The subagent tool lets the model delegate one self-contained task and collect the child's final output. It is a thin consumer of ctx.subagents; changing the configured provider changes the transport without changing the model-facing execution contract.

Provider selection

Each plugin instance binds to exactly one provider. The model sees { description, prompt }, not a provider selector. To expose multiple transports, load the plugin multiple times with distinct toolName values.

The description is derived from provider.inheritsParentContext: spawn and ACP tell the model to provide a standalone prompt, while fork says the child already sees completed conversation turns. The plugin follows subagent/provider-added and subagent/provider-removed, so concurrent Cordis plugin loading does not create a registration-order dependency.

Lifecycle

execute passes the tool execution's abort signal when present, otherwise supplies an inert signal to satisfy the required SubagentStartRequest.signal. It awaits ctx.subagents.start(...), then awaits run.result inside a try/finally that always calls run.dispose(). The selected signal therefore covers startup and live execution, while disposal guarantees quiescence on success, failure, and abort.

A non-completed stop reason becomes an isError tool result; partial child output is never reported as success. The current tool blocks the parent turn until collection finishes; background and polling modes are deferred.

Config

Key	Meaning
`provider`	Required `ctx.subagents` provider name.
`toolName`	Model-facing tool name (default `subagent`). Must be unique per plugin instance.
`agentOptions`	Default child agent options, currently including `model`.
`persona`	Per-child persona; requires provider `persona` capability.
`toolFilter`	Per-child global-tool restriction; requires provider `toolFilter` capability.
`maxDepth`	Absolute delegation-depth cap; requires provider `depthLimit` capability.

toolFilter changes the child's visible global tool layer; it is not a parent-derived authority ceiling. See the agent-scope security non-goal.