib/compute/derivation_engine.dart
index 0a8002c1b..8a0437de5 100644
--- a/lib/compute/derivation_engine.dart
+++ b/lib/compute/derivation_engine.dart
@@ -1825,7 +1825,13 @@ import 'vendor_sleep.dart';
 // carries a workout-raised headline; a logged nap over the main sleep is
 // counted once; an implausible stored age is named as the reason strain,
 // calories and zones are absent.
-const int kAlgoVersion = 116;
+// 116 → 117 (#624): the cross-day rollup reads each night's onset/wake/mid-sleep
+// on the clock it was lived on (`clock_shift_sec`, recovered from the stored
+// `sleep_onset_sec`), so after a zone change the Sleep Coach targets, typical
+// wake, chronotype and social jetlag no longer move by the zone difference. A
+// re-derive keeps the stored night's clock. Unchanged for a user who has not
+// changed zone. Edge-only.
+const int kAlgoVersion = 117;
 /// The sibling SHAs this version was derived against, asserted against
 /// pubspec.yaml in test/db_serve_version_and_reads_test.dart.
 ///
@@ -3249,6 +3255,13 @@ class DerivationEngine {
           await _withWearableEdge(await LocalDb.lastDecodedRecTs()) ?? 0;
       if (dataNowSec <= 0) {
         _log('derive: no decoded data');
+        // A restored backup can hold every day and no decoded data. The
+        // rollup is built from stored days, so a zone change still rebuilds
+        // it here; otherwise the reader keeps abstaining on the old zone.
+        if (await _crossDayZoneStale()) {
+          await _refreshBaselines();
+          await _runCrossDay(profile);
+        }
         return 0;
       }
       final finalized = await LocalDb.finalizedDayIds(kAlgoVersion);
@@ -3275,7 +3288,9 @@ class DerivationEngine {
         // the todo set; re-score it here too rather than leave it a pass.
         final rescored =
             await _quietLevelRepass(profile, dataNowSec, scope.rawDays);
-        if (rescored > 0) {
+        // A zone change with no day to derive still moves every past night's
+        // clock: rebuild the rollup, or it keeps the old zone's reading.
+        if (rescored > 0 || await _crossDayZoneStale()) {
           await _refreshBaselines();
           await _runCrossDay(profile);
           await _runNotifications();
@@ -6086,6 +6101,32 @@ class DerivationEngine {
       }
     }
 
+    // RE-DERIVING KEEPS THE NIGHT'S OWN CLOCK. The pipeline freezes
+    // `sleep_onset_sec`/`midsleep_sec` with the phone's zone NOW, so re-deriving
+    // a night lived before a trip (re-analyze, a rescan, a version bump) would
+    // overwrite the only record of the zone it was lived in, and the cross-day
+    // rollup would read it on the new clock. Carry the stored row's shift.
+    //
+    // Two numbers off the stored row, extracted in SQLite: decoding the whole
+    // previous bundle here cost a full payload read and curve expansion on
+    // this isolate for every derived day, to learn nothing for anyone who has
+    // not changed zone.
+    final prevClock = await LocalDb.storedNightClock(day.date);
+    if (prevClock != null) {
+      final onsetMs = prevClock.onsetMs;
+      final shift = recordedClockShiftSec(
+        onsetSec: onsetMs == null ? null : (onsetMs / 1000).round(),
+        onsetClockSec: prevClock.onsetClockSec,
+      );
+      final s = bundle['scalars'];
+      if (shift != 0 && s is Map) {
+        for (final k in const ['sleep_onset_sec', 'midsleep_sec']) {
+          final v = shiftRecordedClockSec(s[k] as num?, shift);
+          if (v != null) s[k] = v;
+        }
+      }
+    }
+
     final scalars =
         (bundle['scalars'] as Map?)?.cast<String, dynamic>() ?? const {};
     double? sc(String k) => (scalars[k] as num?)?.toDouble();
@@ -6780,6 +6821,9 @@ class DerivationEngine {
   Future<bool> _runCrossDay(Profile profile) async {
     try {
       final reviewRevision = await LocalDb.activityReviewRevision();
+      // The zone the inputs are read in, taken BEFORE they are read: a change
+      // during the build must not stamp old-zone shifts with the new zone.
+      final zone = crossDayZoneStamp();
       final days = await _crossDayInputDays();
       if (days.length < 3) {
         _log('crossday: only ${days.length} usable day(s) — skip');
@@ -6824,7 +6868,8 @@ class DerivationEngine {
                 )
                 ..['algo_version'] = kAlgoVersion
                 ..['built_for_day'] = builtForDay
-                ..['built_at_epoch'] = builtAtEpoch;
+                ..['built_at_epoch'] = builtAtEpoch
+                ..['zone'] = zone;
           // Encode-safety BEFORE jsonEncode, never a try/catch around it: one
           // non-finite leaf must cost that leaf, not the whole artifact.
           final paths = <String>[];
@@ -6835,6 +6880,12 @@ class DerivationEngine {
         _crossDayTimeout,
         label: 'crossday',
       );
+      if (crossDayZoneStamp() != zone) {
+        // The zone moved while this was built: drop it; the stale check
+        // rebuilds it on the next pass in the new zone.
+        _log('crossday: zone changed during the build; not stored');
+        return false;
+      }
       if (!await LocalDb.putReviewedBaseline('crossday', bundleJson, reviewRevision)) {
         _log('crossday: newer activity review; leaving its refresh queued');
         return false;
@@ -6896,6 +6947,48 @@ class DerivationEngine {
     return out;
   }
 
+  /// The phone zone a `crossday_input` artifact was built in. Its records are
+  /// zone-RELATIVE (`clock_shift_sec` is "this night's clock minus the zone the
+  /// record was built in"), so an artifact built before a flight, served after
+  /// it on the same day, would re-read every past night on the new clock — the
+  /// "Target bedtime 4:00 PM" bug again, until the next rebuild. A mismatch
+  /// (or an artifact without the stamp) rebuilds. Name AND offset: a DST change
+  /// alone rebuilds too, which is one cheap rebuild twice a year.
+  ///
+  /// The abbreviation alone collides (Denver and Phoenix are both "MST" in
+  /// winter), so the stamp also carries the zone's offsets mid-January and
+  /// mid-July: two zones that agree on all three keep every night on the same
+  /// clock anyway.
