CSE Roadmap

Common tier · about 4 hours · 6 parts

Part 2 of 6 · 2 min read

Definitions and setup

Covers: Definitions; What crosses the boundary.

Definitions

Context isolation, sub-agent, orchestrator

  • Context isolation: running a sub-task in a context window separate from the parent's, so neither sees the other's intermediate messages.
  • Sub-agent: an agent invoked by another agent to do one sub-task.
  • Orchestrator (parent): the agent that decides what to delegate and uses the results.

Agents as tools, result strategy, handoff

  • Agents as tools: the sub-agent is wrapped as a tool; the parent calls it with a task string and gets a string back.
  • Result strategy: the rule for what part of the sub-agent's run becomes the tool result (final message, last N messages, all messages, or a custom extractor).
  • Handoff: the information passed from one agent to another, in either direction. Anything not handed off is lost to the receiver.

Typed (structured) result, constraint passing, injection containment

  • Typed result: a return value with a fixed schema (here finding, detail, caveat) instead of free text.
  • Constraint passing: putting the parent's requirements (scope, format, forbidden actions) in the task given to the child, since the child cannot see the parent's context.
  • Injection containment: keeping instructions found in untrusted tool output from reaching an agent that holds more authority.

What crosses the boundary

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each sub-agent re-reads only its own context; only the result crosses the boundaryOne agent, one contextsub-task 1sub-task 2sub-task 3sub-task 4context grows to ~8,000 tokens; every step re-reads all of it355,654 tokens in total; sees every tool output, including the injected oneOrchestrator + 4 sub-agentssub-agent 1~2,000 ctxsub-agent 2~2,000 ctxsub-agent 3~2,000 ctxsub-agent 4~2,000 ctxorchestrator receives 4 small results (~100 tokens each)task goes downWhat crosses the boundary is a design decision: the last message, the last N, everything, or a typed record.Too little loses findings and caveats; too much carries noise and injected text back into the parent.Total here: 178,517 tokens, 50 percent of the single agent, and only the structured result is correct.
Left: one context that grows to the end of the run. Right: four isolated contexts and a small handoff to the orchestrator.

Cost model used by the code: a call with context of c tokens costs system + c, and the context before each call is every message so far. A run of n steps with m tokens per step therefore costs about n * system + m * n^2 / 2. For one agent doing four sub-tasks, n is 60; for four isolated agents, each has n = 15, so the quadratic term is divided by about four.