feat(input): readline keymap — Esc-clear + Ctrl-A/E/W/K/U (#29)

Implement the deferred I1b readline shortcuts in the command input
field (ADR-0049, closing issue #29):

  Esc      clear a partly-typed command (only when no completion memo)
  Ctrl-A   cursor to line start (Home alias)
  Ctrl-E   cursor to line end (End alias)
  Ctrl-W   delete the previous word (readline-style, UTF-8 safe)
  Ctrl-K   kill to end of line
  Ctrl-U   kill to start of line

Esc precedence is preserved: a live Tab-completion memo still wins
(Esc undoes the completion first, ADR-0022); Esc clears only when no
memo is alive. While a sidebar panel is focused (Ctrl-O), Esc exits
navigation mode upstream and never clears the input draft. Cursor-only
keys leave history navigation intact like Home/End; buffer-mutating
keys end it like Backspace.

New helpers clear_input / delete_prev_word / kill_to_end /
kill_to_start in src/app.rs. 22 new Tier-1 tests (2458 pass / 0 fail
/ 0 skip, clippy clean). ADR-0049 amends ADR-0046's OOS list;
requirements.md I1b marked done.

docs/adr/0046-sidebar-navigation-and-responsive-input-hint.md

@@ -525,7 +525,9 @@ All tiers green, zero skips; clippy clean (nursery).
   submits over a multi-logical-line buffer. DA3/DA4 keep a single
   logical line; this remains a separate, deferred feature.
 - **Readline shortcuts (I1b)** — Ctrl-A/E/W/K/U stay reserved-deferred;
-  not touched here.
+  not touched here. *(Superseded 2026-06-12: I1b is now in scope and
+  decided by **ADR-0049** — Esc-clear + Ctrl-A/E/W/K/U in the input
+  field, issue #29.)*
 - **Cross-session sidebar persistence** — visibility is session-only
   (DB1); persisting it would amend ADR-0015.
 - **The output panel as a third navigation focus target** — navigation

