Verify Launchplane merge-train branch cleanup

[cbusillo]

Summary

During branch hygiene in cbusillo/codex-skills, several old Launchplane train batch branches remained on GitHub:

launchplane/train/cbusillo/codex-skills/main/merge-train-batch-cbusillo-codex-skills-main-575bb16efbeb0e55
launchplane/train/cbusillo/codex-skills/main/merge-train-batch-cbusillo-codex-skills-main-7d4767c789b5fe2f
launchplane/train/cbusillo/codex-skills/main/merge-train-batch-cbusillo-codex-skills-main-9a462ec25c45210b
launchplane/train/cbusillo/codex-skills/main/merge-train-batch-cbusillo-codex-skills-main-a29abfe7ff6217d4
launchplane/train/cbusillo/codex-skills/main/merge-train-batch-cbusillo-codex-skills-main-d6efe6b170017978

These refs are from May 13-20, 2026. They may predate current cleanup behavior, but we should verify Launchplane train branch cleanup is implemented and covered.

Questions To Answer

• Does current Launchplane delete train batch branches after successful merge/train closeout?
• If yes, when did that behavior land, and do these old refs predate it?
• If no, add cleanup after successful train completion and safe cancellation paths.
• Should Launchplane provide an audit/cleanup command for old train refs that are no longer active?

Acceptance Criteria

• Current expected behavior for train branch cleanup is documented or tested.
• Successful merge-train completion removes no-longer-needed train batch refs, or records why they must remain.
• Stale historical train refs can be identified safely without confusing them with active trains.
• If this was already fixed after these refs were created, close this with the version/PR/date that fixed it.