99a778d63f
Implement the continuable background subagents RFC: a durable child session with a series of Task-backed activations, each disposing its run before the Task settles. - dsh-subagent: rename SubagentRun.sendMessage to strict steer, drop run-level resume, add SubagentProvider.resume dispatch via SubagentService.resume, the continuation start field, and the versioned model-hidden subagent/descriptor session event. - dsh-subagent-inprocess/-spawn/-fork: publish the control-allocated child id, append the descriptor inside the initial turn, implement cold resume from the child's own transcript under the live parent scope, and strict running-only steer. - dsh-subagent-control (new): SubagentControlService owning stable child ids, descriptor snapshot/fold/authorization, Task-backed activation with settle-then-dispose ordering, the process-local active-run association, and steer-or-resume sendMessage routing. - dsh-tool-subagent: background route branches on the provider's resume capability (continuable via the control service; one-shot task for ACP), returning both child and task ids. - dsh-tool-subagent-control (new): the globally named send_message tool rendering steered/started routes. Keyless coverage spans Task ownership and disposal ordering, running delivery, cold follow-up, descriptor rejection and rollback, known-id reconstruction, kill during lookup, admission races, and a new subagent-continuable ACP snapshot scenario.
@deepseek-ai/dsh-tool-subagent-control
The globally named send_message tool: a thin adapter over ctx.subagentControl.sendMessage(). Provider-bound @deepseek-ai/dsh-tool-subagent instances register distinct delegation tools per transport; this separately loaded package registers the one shared control tool, so multiple delegation tools never register duplicate global controls.
The tool performs no lifecycle routing. The control service decides between live delivery to the running activation's existing Task and a fresh Task that cold-resumes the durable child; the tool renders which route was taken and the relevant Task id. A control-service throw becomes an errored tool result stating the message was not delivered.
Model Experience
Tool schema
What the model sees
The generated send_message schema: subagent_id and message, with delivery-or-continue semantics and the task_output collection path described.
Token effect
Fixed schema cost per parent request.
KV Cache effect
Prefix-stable; the schema does not change at runtime.
Delivery result
What the model sees
message delivered to running task <taskId> when the message joined the running activation, or message started task <taskId> continuing subagent <subagent_id> when it cold-resumed the child. Failures are errored results whose message states the message was not delivered (unknown or foreign child, ownership conflict, settlement race, no live-delivery capability).
Token effect
One short acknowledgement per call; the child's response enters parent history only when collected through task_output or injected by the task completion notice.
KV Cache effect
Append-only; newly visible content follows the reusable request prefix and does not invalidate existing KV-cache entries.
Known Limitations and Deferred Work
- A delivered message has no independent result — its effect is reflected in the current Task's eventual result; only a started follow-up owns a fresh Task result.
- Delivery can lose timing races — a message racing task settlement, cancellation, or cleanup fails explicitly rather than falling through to cold resume; the model retries after the task settles.