replace analytics double-count prevention with buffer supersede

The Plug records a pageview with a known ID (plug_ref) into the ETS
buffer. When JS connects, the LiveView hook supersedes that event by
ID and records its own with full data (screen_size from connect params).
If JS never connects, the Plug's event flushes normally after 10s.

Also fixes: admin browsing no longer leaks product_view events — the
Plug now sets no analytics session data for admins, so all downstream
visitor_hash guards naturally filter them out.

Replaces the previous time-based skip logic which was brittle and
race-prone. The supersede approach is deterministic and handles both
the ETS buffer and already-flushed DB cases.

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

lib/berrypod_web/analytics_hook.ex

@@ -1,19 +1,25 @@
 defmodule BerrypodWeb.AnalyticsHook do
   @moduledoc """
-  LiveView on_mount hook for analytics — Layer 2 of the progressive pipeline.
+  LiveView on_mount hook for analytics.
 
-  Reads analytics data from the session (set by the Plugs.Analytics plug) and
-  tracks subsequent SPA navigations via handle_params. Skips the initial mount
-  since the plug already recorded that pageview.
+  Reads session data prepared by the Plugs.Analytics plug (visitor hash,
+  browser, OS, referrer, UTMs) and records pageviews for SPA navigations.
 
-  Also handles the `analytics:screen` event from the JS hook (Layer 3) to
-  capture screen width for device classification.
+  The Plug records an initial pageview into the ETS buffer with a unique
+  `plug_ref`. When JS connects, this hook tells the buffer to drop that
+  event (by ref) and records its own pageview with full data (screen_size).
+  If JS never connects (no-JS user), the Plug's event flushes to the DB
+  after the normal 10-second buffer interval. No timing heuristics needed.
+
+  Screen width is read from the LiveSocket connect params, so it's available
+  on every LiveView mount without relying on a separate JS hook event.
   """
 
   import Phoenix.Component, only: [assign: 3]
-  import Phoenix.LiveView, only: [attach_hook: 4, connected?: 1]
+  import Phoenix.LiveView, only: [attach_hook: 4, connected?: 1, get_connect_params: 1]
 
   alias Berrypod.Analytics
+  alias Berrypod.Analytics.Buffer
 
   def on_mount(:track, _params, session, socket) do
     socket =
@@ -26,56 +32,71 @@ defmodule BerrypodWeb.AnalyticsHook do
       |> assign(:analytics_utm_source, session["analytics_utm_source"])
       |> assign(:analytics_utm_medium, session["analytics_utm_medium"])
       |> assign(:analytics_utm_campaign, session["analytics_utm_campaign"])
-      |> assign(:analytics_screen_size, session["analytics_screen_size"])
       |> assign(:analytics_country_code, session["country_code"])
-      |> assign(:analytics_initial_mount, true)
+      |> assign(:analytics_plug_ref, session["analytics_plug_ref"])
 
     socket =
-      if connected?(socket) and socket.assigns.analytics_visitor_hash do
+      if connected?(socket) do
+        # Supersede the Plug's buffered event — we'll record our own with screen_size
+        if plug_ref = socket.assigns[:analytics_plug_ref] do
+          Buffer.supersede(plug_ref)
+        end
+
+        screen_size = screen_size_from_connect_params(socket)
+
         socket
-        |> attach_hook(:analytics_params, :handle_params, &handle_analytics_params/3)
+        |> assign(:analytics_screen_size, screen_size)
+        |> assign(:analytics_plug_ref, nil)
         |> attach_hook(:analytics_events, :handle_event, &handle_analytics_event/3)
+        |> then(fn s ->
+          if s.assigns.analytics_visitor_hash do
+            attach_hook(s, :analytics_params, :handle_params, &handle_analytics_params/3)
+          else
+            s
+          end
+        end)
       else
-        socket
+        assign(socket, :analytics_screen_size, nil)
       end
 
     {:cont, socket}
   end
 
+  defp screen_size_from_connect_params(socket) do
+    case get_connect_params(socket) do
+      %{"screen_width" => width} when is_integer(width) -> classify_screen(width)
+      _ -> nil
+    end
+  end
+
   defp handle_analytics_params(_params, uri, socket) do
-    # Skip the initial mount — the plug already recorded this pageview
-    if socket.assigns.analytics_initial_mount do
-      {:cont, assign(socket, :analytics_initial_mount, false)}
+    if admin?(socket) do
+      {:cont, socket}
     else
-      # Skip if admin user is browsing
-      if admin?(socket) do
-        {:cont, socket}
-      else
-        pathname = URI.parse(uri).path
+      pathname = URI.parse(uri).path
 
-        Analytics.track_pageview(%{
-          pathname: pathname,
-          visitor_hash: socket.assigns.analytics_visitor_hash,
-          referrer: socket.assigns.analytics_referrer,
-          referrer_source: socket.assigns.analytics_referrer_source,
-          utm_source: socket.assigns.analytics_utm_source,
-          utm_medium: socket.assigns.analytics_utm_medium,
-          utm_campaign: socket.assigns.analytics_utm_campaign,
-          country_code: socket.assigns.analytics_country_code,
-          screen_size: socket.assigns.analytics_screen_size,
-          browser: socket.assigns.analytics_browser,
-          os: socket.assigns.analytics_os
-        })
+      Analytics.track_pageview(%{
+        pathname: pathname,
+        visitor_hash: socket.assigns.analytics_visitor_hash,
+        referrer: socket.assigns.analytics_referrer,
+        referrer_source: socket.assigns.analytics_referrer_source,
+        utm_source: socket.assigns.analytics_utm_source,
+        utm_medium: socket.assigns.analytics_utm_medium,
+        utm_campaign: socket.assigns.analytics_utm_campaign,
+        country_code: socket.assigns.analytics_country_code,
+        screen_size: socket.assigns.analytics_screen_size,
+        browser: socket.assigns.analytics_browser,
+        os: socket.assigns.analytics_os
+      })
 
-        # Clear referrer/UTMs after first SPA navigation — they only apply to the entry
-        {:cont,
-         socket
-         |> assign(:analytics_referrer, nil)
-         |> assign(:analytics_referrer_source, nil)
-         |> assign(:analytics_utm_source, nil)
-         |> assign(:analytics_utm_medium, nil)
-         |> assign(:analytics_utm_campaign, nil)}
-      end
+      # Clear referrer/UTMs after first tracked navigation — they only apply to the entry
+      {:cont,
+       socket
+       |> assign(:analytics_referrer, nil)
+       |> assign(:analytics_referrer_source, nil)
+       |> assign(:analytics_utm_source, nil)
+       |> assign(:analytics_utm_medium, nil)
+       |> assign(:analytics_utm_campaign, nil)}
     end
   end
 
@@ -96,7 +117,7 @@ defmodule BerrypodWeb.AnalyticsHook do
   defp handle_analytics_event("analytics:screen", %{"width" => width}, socket)
        when is_integer(width) do
     screen_size = classify_screen(width)
-    {:cont, assign(socket, :analytics_screen_size, screen_size)}
+    {:halt, assign(socket, :analytics_screen_size, screen_size)}
   end
 
   defp handle_analytics_event(_event, _params, socket), do: {:cont, socket}