deepseek-harness/packages/subagent/subagent-spawn

@deepseek-ai/dsh-subagent-spawn

The spawn provider creates a fresh child Agent in the current process. The child has its own session, sees no parent conversation history, and reuses the host's agent factory and LLM/tool services.

Behavior

start(request) delegates to startInProcessRun with no seed and awaits publication before returning. The child receives parent working-directory/session lineage and inherits the parent model unless overridden, but starts with an empty conversation.

The shared driver owns depth checking, persona and tool-filter setup, structured output, required-signal cancellation, one-shot execution, result reading, and quiescent disposal. A startup rejection leaves no published child; provider unload after fulfillment does not revoke the holder-owned run.

Capabilities

Spawn advertises { outputSchema: true, depthLimit: true, toolFilter: true, persona: true } because it controls the child's creation window and can enforce all four features.

Config

Key	Meaning
providerName	Registry name on ctx.subagents (default spawn).

Model Experience

Child-agent request

What the model sees: The fresh child receives the standalone task content verbatim, inherits the parent model and workspace by default, and sees the global prompt with any configured child-scoped persona shadow. A tool filter removes global wire schemas, executable lookup, and Code Mode SDK bindings for that child but leaves independently registered guidance. It receives zero parent conversation messages; the filter is visibility/composition, not an authority grant inherited from the parent.

Token effect: The child pays for a new independent context and history; no parent-history tokens are duplicated. Persona changes this child's repeated prompt cost, while filtering changes its schema or generated SDK cost.

Parent tool result, indirectly

What the model sees: Through dsh-tool-subagent, the parent receives only the child's final output or stop-reason error.

Token effect: Parent input grows by one data-dependent result retained until compaction.

Known Limitations and Deferred Work

• Runs expose no sendMessage/resume — the optional runtime capabilities are absent on in-process runs.
• Fresh means no parent transcript — the child inherits cwd, lineage, model, and explicitly configured persona/tool restrictions, but none of the parent's conversation; use the fork provider when completed-turn context is required.