Function execute_plane_batch 

pub fn execute_plane_batch(
    tracker: &mut FailureTracker,
    family: &str,
    work: impl IntoIterator<Item = PreparedWork>,
    operation: impl FnMut(&FullKey, &[u8]) -> Result<(), WorkerFailure>,
) -> Result<Vec<ProcessedFanout>, DedupError>

Runs a plane-worker operation once per full key and fans its disposition out to all paths sharing the key. operation is where the worker hashes, puts, derives, and publishes; this coordinator never runs on a watcher thread.