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feat(subagent): continuable background subagents

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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.
This commit is contained in:
Dudu-0223
2026-07-23 17:07:38 +08:00
committed by imccyu
parent 76ff841279
commit 99a778d63f
83 changed files with 3167 additions and 627 deletions
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15
packages/subagent/subagent-inprocess/README.md
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@@ -2,7 +2,7 @@
English | [中文](README.zh.md)
This package is the shared run driver for the two in-process providers. Spawn passes no session seed; fork passes the parent's completed-turn prefix. Everything else—depth, child creation, optional child customization, result reading, cancellation, and disposal—has one implementation here.
This package is the shared run driver for the two in-process providers. Spawn passes no session seed; fork passes the parent's completed-turn prefix. Everything else—depth, child creation and cold resume, optional child customization, result reading, cancellation, strict steering, and disposal—has one implementation here.
## Start contract
@@ -11,21 +11,27 @@ This package is the shared run driver for the two in-process providers. Spawn pa
The driver follows this sequence:
1. Validate the parent depth and optional absolute `maxDepth`, then derive child depth as parent depth plus one and persist it in the child session header.
2. Call `parent.ctx.agents.create` directly, passing the required request signal into the factory's creation transaction.
3. During that transaction's unpublished setup window, install the requested persona, tool restriction, and structured-output runtime.
2. Call `parent.ctx.agents.create` directly, passing the required request signal into the factory's creation transaction. A continuable request publishes exactly `request.continuation.sessionId` instead of an internally minted id.
3. During that transaction's unpublished setup window, install the requested persona, tool restriction, structured-output runtime, and — for a continuable request — the one-shot `agent/pre-step` contribution that appends the `subagent/descriptor` event after the initial `turn/start` and before the first request, so the descriptor reaches persistence with that turn's flush.
4. Publish the child, retain the returned `AgentHandle`, and drive one task with `child.followup(prompt)` followed by `child.whenIdle()`.
5. Read the child's own last assistant message and latest message-triggered turn reason, excluding any fork seed and later between-turn records.
5. Read the child's own last assistant message and latest message-triggered turn reason, excluding any fork seed and later plugin-owned zero-step turns.
The child gets the parent's working-directory/session lineage and inherits the parent provider, model, and output-token cap unless `request.agentOptions` overrides them. It gets a fresh flat registration scope: parent ownership does not import parent tool restrictions or establish an authority subset.
When the optional sandbox-policy or approval service is composed, the driver snapshots the parent's explicit session override before child creation and appends a source-tagged event during unpublished setup, after any fork history and before session publication. It never copies deployment defaults or one-shot grants; later child switches still win. See the [policy-inheritance decision](../../../.agents/notes/implemented/feature/2026-07-25-subagent-policy-inheritance.md).
## Cold resume
`resumeInProcessRun(request): Promise<SubagentRun>` reconstructs a persisted continuable child under the live parent's scope: `parent.ctx.agents.resume` loads the child's own transcript through persistence (a fork child's log already contains its seed prefix, so resume never re-forks current parent history), the descriptor's persona and tool filter are reapplied in the unpublished setup window, and the descriptor's `agentProvider`/`agentModel` become the runtime options. The persisted header stays authoritative for lineage and the delegation-depth floor. The activation's result boundary is the resumed log length: only this follow-up turn's output becomes the run result. Publication, abort handoff, and disposal follow the same contract as start.
## Cancellation and ownership
The required request signal covers both startup and the live run. Before publication, `AgentCreationTransaction` observes it, rolls back, and rejects. The factory detaches that creation-only listener before returning; the driver immediately checks the signal once more before installing a minimal live-run listener, closing the handoff race. After publication, abort cancels the child.
After fulfillment, the caller owns the run. Provider-plugin unload does not revoke it. `dispose()` removes the live abort listener, records cancellation, and delegates to the returned `AgentHandle.dispose()`, whose memoized quiescence transaction stops the loop, removes the agent and session, and unwinds scoped registrations. Cancellation owns every non-completed in-flight outcome and reports `aborted`; an already-completed turn remains completed.
Runs expose the strict `steer` capability: a synchronous `AgentStatus.running` check and `Agent.steer()` call share one frame, so delivery joins the observed turn or throws. The Agent-level idle fallback (queue and start a new turn) is deliberately not reachable through the run — that would start an untracked turn after the run's result was read.
## Spawn and fork inputs
`InProcessRunOptions` is `{ seed?: SessionEvent[] }`. Spawn omits it. Fork supplies a balanced completed-turn prefix and records its length so the result reader never mistakes a seeded parent message for child output.
@@ -110,5 +116,4 @@ Append-only; newly visible content follows the reusable request prefix and does
## Known Limitations and Deferred Work
- **Runs expose no `sendMessage`/`resume`** — the optional runtime capabilities are absent on in-process runs.
- **Structured capture accepts the `defineTool` schema subset only** — unsupported JSON Schema constructs fail before the child is created; a provider needing a broader schema vocabulary requires a different runtime.