refactor: move run accumulation out of the view model into the domain

The view model was doing two jobs. Alongside presentation state it held what
happened during a run — the interval series, the rule that iperf3's omitted
warm-up intervals do not count, the retained end summary — and the screen
computed mean and peak inline in a widget builder. All of that is the part
that has to be correct, and all of it would have been rewritten by anyone
replacing the UI.

Iperf3Session accumulates a run in the domain layer: samples, totals, errors,
whether it was stopped, and the statistics over them. The view model now feeds
it events and keeps only a formatted transcript and the repaint schedule; the
screen reads every displayed number off the session and derives none.

Two details the session now owns rather than leaving to a caller. Omitted
intervals are excluded, so a warm-up cannot drag the mean down. And
totalRetransmits stays null when no interval reported a count — UDP does not
measure retransmits, and "not measured" must not render as zero.

The aggregation tests move with the logic, into a pure-Dart test with no
widgets or bindings involved.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/domain/models/iperf3_session.dart

@@ -0,0 +1,114 @@
+import 'package:iperf3gui/domain/models/iperf3_event.dart';
+
+/// The accumulated state of one iperf3 run.
+///
+/// Fed the event stream one report at a time, this is the answer to "what
+/// happened during this test" — the interval series, the end totals, any
+/// errors, and the statistics derived from them.
+///
+/// It lives in the domain layer on purpose: it is what has to be *correct*,
+/// independent of how anything chooses to draw it. A different UI, a headless
+/// run or a future export path all consume the same object, and none of them
+/// re-derive a mean or re-decide whether a warm-up interval counts.
+class Iperf3Session {
+  Iperf3Start? _start;
+
+  /// Connection details, once the run has reported them.
+  Iperf3Start? get start => _start;
+
+  final List<Iperf3Interval> _intervals = [];
+
+  /// Throughput samples in arrival order, warm-up intervals excluded.
+  List<Iperf3Interval> get intervals => List.unmodifiable(_intervals);
+
+  Iperf3End? _summary;
+
+  /// Sent/received totals, once the run has finished.
+  Iperf3End? get summary => _summary;
+
+  final List<String> _errors = [];
+
+  /// Errors reported during the run, in order.
+  List<String> get errors => List.unmodifiable(_errors);
+
+  bool _stopped = false;
+
+  /// Whether the run ended because it was asked to stop.
+  bool get stopped => _stopped;
+
+  /// Whether iperf3 reported any error.
+  bool get hasError => _errors.isNotEmpty;
+
+  /// Whether anything at all has been recorded.
+  bool get isEmpty =>
+      _start == null && _intervals.isEmpty && _summary == null && !hasError;
+
+  /// How many throughput samples have been recorded.
+  int get sampleCount => _intervals.length;
+
+  /// Throughput of the most recent sample, or null before the first one.
+  double? get latestBitsPerSecond =>
+      _intervals.isEmpty ? null : _intervals.last.bitsPerSecond;
+
+  /// Mean throughput across the samples, or null before the first one.
+  ///
+  /// This is the mean of the per-interval rates, which is not identical to the
+  /// run's overall rate when intervals differ in length — prefer
+  /// [summary]'s totals for the headline figure once it is available.
+  double? get meanBitsPerSecond {
+    if (_intervals.isEmpty) return null;
+    final total = _intervals.fold<double>(0, (sum, i) => sum + i.bitsPerSecond);
+    return total / _intervals.length;
+  }
+
+  /// Highest sampled throughput, or null before the first sample.
+  double? get peakBitsPerSecond {
+    if (_intervals.isEmpty) return null;
+    return _intervals
+        .map((i) => i.bitsPerSecond)
+        .reduce((a, b) => a > b ? a : b);
+  }
+
+  /// Total bytes across the recorded samples.
+  int get sampledBytes => _intervals.fold<int>(0, (sum, i) => sum + i.bytes);
+
+  /// Total retransmits across the samples, or null if none were reported.
+  ///
+  /// UDP tests report no retransmit counts, so null means "not measured"
+  /// rather than zero.
+  int? get totalRetransmits {
+    final reported =
+        _intervals.map((i) => i.retransmits).whereType<int>().toList();
+    if (reported.isEmpty) return null;
+    return reported.fold<int>(0, (sum, r) => sum + r);
+  }
+
+  /// Record one report.
+  void add(Iperf3Event event) {
+    switch (event) {
+      case Iperf3Start e:
+        _start = e;
+      case Iperf3Interval e:
+        // Warm-up intervals (-O) are marked omitted by iperf3 and must not
+        // drag the statistics down.
+        if (!e.omitted) _intervals.add(e);
+      case Iperf3End e:
+        _summary = e;
+      case Iperf3Error e:
+        _errors.add(e.message);
+      case Iperf3Stopped _:
+        _stopped = true;
+      case Iperf3LogLine _:
+        break;
+    }
+  }
+
+  /// Forget everything, ready for another run.
+  void clear() {
+    _start = null;
+    _intervals.clear();
+    _summary = null;
+    _errors.clear();
+    _stopped = false;
+  }
+}

lib/ui/features/test_run/test_run_screen.dart

@@ -195,29 +195,31 @@ class _TestRunContentState extends State<_TestRunContent> {
             ),
             const SizedBox(height: 12),
 
