As per title, I want to add a custom-action button to the left of the standard editor-actions button. The purpose is to give admins a really obvious way to view the live page at the current node, because ex-WordPress admins keep clicking the [Preview] button, which creates a new version (a long standing bug) that is an utter PITA to clear - there really needs to be a 'delete draft' option, but that's a separate topic.

Something like below. The part I'm not so clear on is how to add a button to the 'editor-actions' div, without resorting to an ugly hack.

Any suggestions or pointers to docs would be appreciated.