+  static String crossDayZoneStamp() {
+    final now = DateTime.now();
+    int offsetAt(int month) => DateTime.fromMillisecondsSinceEpoch(
+            DateTime.utc(now.year, month, 15, 12).millisecondsSinceEpoch)
+        .timeZoneOffset
+        .inMinutes;
+    return zoneStampOf(now.timeZoneName, now.timeZoneOffset.inMinutes,
+        offsetAt(1), offsetAt(7));
+  }
+
+  @visibleForTesting
+  static String zoneStampOf(
+          String name, int nowOffsetMin, int janOffsetMin, int julOffsetMin) =>
+      '$name|$nowOffsetMin|$janOffsetMin|$julOffsetMin';
+
+  /// Whether the stored cross-day ROLLUP was built in another zone. The
+  /// rollup, not its inputs: [_refreshBaselines] re-stamps the inputs before
+  /// the rollup is written, so a rollup that then timed out would read as
+  /// current on the inputs' stamp and never be retried.
+  Future<bool> _crossDayZoneStale() async {
+    final raw = (await LocalDb.baseline('crossday'))?['payload_json'];
+    if (raw is! String || raw.isEmpty) return false;
+    try {
+      final decoded = jsonDecode(raw);
+      return decoded is Map && decoded['zone'] != crossDayZoneStamp();
+    } catch (_) {
+      return false;
+    }
+  }
+
   Future<List<Map<String, dynamic>>> _crossDayInputDays() async {
     final reviewRevision = await LocalDb.activityReviewRevision();
     final artifact = await LocalDb.baseline('crossday_input');
@@ -6908,7 +7001,8 @@ class DerivationEngine {
         // day makes `_todayNum` read yesterday's strain and nap minutes as
         // today's (§3.3). See [crossDayArtifactUsableToday].
         if (crossDayArtifactUsableToday(decoded, LocalDb.localDayLabelNow()) &&
-            (decoded as Map)['review_revision'] == reviewRevision) {
+            (decoded as Map)['review_revision'] == reviewRevision &&
+            decoded['zone'] == crossDayZoneStamp()) {
           final rows = decoded['days'] as List;
           return [
             for (final row in rows)
@@ -6934,6 +7028,7 @@ class DerivationEngine {
     final rows = await LocalDb.recentDayResults(_crossDayWindow);
     final today = LocalDb.localDayLabelNow();
     final imported = await LocalDb.importedDates();
+    final zone = crossDayZoneStamp();
     final (days, json) = await _runIsolateCancellable(() {
       final days = <Map<String, dynamic>>[];
       for (final row in rows.reversed) {
@@ -6957,6 +7052,7 @@ class DerivationEngine {
           'algo_version': kAlgoVersion,
           'built_for_day': today,
           'review_revision': reviewRevision,
+          'zone': zone,
           'days': days,
         })
       );
@@ -7136,6 +7232,10 @@ class DerivationEngine {
     final tstSec = (acctVal?['tst_sec'] as num?)?.toDouble();
     final inBedSec = (acctVal?['in_bed_sec'] as num?)?.toDouble();
     final observedSec = (acctVal?['observed_in_bed_sec'] as num?)?.toDouble();
+    final clockShift = recordedClockShiftSec(
+      onsetSec: onsetMs == null ? null : (onsetMs / 1000).round(),
+      onsetClockSec: sc('sleep_onset_sec'),
+    );
 
     return {
       'date': date,
@@ -7164,6 +7264,17 @@ class DerivationEngine {
       'efficiency': sc('efficiency'),
       'onset_sec': onsetMs == null ? null : (onsetMs / 1000).round(),
       'wake_sec': offsetMs == null ? null : (offsetMs / 1000).round(),
+      // Which clock the night was LIVED on, relative to the phone's zone now.
+      // `onset_sec`/`wake_sec` are absolute instants with no zone attached;
+      // SLP-09's `sleep_onset_sec` scalar froze the onset's LOCAL clock in the
+      // zone the phone was in when the day was derived, and the gap between
+      // the two readings is the zone change. Without it a flight slid every
+      // past wake by the shift and the Sleep Coach printed "Target bedtime
+      // 4:00 PM / Target wake 1:31 AM" after 7 h west.
+      //
+      // Only the shift is written: a night recorded in this zone (the shift
+      // is 0) carries no new key and reads exactly as before.
+      if (clockShift != 0) 'clock_shift_sec': clockShift,
       'tst_min': tstSec == null ? null : (tstSec / 60).round(),
       // Fraction of the night we actually watched — wall-clock in-bed minus the
       // seconds nobody observed, over in-bed. TS-11 drops a morning whose night
@@ -7184,7 +7295,10 @@ class DerivationEngine {
       // does not exist far enough back. `circadianNonparametric` documents HR
       // as an accepted input alongside activity. 24 numbers a day, so the
       // artifact stays small.
-      'hourly_hr': hourlyHrProfile(series?['hr_curve']),
+      // Binned on the clock the day was lived on, like onset and wake: after a
+      // flight the phone's hours are not the hours that day's HR was lived in.
+      'hourly_hr':
+          hourlyHrProfile(series?['hr_curve'], clockShiftSec: clockShift),
     };
   }
 
@@ -7195,7 +7309,11 @@ class DerivationEngine {
   /// it, so a bin is always a mean over genuine readings — never an average of
   /// one stray second, and never an imputed value. Gaps stay null and the
   /// consumer excludes the day; nothing is filled in.
-  static List<double?> hourlyHrProfile(Object? hrCurve, {int minMinutes = 5}) {
+  ///
+  /// [clockShiftSec] moves each sample onto the day's own clock (see
+  /// [recordedClockShiftSec]); 0 bins on the phone's current local hour.
+  static List<double?> hourlyHrProfile(Object? hrCurve,
+      {int minMinutes = 5, int clockShiftSec = 0}) {
     final sums = List<double>.filled(24, 0);
     final counts = List<int>.filled(24, 0);
     if (hrCurve is List) {
@@ -7207,7 +7325,9 @@ class DerivationEngine {
         // LOCAL hour. The day model is local-midnight-to-midnight, so the UTC
         // hour would smear a user's evening into the next bin (and, for a
         // non-integral-offset zone, into the wrong one entirely).
