Module-owned versioned migrations for phoenix_kit_billing — the decentralized-migrations protocol that core's mix phoenix_kit.update discovers via migration_module/0: current_version/0 + migrated_version_runtime/1 + idempotent up/1 + version-aware down/1. phoenix_kit_legal (over phoenix_kit_consent_logs) is the closest sibling example of this exact situation — a core-created table whose future shape a module chain adopts.

Ownership situation — read before touching

phoenix_kit_payment_provider_configs is one of core's V135 baseline tables. Nothing in this package's lib/ reads or writes it today — it is currently orphaned application-code-wise, though core still creates it (and can still roll it back on its own baseline down). Payment provider credentials this package actually reads and writes today live in phoenix_kit_settings, via PhoenixKitBilling.Providers — this version changes NONE of that.

V1 is purely an ADOPTION step:

• on existing installs the table is already there (core V135), the CREATE TABLE IF NOT EXISTS finds it, and the only new object is the pkb_schema:1 marker — from then on this chain owns the table's future shape;
• on a hypothetical future install whose core baseline no longer creates the table, the same statements create it — shape-identical to core's V135, with core's exact index and constraint names.

Because V1 changes no shape, core's ExpectedSchema manifest (which still audits the V135 shape of this table) stays accurate and NO core release is required for this version. A version that DOES change shape (V2+) is a separate, deliberate step — not in scope here.

What down/1 is NOT

down/1 unstamps the version marker; it NEVER drops phoenix_kit_payment_provider_configs. The table is core-created, and rolling back this module's chain must not destroy it — only core's own baseline rollback does that.

The migrated version is tracked as a pkb_schema:<N> COMMENT on phoenix_kit_payment_provider_configs (the marker convention from the projects/legal chains, namespaced). A marker-less table reads as version 0 — the core-baseline shape before this chain existed.