Adds the unmerged-conflict guard flagged in PR review: before the dirty-tree
flow can run, check `git ls-files -u` and refuse to auto-commit if unresolved
merge conflict markers are present (e.g. left behind by a prior run's failed
`git stash pop`). Without this, a re-run's `git add -A` would silently stage
literal <<<<<<< / ======= / >>>>>>> markers into a real commit and push them
to origin/main.
Also expands every failure-path message (stash-push failure, stash-pop
conflict vs. untracked-file-collision, resync failure, true divergence,
manual-abort cases) to include concrete, copy-pasteable remediation command
sequences with multiple options (resolve-in-place vs. abandon-and-reapply vs.
drop-if-unneeded), rather than a single generic hint. The true-divergence
message now also tells the operator to check `git stash list` first, so a
stash created by the new dirty+stale path isn't confused with a second
manually-created one.
No change to the common dirty-but-current or clean-but-stale behavior.
Bot
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