Struct ModelSelection 

pub struct ModelSelection<'a> {
    pub prompt: &'a Message,
    pub history: &'a [Message],
    pub request_patch: Option<&'a RequestPatch>,
    pub previous_model: Option<&'a ModelHandle>,
    pub default_model: &'a ModelHandle,
    pub selected_model: &'a ModelHandle,
}

Available on crate feature agent only.

Model-selection event resolved after completion-call hooks and before request preparation.

The runner default is the first candidate. A HookStack threads every ModelSelectionAction::Select into later hooks in registration order, so selected_model always reflects all earlier decisions for this event.

Ordering per CallModel step: completion-call hooks resolve first; only if they proceed does this event fire, carrying the merged RequestPatch in request_patch; only after selection resolves does request preparation run against the selected model’s captured ProviderCapabilities, and only then is the attempt issued. Selection therefore runs once per CallModel step whose completion-call hooks proceed — including model-turn retries and post-tool calls — and never after a completion-call stop.

Selection is synchronous, local, and non-blocking: a hook may read and write the run Scratchpad, but must not perform blocking I/O. In-flight attempts never rebind — the selected handle is cloned into the prepared attempt and executes it to completion.

previous_model reflects issued attempts only: it advances immediately before the selected model’s unary or streaming operation is invoked, so a provider attempt that returns an error still counts, while a completion-call stop, a selection stop, or a request-preparation failure does not. An extraction or run default set via using_model(...) is the default candidate for every retry, not a hard pin: selection hooks may override it on each retry.

Fields

prompt: &'a Message

Prompt for the pending model call.

history: &'a [Message]

Canonical history visible to the pending model call.

request_patch: Option<&'a RequestPatch>

Merged per-turn request patch from this step’s completion-call hooks (in hook registration order), when any hook patched the request.

previous_model: Option<&'a ModelHandle>

Model that executed the preceding issued attempt in this run, if any.

default_model: &'a ModelHandle

Runner default used as the initial candidate for this call.

selected_model: &'a ModelHandle

Candidate after all earlier model-selection hooks.

Implementations

impl<'a> ModelSelection<'a>

pub fn new( prompt: &'a Message, history: &'a [Message], request_patch: Option<&'a RequestPatch>, previous_model: Option<&'a ModelHandle>, default_model: &'a ModelHandle, selected_model: &'a ModelHandle, ) -> ModelSelection<'a>

Construct a ModelSelection event from its parts.

Provided so that custom model-selection routers can be unit-tested outside this crate without restating every field.

Trait Implementations

impl<'a> Clone for ModelSelection<'a>

fn clone(&self) -> ModelSelection<'a>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a> Copy for ModelSelection<'a>