The Sub-Agent Brief Writer

Write the brief a coordinator gives a sub-agent.

Sub-agent purpose: [DESCRIBE]
What the coordinator knows: [DESCRIBE]
What the sub-agent needs to know: [DESCRIBE]
What it should return: [DESCRIBE]

Produce a brief covering:
1. The task, stated completely — the sub-agent has none of the
   coordinator's context
2. Everything it needs that it cannot discover
3. What it must NOT do
4. The exact output format expected
5. What "done" means for this sub-task
6. What to do if the task is impossible as specified
7. Budget or scope limits

Rules:
- Brief completely the first time. Launch-wait-rebrief cycles are
  the main cost of multi-agent systems.
- Do not assume shared context. The sub-agent knows only what you
  tell it.
- Specify the return format precisely, or the coordinator spends
  tokens parsing prose.
- Include the constraint that a sub-agent should not expand its own
  scope

Then: what will the coordinator do if the sub-agent returns
something malformed or incomplete?