Frontend session startup and user-facing initialization

This stage happens after the backend services are ready, but before the user can really start working. It is where Codex turns its prepared engine into something a person or script can use.

For the interactive terminal app, the TUI startup path opens the front door. It loads settings, connects to the app server, guides first-time users through sign-in and trust choices, checks project setup, and builds or resumes the visible chat. It also takes careful control of the terminal window: drawing the interface, reading keys, handling resize and suspend, showing notifications, and restoring the shell when finished.

For non-interactive use, exec mode starts a single scripted session instead of a full screen app. It gathers the prompt, configuration, saved session details, or review request, then runs once and writes predictable output, such as JSON lines for other programs to read. The resume helper makes sure an old conversation restarts with the right folder and model. Together, these parts make Codex ready for either a human at a terminal or an automation script.