Method spawnChildSession

packages/runtime/src/session-manager.ts:2371–2402

* Create and run a durable linked child Session without changing the * parent-facing agent_spawn compatibility path. * * Cross-session provenance lives on the child header. The first AgentRun * intentionally carries no parentRunId, so it is an ordinary session-inline * run and every l

(
    parentSessionId: string,
    input: SpawnChildSessionInput,
  )

   * run and every later child turn can reuse only the child's own history.
   */
  async spawnChildSession(
    parentSessionId: string,
    input: SpawnChildSessionInput,
  ): Promise<SpawnChildSessionResult> {
    const resolvedInput = await this.resolveChildSessionSelector(input);
    const spawnKey = childSessionSpawnKey(parentSessionId, resolvedInput);
    const requestFingerprint = childSessionRequestFingerprint(parentSessionId, resolvedInput);
    const inFlight = this.childSessionSpawns.get(spawnKey);
    if (inFlight) {
      if (inFlight.requestFingerprint !== requestFingerprint) {
        throw new Error('Child-session spawn identity was reused for different work');
      }
      return await inFlight.promise;
    }
    const runtimeOwner = {
      execution: this.runtimeKernel.claimExecution(parentSessionId),
    };
    const promise = this.spawnChildSessionOnce(
      parentSessionId,
      resolvedInput,
      requestFingerprint,
      runtimeOwner,
    ).finally(() => runtimeOwner.execution.release());
    this.childSessionSpawns.set(spawnKey, { requestFingerprint, promise });
    try {
      return await promise;
    } finally {
      if (this.childSessionSpawns.get(spawnKey)?.promise === promise) {
        this.childSessionSpawns.delete(spawnKey);
      }
    }
  }

  private async resolveChildSessionSelector(
    input: SpawnChildSessionInput,