Merge branch 'train-days' into integration

# Conflicts:
#	apps/train/halkyon_train_flutter/lib/src/app/train_paths.dart
#	docs/adr/0030-halkyon-train.md

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

@@ -0,0 +1,62 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_train_flutter/src/feature/workout/widget/workout_chart.dart';
+import 'package:material_ui/material_ui.dart';
+
+void main() {
+  /// A heart rate from 60 at second 0 to 120 at second 100, in steps of 10
+  /// a second.
+  Future<void> pumpChart(WidgetTester tester) => tester.pumpWidget(
+    MaterialApp(
+      home: Scaffold(
+        body: SizedBox(
+          width: 400,
+          child: WorkoutChart(
+            title: 'Heart rate',
+            points: [
+              for (var second = 0; second <= 100; second += 10)
+                (x: second.toDouble(), value: 60 + second * 0.6),
+            ],
+            label: (value) => '${value.round()} bpm',
+            xLabel: (x) => 'at ${x.round()} s',
+          ),
+        ),
+      ),
+    ),
+  );
+
+  testWidgets('held, the value and its moment under the finger show beside '
+      'the title, following the finger, and go when it lifts', (
+    tester,
+  ) async {
+    await pumpChart(tester);
+    final plot = find.byKey(WorkoutChart.plotKey);
+    final box = tester.getRect(plot);
+    expect(find.text('at 0 s'), findsNothing);
+
+    // Held at the plot's start: the first point.
+    final gesture = await tester.startGesture(
+      box.centerLeft + const Offset(1, 0),
+    );
+    await tester.pump(const Duration(milliseconds: 600));
+    expect(find.text('60 bpm · at 0 s'), findsOneWidget);
+
+    // Dragged to the middle: second 50, 90 bpm.
+    await gesture.moveTo(box.center);
+    await tester.pump();
+    expect(find.text('90 bpm · at 50 s'), findsOneWidget);
+    expect(find.text('60 bpm · at 0 s'), findsNothing);
+
+    await gesture.up();
+    await tester.pump();
+    expect(find.textContaining(' · at '), findsNothing);
+  });
+
+  testWidgets('a tap shows nothing: only a long press inspects', (
+    tester,
+  ) async {
+    await pumpChart(tester);
+    await tester.tap(find.byKey(WorkoutChart.plotKey));
+    await tester.pump();
+    expect(find.textContaining(' · at '), findsNothing);
+  });
+}