Function ensure_schema_compatible 

pub async fn ensure_schema_compatible(
    pool: &DbPool,
) -> Result<(), SchemaCompatibilityError>

Validate that the target database’s SQLx migration history matches the bundled Runledger migrations.

Unlike migrate, this does not apply pending migrations. It is intended for deployments that manage DDL outside the application process but still want a startup guardrail. This check is read-only, but it relies on the _sqlx_migrations history table being present and up to date. When present, it also uses Runledger’s own runledger_migration_history table to detect migrations applied by newer Runledger releases.