Adopting the six v0-era PRs surfaced two conflict-shaped cases the merge
leg handled only by luck. Behind-main branches are refused outright by
the repo's block_on_outdated_branch protection, so the leg now refreshes
every branch against origin/main before merging — which is also where a
textual conflict should surface, as diff text the loop resolves only
where it authored the hunks, otherwise abandoning the PR to a human
with a comment. And the one guard no mergeability check provides is the
push run on main after the merge: three PRs touching the same file can
merge cleanly and contradict each other, so a red main now halts the
loop instead of the tick reporting merged and moving on.
Closes#238
logan