Verify kickoff ancestry before the first edit

Kickoff automation is not proof that a feature branch or PR has the requested ancestry. This matters when work must start from a non-default integration branch, especially if the local checkout was already on another feature branch or the repository default differs from the requested PR base. The limit is that tools which explicitly pin both the starting commit and PR base may already enforce this invariant, but the read-only verification is still cheap.

Method: before the first code edit, fetch the requested base and verify all three surfaces independently: (1) the target base is an ancestor of HEAD, (2) target..HEAD contains only the expected kickoff commit(s), and (3) the PR reports the exact requested base and head. If any check fails, correct ancestry and retarget the PR before implementation; once real edits accumulate, disentangling inherited commits becomes riskier and noisier.

Evidence/example (2026-09-14, source: local git and GitHub PR metadata): during COR-4234 in e3-solutions/theft, a kickoff helper created the requested issue branch from the current local feature lineage and opened PR #873 against main even though delivery required staging. The mismatch was found before code edits. Rebasing the empty kickoff commit onto the fetched origin/staging commit and retargeting the PR produced the intended clean diff without discarding implementation work.