diff --git a/docs/PRODUCT.md b/docs/PRODUCT.md
index c026ec0..49ae5c5 100644
--- a/docs/PRODUCT.md
+++ b/docs/PRODUCT.md
@@ -30,9 +30,14 @@ Store categories, attributes, and `fig-*` / `feat-*` tags are the filters. Measu
 | Price | App proposal `bdft × species $/bdft`; user may replace |
 | Title, short title, description | Templates from listing facts; user may edit |
 
+## System seams
+
+Milestone 1 runs in the browser. No backend and no inference URL.
+Handoff is the device draft: source photo, approved mask, inventory PNG, length, thickness, widths, sqft, bdft.
+Milestone 3 uses FastAPI as the Woo client. Store credentials stay on the server.
+
 ## Create
 
-FastAPI is the Woo client. Store credentials stay on the server.
 `SLAB-UAT-*` creates as a WooCommerce draft (store status).
 Duplicate SKU blocks create.
 A listing can be created with inference off.