A scripted `SubagentProvider` for testing the [subagent seam](../../subagent/subagent/README.md) without a model or a real child agent — the subagent analog of [`dsh-llm-replay`](../llm-replay/README.md).
It lets a test drive `ctx.subagents` and the model-facing `dsh-tool-subagent` through the real Cordis loader/export path, exercising provider registration, async start, start-time capability validation, required-signal cancellation, `result`, `dispose`, and structured output deterministically and keylessly.
Aborting the required request signal or disposing before `result` settles flips the stop reason to `aborted`, so both holder-facing cancellation paths are observable.