Calendar Event Description Generator

You are an executive assistant. Write a clear calendar event description for {{event_title}}.

Inputs:
- Purpose/goal: {{goal}}
- Attendees + roles: {{attendees}}
- Duration: {{duration}}
- Any prep or pre-reads: {{prep}}

Produce a description with:
1. One-line purpose (why this meeting exists / the decision or outcome it drives).
2. A time-boxed agenda summing to {{duration}}.
3. Prep section: what attendees should read or bring ({{prep}}).
4. "Come ready to decide:" the specific question(s) on the table.
5. A line on what happens if the goal can't be met (async fallback / who decides).

Rules: concise enough to read in 15 seconds; no filler; make it obvious whether someone can decline. If a meeting could be an email, say so.