-            // Live throughput figures, derived from the parsed interval series
+            // Live throughput figures. Every number here is read off the
+            // session; none are computed in the widget tree.
             Consumer<TestRunViewModel>(
               builder: (context, vm, _) {
-                final intervals = vm.intervals;
-                if (intervals.isEmpty) return const SizedBox.shrink();
-                final rates =
-                    intervals.map((i) => i.bitsPerSecond).toList(growable: false);
-                final latest = rates.last;
-                final peak = rates.reduce((a, b) => a > b ? a : b);
-                final mean = rates.reduce((a, b) => a + b) / rates.length;
-                final summary = vm.summary?.sent;
+                final session = vm.session;
+                final latest = session.latestBitsPerSecond;
+                final mean = session.meanBitsPerSecond;
+                final peak = session.peakBitsPerSecond;
+                if (latest == null || mean == null || peak == null) {
+                  return const SizedBox.shrink();
+                }
+                final total = session.summary?.sent;
                 return Padding(
                   padding: const EdgeInsets.only(bottom: 12),
                   child: Row(
                     mainAxisAlignment: MainAxisAlignment.spaceBetween,
                     children: [
                       _Stat(
-                        label: summary != null ? 'total' : 'now',
-                        value: formatBitrate(summary?.bitsPerSecond ?? latest),
+                        label: total != null ? 'total' : 'now',
+                        value: formatBitrate(total?.bitsPerSecond ?? latest),
                       ),
                       _Stat(label: 'avg', value: formatBitrate(mean)),
                       _Stat(label: 'peak', value: formatBitrate(peak)),
-                      _Stat(label: 'samples', value: '${rates.length}'),
+                      _Stat(
+                          label: 'samples', value: '${session.sampleCount}'),
                     ],
                   ),
                 );

lib/ui/features/test_run/test_run_view_model.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:flutter/foundation.dart';
 import 'package:iperf3gui/domain/models/iperf3_event.dart';
 import 'package:iperf3gui/domain/models/iperf3_result.dart';
+import 'package:iperf3gui/domain/models/iperf3_session.dart';
 import 'package:iperf3gui/domain/models/test_configuration.dart';
 import 'package:iperf3gui/domain/services/iperf3_runner.dart';
 import 'package:iperf3gui/ui/features/test_run/iperf3_event_formatter.dart';
@@ -12,8 +13,10 @@ enum TestRunState { idle, running, completed, error }
 
 /// ViewModel for managing test run state.
 ///
-/// Subscribes to [Iperf3Runner.events] so the transcript and the interval
-/// series both grow while the test runs, rather than appearing at the end.
+/// Presentation only. What happened during a run is accumulated by
+/// [Iperf3Session] in the domain layer; this class subscribes to
+/// [Iperf3Runner.events], feeds that session, keeps a formatted transcript for
+/// display, and decides when to repaint.
 class TestRunViewModel extends ChangeNotifier {
   final Iperf3Runner iperf3Service;
 
@@ -41,24 +44,14 @@ class TestRunViewModel extends ChangeNotifier {
 
   final StringBuffer _transcript = StringBuffer();
 
-  /// Human-readable output accumulated so far.
+  /// Human-readable output accumulated so far. Display only — the structured
+  /// record of the run is [session].
   String get output => _transcript.toString();
 
-  final List<Iperf3Interval> _intervals = [];
+  final Iperf3Session _session = Iperf3Session();
 
-  /// Per-interval throughput samples, in arrival order. Structured, so a chart
-  /// can be driven from this without re-parsing text.
-  List<Iperf3Interval> get intervals => List.unmodifiable(_intervals);
-
-  Iperf3Start? _start;
-
-  /// Connection details reported at the start of the run.
-  Iperf3Start? get start => _start;
-
-  Iperf3End? _summary;
-
-  /// Totals reported at the end of the run.
-  Iperf3End? get summary => _summary;
+  /// The accumulated run: interval series, totals, errors and their statistics.
+  Iperf3Session get session => _session;
 
