You are designing a prompt that must return strict JSON. Task: {{task_description}}
Required fields and types: {{fields_description}}

Write:
1. The instruction prompt the model should receive, stating the JSON shape explicitly and that no extra text or markdown fencing should surround it.
2. How the model should represent a field it cannot determine (e.g. null, or an explicit "unknown") rather than guessing or omitting the key.
3. One example of valid output for this schema.