Campaign Arc Structure Planner

As a Game Master, design a complete campaign arc structure for: {{campaign_premise}}

Develop a three-act structure:

Act 1 (Sessions 1-{{act1_sessions}}):
- Inciting incident and initial mystery
- Introduction of main antagonist forces
- First major revelation

Act 2 (Sessions {{act1_sessions}}-{{act2_end}}):
- Escalating challenges and stakes
- Midpoint twist that changes everything
- Character-defining moments for each PC

Act 3 (Final sessions):
- Convergence of plot threads
- Climactic confrontation
- Resolution and epilogue hooks