fix(db): idempotent refund_accounts currency migration for re-apply

[5ran6]

Jira Issue

Jira Issue: (Atlassian MCP not authenticated — please file a KAN Bug labeled noblocks and update this link)

Description

After #678 retimestamped migrations, main migrate tried to apply 20260817180000_refund_accounts_per_currency.sql and failed:

ERROR: relation "refund_accounts_one_per_wallet_currency" already exists (SQLSTATE 42P07)

Notices showed currency already exists and refund_accounts_one_per_wallet already gone — the #667 DDL was applied to production (stable path) but never recorded under the new version id. The identity migrations never ran because this file aborted first.

Make the unique-constraint add idempotent via a pg_constraint existence check (same pattern as 20260817180200). Column add / old-constraint drop were already safe.

Self-review

• Reviewed against failing migrate log
• CodeRabbit / CI green

References

• Failing migrate: https://github.com/paycrest/noblocks/actions/runs/32049797292/job/95447501567
• Blocked promotion: Promoting Main to Stable #677
• Prior retimestamp fix: fix(db): retimestamp migrations blocked behind applied EPL season #678

Testing

• After merge, main migrate should skip the existing unique constraint, record 20260817180000, then apply 20260817180100–20260817180400

• Confirm no 42P07 on refund_accounts

• This change adds test coverage for new/changed/fixed functionality

Staging

• Staging noblocks checked (wallet and transaction flows)

Checklist

• I have added documentation and tests for new/changed functionality in this PR
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not main
• If this PR adds a database migration, it follows expand/contract: the new code works against the pre-migration schema, the currently deployed code keeps working against the post-migration schema, and destructive changes (drops, renames, tightened constraints) are deferred until the old application version is no longer serving — migrations are applied around the deploy, not strictly before or after it

By submitting a PR, I agree to Paycrest's Contributor Code of Conduct and Contribution Guide.

  

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