delegate_to_agent tool: delegate to static subagent by name

[ludusrusso]

Parent PRD

#34

What to build

A new delegate_to_agent tool available to the main agent (and other static agents). Looks up a static agent by name, loads its SOUL/MEMORY/config, creates a provider from the agent's model, runs a full agent loop with the agent's system prompt and tools, and returns the final text response.

The delegated session does NOT persist memory (one-shot delegation, not a full session).

Acceptance criteria

• delegate_to_agent tool with input: agent_name (required), prompt (required)
• Looks up agent by name via Home.Agent()
• Loads agent's SOUL.md, MEMORY.md, and config.yaml
• Builds system prompt using agent's identity (same as agent.Prepare flow)
• Resolves agent's model via provider Container
• Runs agent loop with agent's system prompt and tools
• Returns final text response to caller
• Does NOT run memory curation (no Finalize)
• Error when agent doesn't exist
• Tests with mock provider and temp agent directory

Blocked by

• Blocked by Home.Agent: directory scaffolding for static subagents #41 (Home.Agent directory scaffolding)
• Blocked by Agent config.yaml: parsing and model resolution #42 (agent config.yaml parsing)

User stories addressed

• User story 11 (delegate to static agent)