Fix shared preview links breaking after a second publish

A token's page could stop being node.head_id (superseded by a newer
draft) while still being published_at.present? - the old check only
compared against the current head, so a superseded page fell through
to direct rendering instead of redirecting, serving a stale frozen
snapshot indefinitely instead of the current live content.

Also handles scheduled publishing correctly: a page can be head_id but
not yet public? (published_at in the future) - that case must still
render directly, not redirect into a 404 on the not-yet-live public
URL.

1 files changed, 7 insertions, 2 deletions

diff --git a/app/controllers/shared_previews_controller.rb b/app/controllers/shared_previews_controller.rb
index a8a540f..d482466 100644
--- a/app/controllers/shared_previews_controller.rb
+++ b/app/controllers/shared_previews_controller.rb
@@ -1,9 +1,14 @@
 class SharedPreviewsController < ApplicationController
   def show
     @page = Page.find_by!(preview_token: params[:token])
+    node  = @page.node
 
-    if @page.node && @page.node.head_id == @page.id
-      redirect_to node_path(@page.node)
+    was_published    = @page.published_at.present?
+    superseded       = was_published && node && node.head_id != @page.id
+    currently_public = was_published && node && node.head_id == @page.id && @page.public?
+
+    if superseded || currently_public
+      redirect_to node_path(node)
       return
     end