Merge remote-tracking branch 'origin/worktree-agent-scope-design' into codex/package-readme-limitations-audit-20260712
# Conflicts: # packages/core/scope/README.md # packages/session-persistence/session-persistence-jsonl/README.md # packages/session-persistence/session-persistence-sqlite/README.md # packages/subagent/subagent-acp/README.md # packages/subagent/subagent-fork/README.md # packages/subagent/subagent-inprocess/README.md # packages/subagent/subagent/README.md # packages/subagent/tool-subagent/README.md # packages/support/invariants/README.md # packages/support/subagent-mock/README.md # packages/workflow/workflow-workerthread/README.md # packages/workflow/workflow/README.md
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# @deepseek-ai/dsh-subagent
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The **subagent seam**: an abstract `SubagentService` (`ctx.subagents`) for an agent delegating work to another agent. A *subagent* is a child agent; a `SubagentProvider` is one transport for running it.
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The subagent seam lets one agent delegate work to a child through a named provider. Callers use one service API (`ctx.subagents`); providers decide whether the child runs in this process, in another process, or through a future transport.
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This package is the interface third of the capability seam, split so each concern evolves (and swaps) independently:
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## Package roles
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The family separates the stable interface from implementations and model-facing tools:
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| Package | Role |
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|---|---|
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| `@deepseek-ai/dsh-subagent` (this) | the interface: registry service + vocabulary types |
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| `@deepseek-ai/dsh-subagent-spawn` | an implementation: fresh in-process child |
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| `@deepseek-ai/dsh-subagent-fork` | an implementation: in-process child seeded from the parent's log |
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| `@deepseek-ai/dsh-subagent-acp` | an implementation: ACP client driving another process |
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| `@deepseek-ai/dsh-tool-subagent` | the model-facing tool over `ctx.subagents` |
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| `@deepseek-ai/dsh-subagent` | Provider registry, request/result types, and lifecycle events. |
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| `@deepseek-ai/dsh-subagent-spawn` | Fresh in-process child. |
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| `@deepseek-ai/dsh-subagent-fork` | In-process child seeded with completed parent turns. |
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| `@deepseek-ai/dsh-subagent-acp` | Fresh out-of-process ACP child. |
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| `@deepseek-ai/dsh-tool-subagent` | Model-facing tool over one configured provider. |
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Unlike the bash seam (one executor per context, second load throws), **multiple providers coexist** here. Each registers under a unique name and a caller picks one by name — the shape mirrors the LLM adapter registry (`LlmService.registerAdapter`), not the single-service bash executor. This is the requirement that rules out the bash shape: an agent may want an in-process child for a cheap subtask and an out-of-process ACP child for an isolated one, in the same runtime.
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Multiple providers may coexist under different names. This lets a deployment expose, for example, a cheap in-process child and an isolated ACP child without changing the service contract.
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## Service API (`ctx.subagents`)
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## Service API
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| Member | Semantics |
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`SubagentService` has four main operations:
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| Member | Meaning |
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|---|---|
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| `registerProvider(provider)` | Register a frozen acceptance snapshot under `provider.name`; later caller mutation cannot change registry behavior or HMR cleanup, while `start` stays bound to the original provider receiver. Throws `SubagentError('DUPLICATE_PROVIDER')` on a name clash. Effect-scoped (HMR-safe); returns the disposer. |
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| `getProvider(name)` | Look up the frozen registry snapshot (`undefined` if absent). |
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| `list()` | Registered provider names (insertion order). |
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| `start(name, request)` | Resolve the provider (`NO_PROVIDER` if absent), validate every requested START-TIME capability (`UNSUPPORTED_CAPABILITY` for the first unmet one — before any child is created), then delegate to `provider.start`. Emit `subagent/start` only after `run.started` fulfills and the paired `subagent/end` after that started run settles; a pre-publication readiness rejection emits neither. |
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| `registerProvider(provider)` | Register one trusted same-process implementation by name. Registration is effect-scoped; removing it prevents new starts but does not revoke runs already returned to callers. Duplicate names fail loud. |
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| `getProvider(name)` | Return the provider, or `undefined` when absent. |
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| `list()` | Return provider names in insertion order. |
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| `start(name, request)` | Validate requested capabilities and semantic values, then await the provider until a real child is ready. Fulfillment returns a holder-owned `SubagentRun`; rejection means the provider has already cleaned every partial startup resource. |
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## Capabilities: two kinds, discovered two ways
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`SubagentStartRequest.signal` is required and is the canonical cancellation channel. An abort before publication makes `start()` reject after rollback; an abort after publication cancels the live child. The request may also select a model, require structured output, cap delegation depth, restrict child tools, or set a child persona.
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- **Start-time features** (`outputSchema`, `depthLimit`, `toolFilter/persona`) are a static `provider.capabilities` descriptor, checked by the service BEFORE a run exists. A request that needs one the provider lacks is **rejected loud** (`UNSUPPORTED_CAPABILITY`), never accepted-then-ignored.
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- **Runtime features** (steering, resume) are **optional methods** on `SubagentRun` (`sendMessage?`, `resume?`). The method's presence IS the capability; TS narrowing is the discovery mechanism — a consumer cannot call an absent method without narrowing first, so there is no silent degradation path.
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Same-process requests, descriptors, results, and event payloads are trusted typed values borrowed as immutable. The service does not clone or freeze them; serialization and hostile-input validation belong at actual process, worker, persistence, and model boundaries.
