Execute agent

How a durable turn handles overlap. reject (default) answers CONVERSATION_BUSY naming the occupant execution, its phase, and a Retry-After; supersede cancels and replaces; queue runs afterward; steer durably appends new user-message deltas to the same execution at a safe boundary, attaches through the host’s slot claim when the host has not started yet, or starts the next execution if completion wins. Steer requires a conversationId, preserves configuration and authority, cannot combine with coalesce, and rejects unsupported lanes. auto sends the same user-message deltas as steer and lets a classifier choose: while a turn runs, a message that belongs to it steers and an independent one queues as the next turn; with nothing running it is an ordinary turn with no route report. A routed or downgraded answer reports the route in X-Runtype-Busy-Message-Route / -Source (plus -Probability and -Model when the classifier answered) and, on JSON bodies, busyMessageRoute. Where auto cannot route (in-process execution, stored history, no conversationId, coalesce, Prefer: respond-async) it keeps the default admission and reports source disabled. Other policies remain ignored on in-process execution.

Send true to fold this request into an already-pending turn for the same conversation instead of starting a second one. The response is the pending execution. Any other value (or omitting the header) starts a new turn.

Caller-chosen key that makes admission idempotent: a retry with the same key returns the ORIGINAL execution rather than starting a second turn, and consumes no additional quota. Scoped to the durable lane.