First step toward making mutation events first-class nodes in the
correlation graph. Today the graph silently reflects post-mutation
state with no marker of the transition; this helper lands the
emitter the mutator and deploy paths will call.
- decnet/mutator/events.py: emit_decky_mutated(bus, *, decky,
old_services, new_services, trigger, actor=None, log_path=None)
writes an RFC 5424 line (service=mutator, hostname=<decky>,
MSGID=decky_mutated, SD params for old/new services + trigger +
optional actor) to DECNET_INGEST_LOG_FILE, then fire-and-forget
publishes on decky.<id>.mutation. Either side failing is soft —
the other path still completes.
- MutationTrigger Literal covers creation, retirement, scheduled,
operator, behavioral, healer, federation. Reserved values for v2/v3
(behavioral + federation) stay nullable so the schema is stable.
- decnet/bus/topics.py: DECKY_MUTATION constant + decky_mutation(id)
builder. Distinct from DECKY_STATE ("current shape") because a
mutation is a transition event, not a steady-state snapshot.
- Empty-set symmetry: creation emits old_services=[], retirement
emits new_services=[]. Every decky lifecycle becomes a well-formed
fold sequence on the correlator side.
- 4 new tests: FakeBus + correlator parser round-trip; creation and
retirement empty-set cases; bus=None still writes syslog;
unwritable log path doesn't block bus publish. 95 tests green
across test_mutator + tests/bus.