fix(train): a day's skin temperature in time order, and its heart rate a point a minute without lost contact

The skin temperature's line ran backwards in places: the band's samples
aren't always in time order, and neither the Loop's lines, nor the kept
day, nor the chart sorted them. They are sorted now, a time given twice
kept once, as the lines are read and as a kept day is opened, and
WorkoutChart draws any points in the order of their x, from the least
to the most.

The heart rate spiked down: the band writes 0 where it lost contact,
and each run's mean, the chart's one point a run, counted those in. A
value that isn't a heart's rate is 0, none read, in its place (so the
samples after keep their times), left out of every mean, days kept
before included; the chart draws the samples a point a minute, averaged
across runs, rather than one mean a run, which zigzagged where runs lay
close. ADR 0030, D65.

Whats-New: A day's skin temperature no longer runs backwards, and its heart rate no longer drops where the band lost contact.
Whats-New-De: Die Hauttemperatur eines Tages läuft nicht mehr rückwärts, und sein Puls fällt nicht mehr ab, wo das Band den Kontakt verlor.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/train/halkyon_train_flutter/lib/src/feature/day/data/day_payload.dart

@@ -89,11 +89,12 @@ DayContent? decodeDay(ByteData payload) => _read(payload, 'day', (json) {
       ),
       _ => null,
     },
-    skin: [
+    // In order also where a day was kept before it was sorted (D65).
+    skin: skinInOrder([
       for (final sample in _list(json['skin']))
         if (sample case [final int ms, final num celsius])
           (Duration(milliseconds: ms), celsius.toDouble()),
-    ],
+    ]),
   );
 });
 

apps/train/halkyon_train_flutter/lib/src/feature/day/data/loop_lines.dart

@@ -73,9 +73,10 @@ final class LoopLines() {
               HeartRun(
                 at: Duration(seconds: run['at']! as int),
                 trigger: _triggers[run['trigger']] ?? HeartTrigger.unknown,
+                // What the band couldn't read is none, in its place (D65).
                 bpm: [
                   for (final bpm in _list(run['bpm']))
-                    if (bpm is int) bpm,
+                    if (bpm is num) heartRateOrNone(bpm.round()),
                 ],
               ),
         ];
@@ -102,11 +103,11 @@ final class LoopLines() {
           sessions[session.id] = session;
         }
       case 'skin':
-        skins[date] = [
+        skins[date] = skinInOrder([
           for (final sample in _list(json['samples']))
             if (sample case [final num ms, final num celsius])
               (Duration(milliseconds: ms.round()), celsius.toDouble()),
-        ];
+        ]);
     }
   }
 

apps/train/halkyon_train_flutter/lib/src/feature/day/model/day.dart

@@ -166,9 +166,14 @@ final class const HeartRun({
   required final HeartTrigger trigger,
   required final List<int> bpm,
 }) with Equatable {
-  /// Its samples' mean, as the day's chart shows it; null without one.
+  /// Its samples' mean, those the band couldn't read (0) left out (D65);
-  int? get mean =>
+  /// null without one read.
-      bpm.isEmpty ? null : (bpm.reduce((a, b) => a + b) / bpm.length).round();
+  int? get mean {
+    final read = bpm.where(isHeartRate).toList();
+    return read.isEmpty
+        ? null
+        : (read.reduce((a, b) => a + b) / read.length).round();
+  }
 
