Function validate_env_map 

pub fn validate_env_map<S: BuildHasher>(
    env: &HashMap<String, String, S>,
) -> Result<(), EnvValidationError>

Validate user-provided environment variables before merging/execution.

This enforces structural safety only (name shape + size + control chars), not semantic typing for values.

Errors

Returns EnvValidationError when key names, value bytes, or total map size exceed the runtime limits.