wdt.h provides a wdt_enable() function, which conveniently abstracts enabling the watchdog and setting the timeout at the same time.

A similarly easy way to enable interrupt (and probably also interrupt + reset) mode would be a useful addition.

I'm not sure how this API would look. This could be a a function wdt_enable_interrupt() and wdt_enable_reset_and_interrupt() to set the timeout and enable just the interrupt or both reset and the interrupt (function names would need some work).

Alternatively, having a separate function to set the timeout and one to enable (just) the interrupt mask (which I think doesn't require the WDCE dance) would also work, then thos can be combined for interrupt-only mode, and wdt_enable with the enable interrupt mask function would enable system+reset.