ADR-0112: The TUI is deferred after a successful Ck spike

• Status: Accepted
• Date: 2026-06-27
• Deciders: jka
• Decision: no D number; see spike/probes/VERDICT.md

Context

ADR-0004 chose Ck for the terminal frontend, with an open question: can Ck carry an editor TUI? A throwaway spike was specified with six pass/fail criteria: build and run, the text widget as a code editor, layout reflow on terminal resize, keyboard coverage, Unicode, and redraw correctness. A second question was when to build the TUI: two frontends kept in step over a protocol that is still changing double the work of every change.

Decision

The spike was run against vzvca/ck8.6 at commit 1a991e3 with Tcl 8.6.16 and ncursesw 6.5. Results:

• Pass: builds (with legacy C flags under GCC 14); the text widget handles a 5000-line buffer with scrolling, editing and foreground-colour tags; layout reflows on resize; BMP Unicode including box drawing and wide CJK renders; redraw is clean.
• Findings: Ck has no <Configure> event. It reports resizes through <Expose>, and re-layout must be guarded by an actual width change to avoid a loop.
• Weak: keyboard. In tmux every chord arrived; on a plain Debian terminal only Ctrl+A reached the application. Cross-terminal key handling is real work, and Cygwin was not tested.

On that basis the TUI is deferred to a separate, later effort, which may be done by someone else. It is not active work. Core and GUI are the focus.

Consequences

• The protocol (ADR-0002, ADR-0011) remains the public contract, so a TUI or any other client can attach later without core changes.
• Every new operation is designed as structured data a terminal client could use.
• The spike and its verdict are the starting kit for whoever builds the TUI. If Ck's keyboard handling cannot be made good, the fallback is a TUI in another language against the same protocol.
• TUI-only decisions (ADR-0005, ADR-0006, ADR-0009, ADR-0014) remain accepted but unimplemented.