feat(products): export hosted detail URL for fetched images; snapshot carries status (SD-0002 §6.5.5, INV-16)

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

backend/app/domains/products/serialize.py

@@ -14,6 +14,7 @@ from collections.abc import Iterable, Iterator
 from decimal import Decimal
 
 from .diff import CatalogProduct
+from .hosted import EXPORT_RENDITION, image_url
 from .models import (
     IMAGE_COLUMNS,
     OPTION_VALUE_COLUMNS,
@@ -51,14 +52,14 @@ def _cell(value: object) -> str:
     return str(value)
 
 
-def catalog_to_csv(products: Iterable[CatalogProduct]) -> Iterator[str]:
+def catalog_to_csv(products: Iterable[CatalogProduct], base_url: str = "") -> Iterator[str]:
     """Stream canonical CSV text, header first, one product block at a time."""
     buf = io.StringIO()
     writer = csv.writer(buf)
     writer.writerow(HEADER)
     yield _drain(buf)
     for product in products:
-        for row in _product_rows(product):
+        for row in _product_rows(product, base_url):
             writer.writerow([row.get(col, "") for col in HEADER])
         yield _drain(buf)
 
@@ -70,7 +71,7 @@ def _drain(buf: io.StringIO) -> str:
     return text
 
 
-def _product_rows(product: CatalogProduct) -> list[dict[str, str]]:
+def _product_rows(product: CatalogProduct, base_url: str = "") -> list[dict[str, str]]:
     """The product's CSV rows (§6.5.1 grammar): product fields + option names on
     the first row; one variant per row; images interleaved; image-only rows when
     a product has more images than variants."""
@@ -90,13 +91,18 @@ def _product_rows(product: CatalogProduct) -> list[dict[str, str]]:
         if i < len(product.variants):
             _write_variant(row, product, product.variants[i])
         if i < len(product.images):
-            _write_image(row, product.images[i])
+            _write_image(row, product.images[i], base_url)
         rows.append(row)
     return rows
 
 
-def _write_image(row: dict[str, str], image) -> None:
-    row["Image Src"] = image.source_url
+def _write_image(row: dict[str, str], image, base_url: str) -> None:
+    # Fetched images export the platform-hosted URL (INV-12/16); everything
+    # else keeps the original source_url so nothing is lost (§6.5.5).
+    if image.status == "fetched":
+        row["Image Src"] = image_url(base_url, image.id, EXPORT_RENDITION)
+    else:
+        row["Image Src"] = image.source_url
     row["Image Position"] = str(image.position)
     if image.alt_text is not None:
         row["Image Alt Text"] = image.alt_text