Add Emacs/readline editing mode

[colonelpanic8]

Summary

• add a persisted client-local keyboard editing mode with Browser default and Emacs / readline options
• support common readline movement, deletion, kill/yank, transpose, and word-navigation bindings across text inputs and contenteditable editors
• make Control-N and Control-P navigate command palettes, comboboxes, selects, menus, and other candidate lists while the mode is active
• preserve terminal-native key handling

Why

Browser text controls do not consistently provide Emacs/readline editing shortcuts across platforms, and candidate-selection surfaces only respond to arrow keys. This mode provides a consistent opt-in editing experience throughout T3 Code.

Validation

• vp test run packages/contracts/src/settings.test.ts apps/web/src/emacsReadlineBindings.test.ts apps/web/src/AppRoot.test.tsx (39 tests)
• targeted contracts and web type checks
• targeted formatter and lint checks
• isolated live web verification of mode persistence, Control-A, Control-E, Control-W, Control-Y, and Control-N/Control-P command-palette navigation

---

Note

Medium Risk
A global capture-phase keyboard listener and new precedence between readline chords, default shortcuts, and Lexical composer edits can change keyboard behavior app-wide when the mode is enabled.

Overview
Adds an opt-in keyboardEditingMode client setting (default vs Emacs / readline) in General settings, persisted through contracts and desktop client settings.

When Emacs mode is on, EmacsReadlineBindings registers a capture-phase keydown handler that applies readline chords to plain inputs, textareas, and generic contenteditable surfaces, maps Control-N/P to arrow navigation for open candidate pickers (with focus scoping), and skips terminals and keybinding-capture fields. Custom app shortcuts still win over readline via new resolveCustomShortcutCommand and optional source (default | user) on resolved keybindings; server runtime marks shipped defaults as default.

The Lexical composer gets a dedicated plugin that treats mention/skill chips as single logical characters, integrates kill/yank with chip reconstruction, and uses data-emacs-readline-managed so the global handler defers mutations to the editor.

^{Reviewed by Cursor Bugbot for commit 4189d3c. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add Emacs/readline editing mode for text inputs and the composer

• Adds a new EmacsReadlineBindings component that registers a global capture-phase keydown listener, routing Ctrl/Alt chords through an Emacs/readline keybinding engine (emacsReadlineBindings.ts) for all text inputs, textareas, and contenteditable elements.
• Implements grapheme-aware cursor movement, word/line navigation, kill/yank with a process-wide kill ring, transpose, and delete operations across plain text controls and contenteditable hosts.
• Adds ComposerEmacsReadlinePlugin to the Lexical composer, treating inline mention/skill chips as single logical characters and integrating kill/yank with the kill ring; transpose across inline tokens is a no-op.
• Adds a keyboardEditingMode setting ('default' | 'emacs') to ClientSettings, exposed in the General settings panel; Emacs mode is off by default.
• Extends the keybinding system with a source field ('default' | 'user') on resolved rules and a resolveCustomShortcutCommand API so Emacs key chords can yield to explicit user-defined application shortcuts without conflicting with built-in defaults.

^{Macroscope summarized 4189d3c.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a complete new feature (Emacs/readline editing mode) with ~2200 lines of new logic, new components, global event handling, and settings integration. New features of this scope warrant human review.

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 4 potential issues.

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^{Reviewed by Cursor Bugbot for commit 048b91d. Configure here.}