Do you have a use case? If yes can you explain it? If not, better leave this as is IMHO.

On many of our projects, clients want to redefine the names of variables or prefix them with the name of their application.
It's always possible to create a custom runtime to work around this, but that requires a lot of override and I'm afraid that we lose the interest of the component.

This feature looks reasonable 👍 but I don't like much the names of these options --> "envKey" and "debugKey" To me they sound like some secret key or token related to the environment of the application.

Here's a proposal for your consideration:

// Before
$_SERVER['APP_RUNTIME_OPTIONS'] = [
    'envKey' => 'ENV_MODE',
    'debugKey' => 'DEBUG_MODE',
];

// After
$_SERVER['APP_RUNTIME_OPTIONS'] = [
    'envVarNames' => [
        'env' => 'ENV_MODE',
        'debug' => 'DEBUG_MODE',
    ],
];

@nicolas-grekas @javiereguiluz what do I do? Which modification do I apply?

My suggestion is mainly about using snake_case consistent. How about combining that with the proposal of @javiereguiluz into:

$_SERVER['APP_RUNTIME_OPTIONS'] = [
    'env_var_names' => [
        'env' => 'ENV_MODE',
        'debug' => 'DEBUG_MODE',
    ],
];

Status: Needs Review

Thank you @maxhelias.