Fix replay 2D black canvas and journey UX clarity

Stored analysis overlays now use the decoded frame; latch resets and draw failures surface. Verified with bare-video, replay-wiring, visual_policy, and analysis-progress tests.

shared/tests/test_visual_policy.py

@@ -145,3 +145,16 @@ def test_paint_domain_background_colours() -> None:
     )
     assert tuple(canvas[0, 0]) == (1, 2, 3)
     assert tuple(canvas[1, 1]) == (10, 20, 30)
+
+
+def test_select_flow_samples_screens_non_finite_tips() -> None:
+    """Sparse recovered fields put NaN off the recorded cells; cast must stay quiet."""
+    h, w = 30, 30
+    flow = np.full((h, w, 2), np.nan, dtype=np.float64)
+    flow[15, 15] = (0.5, 0.0)
+    policy = VisualPolicy(flow_on_px=0.4, flow_grid_spacing=10, flow_edge_margin=0)
+    with np.errstate(invalid="raise"):
+        samples = select_flow_samples(flow, None, policy)
+    pairs = set(zip(samples.rows.tolist(), samples.cols.tolist()))
+    assert (15, 15) in pairs
+    assert samples.active_count >= 1