0 is out of stock and nothing is available from now on

src/models/orders.rs

@@ -65,11 +65,15 @@ pub async fn place(
             .one(&txn)
             .await?
             .ok_or_else(|| Error::BadRequest("a product is no longer available".to_string()))?;
-        if variant.stock < *qty {
-            return Err(Error::BadRequest(format!(
-                "not enough stock for {}",
-                product.name
-            )));
+        // Tracked variants can't oversell; untracked ones (stock = None) are
+        // always available and never decremented.
+        if let Some(on_hand) = variant.stock {
+            if on_hand < *qty {
+                return Err(Error::BadRequest(format!(
+                    "not enough stock for {}",
+                    product.name
+                )));
+            }
         }
         currency = product.currency.clone();
         // Snapshot the price the buyer actually pays — public sale or, for a
@@ -78,9 +82,11 @@ pub async fn place(
         let unit_price_cents = pricing::price_variant(ctx, &variant, user).await?.price_cents;
         subtotal += unit_price_cents * i64::from(*qty);
 
-        let mut active = variant.clone().into_active_model();
-        active.stock = Set(variant.stock - *qty);
-        active.update(&txn).await?;
+        if let Some(on_hand) = variant.stock {
+            let mut active = variant.clone().into_active_model();
+            active.stock = Set(Some(on_hand - *qty));
+            active.update(&txn).await?;
+        }
 
         snapshots.push((product.id, variant.id, product.name, variant.label, unit_price_cents, *qty));
     }