Use full-screen mode rather than auto-hiding the ribbon.

You can still exit full-screen mode with the escape key.

This approach has both advantages and disadvantages compared to the previous approach.

Advantages:
- tapping the option (= alt) key no longer triggers the ribbon overlay on the way to typing another keyboard equivalent
- using alt commands to control dictation no longer triggers the ribbon overlay either
- slightly more space for writing
- works more reliably (it wasn’t really possible to auto-hide the ribbon from VBA)

Disadvantages:
- requires an extra click or keyboard shortcut to get back to full-screen mode after interacting with the ribbon
- no collapsed ribbon area which we can use for status display
- using alt commands nearly invisibly redirects focus from the window (only the lack of a blinking insertion point indicates what is going on).

The last disadvantage is the most annoying in daily use.  I may be able to work around it with an AutoHotKey macro.