fix(shot): A1 — blank-retry keeps the LARGER frame (retry snapped to temp path, os.replace only if >= first; worse late frame discarded + temp cleaned); regression test [9999,4801]->9999; 207 unit tests pass, lint PASS

tests/unit/test_screenshot.py

@@ -94,6 +94,19 @@ def test_snap_retry_keeps_late_frame_even_if_still_blank(tmp_path):
     S._snap_with_blank_retry(page, out)
     assert page.shots == 2
     assert os.path.getsize(out) == 4801
+    assert not os.path.exists(out + ".retry"), "temp retry frame must be cleaned up"
+
+
+def test_snap_retry_never_regresses_to_smaller_frame(tmp_path):
+    """Adversary finding A1: a partial-but-real first frame (just under the threshold) must
+    survive a retry that comes back WORSE (page regressed to blank during the extra settle) —
+    the larger frame wins."""
+    out = str(tmp_path / "shot.png")
+    page = _FakePage([9999, 4801])
+    S._snap_with_blank_retry(page, out)
+    assert page.shots == 2
+    assert os.path.getsize(out) == 9999, "retry must never overwrite a larger frame (A1)"
+    assert not os.path.exists(out + ".retry"), "temp retry frame must be cleaned up"
 
 
 def test_blank_threshold_brackets_observed_sizes():