feat: wire Umami events in builder page (build_started, part_selected, affiliate_link_clicked, build_shared, build_saved)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/(app)/(builder)/builder/page.tsx

@@ -28,6 +28,7 @@ import { X, Link2, Square, CheckSquare } from "lucide-react";
 
 import { useApi } from "@/lib/api";
 import { useAuth } from "@/context/AuthContext";
+import { trackBuildStarted, trackPartSelected, trackAffiliateLinkClicked, trackBuildShared, trackBuildSaved } from "@/lib/analytics";
 
 import { CATEGORIES } from "@/data/gunbuilderParts";
 import { BUILDER_SLOTS, isSlotSatisfied } from "@/data/builderSlots";
@@ -369,20 +370,33 @@ function GunbuilderPageContent() {
   useEffect(() => {
     if (typeof window === "undefined") return;
 
-    // Hydrate persisted build state only. URL actions (platform/select/remove)
+    // Intentional: Object.keys(...).length > 0 tightens the original condition.
-    // are handled by the dedicated useSearchParams effect later in this file.
+    // Previously, an empty {} from localStorage would call setBuild(normalizeBuildState({})),
+    // which is a no-op. The new check skips that call, which is safe and correct.
+    let hasBuild = false;
     const stored = localStorage.getItem(STORAGE_KEY);
     if (stored) {
       try {
         const parsed = JSON.parse(stored);
-        if (parsed && typeof parsed === "object") {
+        if (parsed && typeof parsed === "object" && Object.keys(parsed).length > 0) {
           setBuild(normalizeBuildState(parsed));
+          hasBuild = true;
         }
       } catch {
         // ignore
       }
     }
 
+    // Fire build_started only for genuinely new builds:
+    // - No existing parts in localStorage
+    // - No ?select= param (share-link arrivals have empty localStorage but are not starting fresh)
+    // Use window.location.search directly: this effect runs at mount before any router
+    // processing, making window.location.search the authoritative source of the landing URL.
+    const hasSelectParam = new URLSearchParams(window.location.search).has("select");
+    if (!hasBuild && !hasSelectParam) {
+      trackBuildStarted();
+    }
+
     // Signal that hydration is complete - this allows URL param processing to run
     setIsHydrated(true);
   }, []);
@@ -842,6 +856,7 @@ function GunbuilderPageContent() {
         type: "success",
         message: "Saved to your Vault ✅ ",
       });
+      trackBuildSaved();
 
       // Close modal + reset inputs for next variant
       setSaveAsOpen(false);
@@ -889,8 +904,10 @@ function GunbuilderPageContent() {
         }
         return next;
       });
+      const partName = parts.find((p) => String(p.id) === String(partId))?.name ?? String(partId);
+      trackPartSelected(categoryId, partName, String(partId));
     },
-    [build]
+    [build, parts]
   );
   // Handle URL query parameters (?select, ?remove) and keep platform synced + canonical
   useEffect(() => {
@@ -1055,6 +1072,7 @@ function GunbuilderPageContent() {
 
     try {
       await navigator.clipboard.writeText(shareUrl);
+      trackBuildShared();
       setShareStatus("Shareable link copied to clipboard.");
     } catch {
       setShareStatus("Could not copy link to clipboard.");
@@ -1074,6 +1092,7 @@ function GunbuilderPageContent() {
           text: "Check out my Battl Build.",
           url: shareUrl,
         });
+        trackBuildShared(); // fires only on successful share, not on cancel
         setShareStatus("Share dialog opened.");
       } catch {
         setShareStatus(
@@ -1704,6 +1723,14 @@ function GunbuilderPageContent() {
                                             target="_blank"
                                             rel="noopener noreferrer"
                                             className="inline-flex items-center gap-1.5 whitespace-nowrap rounded-md border border-amber-600 bg-amber-500 px-3 py-1.5 text-xs font-semibold text-black hover:bg-amber-400 transition-colors"
+                                            onClick={() => {
+                                              try {
+                                                const retailer = new URL(selectedPart.affiliateUrl).hostname.replace(/^www\./, "");
+                                                trackAffiliateLinkClicked(selectedPart.name, retailer);
+                                              } catch {
+                                                // ignore malformed URLs — if affiliateUrl is malformed, the link href is also broken
+                                              }
+                                            }}
                                           >
                                             Buy
                                           </a>