feat(memory): add incremental transcript compaction

tests/unit/utils/test_image_hash.py

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Perceptual-hash stability and distance behavior (M4 similarity hint)."""
+
+import io
+
+from PIL import Image, ImageDraw
+
+from artemis.utils.image_hash import HASH_SIZE, dhash_hex, hamming_distance_hex
+
+
+def _screen(draw_fn, size=(270, 600), quality=85) -> bytes:
+    img = Image.new("RGB", size, "white")
+    draw_fn(ImageDraw.Draw(img))
+    buf = io.BytesIO()
+    img.save(buf, format="JPEG", quality=quality)
+    return buf.getvalue()
+
+
+def _login_screen(d):
+    d.rectangle([20, 40, 250, 90], fill="#3355ff")
+    d.rectangle([30, 200, 240, 250], outline="#333333", width=4)
+    d.rectangle([30, 300, 240, 350], outline="#333333", width=4)
+    d.rectangle([60, 450, 210, 510], fill="#22aa66")
+
+
+def _settings_screen(d):
+    for y in range(60, 560, 80):
+        d.rectangle([10, y, 260, y + 50], fill="#dddddd")
+    d.ellipse([200, 20, 250, 45], fill="#aa2222")
+
+
+def test_dhash_is_stable_for_identical_bytes():
+    img = _screen(_login_screen)
+    assert dhash_hex(img) == dhash_hex(img)
+    assert len(dhash_hex(img)) == HASH_SIZE * HASH_SIZE // 4
+
+
+def test_dhash_survives_jpeg_reencoding_with_small_distance():
+    original = _screen(_login_screen, quality=95)
+    with Image.open(io.BytesIO(original)) as img:
+        buf = io.BytesIO()
+        img.save(buf, format="JPEG", quality=60)
+    reencoded = buf.getvalue()
+
+    distance = hamming_distance_hex(dhash_hex(original), dhash_hex(reencoded))
+    assert distance is not None and distance <= 4
+
+
+def test_dhash_separates_different_screens():
+    distance = hamming_distance_hex(
+        dhash_hex(_screen(_login_screen)), dhash_hex(_screen(_settings_screen))
+    )
+    assert distance is not None and distance > 8
+
+
+def test_dhash_best_effort_on_garbage():
+    assert dhash_hex(None) is None
+    assert dhash_hex(b"") is None
+    assert dhash_hex(b"not an image at all") is None
+
+
+def test_hamming_distance_edge_cases():
+    assert hamming_distance_hex(None, "ff") is None
+    assert hamming_distance_hex("ff", None) is None
+    assert hamming_distance_hex("ff", "ffff") is None  # length mismatch
+    assert hamming_distance_hex("zz", "aa") is None  # not hex
+    assert hamming_distance_hex("00ff", "00ff") == 0
+    assert hamming_distance_hex("0000", "000f") == 4