-        final h = DateTime.fromMillisecondsSinceEpoch(t * 1000).hour;
+        final lt = DateTime.fromMillisecondsSinceEpoch(t * 1000);
+        final sod = lt.hour * 3600 + lt.minute * 60 + lt.second;
+        final h = ((sod + clockShiftSec) % 86400) ~/ 3600;
         if (h < 0 || h > 23) continue;
         sums[h] += v;
         counts[h] += 1;
diff --git a/lib/compute/inputs/canonical.dart b/lib/compute/inputs/canonical.dart
index e5c231d7d..ff4b2ca8b 100644
--- a/lib/compute/inputs/canonical.dart
+++ b/lib/compute/inputs/canonical.dart
@@ -18,7 +18,7 @@ import '../../ble/adapters/_registry.dart'
 import '../../data/day_label.dart';
 import '../../data/db.dart';
 import '../crossday_pipeline.dart' show buildCrossDayBundle;
-import '../derivation_engine.dart' show kAlgoVersion;
+import '../derivation_engine.dart' show DerivationEngine, kAlgoVersion;
 import '../substrate.dart';
 import '../vendor_sleep.dart';
 import 'colmi_inputs.dart';
@@ -1412,7 +1412,12 @@ Map _decode(Object? raw) => raw is String ? jsonDecode(raw) as Map : const {};
 Future<Map> crossDayAsOf(String date) async {
   final stored = _decode((await LocalDb.baseline('crossday'))?['payload_json']);
   final recent = stored['recent'];
+  // Both artifacts read each night on its lived clock relative to the zone
+  // they were built in; read in another zone they move every night by the
+  // difference, so they are served only in the zone they were built in.
+  final zone = DerivationEngine.crossDayZoneStamp();
   if ((stored['algo_version'] as num?)?.toInt() == kAlgoVersion &&
+      stored['zone'] == zone &&
       recent is List && recent.isNotEmpty && recent.last is Map &&
       (recent.last as Map)['date'] == date) {
     return stored;
@@ -1424,7 +1429,8 @@ Future<Map> crossDayAsOf(String date) async {
     final input = jsonDecode(raw);
     if (input is! Map ||
         (input['algo_version'] as num?)?.toInt() != kAlgoVersion ||
-        input['review_revision'] != reviewRevision) {
+        input['review_revision'] != reviewRevision ||
+        input['zone'] != zone) {
       return const <String, dynamic>{};
     }
     final days = <Map<String, dynamic>>[
diff --git a/lib/compute/onehz_pipeline.dart b/lib/compute/onehz_pipeline.dart
index 9c83f05f4..9f188d117 100644
--- a/lib/compute/onehz_pipeline.dart
+++ b/lib/compute/onehz_pipeline.dart
@@ -1911,7 +1911,12 @@ Map<String, dynamic> deriveDayBundle(Map<String, dynamic> inputJson) {
 ///
 /// Any fixed hour would do; 04:00 is the one furthest from a normal bedtime
 /// AND from a normal wake time, so neither series sits near the wrap.
-const int _sleepClockAnchorSec = 4 * 3600;
+///
+/// Public because the cross-day rollup reads `sleep_onset_sec` back to learn
+/// which clock a stored night was LIVED on (crossday_pipeline's
+/// `recordedClockShiftSec`); decoding it with a second copy of this number
+/// is the drift that would quietly put every night an anchor-change off.
+const int kSleepClockAnchorSec = 4 * 3600;
 
 /// A sleep instant's LOCAL clock position, in seconds either side of 04:00 —
 /// negative before, positive after. Null for an absent window (never 0, which
@@ -1932,7 +1937,7 @@ double? sleepClockOffsetSec(int epochSec) {
   if (epochSec <= 0) return null;
   final local = epochSec + tzOffsetSecondsAt(epochSec);
   final secOfDay = ((local % 86400) + 86400) % 86400;
-  var offset = secOfDay - _sleepClockAnchorSec;
+  var offset = secOfDay - kSleepClockAnchorSec;
   if (offset > 43200) offset -= 86400;
   if (offset <= -43200) offset += 86400;
   return offset.toDouble();
diff --git a/lib/data/db.dart b/lib/data/db.dart
index 1dfb259b8..01639369d 100644
--- a/lib/data/db.dart
+++ b/lib/data/db.dart
@@ -9113,6 +9113,42 @@ class LocalDb {
     return rows.isEmpty ? null : _withDate(rows.first);
   }
 
+  /// The two numbers a re-derive needs to keep a stored night on the clock it
+  /// was lived on: the served row's sleep onset instant (ms) and the
+  /// `sleep_onset_sec` clock it froze. Read with json_extract, so the bundle is
+  /// never decoded on the calling isolate — a re-derive runs this for every
+  /// day. Null when the day has no served row, the row is a skip marker, or
+  /// the payload is malformed.
+  static Future<({num? onsetMs, num? onsetClockSec})?> storedNightClock(
+      String dayId) async {
+    final db = await instance;
+    // Nested CASE: json_extract raises on a malformed document and only CASE
+    // branches are evaluated lazily.
+    final rows = await db.rawQuery(
+      'SELECT '
+      "CASE WHEN json_valid(payload_json) THEN CASE WHEN "
+      "json_type(payload_json, '\$.skipped') = 'true' THEN 1 ELSE 0 END "
+      'ELSE 1 END AS bad, '
+      "CASE WHEN json_valid(payload_json) THEN "
+      "json_extract(payload_json, '\$.sleep.window.value.onset_ms') END "
+      'AS onset_ms, '
+      "CASE WHEN json_valid(payload_json) THEN "
+      "json_extract(payload_json, '\$.scalars.sleep_onset_sec') END "
+      'AS onset_clock, skipped '
+      'FROM day_result WHERE day_id = ? AND algo_version <= ? '
+      'ORDER BY algo_version DESC LIMIT 1',
+      [dayId, _servedAlgoCeiling],
+    );
+    if (rows.isEmpty) return null;
+    final r = rows.first;
+    if (r['bad'] == 1 || (r['skipped'] as num?)?.toInt() == 1) return null;
+    final onset = r['onset_ms'], clock = r['onset_clock'];
+    return (
+      onsetMs: onset is num ? onset : null,
+      onsetClockSec: clock is num ? clock : null,
+    );
+  }
+
   /// The `readiness_absent_diag` diagnostic off [day]'s stored bundle — per
   /// input `{value, baseline_n}` plus the composite's own `note`. Produced on
   /// every day readiness comes back absent; null when [day] is null, has no
diff --git a/test/crossday_as_of_zone_test.dart b/test/crossday_as_of_zone_test.dart
new file mode 100644
index 000000000..bc8ae34fe
--- /dev/null
+++ b/test/crossday_as_of_zone_test.dart
@@ -0,0 +1,149 @@
+// The cross-day artifacts hold each night on its lived clock relative to the
+// zone they were built in. Read in another zone, every night moves by the
+// difference, so a past day's rollup is served only in the zone it was built
+// in; elsewhere it abstains until the next pass rebuilds it.
