Mine implies a heuristic of "make repeated attempts at re-intepreting the comment using different background assumptions".

I don't see how "treat everyone's comments as though they were made by a sane , intelligent, person" entails that without extra background assumptions. And I expect that once those extra assumptions are spelled out, the "may .or may have been having an off day" version will imply the same action(s) as your original version.

As I have explained, it provides its own evidence.

Well, when I've disagreed with people in discussions, my own experience has been that behaving according to my baseline impression of how much sense they're making gets me closer to understanding than consciously inflating my impression of how much sense they're making.

Neither of those is much good if interpreting someone who died 100 years ago.

A fair point, but one of minimal practical import. Almost all of the disagreements which confront me in my life are disagreements with live people.