Constant WORKTREES_REGISTRY_LOCK 

pub const WORKTREES_REGISTRY_LOCK: &str = "worktrees.lock";

Basename of the common-dir lock serialising linked-worktree registry mutations (worktree add/remove/prune), the branch-checkout guard + HEAD-write critical sections (checkout/switch, branch -d/-m), and gc’s freeze of the worktree set. Distinct from WORKTREE_LOCK, which guards ONE tree’s worktree/index state.

GLOBAL LOCK ORDER (SPEC-WORKTREE §4.3): a process that takes more than one of these MUST acquire in this order — worktrees.lock ≺ per-tree worktree.lock(s) ≺ refs-history.lock — or two multi-lock takers can stall each other until the 5s timeout.