A second tbd_ship for the same change no longer errors on "branch exists": CreateBranch conflict is tolerated, and if a PR is already open for the head, CreatePullRequest's conflict/validation error resolves it via ListPullRequests (matching head.ref). Identical file content on the branch skips the write, so a resume produces no redundant empty-diff commit. Then the same CI gate runs and merges if now green — so "poll or re-invoke" (the #40 UX) actually works. Test: TestTBDShip_Resume_ExistingBranchAndPR (branch+PR exist, content unchanged → no write, merges when green). First-call paths unchanged. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>