Gate live-content changes on restricted surfaces

publish_draft!, trash!, destroy_from_trash!, attach_asset! and
Asset#destroy_witnessed! now refuse unless the acting user holds redaktion,
and only when the subject is on a restricted surface: the front page, the
updates tree that feeds ~100k subscribers, or disclosure. Drafting,
autosaving, tagging and creating stay free everywhere for everyone.

Enforcement is in the models rather than the controllers, since attach_asset!
and the rest are reachable from rake tasks and internal paths. It follows the
errors.add-plus-bare-raise pattern the rest of Node already uses, so every
existing RecordInvalid rescue reports it with a localised message; only
assets_controller#destroy needed a rescue added.

A nil user is treated as a system context and bypasses the gate. The default
nil on three of those verbs is what makes that reachable, and removing those
defaults once every call site passes a user is the next tightening.

1 files changed, 3 insertions, 0 deletions

diff --git a/app/controllers/nodes_controller.rb b/app/controllers/nodes_controller.rb
index c56fd945..383fb72c 100644
--- a/app/controllers/nodes_controller.rb
+++ b/app/controllers/nodes_controller.rb
@@ -194,6 +194,9 @@ class NodesController < ApplicationController
     @node.publish_draft!(current_user)
     flash[:notice] = t("flash.nodes.published")
     redirect_to node_path(@node)
+  rescue ActiveRecord::RecordInvalid => e
+    flash[:error] = e.message
+    redirect_to node_path(@node)
   end
 
   def unlock