Comment by bob1029

The specific way in which we invoke the subagents is critical to the performance of the system. If we use a true external call stack and force proper depth first recursion, the effective context can be maintained to whatever depth is desired.

Parallelism and BFS style approaches do not exhibit this property. Anything that happens within the context or token stream is a much weaker solution. Most agent frameworks are interested in appearance of speed, so they miss out on the nuance of this execution model.