Resolve preview's page-to-node lookup for every layer

pages_controller#preview loaded a page by id and rendered it
directly, assuming @page.node was always present. True for head and
draft, since both carry a real node_id: false for autosave, which
deliberately has node_id: nil (the mechanism that excludes it from
Node#pages and the revision count). A node with an autosave and no
draft underneath it: lock, start editing, never explicitly save a
draft: loads that autosave directly with no node at all, and any
view code assuming @page.node is real (headline image, credits,
gallery links) raises.

When @page has no node, resolve it by checking autosave_id, then
draft_id, then head_id on Node, and set @page.node in memory only:
the autosave's node_id: nil is never persisted differently. The
existing swap from draft to a fresher autosave, when both exist, is
unchanged.

Three tests: draft with a fresher autosave on top, autosave with no
draft underneath, and the ordinary head-only case with neither.

1 files changed, 13 insertions, 0 deletions

diff --git a/app/controllers/pages_controller.rb b/app/controllers/pages_controller.rb
index 0b7e98f..326fbd4 100644
--- a/app/controllers/pages_controller.rb
+++ b/app/controllers/pages_controller.rb
@@ -6,6 +6,19 @@ class PagesController < ApplicationController
 
   def preview
     @page = Page.find(params[:id])
+    unless @page.node
+      node = Node.find_by(autosave_id: @page.id) ||
+             Node.find_by(draft_id: @page.id) ||
+             Node.find_by(head_id: @page.id)
+      @page.node = node if node
+    end
+
+    node ||= @page.node
+    if node && node.draft_id == @page.id && node.autosave
+      @page = node.autosave
+      @page.node = node
+    end
+
 
     if @page
       template = @page.valid_template