fix(humanize): preserve gaussian magnitude in jitter_point; unify swipe return shape

tests/test_humanize.py

@@ -27,6 +27,28 @@ def test_jitter_point_centered_on_input():
     assert abs(sum(xs) / len(xs)) < 0.3
 
 
+def test_jitter_point_concentrated_near_target():
+    """Regression: jitter must be polar-Gaussian (concentrated near target),
+    not uniform-on-circle (all points at exactly ``radius``).
+
+    For a folded Gaussian with sigma=radius/2, the expected mean distance is
+    ~0.8*sigma ~= 0.4*radius. Using ``< 0.7*radius`` gives a safe margin that
+    fails the previous reprojection bug (mean distance == radius exactly).
+    """
+    rng = random.Random(1234)
+    radius = 5.0
+    n = 5000
+    distances = [
+        math.hypot(x - 0.0, y - 0.0)
+        for x, y in (jitter_point(0.0, 0.0, radius=radius, rng=rng) for _ in range(n))
+    ]
+    mean_distance = sum(distances) / n
+    assert mean_distance < radius * 0.7, (
+        f"mean distance {mean_distance:.3f} is too large; jitter looks like "
+        "uniform-on-circle rather than polar-Gaussian"
+    )
+
+
 def test_jitter_duration_within_spread():
     rng = random.Random(3)
     for _ in range(200):