Centralize configuration management

Prefer centralized configuration objects over environment variables for application settings. Environment variables create inconsistent configuration sources and can lead to maintenance challenges.

Guidelines:

• Use a single, centralized Config structure as the “one true way” to configure your application
• When adding new settings, place them in the appropriate configuration structure rather than reading from environment variables
• Reserve environment variables primarily for bootstrap settings or when absolutely required

For feature flags or experimental options, use structured configuration with appropriate prefixes:

// Preferred
config.experimental_resume = true;

// Instead of
if std::env::var("CODEX_EXPERIMENTAL_RESUME").is_ok() { ... }

When environment variables must be used:

• Load them as early as possible in the application lifecycle before any threads are created
• Document the thread-safety implications clearly
• In tests, configure components explicitly rather than modifying process-wide environment variables

Remember that modifying environment variables is inherently racy in multi-threaded contexts and has been marked as unsafe in recent Rust editions.