Class CommitLock

crates/flowtrace-cli/src/git.rs:22–24

Process-wide lock around any write to the underlying git repo. Why: under the single-repo layout, multiple trace folders share one outer `.git`. Two concurrent `trace` processes will both: (a) write `index.lock` at the same time (libgit2 returns `Locked`), and (b) race HEAD between `revparse` and `commit` (libgit2 returns "current tip is not the first parent"). libgit2's per-process index lock al

/// out of scope. Idempotent: re-entering from the same process serializes
/// via the OS, which is what we want.
struct CommitLock {
    _file: std::fs::File,
}

impl CommitLock {
    fn acquire(repo: &Repository) -> Result<Self> {