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Beside `capabilities` sits one DESCRIPTIVE fact, not validated by the service: `provider.inheritsParentContext` — whether a child sees the parent conversation (`fork`: true — seeded with the completed-turn prefix; `spawn`/`acp`: false). The model-facing consumer (`dsh-tool-subagent`) derives truthful tool wording from it.
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## Capabilities
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## Run lifecycle
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Start-time features are advertised in `provider.capabilities` because the service must reject an unsupported request before child creation:
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`provider.start(request)` returns a `SubagentRun`: a handle with `started` (the publication/readiness promise), `result` (the terminal outcome), `cancel()`, `dispose()`, and the optional runtime methods. `started` resolves only after the provider has established a real child and rejects if the attempt fails or is cancelled first. `result` resolves with a `SubagentResult` (`output`, optional `structured`, `stopReason`) — it does **not** reject on a child-level failure (a model/transport failure resolves with `stopReason: 'error'`), so the consumer maps a non-`completed` reason to an `isError` tool result. The consumer MUST `dispose()` on every path (success, error, abort) to reach child quiescence and avoid leaking an idle child / session.
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- `outputSchema` — enforce a structured final result.
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- `depthLimit` — enforce `maxDepth`.
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- `toolFilter` — apply the requested child tool restriction.
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- `persona` — apply a per-child persona.
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The service also announces provider lifecycle: `subagent/provider-added` (the frozen registry snapshot) fires after a registration and `subagent/provider-removed` (the accepted name) after an unregistration, so a consumer deriving state from a named provider (the model-facing tool wording) mirrors registry membership instead of assuming load order — the cordis Loader starts sibling plugins concurrently, so "listed earlier" does not mean "registered earlier". Run lifecycle is gated by provider readiness: `subagent/start` (payload `SubagentRunInfo`) fires only after `run.started` fulfills, and `subagent/end` (payload `SubagentRunEndInfo`) fires only for that announced run; readiness rejection emits neither. For spawn/fork, the start listener can resolve the published child via `ctx.agents.get(info.id)`; a remote provider need not have a local registry entry. Both events are **observe-only** plain emits. The service observes `result` immediately even while readiness is pending, clones its output before the caller can mutate it, and buffers that end payload until start has fired; a rejecting result cannot become an unhandled detached promise, start always precedes end, and a listener cannot corrupt the caller's result. `subagent/end` carries the cloned output as `lastAssistantMessage` on the settle path and omits it on infrastructure rejection. Any run-affecting decision is out of scope for this observe-only surface.
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Runtime features are optional methods on `SubagentRun`: `sendMessage?` steers a live child, while `resume?` asynchronously creates a continuation run. Method presence is the capability check.
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`inheritsParentContext` is descriptive rather than enforceable. It says only whether the child sees completed parent conversation history (`fork` does; `spawn` and ACP do not), not whether it inherits tools, services, or authority.
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## Ownership and lifecycle
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`provider.start(request): Promise<SubagentRun>` is the ownership-transfer boundary. Before fulfillment, the provider owns setup and must cancel, roll back, and quiesce partial resources on every failure. After fulfillment, the caller owns the run and must call `dispose()` on every path.
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`SubagentRun.result` resolves to `{ output, structured?, stopReason }`. Child-level failures resolve with a non-`completed` reason; only an infrastructure fault that the seam cannot represent may reject. `dispose()` is idempotent, cancels remaining work, and waits for the child resources to quiesce.
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The service emits `subagent/start` only after `start()` has fulfilled. It attaches the result observer before that synchronous notification, so even an already-settled child still produces `subagent/start` before `subagent/end`. In-process start observers can resolve the published child through `ctx.agents.get(info.id)`; remote providers need not publish a local agent.
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Run events are scoped to the delegating parent. Every listener is independently contained: a synchronous throw or rejected returned promise is logged without starving peer listeners or changing the run.
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Provider additions and removals also emit `subagent/provider-added` and `subagent/provider-removed`. Consumers such as the model-facing tool use those events because Cordis may load sibling plugins concurrently; configuration order does not prove registration order.
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## Collection model
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The current model-facing tool collects synchronously: it awaits the child result and disposes the run before returning. Background collection and polling remain outside this seam. See the [capability-seam RFC](../../../docs/rfc/implemented/feature/2026-06-21-subagent-capability-seam.md) and `src/types.ts` for the complete contracts.
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## Known Limitations and Deferred Work
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- **The consumer collects synchronously** — it starts a run and awaits `result`; steering (`sendMessage`) is part of the contract but intentionally unused, and background / poll / spill semantics are deferred to a future redesign unifying long-running-tool handling across subagents and bash ([the seam RFC](../../../docs/rfc/implemented/feature/2026-06-21-subagent-capability-seam.md)).
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- **The lifecycle events are observe-only** — a run-affecting `subagent/end` (an awaited continuation/decision surface) is deferred until a consumer needs one (`FIXME(subagent-continuation)`).
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See `src/types.ts` for the full contracts.
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- **The current consumer collects synchronously** — the model-facing tool starts a run and awaits `result`; steering (`sendMessage`) is part of the seam but intentionally unused, and background/poll/spill semantics are deferred to a future long-running-runtime design.
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- **The lifecycle events are observe-only** — a run-affecting `subagent/end` continuation or decision surface is deferred until a consumer needs one.
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