feat: Audio tab drives timeline audio-mode; drag the band to set the extract region

tests/test_ui_structure.py

@@ -284,6 +284,9 @@ def test_timeline_audio_mode_flag(win):
 
 def test_timeline_audio_band_drag_move(win):
     tl = win._timeline
+    # The band is now wired to the window; fake a loaded file so the window's
+    # _update_audio_region keeps the region instead of clearing it on release.
+    win._file_path = "/x/v.mp4"
     tl._duration = 20.0
     tl._view_start = 0.0; tl._view_span = 20.0     # full view
     tl.resize(400, tl.height() or 80)
@@ -304,6 +307,8 @@ def test_timeline_audio_band_drag_move(win):
 
 def test_timeline_audio_band_resize_right(win):
     tl = win._timeline
+    # Fake a loaded file so the window keeps the region on release (see above).
+    win._file_path = "/x/v.mp4"
     tl._duration = 20.0; tl._view_start = 0.0; tl._view_span = 20.0
     tl.resize(400, tl.height() or 80)
     tl.set_audio_mode(True)
@@ -316,6 +321,22 @@ def test_timeline_audio_band_resize_right(win):
     tl.set_audio_mode(False)
 
 
+def test_timeline_audio_mode_follows_deck(win):
+    win._control_deck.setCurrentWidget(win._tab_audio)
+    assert win._timeline._audio_mode is True
+    win._control_deck.setCurrentWidget(win._tab_export)
+    assert win._timeline._audio_mode is False
+
+
+def test_timeline_audio_region_edit_syncs_cursor_length(win):
+    win._file_path = "/x/v.mp4"
+    win._cursor = 2.0
+    win._spn_audio_len.setValue(3.0)
+    win._timeline.audio_region_changed.emit(5.0, 9.0)   # user dragged the band to [5,9]
+    assert win._cursor == 5.0
+    assert abs(win._spn_audio_len.value() - 4.0) < 1e-6
+
+
 def test_audio_deck_tab_exists(win):
     # The old "Scan" deck tab is now "Audio".
     assert hasattr(win, "_tab_audio")