Delegation guards

The delegation table and the model rules live in the igor skill (## Delegation). This file holds the guards behind them.

Write capability:

Explore and Plan are read-only. They cannot use Edit, Write or NotebookEdit. Never dispatch them for a task that must produce a file (report, design, plan, research note); use them only when the answer comes back in the reply text.
Prefer Spire's pinned read-only agents over Explore. Use scout or search for lookups.
Tasks that produce a file need a write-capable agent: general-purpose (omit subagent_type) or a pinned agent with Edit/Write (researcher, adept, athanor, planner, attacker, reviewer). Research that must produce a written report goes to researcher.

Sub-delegation:

Agent types without the Agent tool cannot spawn children: scout, search, researcher, planner, attacker, reviewer, Explore and Plan are safe leaves. general-purpose agents have the Agent tool and can sub-delegate: give them the leaf-brief line, or route fan-out work to athanor on purpose. Expect a second, differently-task-id'd notification only when you dispatched something allowed to fan out.

Add new agents and heuristics to the igor skill's table as they prove out.