Function plan_capture 

pub fn plan_capture(
    valid: &[String],
    cached: &HashSet<String>,
    baseline: &HashSet<String>,
    max_per_pass: usize,
) -> CapturePlan

Decide what to capture, from state alone.

valid are the hashes currently valid in the nix store, cached the hashes the cache already holds, baseline the hashes that existed when the watcher started (empty for a full backfill).

A candidate is a path that is valid, not cached, and not in the baseline. Order is deterministic (sorted) so a bounded pass is reproducible rather than dependent on hash-map iteration order — an operator re-running a pass against unchanged state gets the same answer.