The mutation-event stream landed this session closes the "deckies are
atomic nodes" gap for service-list changes, but substrate identity is
really ``(service, implementation_fingerprint)``. A base-image
rebuild that rotates OpenSSH 8.4 → 9.2 without changing the service
list is invisible to the correlation graph today because the prober's
dedup set is in-memory and per-run — no cross-run diff, no
"fingerprint changed" event.
DEBT-032 documents the required piece: a per-(decky, service,
probe_type) persistence layer + diff-on-change emission, with the
correlator's existing mutation-marker interleaving pattern as the
model for fingerprint markers. A mutation-vs-fingerprint divergence
detector then falls out of the data model for free — fingerprint drift
without a preceding mutation ⇒ substrate_divergence finding.