+
+import 'dart:convert';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:path/path.dart' as p;
+import 'package:sqflite_common_ffi/sqflite_ffi.dart';
+
+import 'package:openstrap_edge/compute/derivation_engine.dart';
+import 'package:openstrap_edge/compute/profile.dart';
+import 'package:openstrap_edge/compute/inputs/canonical.dart'
+    show crossDayAsOf;
+import 'package:openstrap_edge/data/db.dart';
+
+Map<String, dynamic> _day(String date, int onset) => {
+      'date': date,
+      'rhr': 52,
+      'rmssd': 60,
+      'readiness': 70,
+      'onset_sec': onset,
+      'wake_sec': onset + 8 * 3600,
+      'tst_min': 450,
+      'efficiency': 95,
+    };
+
+Future<void> _putInput(String zone) async {
+  final base = DateTime.utc(2026, 9, 1, 22).millisecondsSinceEpoch ~/ 1000;
+  final days = [
+    for (var i = 0; i < 5; i++)
+      _day('2026-09-0${i + 2}', base + i * 86400),
+  ];
+  await LocalDb.putBaseline(
+    'crossday_input',
+    jsonEncode({
+      'algo_version': kAlgoVersion,
+      'built_for_day': '2026-09-06',
+      'review_revision': await LocalDb.activityReviewRevision(),
+      'zone': zone,
+      'days': days,
+    }),
+  );
+}
+
+void main() {
+  setUpAll(() async {
+    sqfliteFfiInit();
+    databaseFactory = databaseFactoryFfi;
+    LocalDb.dbName = 'openstrap_crossday_as_of_zone_test.db';
+    final dir = await databaseFactory.getDatabasesPath();
+    await databaseFactory.deleteDatabase(p.join(dir, LocalDb.dbName));
+  });
+
+  tearDownAll(() async {
+    await LocalDb.close();
+    final dir = await databaseFactory.getDatabasesPath();
+    await databaseFactory.deleteDatabase(p.join(dir, LocalDb.dbName));
+  });
+
+  test('inputs built in this zone rebuild a past day', () async {
+    await _putInput(DerivationEngine.crossDayZoneStamp());
+    expect(await crossDayAsOf('2026-09-05'), isNotEmpty);
+  });
+
+  test('inputs built in another zone abstain', () async {
+    await _putInput('Elsewhere|-420');
+    expect(await crossDayAsOf('2026-09-05'), isEmpty);
+  });
+
+  test('zones sharing an abbreviation do not share a stamp', () {
+    // Denver and Phoenix both read "MST" in January; only Denver moves in July.
+    final denver = DerivationEngine.zoneStampOf('MST', -420, -420, -360);
+    final phoenix = DerivationEngine.zoneStampOf('MST', -420, -420, -420);
+    expect(denver, isNot(phoenix));
+    expect(DerivationEngine.crossDayZoneStamp(),
+        DerivationEngine.crossDayZoneStamp(),
+        reason: 'stable within one zone');
+  });
+
+  test('a restored backup with no band data rebuilds an old-zone rollup',
+      () async {
+    // Stored days, no decoded rows, and a rollup from before a flight.
+    for (var i = 0; i < 5; i++) {
+      final day = '2026-09-0${i + 2}';
+      final onset =
+          DateTime.utc(2026, 9, i + 1, 22).millisecondsSinceEpoch ~/ 1000;
+      await LocalDb.putDayResult(
+        dayId: day,
+        algoVersion: kAlgoVersion,
+        finalized: true,
+        rhr: 52,
+        readiness: 70,
+        windowJson: '{}',
+        payloadJson: jsonEncode({
+          'scalars': {'rhr': 52, 'readiness': 70, 'efficiency': 95},
+          'sleep': {
+            'window': {
+              'value': {
+                'onset_ms': onset * 1000,
+                'offset_ms': (onset + 8 * 3600) * 1000,
+              },
+            },
+            'accounting': {
+              'value': {'tst_sec': 27000},
+            },
+          },
+        }),
+      );
+    }
+    await LocalDb.putBaseline(
+      'crossday',
+      jsonEncode({
+        'algo_version': kAlgoVersion,
+        'zone': 'Elsewhere|-420|-420|-420',
+        'recent': const [],
+      }),
+    );
+    // The inputs were already re-read in this zone before the rollup write
+    // failed: the retry has to go by the rollup's own stamp.
