Function check_memory_base_sha256 

fn check_memory_base_sha256(
    filename: &str,
    base: &str,
    current: Option<&str>,
) -> Result<(), String>

The optimistic-concurrency check behind base_sha256 (SPEC_MEMORY_FOLLOWS_THE_AGENT_2026_09_24.md §2.4): Ok when current still hashes to base, otherwise an error starting conflict: — the marker the frontend keys its “changed since you started editing” banner on. A file that no longer exists is a conflict too: the draft’s base is gone, and silently re-creating it would undo someone else’s delete.