Cross-platform file locks for the index file watcher, using std’s native File::{lock, try_lock, unlock} (stable since Rust 1.89 — flock on Unix, LockFileEx on Windows, no
external crate). Two distinct locks coordinate writers without an HTTP daemon:
Background file watcher: keeps the active index (and dirty-worktree overlay) fresh as files
change, so graph/symbol queries reflect uncommitted edits without waiting for a commit.