fix(test): phash 'far' case needs structured images — solid colors phash-collapse

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_phash_util.py

@@ -10,6 +10,18 @@ def _img(color, size=(64, 64)):
     return Image.new("RGB", size, color)
 
 
+def _split(orient, size=64):
+    """A structured image (half black / half white) so it has real DCT
+    content — solid colors all phash-collapse to the same value."""
+    im = Image.new("L", (size, size), 0)
+    px = im.load()
+    for y in range(size):
+        for x in range(size):
+            if (x if orient == "v" else y) >= size // 2:
+                px[x, y] = 255
+    return im.convert("RGB")
+
+
 def test_compute_phash_stable_and_hex():
     h1 = compute_phash(_img((10, 120, 200)))
     h2 = compute_phash(_img((10, 120, 200)))
@@ -22,8 +34,9 @@ def test_compute_phash_none_for_non_image():
 
 
 def test_find_similar_none_when_far():
-    new = compute_phash(_img((0, 0, 0)))
-    cand = (compute_phash(_img((255, 255, 255))), 100, 100, 7)
+    # Vertical vs horizontal split = structurally orthogonal → far apart.
+    new = compute_phash(_split("v"))
+    cand = (compute_phash(_split("h")), 100, 100, 7)
     rel, mid = find_similar(new, 50, 50, [cand], threshold=2)
     assert rel == "none" and mid is None