Restore compatibility with released SQLite Integration after canonical driver migration #151

Problem

MDI 0.8.5 migrated to WP_MySQL_On_SQLite in #150, but that symbol only exists on unreleased SQLite Database Integration trunk after WordPress/sqlite-database-integration#449. The latest releases, including 3.0.0-rc.6 and 3.0.0-rc.7, expose the PDO-compatible driver as WP_PDO_MySQL_On_SQLite.

A site running MDI 0.8.5 with released SQLite Integration now fatals during db.php bootstrap:

Fatal error: Class "WP_MySQL_On_SQLite" not found

This blocks all WordPress and WP-CLI operations before plugins can load.

Required outcome

• MDI boots against the currently released SQLite Integration PDO driver and unreleased renamed driver.
• The compatibility boundary is explicit and constrained to the equivalent PDO API, rather than restoring the deprecated WP_SQLite_Driver result API.
• Runtime coverage exercises both released and renamed class surfaces through the real drop-in boot path.
• Unsupported SQLite driver surfaces fail early with an actionable compatibility error instead of an undeclared parent-class fatal.
• Existing query/result, persistence, information-schema, and primary-mode behavior remains unchanged.

Evidence

• Installed released driver: SQLITE_DRIVER_VERSION = 3.0.0-rc.6, class WP_PDO_MySQL_On_SQLite.
• Latest release 3.0.0-rc.7 predates Simplify MDI to the native backend: retire SQLite and MySQL backends, remove stale-drop-in compatibility #449 and also lacks WP_MySQL_On_SQLite.
• WP_MySQL_On_SQLite rename merged on 2026-07-15 in Simplify the MySQL-on-SQLite driver API WordPress/sqlite-database-integration#449.
• MDI Refactor MDI onto the canonical SQLite PDO API #150 merged on 2026-07-28 and release 0.8.5 followed.