Remove Auto-increment Sequence from Plans Table

Problem

The plans table uses auto-increment IDs which creates inconsistencies across Cells in the new architecture. Each Cell could have different IDs for the same plan (e.g., 'premium' could be ID 4 in one cell, ID 5 in another).

Solution

Remove the auto-increment sequence from the plans.id column while keeping existing IDs unchanged.

Implementation (High-Level)

1. Migration to remove sequence default
   • Remove the nextval() default from plans.id column
   • Keep all constraints (PRIMARY KEY, NOT NULL, UNIQUE)
   • No data changes needed
2. Update Plan model
   • Add before_validation callback to set ID when creating new plans
   • Use Plan.maximum(:id).to_i + 1 for ID generation
   • Existing safe_find_or_create_by in Plan.default and Plan.free already handles race conditions
3. No changes needed to referencing tables
   • All foreign keys remain valid
   • No data migration required

Why This Is Safe

• Production (GitLab.com): All plans already exist, never recreated
• Self-managed: Only uses default plan (rarely created)
• New Cells: Copy plans table from legacy cell during setup
• Race conditions: Handled by unique constraint + safe_find_or_create_by

Benefits

• Minimal code changes (~10 lines)
• No data migration needed
• Easy rollback (just restore the sequence default)
• Ensures consistent plan IDs across all Cells

Risks

• Minimal: Plans are rarely created (only during initial setup)
• Handled: Any race condition fails safely with unique constraint violation