+    await _putInput(DerivationEngine.crossDayZoneStamp());
+    await DerivationEngine().run(const Profile(
+      ageYears: 35,
+      sex: 'm',
+      weightKg: 75,
+      heightCm: 178,
+    ));
+    final rollup = jsonDecode(
+        (await LocalDb.baseline('crossday'))!['payload_json'] as String) as Map;
+    expect(rollup['zone'], DerivationEngine.crossDayZoneStamp());
+  });
+
+  test('a stored rollup from another zone is not served as current',
+      () async {
+    await _putInput('Elsewhere|-420');
+    await LocalDb.putBaseline(
+      'crossday',
+      jsonEncode({
+        'algo_version': kAlgoVersion,
+        'zone': 'Elsewhere|-420',
+        'recent': [
+          {'date': '2026-09-06'},
+        ],
+      }),
+    );
+    expect(await crossDayAsOf('2026-09-06'), isEmpty);
+  });
+}
diff --git a/test/fixtures/whoop_freeze/gen4_minus0400.json b/test/fixtures/whoop_freeze/gen4_minus0400.json
index 2509c77ca..887783571 100644
--- a/test/fixtures/whoop_freeze/gen4_minus0400.json
+++ b/test/fixtures/whoop_freeze/gen4_minus0400.json
@@ -2,7 +2,7 @@
  "day_result": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-13",
     "day_confidence": 0.6,
@@ -24902,7 +24902,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-14",
     "day_confidence": 0.6,
@@ -49595,7 +49595,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-15",
     "day_confidence": 0.6,
@@ -73355,7 +73355,7 @@
  "metric_series_version": [
   {
    "date": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73363,7 +73363,7 @@
   },
   {
    "date": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73371,7 +73371,7 @@
   },
   {
    "date": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73381,7 +73381,7 @@
  "wake_day_features": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-13",
     "active_min": 90,
@@ -74589,7 +74589,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-14",
     "active_min": 240,
@@ -75797,7 +75797,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-15",
     "active_min": 40,
diff --git a/test/fixtures/whoop_freeze/gen4_plus0530.json b/test/fixtures/whoop_freeze/gen4_plus0530.json
index 4f489c854..f56647ae3 100644
--- a/test/fixtures/whoop_freeze/gen4_plus0530.json
+++ b/test/fixtures/whoop_freeze/gen4_plus0530.json
@@ -2,7 +2,7 @@
  "day_result": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-13",
     "day_confidence": 0.6,
@@ -24902,7 +24902,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-14",
     "day_confidence": 0.6,
@@ -49595,7 +49595,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-15",
     "day_confidence": 0.6,
@@ -73355,7 +73355,7 @@
  "metric_series_version": [
   {
    "date": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73363,7 +73363,7 @@
   },
   {
    "date": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73371,7 +73371,7 @@
   },
   {
    "date": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73381,7 +73381,7 @@
  "wake_day_features": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-13",
     "active_min": 90,
@@ -74589,7 +74589,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-14",
     "active_min": 240,
@@ -75797,7 +75797,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-15",
     "active_min": 40,
diff --git a/test/fixtures/whoop_freeze/gen4_utc.json b/test/fixtures/whoop_freeze/gen4_utc.json
index 080f8e0ad..685a4c57b 100644
--- a/test/fixtures/whoop_freeze/gen4_utc.json
+++ b/test/fixtures/whoop_freeze/gen4_utc.json
@@ -2,7 +2,7 @@
  "day_result": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-13",
     "day_confidence": 0.6,
@@ -24902,7 +24902,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-14",
     "day_confidence": 0.6,
@@ -49595,7 +49595,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-15",
     "day_confidence": 0.6,
@@ -73355,7 +73355,7 @@
  "metric_series_version": [
   {
    "date": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73363,7 +73363,7 @@
   },
   {
    "date": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73371,7 +73371,7 @@
   },
   {
    "date": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen4",
    "coverage_devices": "",
@@ -73381,7 +73381,7 @@
  "wake_day_features": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-13",
     "active_min": 90,
@@ -74589,7 +74589,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-14",
     "active_min": 239,
@@ -75797,7 +75797,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-15",
     "active_min": 40,
diff --git a/test/fixtures/whoop_freeze/gen5_minus0400.json b/test/fixtures/whoop_freeze/gen5_minus0400.json
index c1752aa1d..9c0ce70c2 100644
--- a/test/fixtures/whoop_freeze/gen5_minus0400.json
+++ b/test/fixtures/whoop_freeze/gen5_minus0400.json
@@ -2,7 +2,7 @@
  "day_result": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-13",
     "day_confidence": 0.6,
@@ -25080,7 +25080,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-14",
     "day_confidence": 0.6,
@@ -49946,7 +49946,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-15",
     "day_confidence": 0.6,
@@ -73868,7 +73868,7 @@
  "metric_series_version": [
   {
    "date": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73876,7 +73876,7 @@
   },
   {
    "date": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73884,7 +73884,7 @@
   },
   {
    "date": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73894,7 +73894,7 @@
  "wake_day_features": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-13",
     "active_min": 90,
@@ -75102,7 +75102,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-14",
     "active_min": 240,
@@ -76310,7 +76310,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-15",
     "active_min": 40,
diff --git a/test/fixtures/whoop_freeze/gen5_plus0530.json b/test/fixtures/whoop_freeze/gen5_plus0530.json
index 05bb93f35..2efc7740d 100644
--- a/test/fixtures/whoop_freeze/gen5_plus0530.json
+++ b/test/fixtures/whoop_freeze/gen5_plus0530.json
@@ -2,7 +2,7 @@
  "day_result": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-13",
     "day_confidence": 0.6,
@@ -25080,7 +25080,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-14",
     "day_confidence": 0.6,
@@ -49946,7 +49946,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-15",
     "day_confidence": 0.6,
@@ -73868,7 +73868,7 @@
  "metric_series_version": [
   {
    "date": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73876,7 +73876,7 @@
   },
   {
    "date": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73884,7 +73884,7 @@
   },
   {
    "date": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73894,7 +73894,7 @@
  "wake_day_features": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-13",
     "active_min": 90,
@@ -75102,7 +75102,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-14",
     "active_min": 240,
@@ -76310,7 +76310,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-15",
     "active_min": 40,
diff --git a/test/fixtures/whoop_freeze/gen5_utc.json b/test/fixtures/whoop_freeze/gen5_utc.json
index f09f6882b..8415368ca 100644
--- a/test/fixtures/whoop_freeze/gen5_utc.json
+++ b/test/fixtures/whoop_freeze/gen5_utc.json
@@ -2,7 +2,7 @@
  "day_result": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-13",
     "day_confidence": 0.6,
@@ -25080,7 +25080,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-14",
     "day_confidence": 0.6,
@@ -49946,7 +49946,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "date": "2026-07-15",
     "day_confidence": 0.6,
@@ -73868,7 +73868,7 @@
  "metric_series_version": [
   {
    "date": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73876,7 +73876,7 @@
   },
   {
    "date": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73884,7 +73884,7 @@
   },
   {
    "date": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "source": "band",
    "device_family": "gen5",
    "coverage_devices": "",
@@ -73894,7 +73894,7 @@
  "wake_day_features": [
   {
    "day_id": "2026-07-13",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-13",
     "active_min": 90,
@@ -75102,7 +75102,7 @@
   },
   {
    "day_id": "2026-07-14",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-14",
     "active_min": 239,
@@ -76310,7 +76310,7 @@
   },
   {
    "day_id": "2026-07-15",
-   "algo_version": 116,
+   "algo_version": 117,
    "payload_json": {
     "day_id": "2026-07-15",
     "active_min": 40,
diff --git a/test/sleep_coach_timezone_test.dart b/test/sleep_coach_timezone_test.dart
new file mode 100644
index 000000000..cae229371
--- /dev/null
+++ b/test/sleep_coach_timezone_test.dart
@@ -0,0 +1,294 @@
+// SLEEP COACH ACROSS A TIME-ZONE CHANGE.
