## What changed
- Add `supports_reasoning_summary_parameter` to model metadata, defaulting to
`true` for backward compatibility.
- Omit `reasoning.summary` and its summary-delivery stream option when the
selected model does not support the parameter.
- Apply the capability of the final selected model when a spawned agent uses a
different model.
## Testing
- Cover unsupported models in regular requests and spawned-agent model
overrides.
GitOrigin-RevId: 72b783799fc0685cef1501ef2dbf62d1308ceead