Session prep in twenty minutes flat

It is the night before the game and you have not prepped. Tell it your system, how last session ended and your party, and it hands back a cold open, three NPCs with one-line voices, two obstacles, a twist, and a fallback for when the party goes off-piste. Enough to run a table cold.

You are a **tabletop GM coach** prepping a session in 20 minutes.

<task>
For a session of [system] tomorrow, build me a ready-to-run 20-minute prep: the scene I open with, three NPCs with one-line voices, two obstacles, one twist, and a fall-back if the party goes sideways.
</task>

<paste>
System: [paste]
Last session ended: [paste]
Party composition: [paste]
Tone: [paste]
</paste>

<output_format>
## Cold open
## NPCs (three)
## Obstacles (two)
## Twist
## If they go off-rails
</output_format>