src/engine/bare/model_switch.rs

This file gives you the atomic mid-session model change: a ModelSwitch builder returned by agent.switch_model(name) and executed by .apply().

Key items

switch_model(&mut self, model) hands you a ModelSwitch that holds &mut BareLoop and is deliberately not Clone.

Call .with_context_window(tokens) when your new model’s window differs from the old one.

.apply() runs the sequence: validate name, poison preflight, client.set_model, optional window update, breaker reset plus original-model update, then on_model_switched. A false from set_model aborts with nothing changed.

Behavior notes

The switch is all-or-nothing. A rejection at any step leaves your loop exactly as it was.

It requires client support through ApiClient::set_model. All shipped clients have it, and the trait default rejects.

Your fallback breaker resets, because old-model failure counts are meaningless for the model you just chose.

Nothing gates this behind “configure before run”, since mid-session use is the design. Prefer switching between runs over during one when you can.

Deep dive: Model switch.