vendor imports beyond the committers guide?

Hi,

there's the edge case when we already have code in contrib which was
previously directly committed and now should come out of a vendor
branch.

(1) how does one properly seed that case?

(2) given I couldn't see that mentioned either anywhere, for local
changes, they only live in main and stable/ but vendor doesn't have them
so in case of conflict they'll show up with the merge from vendor to
main and need to be resolved then?

/bz

-- 
Bjoern A. Zeeb                                                     r15:7