fix: cap ring related products to 45 and add 502 retry in watch mode

Previously every watch JSON request and product page load called
get_ring_related_products with forward=len(ring), loading ALL products
in the shop from the DB. For large rings this caused worker memory to
spike, triggering uwsgi reload-on-rss kills and producing 502s.

Cap related items to 42 forward + 3 backward (matching the sidebar
display limit). The watch JSON endpoint now accepts a dir query param
so the client can signal travel direction — when going backward the
allocation flips to 3 forward + 42 backward.

Also adds retry with backoff (up to 2 retries, 1s/2s delay) in
fetchWatchData() for transient 502/503/504 responses during worker
recycling.

make_post_sell/static/js/watch.js

@@ -413,11 +413,20 @@
         });
     }
 
-    // --- Fetch watch JSON ---
-    function fetchWatchData(productId) {
-        return fetch('/watch/' + productId + '/json', {
+    // --- Fetch watch JSON (with retry for transient 502s) ---
+    function fetchWatchData(productId, attempt) {
+        attempt = attempt || 0;
+        var url = '/watch/' + productId + '/json?dir=' + ringDirection;
+        return fetch(url, {
             headers: {'X-Requested-With': 'XMLHttpRequest'}
         }).then(function(r) {
+            if (r.status >= 502 && r.status <= 504 && attempt < 2) {
+                return new Promise(function(resolve) {
+                    setTimeout(resolve, (attempt + 1) * 1000);
+                }).then(function() {
+                    return fetchWatchData(productId, attempt + 1);
+                });
+            }
             if (!r.ok) throw new Error('Watch fetch failed');
             return r.json();
         });

make_post_sell/views/product.py

@@ -98,7 +98,7 @@ def product(request):
         from ..models.product import get_ring_related_products, get_related_products
         ring = product.shop.discovery_ring
         if ring:
-            related_products = get_ring_related_products(product, ring, forward=len(ring))
+            related_products = get_ring_related_products(product, ring, forward=42)
         else:
             related_products = get_related_products(product)
 

make_post_sell/views/watch.py

@@ -106,7 +106,16 @@ def watch_json(request):
     # Use existing discovery ring — never recompute during a request
     ring = request.shop.discovery_ring
     if ring:
-        related = get_ring_related_products(product, ring, forward=len(ring))
+        # Client sends dir=-1 when traveling backward through the ring.
+        # Flip forward/backward so the sidebar shows items in the travel direction.
+        try:
+            direction = int(request.params.get("dir", "1"))
+        except (ValueError, TypeError):
+            direction = 1
+        if direction == -1:
+            related = get_ring_related_products(product, ring, forward=3, backward=42)
+        else:
+            related = get_ring_related_products(product, ring, forward=42, backward=3)
     else:
         related = get_related_products(product)