+//
+// A user flew 7 h west and, at 08:33 local, the Sleep tab read "Target bedtime
+// 4:00 PM / Target wake 1:31 AM". The cross-day rollup took the typical wake
+// as the median of every past wake INSTANT converted with the phone's CURRENT
+// zone, so 08:31 wakes recorded at UTC+2 re-read as 01:31 and the bedtime
+// backed off them landed mid-afternoon.
+//
+// The fix keeps the targets a LOCAL CLOCK schedule: each night is read on the
+// clock it was lived on (recovered from the per-day `sleep_onset_sec` scalar,
+// which froze the onset's local clock at derive time) and that schedule is
+// applied in whatever zone the phone is in now.
+//
+// These tests build the rows by hand with the history's zone written out
+// explicitly (UTC+2, or Europe's CEST→CET), so they assert the same answer in
+// ANY runner zone. Under the old code they fail in every zone except the one
+// the history was recorded in. Worth running under a few zones, e.g.
+//   TZ=Etc/GMT+5 flutter test test/sleep_coach_timezone_test.dart   (UTC−5)
+//   TZ=America/New_York flutter test test/sleep_coach_timezone_test.dart
+//   TZ=Europe/Amsterdam flutter test test/sleep_coach_timezone_test.dart
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:openstrap_edge/compute/crossday_pipeline.dart';
+import 'package:openstrap_edge/compute/derivation_engine.dart';
+import 'package:openstrap_edge/compute/onehz_pipeline.dart'
+    show kSleepClockAnchorSec, sleepClockOffsetSec;
+
+/// Epoch seconds for wall-clock [h]:[m] on [y]-[mo]-[d] in a zone at
+/// [offsetMin] from UTC.
+int _at(int y, int mo, int d, int h, int m, int offsetMin) =>
+    DateTime.utc(y, mo, d, h, m).millisecondsSinceEpoch ~/ 1000 -
+    offsetMin * 60;
+
+/// What `sleepClockOffsetSec` would have written for [localH]:[localM] —
+/// signed seconds either side of 04:00 — had the phone been in that zone.
+double _clockAsRecorded(int localH, int localM) {
+  var off = localH * 3600 + localM * 60 - kSleepClockAnchorSec;
+  if (off > 43200) off -= 86400;
+  if (off <= -43200) off += 86400;
+  return off.toDouble();
+}
+
+String _label(DateTime d) =>
+    '${d.year}-${d.month.toString().padLeft(2, '0')}-'
+    '${d.day.toString().padLeft(2, '0')}';
+
+/// One stored day as `day_result` holds it: the sleep window as absolute
+/// instants, plus the onset's frozen local clock in `scalars`.
+({Map<String, dynamic> row, Map<String, dynamic> payload}) _stored({
+  required String day,
+  required int onsetSec,
+  required int wakeSec,
+  required double? onsetClockSec,
+}) =>
+    (
+      row: {'day_id': day, 'finalized': 1},
+      payload: {
+        'scalars': {
+          'efficiency': 95.0,
+          'sleep_onset_sec': ?onsetClockSec,
+        },
+        'sleep': {
+          'window': {
+            'value': {'onset_ms': onsetSec * 1000, 'offset_ms': wakeSec * 1000},
+          },
+          'accounting': {
+            'value': {'tst_sec': (wakeSec - onsetSec) * 0.95},
+          },
+        },
+      },
+    );
+
+/// Three weeks of nights lived at UTC+2: in bed 23:30, up 07:45 (one night
+/// falls asleep after midnight, 00:20, so the day boundary is crossed).
+List<({Map<String, dynamic> row, Map<String, dynamic> payload})> _europe() {
+  const tz = 120;
+  final out = <({Map<String, dynamic> row, Map<String, dynamic> payload})>[];
+  for (var i = 0; i < 21; i++) {
+    // The night of Sep i+1 → the morning of Sep i+2 (labelled by the morning).
+    final late = i == 10;
+    final onset = late
+        ? _at(2026, 9, i + 2, 0, 20, tz)
+        : _at(2026, 9, i + 1, 23, 30, tz);
+    final wake = _at(2026, 9, i + 2, 7, 45, tz);
+    out.add(_stored(
+      day: _label(DateTime(2026, 9, i + 2)),
+      onsetSec: onset,
+      wakeSec: wake,
+      onsetClockSec: late ? _clockAsRecorded(0, 20) : _clockAsRecorded(23, 30),
+    ));
+  }
+  return out;
+}
+
+List<Map<String, dynamic>> _records(
+  List<({Map<String, dynamic> row, Map<String, dynamic> payload})> stored,
+) => [
+      for (final s in stored)
+        DerivationEngine.crossDayInputRecord(s.row, s.payload,
+            today: '2026-12-31', imported: const {})!,
+    ];
+
+Map<String, dynamic> _coach(List<Map<String, dynamic>> days) =>
+    (buildCrossDayBundle(days, const {})['sleep_coach'] as Map)
+        .cast<String, dynamic>();
+
+double _min(Map<String, dynamic> coach, String key, String field) =>
+    (((coach[key] as Map)['value'] as Map)[field] as num).toDouble();
+
+/// Circular distance in minutes on a 24 h clock.
+double _clockDist(double a, double b) {
+  final d = (a - b).abs() % 1440;
+  return d > 720 ? 1440 - d : d;
+}
+
+void main() {
+  group('history recorded at UTC+2, phone now elsewhere', () {
+    test('targets read ~23:30 / 07:45 local, not 16:00 / 01:31', () {
+      final days = _records(_europe());
+      final coach = _coach(days);
+      final wake = _min(coach, 'wake', 'wake_min_of_day');
+      final bed = _min(coach, 'bedtime', 'bedtime_min_of_day');
+      final needSec = _min(coach, 'need', 'need_sec');
+
+      // Target wake = the bedtime plus the in-bed time it was backed off, so it
+      // lands back on the typical wake: 07:45 on the clock the user lives by.
+      expect(_clockDist(wake, 7 * 60 + 45), lessThan(1.0),
+          reason: 'target wake $wake min');
+      // Bedtime is that wake minus need ÷ efficiency, on the same clock.