   @override
   List<Object?> get props => [at, trigger, bpm];
@@ -261,3 +266,49 @@ String dayKey(DateTime date) =>
 DateTime? dateOfKey(Object? key) => key is String && key.length == 10
     ? DateTime.tryParse('${key}T00:00:00Z')
     : null;
+
+/// Whether [bpm] is a heart's rate the band read: the band writes 0 where it
+/// lost contact (D65), and nothing beyond 250 is one.
+bool isHeartRate(int bpm) => bpm > 0 && bpm <= 250;
+
+/// [bpm] as a run keeps it: what isn't a heart's rate (`isHeartRate`) is 0,
+/// none read, in its place, so the samples after keep their times (D65).
+int heartRateOrNone(int bpm) => isHeartRate(bpm) ? bpm : 0;
+
+/// How far apart a 24/7 run's samples are: a second, as the Loop measures
+/// (Polar's SDK gives a run's start and its samples alone).
+const heartSampleInterval = Duration(seconds: 1);
+
+/// [runs]' samples a point a minute (D65): each minute's start in the band's
+/// day and the mean of the samples read in it, across runs, in time order.
+/// One mean a run zigzagged where runs lay close, and dropped to the zeros
+/// of contact lost.
+List<(Duration, int)> heartByMinute(Iterable<HeartRun> runs) {
+  final sums = <int, (int, int)>{};
+  for (final run in runs) {
+    for (final (index, bpm) in run.bpm.indexed) {
+      if (!isHeartRate(bpm)) {
+        continue;
+      }
+      final minute = (run.at + heartSampleInterval * index).inMinutes;
+      final (sum, count) = sums[minute] ?? (0, 0);
+      sums[minute] = (sum + bpm, count + 1);
+    }
+  }
+  return [
+    for (final minute in sums.keys.toList()..sort())
+      if (sums[minute] case (final sum, final count))
+        (Duration(minutes: minute), (sum / count).round()),
+  ];
+}
+
+/// [samples] of skin temperature in time order, a time given twice once, its
+/// first (D65): the band's list isn't always in order, and the chart drew it
+/// backwards.
+List<(Duration, double)> skinInOrder(Iterable<(Duration, double)> samples) {
+  final seen = <Duration>{};
+  return [
+    for (final sample in samples.toList()..sort((a, b) => a.$1.compareTo(b.$1)))
+      if (sample.$2.isFinite && seen.add(sample.$1)) sample,
+  ];
+}

apps/train/halkyon_train_flutter/lib/src/feature/day/widget/day_screen.dart

@@ -261,7 +261,7 @@ class const _Times(final DayContent _day) extends StatelessWidget {
   }
 }
 
-/// The day's 24/7 heart rate: each measurement's mean at its start.
+/// The day's 24/7 heart rate: its samples a point a minute (D65).
 class const _Heart(final List<HeartRun> _runs) extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
@@ -269,9 +269,8 @@ class const _Heart(final List<HeartRun> _runs) extends StatelessWidget {
     return WorkoutChart(
       title: l10n.dayHeartRate,
       points: [
-        for (final run in _runs)
+        for (final (at, bpm) in heartByMinute(_runs))
-          if (run.mean case final mean?)
+          (x: at.inSeconds.toDouble(), value: bpm.toDouble()),
-            (x: run.at.inSeconds.toDouble(), value: mean.toDouble()),
       ],
       label: (value) => l10n.dayBpm(value.round()),
       // Each run's start is the band's time of day.

apps/train/halkyon_train_flutter/lib/src/feature/workout/widget/workout_chart.dart

@@ -37,7 +37,7 @@ class _WorkoutChartState() extends State<WorkoutChart> {
 
   /// The point whose x is nearest to [dx] across a plot [width] wide.
   ChartPoint _nearest(double dx, double width) {
-    final points = widget.points;
+    final points = chartInOrder(widget.points);
     final first = points.first.x;
     final span = max(points.last.x - first, 1);
     final x = first + (dx / max(width, 1)).clamp(0, 1) * span;
@@ -63,7 +63,7 @@ class _WorkoutChartState() extends State<WorkoutChart> {
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
-    final points = widget.points;
+    final points = chartInOrder(widget.points);
     final label = widget.label;
     final inverted = widget.inverted;
     final values = [for (final point in points) point.value];
@@ -156,6 +156,17 @@ class _WorkoutChartState() extends State<WorkoutChart> {
   }
 }
 
