1ad0f26b92
The aborted-mid-stream case raced the abort against the child's chunk delivery across two pipes and lost under full-suite load. Replace it with a same-pipe ordering probe: the fake streams one text-delta chunk and then answers the prompt with a malformed (non-accepted) result, so frame order guarantees the chunk precedes the failure — the accumulated partial text must survive into the error result. Same code path (collectOutput without a complete assistant/message), no timing window.
subagent/ — subagent capability family
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The subagent seam: an agent delegating work to a child agent. Like the bash and llm families this is a capability seam (see capability seams) — 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 |
subagent-inprocess/ |
Shared in-process run driver (no provider; one cleanup effect per run) | — |
subagent-spawn/ |
In-process backend: a fresh child agent | (registers on ctx.subagents) |
subagent-fork/ |
In-process backend: a child seeded with the parent's completed-turn prefix | (registers on ctx.subagents) |
subagent-subprocess/ |
Shared out-of-process machinery: env scrub, dispose ladder, cwd resolution, isolated config dirs (pure lib; registers nothing) | — |
subagent-acp/ |
Out-of-process backend: a child agent in a spawned subprocess, driven over ACP | (registers on ctx.subagents) |
subagent-sdk/ |
Out-of-process backend: a child harness runtime in a spawned subprocess, driven over stdio JSON-RPC through the TypeScript SDK client | (registers on ctx.subagents) |
tool-subagent/ |
Model-facing subagent delegation tool over ctx.subagents |
(registers on ctx.tools) |
The interface lives at subagent/subagent/. The in-process subagent-spawn / subagent-fork backends share the subagent-inprocess driver (a library with no provider of its own — both depend on it, neither on the other), and the out-of-process subagent-acp / subagent-sdk backends build on the subagent-subprocess library (the credential env scrub, the dispose ladder, child cwd resolution, isolated config dirs). Tests replace only the child boundary with package-local fixtures.
The proposal and design rationale: .agents/notes/implemented/feature/2026-06-21-subagent-capability-seam.md.