Replacing the paid button with the cancel/hide action block cut the old
markup at the first <% end %>, which belonged to the button's inner
if/else, leaving a stray </button></form><% end %> behind. show.erb no
longer compiled and every admin invoice page returned 500; nothing
rendered that page in tests.
Remove the leftovers, render the page in every state (pending, paid,
cancelled, hidden), and compile every view in a test so an unbalanced
template fails CI even when no test visits that page.
Assisted-by: Claude:opus-5
Sergei Poljanski
bf4f270fb4