Git rollback mode selector

Git Rollback Mode Selector

Context

An autonomous process (codegen agent, evolver, migration runner) writes changes into a git worktree. When its own validation fails, you need to decide what happens to those changes. One env var, three modes:

Mode	Behavior	Cost
hard (default)	git reset --hard to pre-change HEAD; discard working tree & index	Fastest clean state; zero artifact of the failed attempt
stash	git stash push --include-untracked the failed attempt; HEAD returns to pre-change state	Attempt is preserved for human review; stash accumulates if failures repeat
none	Leave the tree as-is; log and abort the loop	Lets human inspect the exact failing state in place; next iteration blocked until cleanup

Env var: EVOLVER_ROLLBACK_MODE={hard|stash|none}.

Rules

• Record the pre-change ref. Capture git rev-parse HEAD at the start of each iteration; that's the rollback target. Never trust "the previous commit" — the previous iteration may have already moved HEAD.
• Include untracked. hard must also git clean -fd (scoped to the working dir, not recursively above it) or agents leave orphaned files. stash must use --include-untracked.
• Fail loud on none. When none is chosen and rollback is skipped, the loop must refuse to proceed until a human signals resume. Otherwise the next iteration runs on top of broken state.
• Never --force push automatically. Rollback is local-only. If the failed attempt was already pushed, open an issue / alert; do not rewrite remote history from an autonomous loop.
• Tag the rollback in the audit log. Emit {iteration_id, rollback_mode, pre_ref, post_ref, reason} to the event stream so you can reconstruct what happened even when hard erased the working tree.

Anti-patterns

• Using git checkout . as the rollback — leaves untracked files and staged deletions.
• Using git stash with no --include-untracked — same leak.
• Rolling back across iterations (jumping past more than one pre-ref) — that's not rollback, that's revert; different operation, different semantics.