test(exercice): couverture QA reprise après kill d'app, enchaînement désactivé (ticket #79)

Ajoute le test de reprise de séance après kill d'app avec
auto-enchaînement des chronos d'étapes désactivé
(test/application/use_cases_test.dart). QA n'a trouvé aucun bug de
production sur le chantier "auto-enchaînement des chronos d'étapes"
(#73) — couverture de test supplémentaire uniquement. analyze propre
(mêmes infos préexistantes), 154/154 tests verts, build APK debug
validé. Dernier ticket du chantier (#75 à #79 tous terminés).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/application/use_cases_test.dart

@@ -1281,6 +1281,76 @@ void main() {
     },
   );
 
+  test(
+    'step chaining disabled stops at first elapsed timed boundary after kill',
+    () async {
+      final clock = _FakeClock(DateTime.utc(2026, 7, 17, 12));
+      final session = _sessionWithSnapshot(
+        currentProgramIndex: 0,
+        currentExerciseIndex: 0,
+        currentSetIndex: 0,
+        setsCount: 1,
+        targetReps: 1,
+        autoStartNextTimedStepSnapshot: false,
+        exerciseSteps: [
+          ..._twoTimedSteps(),
+          _step(
+            id: 'step-3',
+            position: 2,
+            name: 'Centre',
+            type: ExerciseStepType.time,
+            defaultTargetValue: 1,
+          ),
+        ],
+      );
+      final repository = _FakeActiveSessionRepository()..session = session;
+
+      await ActiveExerciseStepUseCases(
+        sessionRepository: repository,
+        clock: clock,
+        ids: _FakeIds(),
+        originDeviceId: 'device-1',
+      ).startOrResumeProgress(
+        sessionId: session.metadata.id,
+        programIndex: 0,
+        exerciseIndex: 0,
+        setIndex: 0,
+      );
+      await ActiveExerciseStepUseCases(
+        sessionRepository: repository,
+        clock: clock,
+        ids: _FakeIds(),
+        originDeviceId: 'device-1',
+      ).startTimer(
+        sessionId: session.metadata.id,
+        programIndex: 0,
+        exerciseIndex: 0,
+        setIndex: 0,
+      );
+      clock.value = clock.value.add(const Duration(milliseconds: 4500));
+
+      final reconstructed = ActiveExerciseStepUseCases(
+        sessionRepository: repository,
+        clock: clock,
+        ids: _FakeIds(),
+        originDeviceId: 'device-1',
+      );
+      final view = await reconstructed.startOrResumeProgress(
+        sessionId: session.metadata.id,
+        programIndex: 0,
+        exerciseIndex: 0,
+        setIndex: 0,
+      );
+
+      expect(view.state.status, ActiveExerciseStepProgressStatus.stoppedTimer);
+      expect(view.state.currentStepIndex, 1);
+      expect(view.state.startedAt, isNull);
+      expect(view.state.accumulatedMs, 0);
+      expect(repository.stepResults, hasLength(1));
+      expect(repository.stepResults.single.stepIndex, 0);
+    },
+  );
+
   test(
     'step chaining resolution uses program override before exercise snapshot',
     () async {