Retain live processing timings across UI reruns

tests/test_progress_timing.py

@@ -0,0 +1,45 @@
+from mka.application.progress_timing import ProcessingTimer
+
+
+class FakeClock:
+    def __init__(self, value: float = 0.0) -> None:
+        self.value = value
+
+    def __call__(self) -> float:
+        return self.value
+
+
+def test_completed_duration_is_retained_while_active_stage_increases() -> None:
+    clock = FakeClock(10.0)
+    timer = ProcessingTimer(clock)
+    timer.start_run()
+    timer.start_stage("preparing")
+    clock.value = 18.0
+    timer.finish_stage("preparing")
+    timer.start_stage("transcription")
+
+    clock.value = 20.0
+    first = timer.snapshot()
+    clock.value = 25.5
+    second = timer.snapshot()
+
+    assert first.stage_durations == {"preparing": 8.0, "transcription": 2.0}
+    assert second.stage_durations == {"preparing": 8.0, "transcription": 7.5}
+    assert second.total_duration == 15.5
+
+
+def test_failed_active_stage_and_total_duration_are_frozen() -> None:
+    clock = FakeClock(2.0)
+    timer = ProcessingTimer(clock)
+    timer.start_run()
+    clock.value = 5.0
+    timer.start_stage("transcription")
+    clock.value = 14.0
+    timer.finish_run()
+    clock.value = 99.0
+
+    snapshot = timer.snapshot()
+
+    assert snapshot.stage_durations["transcription"] == 9.0
+    assert snapshot.total_duration == 12.0
+    assert snapshot.running is False