add quantity controls to cart drawer via shared CartHook

Move increment/decrement handlers from Cart LiveView into CartHook so
they work from any page's drawer. Enable show_quantity_controls on the
drawer's cart_item_row. Scope cart tests to #main-content to avoid
duplicate button matches.

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

PROGRESS.md

@@ -48,7 +48,7 @@ Issues found during hands-on testing of the deployed prod site on mobile and des
 - [ ] Real product variants need testing and refinement with live data
 
 ### Cart
-- [ ] Should be able to change quantity in the cart drawer (currently only on cart page?)
+- [x] Should be able to change quantity in the cart drawer (currently only on cart page?)
 - [ ] Cart drawer button → "view basket" feels redundant — streamline the flow
 
 ### Navigation & links

lib/simpleshop_theme_web/cart_hook.ex

@@ -8,10 +8,11 @@ defmodule SimpleshopThemeWeb.CartHook do
   Handles these events so individual LiveViews don't have to:
   - `open_cart_drawer` / `close_cart_drawer` - toggle drawer visibility
   - `remove_item` - remove item from cart
+  - `increment` / `decrement` - change item quantity
   - `{:cart_updated, cart}` info - cross-tab cart sync via PubSub
 
-  LiveViews with custom cart logic (add_to_cart, increment, decrement)
-  can call `update_cart_assigns/2` and `broadcast_and_update/2` directly.
+  LiveViews with custom cart logic (e.g. add_to_cart) can call
+  `update_cart_assigns/2` and `broadcast_and_update/2` directly.
   """
 
   import Phoenix.Component, only: [assign: 3]
@@ -64,6 +65,31 @@ defmodule SimpleshopThemeWeb.CartHook do
     {:halt, socket}
   end
 
+  defp handle_cart_event("increment", %{"id" => variant_id}, socket) do
+    cart = Cart.add_item(socket.assigns.raw_cart, variant_id, 1)
+    new_qty = Cart.get_quantity(cart, variant_id)
+
+    socket =
+      socket
+      |> broadcast_and_update(cart)
+      |> assign(:cart_status, "Quantity updated to #{new_qty}")
+
+    {:halt, socket}
+  end
+
+  defp handle_cart_event("decrement", %{"id" => variant_id}, socket) do
+    current = Cart.get_quantity(socket.assigns.raw_cart, variant_id)
+    cart = Cart.update_quantity(socket.assigns.raw_cart, variant_id, current - 1)
+    new_qty = Cart.get_quantity(cart, variant_id)
+
+    socket =
+      socket
+      |> broadcast_and_update(cart)
+      |> assign(:cart_status, "Quantity updated to #{new_qty}")
+
+    {:halt, socket}
+  end
+
   defp handle_cart_event(_event, _params, socket), do: {:cont, socket}
 
   # Shared info handlers

lib/simpleshop_theme_web/components/shop_components/cart.ex

@@ -105,7 +105,7 @@ defmodule SimpleshopThemeWeb.ShopComponents.Cart do
           <ul role="list" aria-label="Cart items" style="list-style: none; margin: 0; padding: 0;">
             <%= for item <- @cart_items do %>
               <li style="border-bottom: 1px solid var(--t-border-default);">
-                <.cart_item_row item={item} size={:compact} mode={@mode} />
+                <.cart_item_row item={item} size={:compact} show_quantity_controls mode={@mode} />
               </li>
             <% end %>
           </ul>

lib/simpleshop_theme_web/live/shop_live/cart.ex

@@ -8,33 +8,6 @@ defmodule SimpleshopThemeWeb.ShopLive.Cart do
     {:ok, assign(socket, :page_title, "Cart")}
   end
 
-  @impl true
-  def handle_event("increment", %{"id" => variant_id}, socket) do
-    cart = Cart.add_item(socket.assigns.raw_cart, variant_id, 1)
-    new_qty = Cart.get_quantity(cart, variant_id)
-
-    socket =
-      socket
-      |> SimpleshopThemeWeb.CartHook.broadcast_and_update(cart)
-      |> assign(:cart_status, "Quantity updated to #{new_qty}")
-
-    {:noreply, socket}
-  end
-
-  @impl true
-  def handle_event("decrement", %{"id" => variant_id}, socket) do
-    current = Cart.get_quantity(socket.assigns.raw_cart, variant_id)
-    cart = Cart.update_quantity(socket.assigns.raw_cart, variant_id, current - 1)
-    new_qty = Cart.get_quantity(cart, variant_id)
-
-    socket =
-      socket
-      |> SimpleshopThemeWeb.CartHook.broadcast_and_update(cart)
-      |> assign(:cart_status, "Quantity updated to #{new_qty}")
-
-    {:noreply, socket}
-  end
-
   @impl true
   def render(assigns) do
     assigns = assign(assigns, :cart_page_subtotal, Cart.calculate_subtotal(assigns.cart_items))

test/simpleshop_theme_web/live/shop_live/cart_test.exs

@@ -68,7 +68,7 @@ defmodule SimpleshopThemeWeb.ShopLive.CartTest do
 
       html =
         view
-        |> element("button[aria-label='Increase quantity of #{product.title}']")
+        |> element("#main-content button[aria-label='Increase quantity of #{product.title}']")
         |> render_click()
 
       assert html =~ "Quantity updated to 2"
@@ -83,7 +83,7 @@ defmodule SimpleshopThemeWeb.ShopLive.CartTest do
 
       html =
         view
-        |> element("button[aria-label='Decrease quantity of #{product.title}']")
+        |> element("#main-content button[aria-label='Decrease quantity of #{product.title}']")
         |> render_click()
 
       assert html =~ "Your basket is empty"