feat(product): record product views for recommendations

Fire a fire-and-forget view event when an authenticated, non-owner user
opens a product page (deduped per product), POSTing to the new
/api/engagement/v1/views/ endpoint. Silent on failure so tracking never
disrupts browsing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/components/product/ProductDetailView.tsx

@@ -37,6 +37,7 @@ import {
 } from "~/utils/RequestHandler";
 import { useAddToCart } from "~/requestHandler/use-cart-hooks";
 import { useCreateChatThread } from "~/requestHandler/use-chat-hooks";
+import { useRecordProductView } from "~/requestHandler/use-view-hooks";
 import { findVariantId, formatPrice, safeGoBack } from "~/utils/helpers";
 import { useToast } from "~/hooks/use-toast";
 import { useRootData } from "~/hooks/use-root-data";
@@ -76,6 +77,10 @@ export const ProductDetailView = memo(function ProductDetailView({
     setProductActiveStatus(product.isActive || false);
   }, [product.isActive]);
 
+  // Record a product view for the recommendation system (skip the owner's own
+  // product; only tracks authenticated users, deduped per product).
+  useRecordProductView(product.id, { enabled: !isOwner });
+
   // Memoize available colors and sizes
   const { availableColors, availableSizes } = useMemo(
     () => ({

app/requestHandler/use-view-hooks.ts

@@ -0,0 +1,69 @@
+import { useMutation, useQueryClient } from "@tanstack/react-query";
+import { useEffect, useRef } from "react";
+import { useAuthToken } from "../hooks/use-root-data";
+import { getApiBaseUrl } from "../utils/api-config";
+
+/**
+ * Records that the authenticated user viewed a product. Used as a signal for
+ * the recommendation system (alongside bookmarks, follows, orders, semantic
+ * proximity). Fire-and-forget: failures are swallowed so tracking never
+ * disrupts the browsing experience.
+ *
+ * NOTE: this hits /api/engagement/v1/views/ via a direct fetch because the
+ * endpoint is newer than the generated OpenAPI client. Swap to the generated
+ * EngagementApi method once the client is regenerated.
+ */
+export function useTrackProductView() {
+  const token = useAuthToken();
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: async (productId: string) => {
+      if (!token || !productId) return { skipped: true };
+
+      const res = await fetch(`${getApiBaseUrl()}/api/engagement/v1/views/`, {
+        method: "POST",
+        headers: {
+          "Content-Type": "application/json",
+          Authorization: `Bearer ${token}`,
+        },
+        body: JSON.stringify({ productId }),
+      });
+
+      if (!res.ok) {
+        throw new Error(`Failed to track view: ${res.status}`);
+      }
+      return res.json();
+    },
+    onSuccess: () => {
+      // Keep "recently viewed" fresh if/when it's rendered.
+      queryClient.invalidateQueries({ queryKey: ["recentlyViewedProducts"] });
+    },
+    // View tracking is best-effort; never surface errors to the user.
+    onError: () => {},
+  });
+}
+
+/**
+ * Fires a single product-view event when a product page is opened. Dedupes per
+ * productId so React strict-mode double-mounts / re-renders don't double-count
+ * within the same mount, and skips when not authenticated.
+ */
+export function useRecordProductView(
+  productId: string | undefined,
+  options?: { enabled?: boolean }
+) {
+  const token = useAuthToken();
+  const { mutate } = useTrackProductView();
+  const lastTrackedRef = useRef<string | null>(null);
+  const enabled = options?.enabled ?? true;
+
+  useEffect(() => {
+    if (!enabled) return;
+    if (!token || !productId) return;
+    if (lastTrackedRef.current === productId) return;
+
+    lastTrackedRef.current = productId;
+    mutate(productId);
+  }, [productId, token, enabled, mutate]);
+}