Problem

The canonical wordpress.phpunit MySQL runtime fails with only Managed runtime service failed: wordpress-database and diagnostic: { code: 'provision-failed' } when the host has no docker executable.

Observed while running Homeboy's WordPress extension against a component declaring database_type=mysql:

RuntimeServiceProvisionError: Managed runtime service failed: wordpress-database
...
diagnostic: { code: 'provision-failed' }

The host-level cause was confirmed separately: docker: command not found.

Expected

The WP Codebox runtime-service owner should preserve a bounded actionable cause such as provider-unavailable / docker executable not found, including the missing provider command, rather than collapsing process-spawn failures into the generic provision failure.

Scope

• Keep MySQL fail-closed; do not substitute SQLite.
• Improve the structured diagnostic emitted by provisionMysqlDockerService for an unavailable provider executable.
• Add coverage for process spawn ENOENT.

This was discovered while addressing Extra-Chill/data-machine-events#546; DME will retain the canonical MySQL declaration and will not work around the missing provider.