fixed display problem

apps/studio/tests/test_ui_smoke.py

@@ -925,6 +925,59 @@ def test_depth_view_reports_missing_data_and_fixes_its_scale(make_window):
     _finish(window, stuck)
 
 
+def test_the_domain_boundary_is_latched_for_the_session(make_window):
+    """The 2D boundary is the device's island: rebuilt per frame, decided once.
+
+    Same treatment as the depth colour scale above, and for the same reason — a mask
+    that is re-derived every frame redraws an edge that has not moved, and any pixel of
+    difference repaints the whole boundary (measured: a 0.73% area wobble repaints 69%
+    of the boundary band).
+    """
+    import numpy as np
+
+    window, stuck = _running_window(make_window)
+    window.arrow_panel.set_view_mode("arrows_pure")
+    island = np.zeros((8, 8), dtype=bool)
+    island[1:7, 1:7] = True
+    island_wobble = island.copy()
+    island_wobble[1, 1] = False  # one pixel of rim, i.e. 1.6% of a 36-pixel island
+
+    window._last_rendered_view_mode = None
+    stuck.emit(ui_check._fake_packet(0, valid_mask=island))
+    window._on_run_tick()
+    assert np.array_equal(window._domain_mask.mask, island), (
+        "the session never established the device's island"
+    )
+
+    window._last_rendered_view_mode = None
+    stuck.emit(ui_check._fake_packet(1, valid_mask=island_wobble))
+    window._on_run_tick()
+    assert np.array_equal(window._domain_mask.mask, island), (
+        "a rebuilt mask moved the session's boundary"
+    )
+    assert (window._domain_mask.adoptions, window._domain_mask.held) == (1, 1)
+
+    # An island that really changed is adopted rather than frozen out.
+    moved = np.zeros((8, 8), dtype=bool)
+    moved[2:8, 2:8] = True
+    window._last_rendered_view_mode = None
+    stuck.emit(ui_check._fake_packet(2, valid_mask=moved))
+    window._on_run_tick()
+    assert np.array_equal(window._domain_mask.mask, moved), (
+        "a moved island kept the old boundary on screen"
+    )
+    assert window._domain_mask.adoptions == 2
+
+    # A new run is a new session: the previous island must not survive into it.
+    _finish(window, stuck)
+    window._start_run()
+    assert window._domain_mask.mask is None, (
+        "the previous session's island survived into a new run"
+    )
+    window._run_timer.stop()
+    window._stop_run(reason="user_stop")
+
+
 # ------------------------------------------------------------- experiment record
 def test_recording_writes_the_documented_experiment_layout(make_window, record_root):
     import csv