T5 products in the client's inventory

The inventory's product list (test.showInventory) gets the community products the person has: local packs, and
hub products in their library. Hiding one is answered by the proxy (and removes a hub product from the library).
When the library changes, the client is told to load its inventory again, with the server event IMVU sends
after a purchase. A product whose revision or info changes gets a new local ID, since the client keeps product
info for good; names lose characters the client's pages could take as HTML.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

internal/fetch/fetch.go

@@ -42,8 +42,11 @@ type Fetcher struct {
 
 	// OnReady, if set, is called when a product was written (or updated) in the cache.
 	OnReady func(id string)
+	// OnLibrary, if set, is called after the library was read and its products fetched.
+	OnLibrary func()
 
 	mu       sync.Mutex
+	library  map[string]bool // the person's library, as last read
 	inflight map[string]bool
 	failed   map[string]time.Time // products that failed lately (not retried for a while)
 	access   string
@@ -69,6 +72,18 @@ func (f *Fetcher) SyncLibrary(ctx context.Context) {
 		f.logf("fetch: reading the library: %v", err)
 		return
 	}
+	ids := map[string]bool{}
+	for _, e := range lib {
+		ids[e.Product.ID] = true
+	}
+	f.mu.Lock()
+	f.library = ids
+	f.mu.Unlock()
+	defer func() {
+		if f.OnLibrary != nil {
+			f.OnLibrary()
+		}
+	}()
 	for _, e := range lib {
 		if err := f.Ensure(ctx, e.Product.ID); err != nil {
 			f.logf("fetch: %s (%s): %v", e.Product.ID, e.Product.Name, err)
@@ -291,3 +306,10 @@ func copyFile(src, dst string) error {
 	}
 	return out.Close()
 }
+
+// Owned reports whether a product is in the person's library (as last read).
+func (f *Fetcher) Owned(id string) bool {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.library[id]
+}