feat(products): codec detects + maps Shopify dialect at the boundary (INV-17, SLICE-8)

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

backend/tests/test_products_codec.py

@@ -67,3 +67,29 @@ def test_missing_column_message_names_the_column():
     with pytest.raises(FileRejected) as exc:
         parse_csv(_csv("Handle,Vendor", "mug,Acme"))
     assert "'Title'" in exc.value.message
+
+
+def test_parse_detects_and_maps_shopify():
+    data = (
+        "Handle,Title,Body (HTML),Cost per item,Variant Price,Variant Grams,Type,Gift Card\n"
+        "mug,Moon Mug,<p>Grey</p>,9.50,18.00,300,Drinkware,false\n"
+    ).encode("utf-8")
+    parsed = parse_csv(data)
+    assert parsed.dialect == "shopify"
+    cells = parsed.rows[0].cells
+    assert cells["Description"] == "<p>Grey</p>"
+    assert cells["Variant Cost"] == "9.50"
+    assert cells["Variant Weight"] == "300"
+    assert cells["Variant Weight Unit"] == "g"  # synthesized
+    # Type (free-text) and Gift Card warned, never mapped:
+    assert "Type" in parsed.unknown_columns
+    assert "Gift Card" in parsed.unknown_columns
+    assert "product_type" not in str(cells)  # Type never reached canonical
+
+
+def test_parse_canonical_unchanged():
+    data = b"Handle,Title,Description,Variant Price\nmug,Moon Mug,Grey,18.00\n"
+    parsed = parse_csv(data)
+    assert parsed.dialect == "canonical"
+    assert parsed.rows[0].cells["Description"] == "Grey"
+    assert parsed.unknown_columns == []