Specification: Claude screen rules and prompt-aware regions

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

Spec 028 deferred Claude's herdr rules because they read regions the engine lacked: the prompt box, the line above it, and the text after the last horizontal rule. A Claude session started without signaltty's hooks (typed in a shell, no integration install) therefore shows no state. This adds those regions, a hold state, and ships Claude's rules, per docs/14 directive 3.

Acceptance

1. region accepts screen, prompt_box, above_prompt_box and after_last_rule besides title and bottom, following herdr's definitions: a horizontal rule is a line starting with ─ (at least three, or nothing after them); the prompt box is the text between the second-last rule and the next rule. lines (1..=200) keeps the last non-empty lines of any non-title region; bottom stays screen + lines = 12. A missing box or rule falls back as in herdr (empty box, whole screen otherwise).
2. A rule may have state = "hold": when it wins, the pane's state is left unchanged (herdr's skip_state_update), so a transcript viewer or model picker cannot be read as working, blocked or idle.
3. signaltty ships Claude rules ported from herdr (Apache-2.0, attributed), ending in the idle fallback. herdr's osc_progress rule is omitted: signaltty does not track OSC 9;4 progress.
4. Fixtures cover each Claude rule (working spinner and status line, background agents above the box, permission prompts, forms, MCP input, transcript and model picker holds, title states, idle prompt box) and priority conflicts between them. pane.explain labels the new regions.

Scope and clarification

Codex rules need herdr's prompt-marker regions and are the next slice. Fixtures are written from the rules' text, not captured from Claude Code. Rules only apply until the pane's first hook, unchanged from spec 027. No unresolved requirements remain.