+/// [points] in the order of their x, so that a line never runs backwards
+/// (D65); [points] itself where they are in order already.
+List<ChartPoint> chartInOrder(List<ChartPoint> points) {
+  for (var i = 1; i < points.length; i++) {
+    if (points[i].x < points[i - 1].x) {
+      return [...points]..sort((a, b) => a.x.compareTo(b.x));
+    }
+  }
+  return points;
+}
+
 class _LinePainter(
   final List<ChartPoint> _points, {
   required final List<ChartBand> bands,
@@ -180,6 +191,7 @@ class _LinePainter(
         Offset(size.width, size.height),
         gridPaint,
       );
+    // In order (chartInOrder): the first is the least, the last the most.
     final first = _points.first.x;
     final span = max(_points.last.x - first, 1);
     double xOf(double x) => ((x - first) / span).clamp(0, 1) * size.width;

apps/train/halkyon_train_flutter/test/feature/day/day_heart_test.dart

@@ -0,0 +1,63 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_train_flutter/src/feature/day/model/day.dart';
+
+/// A day's 24/7 heart rate as its chart draws it (ADR 0030, D37, D65): the
+/// samples a point a minute, what the band couldn't read left out.
+void main() {
+  test("a run's mean leaves out what the band couldn't read", () {
+    const run = HeartRun(
+      at: Duration.zero,
+      trigger: HeartTrigger.timed,
+      bpm: [70, 0, 72, 0],
+    );
+    const none = HeartRun(
+      at: Duration.zero,
+      trigger: HeartTrigger.timed,
+      bpm: [0, 0],
+    );
+
+    expect(run.mean, 71);
+    expect(none.mean, isNull);
+  });
+
+  test('the samples come a point a minute, averaged across runs, in time '
+      'order, half a run lost contact or not', () {
+    const at = Duration(hours: 7, minutes: 30);
+    final points = heartByMinute([
+      // Later, a run of its own.
+      HeartRun(
+        at: at + const Duration(minutes: 10),
+        trigger: HeartTrigger.highActivity,
+        bpm: const [140, 142],
+      ),
+      // Two minutes a sample a second, every other one not read.
+      HeartRun(
+        at: at,
+        trigger: HeartTrigger.timed,
+        bpm: [
+          for (var i = 0; i < 120; i++)
+            if (i.isOdd) 0 else if (i < 60) 60 else 64,
+        ],
+      ),
+      // Within the first minute too.
+      HeartRun(
+        at: at + const Duration(seconds: 50),
+        trigger: HeartTrigger.manual,
+        bpm: const [90],
+      ),
+      // Nothing read at all.
+      HeartRun(
+        at: at + const Duration(minutes: 20),
+        trigger: HeartTrigger.timed,
+        bpm: const [0, 0, 0],
+      ),
+    ]);
+
+    expect(points, [
+      // 30 samples of 60 and one of 90.
+      (at, 61),
+      (at + const Duration(minutes: 1), 64),
+      (at + const Duration(minutes: 10), 141),
+    ]);
+  });
+}

apps/train/halkyon_train_flutter/test/feature/day/day_payload_test.dart

@@ -65,6 +65,25 @@ void main() {
     expect(decodeHeart(encodeHeart(heart)), heart);
   });
 
+  test('a day kept with its skin temperature out of order comes back in '
+      'order, a time given twice once (D65)', () {
+    final kept = DayContent(
+      date: date,
+      skin: const [
+        (Duration(minutes: 2), 33.5),
+        (Duration.zero, 33.1),
+        (Duration(minutes: 1), 33.3),
+        (Duration.zero, 33.1),
+      ],
+    );
+
+    expect(decodeDay(encodeDay(kept))!.skin, const [
+      (Duration.zero, 33.1),
+      (Duration(minutes: 1), 33.3),
+      (Duration(minutes: 2), 33.5),
+    ]);
+  });
+
   test('a day with nothing but its date comes back so', () {
     final bare = DayContent(date: date);
 

apps/train/halkyon_train_flutter/test/feature/day/loop_lines_test.dart

@@ -188,6 +188,48 @@ void main() {
     },
   );
 
