allow plan to be used as subagent and do not restrict the use of subagents

[aeschli]

No description provided.

[Copilot]

Pull request overview

This PR modifies the Plan agent configuration to enable it to be used as a subagent and removes restrictions on its use of subagents.

Changes:

• Removed infer: 'user' property from the base Plan agent configuration
• Removed agents: [] property that was preventing the Plan agent from using subagents

[digitarald]

Infer: @sbatten added switch_agent tool for the use case of invoking planning, which is the one we want to optomize for. Using planning as a sub-agent wouldn't a) use subagent for research for better results and b) not provide the handoff flow.

No custom subagents: Custom agents can have access to all kind of tools. If the user somehow has a custom agent for specific file operations, it can still be invoked ("Make a TDD plan … let me invoke the TDD agent, but its actually meant for writing tests") and execute or edit code while the plan mode is active.