The shared in-process subagent run driver. A library with no provider or import-time registration that the in-process backends — spawn (a fresh child) and fork (a child seeded with a prefix of the parent's log) — both build on. Each accepted run installs one provider-owned cleanup effect. The backends are thin shells that differ ONLY in the session seed they pass; everything downstream lives here, so neither backend depends on the other.

What it exports

`startInProcessRun(ctx, request, options): SubagentRun`

Runs a child as a child Agent on the same cordis context (ctx.agents):

snapshots the accepted request before asynchronous owner setup: the parent and signal remain identity capabilities but are never reread from the caller-owned record; tool filter, seed, agent options, output schema, and prompt are detached. It computes child depth = depthOf(parent) + 1 and rejects request.maxDepth overflow with SubagentDepthError; outputSchema is asserted before cloning so a hostile value fails as OutputSchemaError, while the prompt passes the session log's lossless-JSON check before and after cloning;
first installs provider ownership, then attaches the request abort listener and creates one run-owner Cordis fiber under parent.ctx; an already-unloading provider therefore leaves no child or orphaned listener. Async child creation goes through that fiber's ctx.agents service with fresh IDs, lineage/seed, inherited model, and an unpublished setup transaction for persona, tool restriction, and structured output. Parent teardown, provider teardown, and manual run.dispose() all dispose this exact node, preventing publication after it becomes inactive and awaiting the same quiescence boundary. startInProcessRun still returns its SubagentRun immediately, and cancellation during creation is recorded and applied when a child exists;
drives the one-shot: child.send(prompt) then await child.whenIdle() (ordering matters — send enqueues synchronously, so whenIdle observes the queued work and resolves on the child's running → idle transition, never before the turn starts); there is deliberately NO re-prompt for a structured child that finished cleanly without calling structured_output — the shortfall maps to an error result for the parent;
reads the result, scoped to the child's OWN events (everything at or after seedLength, so a seeded child that produced no message of its own never returns the seeded parent's last message): the last assistant/message content (deep-cloned — the log is frozen) and the last turn/end.reason mapped to a SubagentStopReason. A structured run surfaces the captured value as result.structured; a structured child that finished cleanly WITHOUT ever capturing settles error (a clean finish without the demanded result is a failure, not a success with a missing field).

dispose() awaits creation or rollback and then delegates to AgentHandle.dispose() (stop and drain → remove agent → detach session → unwind scope); cancel() records its request even before publication and cancels the child immediately once available. A cancel landing before any turn/end still settles aborted, honoring the cancel contract rather than the generic no-turn error.

`InProcessRunOptions`

{ seed?: SessionEvent[] } — the optional child-session seed: absent for spawn, or the parent's balanced completed-turn prefix for fork.

Structured output (package-internal runtime)

attachStructuredRuntime(childCtx, schema) registers the run's whole enforcement surface as SCOPED registrations on the child's agent.ctx — riding the child's fiber (a backend hot-reload mid-run cannot unregister anything; a disposed child leaves no residue) and visible to that child alone (two concurrent structured runs never interact; no placeholder schema, no strip-for-everyone-else, no refcounted global state):

the structured_output capture tool with the run's REAL schema as its registered parameters, validating each call (validateStructuredValue) — violations become an INVALID_ARGS isError the model retries in-turn; a valid call STAGES the value in a WeakMap keyed by that call's ToolExecution object;
the calling instruction as an ordinary order-190 scoped prompt section (the demand travels with the tool, as prompt state of exactly one agent);
a scoped systemPrompt.protect() registration making the capture instruction and schema canonical after the complete assembly waterfall. Canonical absence is protected too: pure Code Mode removes structured_output from the wire and declares it through the SDK. The tool registry separately owns and protects its tools:sdk section and reserved run_code transport; protection guarantees those named contributions, while unrelated listener-added schemas remain the listener's responsibility. The loop logs the finalized assembly as the step's request/header, so the demand remains reconstructable;
a scoped tools/result observer as the commit point: it promotes a staged value only when that same execution's immutable, JSON-safe authoritative result after the complete pre-execute → guards → execute → post-execute pipeline succeeds. For a Code Mode SDK sub-dispatch, the child's opaque parent token matches the enclosing run_code execution's registry-assigned token, so promotion waits for that outer final result without exposing its live object; a runtime failure or post-policy block discards the value. Execution-object identity prevents call-id reuse or another execution from reaching the stage;
a scoped monotonic tools.guard() denial for every call arriving after capture. Guards run after the extensible pre-execute waterfall and cannot return allow, so terminal means terminal within the step regardless of listener order;
a scoped agent/turn-stop terminal policy stopping the child's turn once its output is captured. It runs after ordinary continuation and steering folding, and its terminal state survives turn close and flush, so later listeners cannot leak steering into another step or turn; ordinary queued prompts remain intact.

`depthOf(agent): number`

Delegation depth rides on a merge-extensible AgentOptions.subagentDepth field (0 for a top-level agent, parent + 1 for a child), so a nested spawn reads its parent's depth from parent.options.subagentDepth. depthOf reads it (absent ⇒ 0).

`SubagentDepthError`

Thrown by startInProcessRun when a spawn would exceed the request's maxDepth cap; carries attemptedDepth and maxDepth.