v1.9.0

v1.9.0 — instructions that travel: registries, signatures, envelopes

An instruction document arriving from elsewhere and still being trustworthy:
OCI artifact pull, end-to-end encrypted envelopes (age v1 + JWE compact),
§7.6 wire verification of publisher-signed registry documents, registry
consumer alignment (versionId apply boundary + bindings), and the §7.7
freshness watch that refuses new work when authorization goes stale.

The reference parser is published as agentd-instruction (MIT OR Apache-2.0)
so other implementations of the Instruction Specification link it rather than
reimplement it.

Behaviour change: a machinery block of an identified kind now requires its
name ATTRIBUTE — see the CHANGELOG.