   /// Whether a test is currently in flight.
   bool get isRunning => _state == TestRunState.running;
@@ -118,26 +111,12 @@ class TestRunViewModel extends ChangeNotifier {
   void _resetRunData() {
     _result = null;
     _transcript.clear();
-    _intervals.clear();
-    _start = null;
-    _summary = null;
+    _session.clear();
     _dirty = false;
   }
 
   void _onEvent(Iperf3Event event) {
-    switch (event) {
-      case Iperf3Start e:
-        _start = e;
-      case Iperf3Interval e:
-        // Omitted intervals are warm-up (-O) and are not part of the series.
-        if (!e.omitted) _intervals.add(e);
-      case Iperf3End e:
-        _summary = e;
-      case Iperf3Error _:
-      case Iperf3Stopped _:
-      case Iperf3LogLine _:
-        break;
-    }
+    _session.add(event);
 
     final line = formatIperf3Event(event);
     if (line != null && line.isNotEmpty) {

test/domain/models/iperf3_session_test.dart

@@ -0,0 +1,135 @@
+// Pure-Dart tests for the run aggregate. No widgets, no bindings, no channel —
+// this is the part that has to be correct regardless of what draws it.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:iperf3gui/domain/models/iperf3_event.dart';
+import 'package:iperf3gui/domain/models/iperf3_session.dart';
+
+void main() {
+  Iperf3Interval sample(double start, double bits,
+          {int bytes = 1000, int? retransmits, bool omitted = false}) =>
+      Iperf3Interval(
+        start: start,
+        end: start + 1,
+        bytes: bytes,
+        bitsPerSecond: bits,
+        retransmits: retransmits,
+        omitted: omitted,
+      );
+
+  group('Iperf3Session', () {
+    test('starts empty', () {
+      final session = Iperf3Session();
+      expect(session.isEmpty, isTrue);
+      expect(session.sampleCount, isZero);
+      expect(session.intervals, isEmpty);
+      expect(session.start, isNull);
+      expect(session.summary, isNull);
+      expect(session.errors, isEmpty);
+      expect(session.stopped, isFalse);
+      expect(session.hasError, isFalse);
+    });
+
+    test('statistics are null before any sample', () {
+      final session = Iperf3Session();
+      expect(session.latestBitsPerSecond, isNull);
+      expect(session.meanBitsPerSecond, isNull);
+      expect(session.peakBitsPerSecond, isNull);
+      expect(session.totalRetransmits, isNull);
+    });
+
+    test('records start, intervals and summary', () {
+      final session = Iperf3Session()
+        ..add(const Iperf3Start(targetHost: 'host', targetPort: 5201))
+        ..add(sample(0, 100))
+        ..add(const Iperf3End(
+          sent: Iperf3Total(seconds: 1, bytes: 10, bitsPerSecond: 80),
+        ));
+      expect(session.isEmpty, isFalse);
+      expect(session.start!.targetHost, equals('host'));
+      expect(session.sampleCount, equals(1));
+      expect(session.summary!.sent!.bitsPerSecond, equals(80));
+    });
+
+    test('excludes omitted warm-up intervals from the series', () {
+      final session = Iperf3Session()
+        ..add(sample(0, 10, omitted: true))
+        ..add(sample(1, 100))
+        ..add(sample(2, 200));
+      expect(session.sampleCount, equals(2));
+      expect(session.meanBitsPerSecond, equals(150),
+          reason: 'the omitted 10 would have pulled the mean to ~103');
+    });
+
+    test('computes mean, peak and latest over the samples', () {
+      final session = Iperf3Session()
+        ..add(sample(0, 100))
+        ..add(sample(1, 400))
+        ..add(sample(2, 250));
+      expect(session.latestBitsPerSecond, equals(250));
+      expect(session.peakBitsPerSecond, equals(400));
+      expect(session.meanBitsPerSecond, equals(250));
+    });
+
+    test('sums sampled bytes', () {
+      final session = Iperf3Session()
+        ..add(sample(0, 1, bytes: 1500))
+        ..add(sample(1, 1, bytes: 2500));
+      expect(session.sampledBytes, equals(4000));
+    });
+
+    test('sums retransmits when reported', () {
+      final session = Iperf3Session()
+        ..add(sample(0, 1, retransmits: 2))
+        ..add(sample(1, 1, retransmits: 5));
+      expect(session.totalRetransmits, equals(7));
+    });
+
+    test('retransmits stay null when never reported, not zero', () {
+      // UDP reports no retransmit counts; "not measured" must not read as 0.
+      final session = Iperf3Session()
+        ..add(sample(0, 1))
+        ..add(sample(1, 1));
+      expect(session.totalRetransmits, isNull);
+    });
+
+    test('collects errors in order and flags them', () {
+      final session = Iperf3Session()
+        ..add(const Iperf3Error('first'))
+        ..add(const Iperf3Error('second'));
+      expect(session.hasError, isTrue);
+      expect(session.errors, equals(['first', 'second']));
+      expect(session.isEmpty, isFalse);
+    });
+
+    test('records a stop', () {
+      final session = Iperf3Session()..add(const Iperf3Stopped());
+      expect(session.stopped, isTrue);
+    });
+
+    test('ignores log lines', () {
+      final session = Iperf3Session()..add(const Iperf3LogLine('noise'));
+      expect(session.isEmpty, isTrue);
+    });
+
+    test('clear returns it to the empty state', () {
+      final session = Iperf3Session()
+        ..add(const Iperf3Start(targetHost: 'host'))
+        ..add(sample(0, 100))
+        ..add(const Iperf3Error('boom'))
+        ..add(const Iperf3Stopped())
+        ..add(const Iperf3End())
+        ..clear();
+      expect(session.isEmpty, isTrue);
+      expect(session.stopped, isFalse);
+      expect(session.hasError, isFalse);
+      expect(session.peakBitsPerSecond, isNull);
+    });
+
+    test('exposed collections are unmodifiable', () {
+      final session = Iperf3Session()..add(sample(0, 1));
+      expect(() => session.intervals.add(sample(1, 1)), throwsUnsupportedError);
+      expect(() => session.errors.add('x'), throwsUnsupportedError);
+    });
+  });
+}

