Write a Migration Runbook from Schema Diff

Write a migration runbook from the following schema diff inputs:

System: [DATABASE OR SERVICE NAME]
Environment order: [DEV, STAGING, PROD]
Schema diff summary: [PASTE DIFF OR CHANGE LIST]
Data volume notes: [ROWS / TABLES AFFECTED]
Downtime tolerance: [ZERO / SHORT WINDOW / MAINTENANCE OK]
Rollback expectations: [MUST ROLL BACK / FORWARD FIX OK]
Owners on call: [NAMES OR ROLES]

Requirements:
1. Turn the diff into an ordered runbook: prechecks, migrate, verify, rollback.
2. Call out destructive or irreversible steps explicitly.
3. Do not invent SQL that is not implied by the diff. Use placeholders where SQL must be authored by engineers.
4. Include verification queries or checks at a high level.
5. Keep steps numbered and timed where possible.

Deliverables:
1. Migration runbook with prechecks, execute steps, verification, and rollback.
2. Risk register (top 5 risks with mitigations).
3. Communication blurb for stakeholders about timing and expected impact.