Merge master into fix/subagent-stack-end-result

packages/core/agent/README.md

@@ -62,7 +62,7 @@ The handle every plugin programs against:
 
 - `agent.send(message, options)` — the one delivery primitive over the (`target` × `wakeup`) matrix. `message` is an already identified, frozen `UserMessage`; callers normally create it with `createUserMessage()` before routing begins. `SendOptions` owns only the `target` and `wakeup` policy. Each accepted FIFO occurrence receives its own `InboxItemId`, even when callers reuse a `MessageId`; `agent/inbox/enqueue`/`update` and the terminal `dequeue` or `discard` carry that complete `InboxItem`. `target: 'next-turn'` queues one independent FIFO item that, if admitted, becomes the sole ordinary prompt in its turn. `target: 'next-step'` with `wakeup: true` submits steering, while `target: 'next-step'` with `wakeup: false` injects durable context without running the model. The [one-send-one-turn Agent Note](../../../.agents/notes/implemented/simplification/2026-07-17-one-send-one-turn.md) owns the turn rationale.
 - `agent.reserveTurnAdmission()` — synchronously reserve the idle boundary before any queued waking prompt can claim its turn. An accepted prompt, including a same-tick pending wake, has right of way and makes reservation return `undefined`. Later sends keep their ordinary IDs, FIFO placement, and wakeup facts while held; `acceptsNextStep` remains false, `inject()` is not withheld, `whenIdle()` counts the reservation as activity, and the returned release is idempotent. This narrow coordination capability lets standalone durable operations such as manual compaction finish and flush before queued prompts derive from the session.
-- `agent.updateInbox(itemId, action)` — synchronously edits or removes one still-pending queued occurrence. Edit keeps its `MessageId`, `InboxItemId`, source, and FIFO position while replacing frozen content; remove emits the occurrence's terminal discard. Steering and claimed occurrences return `not-found`.
+- `agent.updateInbox(itemId, action)` — synchronously edits, removes, or strictly steers one still-pending queued occurrence. Edit keeps its `MessageId`, `InboxItemId`, source, and FIFO position while replacing frozen content; remove emits the occurrence's terminal discard. Strict steer requires `acceptsNextStep`, ends the queued occurrence, and accepts the same immutable message as a new steering occurrence with a new `InboxItemId`; a closed window returns `steer-unavailable` without mutation. Pending steering and claimed occurrences return `not-found`.
 - `agent.followup(input)` — the `next-turn`/wakeup preset of `send()`: queue an ordinary follow-up turn and wake the driver.
 - `agent.steer(input)` — the `next-step`/wakeup preset: submit one identified message and receive its `SteeringReceipt`. During prompt admission or an open turn, the message stages for the next safe request boundary without dispatching `agent/prompt-submit`; outside that acceptance window, it becomes a woken queued prompt. `receipt.outcome` resolves `admitted` with the turn and step only after the loop logs the message, captures it in immutable request history, and commits `step/start`. A turn-concluding tool result, broad cancellation, disposal, or pre-admission failure resolves it `rejected`; `cancel(..., { keepInbox: true })` and non-terminal routing preserve pending delivery. Reliable callers await the receipt, while best-effort UI steering may ignore it.
 - `agent.inject(input)` — the `next-step`/no-wakeup preset: append model-facing context without running the model; the next request sees a verbatim user-role message whose provenance is carried by the required `input.source`. During prompt admission or an open turn, injection waits in the outbox for the next safe boundary. Outside that acceptance window, it appends immediately without opening a turn; a context-only admission batch takes this fallback if admission closes without a turn, while context staged beside steering remains pending with it. Persistence reacts to `session/event` independently. Injection emits no `agent/inbox/*` event.