Record the final-state architecture: the five-step loop (Discuss → Plan →
Execute → Verify → Ship) plus shared-infrastructure skills are the privileged
host/core; every other feature is a Capability (plug-in) selectable at install
and toggleable after restart, attaching through ~12 Loop Extension Points.
Adds docs/adr/857-capability-system.md (Status: Proposed) capturing the eight
resolved design decisions, the resolved design details (extension points,
contribution merge, declaration shape, runtime descriptor, deferred trust gate),
alternatives, consequences, and a six-phase rollout. Records the new domain
terms in CONTEXT.md: Capability, Capability Registry, Loop Extension Point,
Runtime Capability.
Runtime/CLI support is itself a Capability (role: runtime) — Claude Code, Codex,
Antigravity tier-1; the seam is declarative-over-primitives so third-party CLI
support lands later as an additive loader, no rework.
Closes#857
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
