chore: drop invoice schema migration functions

[turip]

Overview

Drop the temporary invoice schema migration helper functions after the bulk schema-level-2 backfill has completed.

Note

This PR is intentionally just a collection of cleanups to be merged later. Keep it open until the bulk backfill has been deployed and older OpenMeter versions that still call the scalar function are no longer in use.

This PR is stacked on top of #4729.

Changes

• Drop om_func_migrate_customer_invoices_to_schema_level_2(TEXT).
• Drop om_func_migrate_customer_invoices_to_schema_level_2_bulk(TEXT[]).
• Do not recreate the completed migration helpers on rollback.

Validation

• atlas migrate --env local lint --latest 1
• atlas migrate validate --env local
• git diff --check

Greptile Summary

This PR removes the completed invoice schema migration helpers. The main changes are:

• Drops the scalar invoice migration function.
• Drops the bulk invoice migration function.
• Leaves both functions absent on rollback.
• Registers the migration in the Atlas checksum.

Confidence Score: 4/5

The function-removal migration can break invoice processing while scalar or bulk callers remain deployable.

• Older instances can call the dropped scalar helper during a rolling deployment.
• The current invoice-lock path can call the dropped bulk helper for remaining schema-level-1 invoices.
• The Atlas checksum and comment-only down migration follow repository conventions.

tools/migrate/migrations/20260717062143_drop_invoice_schema_migration_functions.up.sql

Important Files Changed

Filename	Overview
tools/migrate/migrations/20260717062143_drop_invoice_schema_migration_functions.up.sql	Drops both helpers while deployed application versions can still call them.
tools/migrate/migrations/20260717062143_drop_invoice_schema_migration_functions.down.sql	Intentionally keeps the helper functions removed during rollback.
tools/migrate/migrations/atlas.sum	Adds the new up migration using the repository's normal checksum convention.

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
tools/migrate/migrations/20260717062143_drop_invoice_schema_migration_functions.up.sql:1-2
**Function Drops Break Active Callers**

During a rolling deployment, an older instance can still call the scalar helper after this migration drops it. The current invoice-lock path can likewise call the bulk helper when it encounters a schema-level-1 invoice, so either state produces a PostgreSQL `function does not exist` error and blocks invoice processing.

_{Reviews (1): Last reviewed commit: "chore: drop invoice schema migration fun..." | Re-trigger Greptile}

Greptile also left 1 inline comment on this PR.

Context used:

• Context used - CLAUDE.md (source)
• Context used - AGENTS.md (source)

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[greptile-apps]

Function Drops Break Active Callers

During a rolling deployment, an older instance can still call the scalar helper after this migration drops it. The current invoice-lock path can likewise call the bulk helper when it encounters a schema-level-1 invoice, so either state produces a PostgreSQL function does not exist error and blocks invoice processing.

Prompt To Fix With AI

This is a comment left during a code review.
Path: tools/migrate/migrations/20260717062143_drop_invoice_schema_migration_functions.up.sql
Line: 1-2

Comment:
**Function Drops Break Active Callers**

During a rolling deployment, an older instance can still call the scalar helper after this migration drops it. The current invoice-lock path can likewise call the bulk helper when it encounters a schema-level-1 invoice, so either state produces a PostgreSQL `function does not exist` error and blocks invoice processing.

How can I resolve this? If you propose a fix, please make it concise.