test/ui/features/test_run/test_run_view_model_test.dart

@@ -82,48 +82,13 @@ void main() {
       expect(vm.output, isNot(contains('ignored')));
     });
 
-    test('intervals are collected as structured samples', () async {
+    test('events are fed into the session', () async {
       final mock = FakeIperf3Runner();
       mock.onRun = (_) async {
         mock.emit(const Iperf3Interval(
             start: 0, end: 1, bytes: 1000, bitsPerSecond: 8000));
-        mock.emit(const Iperf3Interval(
-            start: 1, end: 2, bytes: 2000, bitsPerSecond: 16000));
-        await Future<void>.delayed(Duration.zero);
-        return const Iperf3Result(rawOutput: '', exitCode: 0);
-      };
-
-      final vm = TestRunViewModel(iperf3Service: mock);
-      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
-
-      expect(vm.intervals, hasLength(2));
-      expect(vm.intervals[1].bitsPerSecond, equals(16000));
-    });
-
-    test('omitted warm-up intervals are excluded from the series', () async {
-      final mock = FakeIperf3Runner();
-      mock.onRun = (_) async {
-        mock.emit(const Iperf3Interval(
-            start: 0, end: 1, bytes: 1, bitsPerSecond: 1, omitted: true));
-        mock.emit(const Iperf3Interval(
-            start: 1, end: 2, bytes: 2000, bitsPerSecond: 16000));
-        await Future<void>.delayed(Duration.zero);
-        return const Iperf3Result(rawOutput: '', exitCode: 0);
-      };
-
-      final vm = TestRunViewModel(iperf3Service: mock);
-      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
-
-      expect(vm.intervals, hasLength(1));
-      expect(vm.intervals.single.bitsPerSecond, equals(16000));
-    });
-
-    test('end event is retained as the summary', () async {
-      final mock = FakeIperf3Runner();
-      mock.onRun = (_) async {
         mock.emit(const Iperf3End(
-          sent: Iperf3Total(
-              seconds: 10, bytes: 987654321, bitsPerSecond: 790000000),
+          sent: Iperf3Total(seconds: 1, bytes: 1000, bitsPerSecond: 8000),
         ));
         await Future<void>.delayed(Duration.zero);
         return const Iperf3Result(rawOutput: '', exitCode: 0);
@@ -132,11 +97,11 @@ void main() {
       final vm = TestRunViewModel(iperf3Service: mock);
       await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
 
-      expect(vm.summary?.sent?.bitsPerSecond, equals(790000000));
-      expect(vm.output, contains('790 Mbits/sec'));
+      expect(vm.session.sampleCount, equals(1));
+      expect(vm.session.summary, isNotNull);
     });
 
-    test('a new run clears the previous interval series', () async {
+    test('a new run clears the previous session', () async {
       final mock = FakeIperf3Runner();
       mock.onRun = (_) async {
         mock.emit(const Iperf3Interval(
@@ -147,10 +112,11 @@ void main() {
 
       final vm = TestRunViewModel(iperf3Service: mock);
       await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
-      expect(vm.intervals, hasLength(1));
+      expect(vm.session.sampleCount, equals(1));
 
       await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
-      expect(vm.intervals, hasLength(1), reason: 'not appended to the old run');
+      expect(vm.session.sampleCount, equals(1),
+          reason: 'not appended to the old run');
     });
 
     test('falls back to result output when nothing streamed', () async {