docs(agent): require frontier-led delegation workflow

Make bounded lower-cost implementation delegation the default for feature work, while keeping architecture, integration, review, and final verification with the frontier lead.

Require explicit disclosure when cheaper-model selection is unavailable and prohibit presenting generic agents as Luna.

AGENTS.md

@@ -10,6 +10,20 @@ creates the implementation plan, decomposes work, assigns non-overlapping file
 ownership, reviews every delivered change, integrates the result, and performs
 the final verification.
 
+This lead/delegate/review sequence is the required default for feature work,
+not an optional optimization. Before writing feature implementation, the lead
+must identify bounded coding slices and dispatch them to cheaper coding agents
+(for example Luna) whenever the orchestration environment exposes those models.
+The frontier lead should normally restrict its own edits to shared contracts,
+cross-cutting or data-loss-sensitive logic, integration fixes, and work that is
+too tightly coupled to delegate safely.
+
+If agent spawning is available but cheaper-model selection is not exposed, the
+lead must say so explicitly before implementation. It must not imply that a
+generic spawned agent is Luna or otherwise cheaper. In that environment the
+lead may use available agents for bounded parallel work, but should explain the
+limitation and still retain the same ownership, review, and verification duties.
+
 Delegate bounded coding tasks to cheaper/lower-cost agents whenever the
 orchestration environment supports model selection. Coding agents should
 implement clearly specified slices; they should not independently redefine the