pub fn plan_thread_drop(options: &ThreadDropOptions) -> ThreadDropDispositionExpand description
Pure preflight for heddle thread drop / drop_thread_silent.
Rules (matching CLI):
- Missing + current lane + no delete flag → refuse
- Missing + delete flag → proceed to delete command
- Missing otherwise → not found
- Found → drop plan (unmount if virtualized, remove checkout if present, abandon record, strip agents, optionally delete ref)