Specification: Codex screen rules and prompt-marker regions

Created: 2026-10-09. Status: clarified.

Codex is the last agent of herdr's set whose rules signaltty lacks. They read regions anchored on Codex's › prompt line and the first lines of the screen. A Codex session started without signaltty hooks therefore shows no state. This adds those regions and ships Codex's rules, per docs/14 directive 3.

Acceptance

1. region accepts top (the first lines non-empty lines, default 12), after_last_prompt, before_current_prompt and without_current_prompt, following herdr: a prompt line is › alone or starting with › ; the current prompt is the last prompt line with no •, ■, ✗ or ✓ block line after it. Without a prompt, after_last_prompt and before_current_prompt read the whole screen; without_current_prompt is the whole screen only when there is no current prompt, otherwise empty.
2. signaltty ships Codex rules ported from herdr (Apache-2.0, attributed), ending in the idle fallback.
3. Fixtures cover each Codex rule (title blocked/working/idle, transcript hold, trust directory and folder prompts, startup update, strong and weak blockers, the timed working status and its reconnect-failed veto) and the region edge cases; pane.explain labels the new regions.

Scope and clarification

Fixtures are written from the rules' text, not captured from Codex. Rules only apply until the pane's first hook, unchanged from spec 027. No unresolved requirements remain.