Enum RoundDecision 

#[non_exhaustive]
pub enum RoundDecision {
    Continue(RoundAdjustment),
    Inject {
        content: Vec<ContentBlock>,
        adjust: RoundAdjustment,
    },
    Stop,
}

The per-turn steering seam, whole: the trait a host implements and every type its signatures make that host name.

Re-exported rather than wrapped, under the rule stated on CancellationToken — a mentra type basis’s surface asks a caller to write is a name basis re-exports, or the caller pins mentra in their own manifest to spell it. And like the token, a strategy is an identity rather than a value: TurnOptions::with_round_strategy hands mentra the caller’s own Arc, so a basis-owned mirror of RoundDecision would be a translation layer with opinions of its own — the opposite of a seam.

The set is exactly what implementing costs. RoundStrategy is the trait (spelled with async_trait, which basis already re-exports); RoundContext and RoundBoundary are its question; RoundDecision, RoundAdjustment, ReasoningChange and RoundToolResult are its vocabulary for answering. The last three are here because the vocabulary’s own signatures demand them: RoundDecision::inject takes ContentBlocks, RoundAdjustment::with_model a ModelInfo, and ReasoningChange::Set a ReasoningOptions — whose effort field an Effort converts into, so switching effort mid-run never names mentra’s own level enum. The decision a RoundStrategy returns at a round boundary.

Construct one with RoundDecision::proceed, RoundDecision::inject, or RoundDecision::stop for the common cases, or the variants directly to carry a RoundAdjustment.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Continue(RoundAdjustment)

Proceed with the default flow. At RoundBoundary::AssistantMessageCommitted this accepts the terminal message and lets the run return; at RoundBoundary::ToolResultsCommitted it advances to the next round. Any carried RoundAdjustment applies to subsequent rounds.

Inject

Do not end the run: append content as a corrective user turn and run another round. At RoundBoundary::AssistantMessageCommitted this prevents the run from returning. Any carried RoundAdjustment applies to that round.

Fields

content: Vec<ContentBlock>

Corrective content appended to the transcript as a user message.

adjust: RoundAdjustment

Model/reasoning override applied before the injected round.

Stop

End the run gracefully at this boundary, committing the transcript exactly as RunOptions::stop does. A stop request asserts nothing about whether the run produced a valid answer.

Implementations

impl RoundDecision

pub fn proceed() -> RoundDecision

Continue with no model/reasoning change.

pub fn inject(content: impl Into<Vec<ContentBlock>>) -> RoundDecision

Inject corrective context and run another round, with no adjustment.

pub fn stop() -> RoundDecision

Request a graceful stop.