Right now it is impossible to get Symfony env variables on the Platform.sh/Ibexa cloud:

APP_DEBUG=1 php bin/console debug:container --env-vars

In Filesystem.php line 654:
Unable to write to the "/app" directory.

It happens because ezdesign.phpstorm.enabled parameter value is true despite the fact that it should be false for Platform.sh:

1. There are two packages that are manipulating ezdesign.phpstorm.enabled: EzPlatformCoreExtension and EzPlatformDesignEngineExtension. And EzPlatformCoreExtension is processed first.
2. https://github.com/ezsystems/ezplatform-core/blob/master/src/EzPlatformCoreBundle/bundle/DependencyInjection/EzPlatformCoreExtension.php#L176-L179 sets ezdesign.phpstorm.enabled to false.
3. https://github.com/ezsystems/ezplatform-design-engine/blob/master/bundle/DependencyInjection/EzPlatformDesignEngineExtension.php#L54 always updates ezdesign.phpstorm.enabled to %kernel.debug% that is default value.

Thats why ezdesign.phpstorm.enabled value is always %kernel.debug%, even on Platform.sh/Ibexa Cloud.