Now that the train has left the station ...

... I think I finally put my finger on the other reason I don't like
about keying "WSA is engaged" off of [action] instead of any wsa: header.

As I understand it, the reasoning is that, since [action] is required
and non-defaulting (and, as it happens, the only such), its presence
indicates that the intent was to to engage WSA.  But the implication is
backwards.  Intending to engage WSA implies wsa:Action (as it happens),
but not vice versa.  The students at the Aveda institute downstairs of
our office are evidently required to wear all-black, but wearing
all-black does not imply that one is studying cosmetology (one might
instead be playing rugby for New Zealand, or one might just like black).

Be that as it may, I accept that the issue is settled.