The Subagent Trap, Explained
Subagents never inherit the coordinator's context. Here's the exact distinction the Claude Architect exam tests — and why 'analyze the findings' silently fails.
If you take only one thing into the Claude Architect – Foundations exam, make it this: a subagent does not inherit the coordinator's context. It's tested almost verbatim, and it's the single most common reason a plausible-looking multi-agent design is the wrong answer.
What actually happens when you spawn a subagent
A coordinator agent gathers findings, then delegates a follow-up task to a subagent via the Task tool. The intuitive instruction looks fine:
Coordinator: "Analyze the findings and write a summary."
Subagent: "...which findings?"The subagent starts with a fresh context window. It cannot see the coordinator's conversation, its tool results, or the documents it read. "The findings" refers to nothing.
Nothing errors. The subagent confidently produces a summary of whatever it can infer — often a hallucinated one. That's what makes this trap dangerous in production and a favourite on the exam.
The fix: pass everything explicitly
The subagent's prompt must carry the payload. Whatever it needs, you serialize into the delegation:
Coordinator → Subagent prompt:
"Here are the 4 findings:
1. ...
2. ...
Summarize them into a 3-bullet executive brief."Fork vs. subagent: pick the right isolation
The trap has a cousin — knowing when to spawn a subagent at all versus forking the session.
| Fork the session | Spawn a subagent | |
|---|---|---|
| Context | Keeps the full prior context | Starts fresh — you must pass what it needs |
| Use when | The new work depends on prior state | The work is isolated and parallelizable |
| Risk | Context bloat, cost | The subagent trap — missing context |
Self-check
A research coordinator has read 5 papers and spawns a subagent to 'compare the methodologies.' What's wrong?
Internalize this one distinction and you'll pick the right answer every time it appears — and ship multi-agent systems that actually work. For the full domain breakdown, see the Architect – Foundations syllabus.