MechGen ABL ↔ SPINE bridge — the type-safe join.
MechGen's MechGen-parse --spine={profile,swarm,frame} emits SPINE-protocol-
shaped JSON (see MechGen/SPINE_COLLABORATION.md). This crate deserializes
those envelopes into the real spine-agentic types, so the mapping is
compile-checked here rather than matched only by field name on the
MechGen side. It is intentionally tiny: a few envelope structs + conversions.
The fact that an ABL agent's capabilities deserialize directly into
Vec<spine_agentic::AgentCapability> is the proof that the two capability
vocabularies line up.