+      final expectedBed = (7 * 60 + 45 - needSec / 0.95 / 60) % 1440;
+      expect(_clockDist(bed, expectedBed), lessThan(1.0));
+      // …which for this history is the late-evening bedtime it kept, not a
+      // mid-afternoon one.
+      expect(_clockDist(bed, 23 * 60 + 30), lessThan(45.0),
+          reason: 'target bedtime $bed min');
+      expect(_clockDist(bed, 16 * 60), greaterThan(300.0));
+      expect(_clockDist(wake, 60 + 31), greaterThan(300.0));
+    });
+
+    test('the record carries the shift only when the zone actually differs',
+        () {
+      final days = _records(_europe());
+      final onset = days.first['onset_sec'] as int;
+      final hereOffsetMin =
+          DateTime.fromMillisecondsSinceEpoch(onset * 1000).timeZoneOffset
+              .inMinutes;
+      if (hereOffsetMin == 120) {
+        // Runner is in the history's own zone: nothing written, old path.
+        expect(days.first.containsKey('clock_shift_sec'), isFalse);
+      } else {
+        expect(days.first['clock_shift_sec'],
+            ((120 - hereOffsetMin) * 60) % 86400);
+      }
+    });
+
+    test('a few nights already lived in the new zone do not move the target',
+        () {
+      // The first nights after landing are derived in the phone's new zone and
+      // carry no shift; read on their own clock they are the same schedule.
+      final stored = _europe();
+      for (var i = 0; i < 3; i++) {
+        final dLocal = DateTime(2026, 9, 23 + i, 23, 30);
+        final onset = dLocal.millisecondsSinceEpoch ~/ 1000;
+        final wake =
+            DateTime(2026, 9, 24 + i, 7, 45).millisecondsSinceEpoch ~/ 1000;
+        stored.add(_stored(
+          day: _label(DateTime(2026, 9, 24 + i)),
+          onsetSec: onset,
+          wakeSec: wake,
+          onsetClockSec: sleepClockOffsetSec(onset),
+        ));
+      }
+      final coach = _coach(_records(stored));
+      expect(_clockDist(_min(coach, 'wake', 'wake_min_of_day'), 7 * 60 + 45),
+          lessThan(1.0));
+    });
+  });
+
+  test('history straddling a DST change keeps its local schedule', () {
+    // Europe leaves CEST (UTC+2) for CET (UTC+1) on 25 Oct 2026. The user went
+    // to bed at 23:30 and woke at 07:45 on BOTH sides; the instants moved by an
+    // hour, the clock did not, and neither should the target.
+    final stored = <({Map<String, dynamic> row, Map<String, dynamic> payload})>[];
+    for (var i = 0; i < 20; i++) {
+      final morning = DateTime(2026, 10, 15 + i);
+      final tz = morning.isBefore(DateTime(2026, 10, 25, 12)) ? 120 : 60;
+      final night = DateTime(2026, 10, 14 + i);
+      stored.add(_stored(
+        day: _label(morning),
+        onsetSec: _at(night.year, night.month, night.day, 23, 30, tz),
+        wakeSec: _at(morning.year, morning.month, morning.day, 7, 45, tz),
+        onsetClockSec: _clockAsRecorded(23, 30),
+      ));
+    }
+    final days = _records(stored);
+    final coach = _coach(days);
+    expect(_clockDist(_min(coach, 'wake', 'wake_min_of_day'), 7 * 60 + 45),
+        lessThan(1.0));
+  });
+
+  test('a night recorded in the current zone reads exactly as before', () {
+    // At home the frozen clock and today's reading agree, so no key is written
+    // and the bundle is identical to one built without the scalar at all.
+    final withClock =
+        <({Map<String, dynamic> row, Map<String, dynamic> payload})>[];
+    final without =
+        <({Map<String, dynamic> row, Map<String, dynamic> payload})>[];
+    for (var i = 0; i < 21; i++) {
+      final onset =
+          DateTime(2026, 9, i + 1, 23, 10).millisecondsSinceEpoch ~/ 1000;
+      final wake =
+          DateTime(2026, 9, i + 2, 7, 5).millisecondsSinceEpoch ~/ 1000;
+      final day = _label(DateTime(2026, 9, i + 2));
+      withClock.add(_stored(
+          day: day,
+          onsetSec: onset,
+          wakeSec: wake,
+          onsetClockSec: sleepClockOffsetSec(onset)));
+      without.add(
+          _stored(day: day, onsetSec: onset, wakeSec: wake, onsetClockSec: null));
+    }
+    final a = _records(withClock);
+    expect(a.any((d) => d.containsKey('clock_shift_sec')), isFalse);
+    expect(_coach(a).toString(), _coach(_records(without)).toString());
+    expect(_clockDist(_min(_coach(a), 'wake', 'wake_min_of_day'), 7 * 60 + 5),
+        lessThan(1.0));
+  });
+
+  test('re-deriving a pre-trip night keeps the clock it was lived on', () {
+    // A re-derive freezes `sleep_onset_sec` in the phone's zone NOW; carrying
+    // the stored row's shift puts it back on the UTC+2 clock, so the cross-day
+    // record is the same as before the re-derive, in any runner zone.
+    for (final prev in _europe()) {
+      final onsetMs = (((prev.payload['sleep'] as Map)['window']
+          as Map)['value'] as Map)['onset_ms'] as int;
+      final onset = onsetMs ~/ 1000;
+      final original =
+          (prev.payload['scalars'] as Map)['sleep_onset_sec'] as double;
+      final rederived = sleepClockOffsetSec(onset);
+      final carried = shiftRecordedClockSec(
+          rederived, storedNightClockShiftSec(prev.payload));
+      expect(carried, original);
+
+      final again = _stored(
+        day: prev.row['day_id'] as String,
+        onsetSec: onset,
+        wakeSec: onset + 8 * 3600,
+        onsetClockSec: carried,
+      );
+      expect(_records([again]).single['clock_shift_sec'],
+          _records([prev]).single['clock_shift_sec']);
+    }
+  });
+
+  test('a day lived at UTC+2 keeps its heart rate in its own hours', () {
+    // One night at UTC+2 plus six minutes of HR at 14:00-14:05 its time. In
+    // any runner zone the record bins that HR at 14, not at the phone's hour.