docs/adr/0049-input-field-readline-keymap.md

@@ -0,0 +1,114 @@
+# ADR-0049: Input-field readline keymap — Esc-clear + Ctrl-A/E/W/K/U (I1b)
+
+## Status
+
+**Accepted + implemented 2026-06-12 (issue #29).** Closes Gitea **#29**
+("Command input keystroke support") and the deferred **I1b** readline
+requirement in `requirements.md`. Every fork below was escalated to the
+user and user-chosen before any code was written; implemented test-first
+(22 new Tier-1 tests in `src/app.rs`, all green; clippy nursery clean).
+
+This ADR **amends ADR-0046**, which explicitly listed "readline
+shortcuts (I1b)" in its out-of-scope set: that item is now in scope and
+decided here. It is orthogonal to ADR-0003's input-*mode* model (simple
+vs advanced, the `:` sigil) — these are editing keys within the input
+field, not mode or sigil changes — and it extends the single-line cursor
+editing already shipped under requirement **I1a** (Left/Right/Home/End/
+Backspace/Delete, `app.rs`).
+
+## Context
+
+The input field already supported in-line cursor editing (I1a): Left/
+Right by char (UTF-8 aware), Home/End to the extremes, Backspace/Delete.
+Two gaps remained, raised in issue #29:
+
+1. No way to **clear a partly-typed command** in one keystroke — a user
+   who started typing the wrong thing had to hold Backspace.
+2. No **readline cursor/kill shortcuts** (Ctrl-A/Ctrl-E and friends) for
+   keyboards without Home/End and for muscle-memory in a command-driven
+   workflow. This is requirement I1b, deferred by ADR-0046.
+
+`Esc` was free in the input field except that a *live Tab-completion
+memo* consumes it first (to undo the completion in one keystroke,
+ADR-0022). Ctrl-A/E/W/K/U were unbound. The existing chords are Ctrl-C
+(quit), Ctrl-O (nav focus cycle, ADR-0046), and Ctrl-`]` (demo caption
+toggle, ADR-0047) — none collide with a/e/w/k/u.
+
+## Decision
+
+Bind the following in the input field (non-modal, non-navigation,
+both input modes), in `App::handle_key`:
+
+| Key       | Action                                            |
+|-----------|---------------------------------------------------|
+| `Esc`     | Clear the input (empty buffer, cursor→0, scroll→0)|
+| `Ctrl-A`  | Cursor to line start (alias of Home)              |
+| `Ctrl-E`  | Cursor to line end (alias of End)                 |
+| `Ctrl-W`  | Delete the word before the cursor                 |
+| `Ctrl-K`  | Kill from the cursor to end of line               |
+| `Ctrl-U`  | Kill from start of line to the cursor             |
+
+Behavioural rules:
+
+- **Esc precedence.** A live completion memo still wins: the first Esc
+  undoes the completion (ADR-0022), and Esc only *clears* when no memo
+  is alive. This is a natural progression — Esc once to back out the
+  completion, Esc again to clear.
+- **Esc does not clear while navigating the sidebar.** When a sidebar
+  panel is focused (Ctrl-O, ADR-0046 DC3), `handle_key` routes every
+  key to the navigation handler *before* the input-field keymap, where
+  Esc exits navigation mode (`nav_exit`). Entering nav mode never
+  touched the input buffer, so Esc-to-close-the-panel returns focus to
+  the input with the partly-typed command intact — it cannot reach the
+  clear binding. Locked by a regression test.
+- **Single Esc clears** (user-chosen over double-Esc). Discoverable and
+  fast; the trade-off (an accidental Esc wipes an unsubmitted line) was
+  accepted. A submitted line is always recoverable from history; only
+  *unsubmitted* draft text is lost.
+- **Cursor-only keys don't touch history navigation.** Ctrl-A/Ctrl-E,
+  like Home/End, move the cursor without ending history recall.
+- **Buffer-mutating keys end history navigation.** Esc-clear and
+  Ctrl-W/K/U call `cancel_history_navigation` (the cleared/edited line
+  *is* the new draft), matching Backspace/Delete.
+- **Ctrl-W is readline-style and UTF-8 safe.** It eats any run of
+  trailing whitespace, then the preceding run of non-whitespace; word
+  boundaries are found on char boundaries so multi-byte words delete
+  cleanly. It only ever deletes back to the cursor (a mid-line Ctrl-W
+  leaves the suffix intact).
+
+Helpers added: `clear_input`, `delete_prev_word`, `kill_to_end`,
+`kill_to_start` (`src/app.rs`), mirroring the existing `cursor_left` /
+`delete_before_cursor` style.
+
+## Forks (all user-chosen)
+
+- **Esc semantics:** single-Esc-clears, *not* double-Esc — discoverable
+  over accident-proof.
+- **Scope:** the *full* I1b set (Esc-clear + Ctrl-A/E/W/K/U), not just
+  the issue's literal Ctrl-A/E + Esc — closes the whole I1b requirement
+  in one pass rather than leaving Ctrl-W/K/U for a follow-up.
+- **Documentation:** a new ADR (this one), recording the input-field
+  keymap convention and amending ADR-0046's OOS list — over folding it
+  into ADR-0046 or shipping it I1a-style with no ADR.
+
+## Consequences
+
+- I1b is complete; `requirements.md` I1b moves to `[x]`.
+- The new keys are **not yet advertised on screen.** Surfacing per-focus
+  keybindings in the bottom status line is issue #27's domain (a
+  separate, in-design UX change); this ADR makes the keys *work*, #27
+  will make them *discoverable*.
+- **Demo-mode badges** (ADR-0047) are *not* extended to the new Ctrl-
+  chords here. Esc already badges as `[ESC]`; Ctrl-A/E/W/K/U are
+  glyph-less and would be invisible in an asciinema cast. Whether to add
+  `[CTRL-A]`…`[CTRL-U]` badges is left to ADR-0047's scope and flagged
+  as a follow-up — it is a cast-polish concern, not a #29 requirement.
+
+## Out of scope
+
+- On-screen keybinding hints for the input field (issue #27).
+- Demo badges for the new chords (ADR-0047 follow-up; flagged above).
+- Multi-line input (I1) and its Ctrl-Enter submit — unrelated, still
+  deferred.
+- Word-wise *cursor motion* (Alt-B/Alt-F) and transpose/yank — not
+  requested; not part of I1b.