Add subagent capability seam: interface, mock backend, model-facing tool

Introduce the `packages/subagent/` group and the abstract subagent seam — an
agent delegating to a child agent — as a named-provider registry (`ctx.subagents`),
unlike the single-implementation bash seam, so multiple transports (in-process,
ACP, future A2A) coexist. This first PR lands the interface, a scripted test
backend, and the model-facing tool, validated through the real cordis load path.

- dsh-subagent: SubagentService registry + SubagentProvider/SubagentRun
  vocabulary + subagent/start|end events. Start-time capabilities (outputSchema,
  depthLimit, toolFilter) are checked pre-start and rejected loud; runtime
  capabilities (sendMessage, resume) are optional methods on SubagentRun.
- dsh-subagent-mock (support): scripted provider for keyless, deterministic
  tests through the real Loader/export path.
- dsh-tool-subagent: the model-facing `subagent` tool, config-bound to one
  provider; synchronous collect with try/finally dispose, signal->cancel
  bridging, and non-completed-stop-reason -> isError mapping.
- Proposed RFC documenting the seam, the fork-vs-spawn-as-separate-backends
  decision, own-session isolation, synchronous-collect scope, and the deferral
  of background/poll/spill to a future unification with bash.
- Wire the new group into tsconfigs, build refs, package hierarchy docs, the
  module graph, and the cordis catalog.

RFC: docs/rfc/proposed/feature/2026-06-21-subagent-capability-seam.md
This commit is contained in:
Tianyi Cui
2026-06-21 22:31:56 +08:00
parent 6b4dc48fbd
commit 1a81f2cccd
26 changed files with 1605 additions and 3 deletions

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# subagent/ — subagent capability family
The subagent seam: an agent delegating work to a child agent. Like the [bash](../bash/README.md) and [llm](../llm/README.md) families this is a capability seam (see [capability seams](../../docs/rfc/implemented/architecture/2026-06-13-capability-seams.md)) — but with one defining difference: **multiple provider implementations coexist in one context**, registered by name, rather than the single-implementation bash shape. The registry mirrors the LLM adapter registry.
| Package | Role | ctx key |
|---|---|---|
| `subagent/` | Abstract subagent seam: named-provider registry + vocabulary | `ctx.subagents` |
| `tool-subagent/` | Model-facing `subagent` delegation tool over `ctx.subagents` | (registers on `ctx.tools`) |
The interface lives at `subagent/subagent/`. Provider implementations live in their own packages — the in-process `dsh-subagent-spawn` / `dsh-subagent-fork` and the out-of-process `dsh-subagent-acp` — plus the test-only `dsh-subagent-mock` in [support](../support/README.md). All **product** packages except the mock.
The proposal and design rationale: [docs/rfc/proposed/feature/2026-06-21-subagent-capability-seam.md](../../docs/rfc/proposed/feature/2026-06-21-subagent-capability-seam.md).