+    final night = _europe().first;
+    final onsetMs = (((night.payload['sleep'] as Map)['window'] as Map)['value']
+        as Map)['onset_ms'] as int;
+    final afternoon = onsetMs ~/ 1000 + 14 * 3600 + 30 * 60; // 23:30 + 14:30
+    final payload = {
+      ...night.payload,
+      'series': {
+        'hr_curve': [
+          for (var i = 0; i < 6; i++) {'t': afternoon + i * 60, 'v': 70 + i},
+        ],
+      },
+    };
+    final hourly = _records([(row: night.row, payload: payload)])
+        .single['hourly_hr'] as List;
+    expect(hourly[14], closeTo(72.5, 1e-9));
+    expect([for (var h = 0; h < 24; h++) if (h != 14) hourly[h]],
+        everyElement(isNull));
+  });
+
+  test('a shifted clock wraps back into ±12 h and null stays null', () {
+    expect(shiftRecordedClockSec(43000, 1000), -42400);
+    expect(shiftRecordedClockSec(-43000, 86400 - 1000), 42400);
+    expect(shiftRecordedClockSec(-16200, 0), -16200);
+    expect(shiftRecordedClockSec(null, 7200), isNull);
+    expect(storedNightClockShiftSec(null), 0);
+    expect(storedNightClockShiftSec(const {'scalars': {}}), 0);
+  });
+
+  test('no frozen clock and no onset → no shift, never a guessed one', () {
+    expect(recordedClockShiftSec(onsetSec: null, onsetClockSec: -16200), 0);
+    expect(recordedClockShiftSec(onsetSec: 1789000000, onsetClockSec: null), 0);
+    expect(
+        recordedClockShiftSec(
+            onsetSec: 1789000000, onsetClockSec: double.nan),
+        0);
+  });
+}
diff --git a/test/stored_night_clock_test.dart b/test/stored_night_clock_test.dart
new file mode 100644
index 000000000..3a752f5a9
--- /dev/null
+++ b/test/stored_night_clock_test.dart
@@ -0,0 +1,108 @@
+// A re-derive carries the stored night's clock forward. It reads two numbers
+// off the stored row with json_extract instead of decoding the bundle; these
+// tests hold that read to what decoding the bundle answered.
+
+import 'dart:convert';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:path/path.dart' as p;
+import 'package:sqflite_common_ffi/sqflite_ffi.dart';
+
+import 'package:openstrap_edge/compute/crossday_pipeline.dart'
+    show recordedClockShiftSec, storedNightClockShiftSec;
+import 'package:openstrap_edge/compute/derivation_engine.dart' show kAlgoVersion;
+import 'package:openstrap_edge/data/db.dart';
+
+Map<String, dynamic> _bundle({int? onsetMs, double? clock}) => {
+      'sleep': {
+        'window': {
+          'value': {'onset_ms': ?onsetMs, 'offset_ms': ?onsetMs},
+        },
+      },
+      'scalars': {'rhr': 52, 'sleep_onset_sec': ?clock},
+      'series': {
+        'hr_curve': [
+          for (var i = 0; i < 50; i++) {'t': 1767225600 + i * 60, 'v': 60},
+        ],
+      },
+    };
+
+Future<void> _put(String day, Object payload,
+        {int? version, bool skipped = false}) =>
+    LocalDb.putDayResult(
+      dayId: day,
+      algoVersion: version ?? kAlgoVersion,
+      payloadJson: payload is String ? payload : jsonEncode(payload),
+      windowJson: '{}',
+      skipped: skipped,
+    );
+
+int _shift(({num? onsetMs, num? onsetClockSec})? c) => c == null
+    ? 0
+    : recordedClockShiftSec(
+        onsetSec: c.onsetMs == null ? null : (c.onsetMs! / 1000).round(),
+        onsetClockSec: c.onsetClockSec,
+      );
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  const name = 'stored_night_clock_test.db';
+
+  setUpAll(() async {
+    sqfliteFfiInit();
+    databaseFactory = databaseFactoryFfi;
+    await LocalDb.close();
+    LocalDb.dbName = name;
+    await databaseFactory.deleteDatabase(
+      p.join(await databaseFactory.getDatabasesPath(), name),
+    );
+  });
+
+  tearDownAll(LocalDb.close);
+
+  test('matches the decoded bundle for a night lived in another zone', () async {
+    // 23:10 local onset, frozen two hours east of wherever the runner is.
+    final onset = DateTime(2026, 9, 1, 23, 10);
+    final onsetMs = onset.millisecondsSinceEpoch;
+    final local = onset.hour * 3600 + onset.minute * 60;
+    var clock = (local + 7200 - 4 * 3600) % 86400;
+    if (clock > 43200) clock -= 86400;
+    final b = _bundle(onsetMs: onsetMs, clock: clock.toDouble());
+    await _put('2026-09-02', b);
+
+    final got = await LocalDb.storedNightClock('2026-09-02');
+    expect(got, isNotNull);
+    expect(_shift(got), storedNightClockShiftSec(b));
+    expect(_shift(got), isNot(0));
+  });
+
+  test('null for no row, a skip marker, or a malformed payload', () async {
+    expect(await LocalDb.storedNightClock('2026-01-01'), isNull);
+
+    await _put('2026-09-03', _bundle(onsetMs: 1, clock: 1), skipped: true);
+    expect(await LocalDb.storedNightClock('2026-09-03'), isNull);
+
+    await _put('2026-09-04', {'skipped': true});
+    expect(await LocalDb.storedNightClock('2026-09-04'), isNull);
+
+    await _put('2026-09-05', '{not json');
+    expect(await LocalDb.storedNightClock('2026-09-05'), isNull);
+  });
+
+  test('reads the served version, not an older one under it', () async {
+    await _put('2026-09-06', _bundle(onsetMs: 1000, clock: 60),
+        version: kAlgoVersion - 1);
+    await _put('2026-09-06', _bundle(), version: kAlgoVersion);
+    final got = await LocalDb.storedNightClock('2026-09-06');
+    expect(got, isNotNull);
+    expect(got!.onsetMs, isNull);
+    expect(got.onsetClockSec, isNull);
+
+    // A newer skip marker hides the older real row, as dayResult does.
+    await _put('2026-09-07', _bundle(onsetMs: 1000, clock: 60),
+        version: kAlgoVersion - 1);
+    await _put('2026-09-07', {'skipped': true},
+        version: kAlgoVersion, skipped: true);
+    expect(await LocalDb.storedNightClock('2026-09-07'), isNull);
+  });
+}