feat(customcurrency): backfill subscription items with currency

[chrisgacsal]

Overview

What

Add a database migration that backfills missing currency codes on legacy priced subscription items and marks updated rows with a timestamped migration annotation.

Why

New subscription items already persist their effective currency, but legacy priced items may still have no currency. These rows must be backfilled before enforcing stricter currency constraints.

How

The migration copies the owning subscription’s fiat currency to unannotated priced items with no currency reference. It preserves existing annotations and explicit fiat/custom currencies. Updated rows receive a dbmigration:backfill_subscription_item_currencies RFC3339 annotation, which also supports targeted rollback. PostgreSQL migration tests cover backfill, exclusion, preservation, and rollback behavior.

This must be merged prior: #4744.

Greptile Summary

The PR adds a data migration that materializes inherited subscription currency on legacy priced items and marks changed rows for rollback.

• Backfills eligible subscription items from their owning subscription.
• Preserves explicit fiat and custom currencies during migration-up.
• Adds PostgreSQL coverage for migration-up and rollback behavior.
• Updates the Atlas migration checksum.

Confidence Score: 4/5

The PR is not yet safe to merge because rollback can corrupt rows that had the migration marker before migration-up.

The up migration skips pre-marked rows, while the down migration still treats every marked row as migration-owned and clears its currency and marker; this previously reported rollback defect remains outstanding.

Files Needing Attention: tools/migrate/migrations/20260810064730_backfill_subscription_item_currencies.down.sql

Important Files Changed

Filename	Overview
tools/migrate/migrations/20260810064730_backfill_subscription_item_currencies.up.sql	Backfills missing fiat currencies on eligible priced subscription items and records a timestamped migration annotation.
tools/migrate/migrations/20260810064730_backfill_subscription_item_currencies.down.sql	Reverts rows selected by the migration annotation.
tools/migrate/subscription_item_currency_backfill_test.go	Covers eligible and excluded rows, annotation preservation, timestamps, and migration rollback.
tools/migrate/migrations/atlas.sum	Registers the new up migration in the Atlas checksum manifest.

_{Reviews (2): Last reviewed commit: "refactor: rm validation from up migratio..." | Re-trigger Greptile}

Summary by CodeRabbit

• Data Updates

  • Legacy subscription items now inherit their subscription currency when eligible.
  • Existing custom, explicit, deleted, annotated, and unpriced items remain unchanged.
  • Updates include migration tracking and timestamps while preserving existing metadata.

• Rollback

  • Backfilled currency values and migration annotations can be safely reverted without removing pre-existing data.

• Tests

  • Added coverage for backfill eligibility, metadata preservation, timestamps, and rollback behavior.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds a transactional migration that backfills eligible subscription-item currencies, records migration annotations, supports rollback, and verifies both directions with integration tests.

Changes

Subscription item currency migration

Layer / File(s)	Summary
Backfill and rollback migration tools/migrate/migrations/20260810064730_backfill_subscription_item_currencies.*.sql	The up migration copies subscription currencies to eligible priced items and records UTC annotations. The down migration removes only backfilled values and annotations.
Migration integration validation tools/migrate/subscription_item_currency_backfill_test.go	The test covers legacy, annotated, deleted, explicitly assigned, custom-currency, unpriced, and already-annotated items during migration and rollback.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• openmeterio/openmeter#4742: Introduces the currency-reference schema and materialization changes used by this backfill.

Suggested labels: area/billing, kind/feature

Suggested reviewers: turip, galexihu

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: backfilling subscription items with currency.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/subscrption-currency-backfill

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In
`@tools/migrate/migrations/20260810064730_backfill_subscription_item_currencies.up.sql`:
- Around line 14-20: Make the up migration record rollback metadata uniquely
owned by this migration, so it cannot match pre-existing markers; update the
down migration to roll back only rows proven changed by this migration. In
tools/migrate/subscription_item_currency_backfill_test.go lines 149-151, retain
the pre-existing-marker fixture, and at lines 221-223 assert that its annotation
remains after rollback.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: e43a122d-2c3d-40c7-b35c-923ddd5e5402

📥 Commits

Reviewing files that changed from the base of the PR and between f343514 and 66fbeff.

⛔ Files ignored due to path filters (1)

• tools/migrate/migrations/atlas.sum is excluded by !**/*.sum, !**/*.sum

📒 Files selected for processing (3)

• tools/migrate/migrations/20260810064730_backfill_subscription_item_currencies.down.sql
• tools/migrate/migrations/20260810064730_backfill_subscription_item_currencies.up.sql
• tools/migrate/subscription_item_currency_backfill_test.go