+  test('skin temperature comes in time order, a time given twice once '
+      '(D65)', () {
+    final lines = LoopLines()
+      ..add(const {
+        'kind': 'skin',
+        'date': '2026-10-28',
+        'samples': [
+          [120000, 33.5],
+          [0, 33.1],
+          [60000, 33.3],
+          [0, 40.0],
+          [60000, 33.3],
+        ],
+      });
+
+    expect(lines.skins[today], const [
+      (Duration.zero, 33.1),
+      (Duration(minutes: 1), 33.3),
+      (Duration(minutes: 2), 33.5),
+    ]);
+  });
+
+  test("heart rate the band couldn't read, 0 or beyond a heart's, counts "
+      'as none read, in its place (D65)', () {
+    final lines = LoopLines()
+      ..add(const {
+        'kind': 'heart',
+        'date': '2026-10-27',
+        'runs': [
+          {
+            'at': 600,
+            'trigger': 'timed',
+            'bpm': [60, 0, 62, 0, 300, -1],
+          },
+        ],
+      });
+
+    final run = lines.hearts[yesterday]!.single;
+    expect(run.bpm, [60, 0, 62, 0, 0, 0]);
+    expect(run.mean, 61);
+  });
+
   test('a later line of a kind and date replaces an earlier one', () {
     final lines = LoopLines()
       ..add(summary)

apps/train/halkyon_train_flutter/test/feature/workout/workout_chart_test.dart

@@ -24,6 +24,21 @@ void main() {
     ),
   );
 
+  test('its points are drawn in the order of their x, never backwards '
+      '(D65); points in order are taken as they are', () {
+    const sorted = [(x: 0.0, value: 1.0), (x: 1.0, value: 2.0)];
+
+    expect(
+      chartInOrder(const [
+        (x: 2.0, value: 3.0),
+        (x: 0.0, value: 1.0),
+        (x: 1.0, value: 2.0),
+      ]),
+      [(x: 0.0, value: 1.0), (x: 1.0, value: 2.0), (x: 2.0, value: 3.0)],
+    );
+    expect(identical(chartInOrder(sorted), sorted), isTrue);
+  });
+
   testWidgets('held, the value and its moment under the finger show beside '
       'the title, following the finger, and go when it lifts', (
     tester,

docs/adr/0030-halkyon-train.md

@@ -696,8 +696,8 @@ Strava. What was found, 27 Oct:
   sealed, so lines written meanwhile wait; the schedule is the phone's, for the last
   person whose app opened with a band, and *Let the band go* stops it. Polar's
   NONREM12 and NONREM3 are shown as light and deep sleep; the chart draws each 24/7
-  measurement's mean at its start; a night's times show in the phone's time zone. Not
+  measurement's mean at its start (a point a minute since D65); a night's times show
-  yet tried with a Loop: whether the SDK's deletion includes its `until` day, and
+  in the phone's time zone. Not yet tried with a Loop: whether the SDK's deletion includes its `until` day, and
   whether the job connects to the band in the background, are for a real band.
 
 - **D39 The Loop's training sessions are workouts** (recommended, the developer's; 28
@@ -1731,6 +1731,19 @@ Strava. What was found, 27 Oct:
     provider takes one from `MAP_DARK_STYLE_URL` (HTTPS, else none: the light style
     in both themes). A dark Liberty made in the app (its colours inverted) was the
     alternative, a style of the app's own for a provider's tiles it can't know.
+  - **The day's charts**: the skin temperature was drawn backwards in places, as the
+    band's samples aren't always in time order and nothing sorted them; they are
+    sorted, a time given twice kept once, as the Loop's lines are read and as a kept
+    day is opened (`skinInOrder`), and every line chart (`WorkoutChart`) draws its
+    points in the order of their x and spans their least to their most
+    (`chartInOrder`). The heart rate spiked down: the band writes 0 where it lost
+    contact, and a run's mean counted those in. A value that isn't a heart's rate
+    (0, or beyond 250) is 0, none read, as the lines are read, kept in its place so
+    the samples after keep their times, and left out of every mean, also of days
+    kept before. The chart draws the samples themselves a point a minute, averaged
+    across runs (`heartByMinute`, a second between a run's samples), not one mean a
+    run, which zigzagged where runs lay close. Dropping the zeros from the list was
+    the alternative; it would have moved the later samples' times.
 ## Consequences
 
 - Train's sensors are one pattern: open profiles read by the app itself, on the phone;