v0.21.4

Added

• deploy.BundleDigest — the bundle-tree digest Candidate.Digest requires,
  now callable. Nothing may be installed without that field, and the only
  implementation of it lived unexported inside the package, so every consumer
  packaging its own application hand-copied the walk, the field order, and the
  length-prefixed encoding out of daemonkit's source: captain-hook, fusekit's
  holder, and cc-notes each carried one. Three transcriptions of a hash are
  three chances to diverge from the value Install and Supersede re-derive
  from the bytes themselves, and a divergence surfaces only as an
  ErrConflict refusal at install time. The digest is byte-identical to what
  the package has always computed — a candidate digested by a hand-copy and
  one digested by the export are the same value, so records already stored
  against a copy stay valid — and one fixture tree's digest is now pinned to a
  constant, so the encoding cannot drift without a test saying so.