ADR-0023: Terminal UI — Textual

Decision: Textual 8.x TUI with four screens; NLP query bar delegates to NLPQueryEngine.

Why Textual over curses / urwid:

• Textual provides a CSS-like layout engine, reactive data binding, and a rich widget library — features that would require thousands of lines in raw curses.
• Works over SSH without X11 forwarding — critical for server deployments.
• Textual’s async event loop integrates cleanly with GNAT’s async client layer.

Screen architecture: Each screen is a self-contained textual.Screen subclass that owns its data fetching. The GNATApp root composes them into a TabbedContent layout with F1–F4 hot keys. Screens do not share state directly — they communicate via app.post_message().

STIXTable / JobTable widgets: Thin DataTable subclasses that define standard column layouts. This avoids repeating column definitions across screens and provides a typed selected_job_id() helper.

Graceful degradation: The Query screen works without a Claude API key (falls back to builtin NLP parser). The Library and Scheduler screens work without a Research Library or active scheduler (they render empty tables with a status bar message).

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