create_agent tool: create static subagent from conversation

[ludusrusso]

Parent PRD

#34

What to build

A new create_agent tool available to the main agent. During conversation, the user can ask the main agent to create a new static subagent. The main agent crafts the SOUL content (acting as interviewer) and calls this tool to persist the agent.

No bootstrap interview flow — the main agent IS the interviewer.

Acceptance criteria

• create_agent tool with input: name (required), soul (required), model (optional)
• Creates directory structure at agents/<name>/ via Home.Agent()
• Writes provided soul content to SOUL.md
• Writes config.yaml with model (or empty for global default)
• Creates empty crons/ and cron-results/ directories
• Returns confirmation message to caller
• Validates agent name (alphanumeric + hyphens)
• Error if agent already exists
• Tests: directory creation, file contents, validation, duplicate name

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 12 (create agent from conversation)