host method
Builds the engine leaf Seed for the eligible mount.step — a
CapabilityHost in the default registry (Track E), a recording fake in
Track D tests. NEVER a Seed the author authored; the carrier is
engine-private (ADR-0008 D2).
Implementation
@override
Seed host(StepMount mount) =>
FakeCapabilityHost(registry: this, mount: mount, key: mount.key);