feat(platform): images port — decode, resolution bar (Q-3), WebP renditions (SD-0002 §6.2)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/tests/test_platform_images.py

@@ -0,0 +1,55 @@
+"""platform/images — pure decode + resolution bar + WebP renditions (SD-0002 §6.2)."""
+import io
+
+from PIL import Image
+
+from app.platform import images
+
+
+def _png(width: int, height: int, color=(120, 80, 200)) -> bytes:
+    buf = io.BytesIO()
+    Image.new("RGB", (width, height), color).save(buf, format="PNG")
+    return buf.getvalue()
+
+
+def _jpeg(width: int, height: int) -> bytes:
+    buf = io.BytesIO()
+    Image.new("RGB", (width, height), (10, 200, 90)).save(buf, format="JPEG")
+    return buf.getvalue()
+
+
+def test_good_image_produces_three_webp_renditions():
+    result = images.process(_png(1200, 900))
+    assert isinstance(result, images.Processed)
+    assert result.source_format == "PNG"
+    assert set(result.renditions) == {"thumb", "card", "detail"}
+    for name, blob in result.renditions.items():
+        with Image.open(io.BytesIO(blob)) as im:
+            assert im.format == "WEBP"
+    with Image.open(io.BytesIO(result.renditions["thumb"])) as im:
+        assert max(im.size) <= images.RENDITIONS["thumb"]
+    with Image.open(io.BytesIO(result.renditions["detail"])) as im:
+        assert max(im.size) <= images.RENDITIONS["detail"]
+
+
+def test_downscale_only_never_upscales_small_source():
+    result = images.process(_png(520, 520))
+    with Image.open(io.BytesIO(result.renditions["detail"])) as im:
+        assert im.size == (520, 520)
+
+
+def test_below_resolution_bar_rejected_low_res():
+    result = images.process(_png(300, 1200))  # shorter side 300 < 500
+    assert isinstance(result, images.Rejected)
+    assert result.reason == "rejected_low_res"
+
+
+def test_not_an_image_rejected_not_image():
+    result = images.process(b"this is not an image")
+    assert isinstance(result, images.Rejected)
+    assert result.reason == "rejected_not_image"
+
+
+def test_jpeg_source_format_preserved_in_result():
+    result = images.process(_jpeg(800, 800))
+    assert result.source_format == "JPEG"