Feature request: Per-agent model selection in Swarm

Currently, Swarm appears to use the session's configured model for all agents. It would be useful if each agent (or role) could use a different model.

Example:

• "coder" → fast coding model
• "reviewer" → stronger reasoning/review model

This would enable workflows such as:

• Fast code generation + high-quality review
• Lower cost by assigning expensive models only where needed
• Easier multi-agent orchestration without manually managing separate sessions

A possible configuration could look like:

[swarm.roles.coder]
model = "..."

[swarm.roles.reviewer]
model = "..."

or any equivalent mechanism for assigning a model when spawning an agent.

Is this something you'd consider adding? If not, what is the recommended way to run Swarm with different models for different agent roles?

No files or tests are named. Start by tracing how Swarm reads the session's model and how it spawns agents, then compare that path with the proposed per-role configuration. Done means distinct roles can select distinct models, with a documented configuration or spawning mechanism and coverage for the example workflow.