With the recent changes to the Stateless mode (#482), we can now add proper support for Google App Engine.

• develop the logic required for WP-Stateless and WordPress to work correctly on Google App Engine.
• add control to Compatibility tab to enable this logic.
  • title: Google App Engine
  • description: Ensures compatibility between WordPress media and Google App Engine in Stateless mode.
• add support for wp-config constant. WP_STATELESS_COMPATIBILITY_GAE
• add support for enabling/disabling via the wp-stateless network settings panel.
• setup assistant: detect if current WordPress site is hosted on App Engine, if so - automatically enable this compatibility and the new Stateless mode.
• add App Engine detection to our standard compatibility checks and prompt the user to enable this compatibility (as we do with other compatibilities).
• display notice when user tries to enable compatibility when mode is set to anything but "Stateless".
  • title: WP-Stateless: Current Mode is not compatible with Google App Engine.
  • description: Google App Engine compatibility requires WP-Stateless in Stateless mode.