refactor(cli): extract keyboard navigation from multiline-input.tsx

(Commit 2.5a)

Extract keyboard handling into dedicated hooks and utilities:
- use-keyboard-navigation.ts: Arrow keys, home/end, word navigation
- use-keyboard-shortcuts.ts: Enter, deletion, emacs bindings
- text-navigation.ts: Text boundary helpers (findLineStart, findLineEnd,
  etc.)
- keyboard-event-utils.ts: Keyboard event helpers (isAltModifier, etc.)

Reduces multiline-input.tsx from ~1,102 to ~560 lines.

All 1,911 CLI tests pass. Reviewed by 4 CLI agents.

Author: brandonkachen

REFACTORING_PLAN.md

@@ -15,8 +15,8 @@ This document outlines a prioritized refactoring plan for the 51 issues identifi
 
 ## Progress Tracker
 
-> **Last Updated:** 2025-01-20 (Commits 2.1–2.4 Complete)
-> **Current Status:** Ready for Commit 2.5a (multiline keyboard navigation)
+> **Last Updated:** 2025-01-20 (Commits 2.1–2.5a Complete)
+> **Current Status:** Ready for Commit 2.5b (multiline editing handlers)
 
 ### Phase 1 Progress
 | Commit | Description | Status | Completed By |
@@ -34,7 +34,7 @@ This document outlines a prioritized refactoring plan for the 51 issues identifi
 | 2.2 | Consolidate block utils + think tags | ✅ Complete | Codebuff |
 | 2.3 | Refactor loopAgentSteps | ✅ Complete | Codex CLI |
 | 2.4 | Consolidate billing duplication | ✅ Complete | Codex CLI |
-| 2.5a | Extract multiline keyboard navigation | ⬜ Not Started | - |
+| 2.5a | Extract multiline keyboard navigation | ✅ Complete | Codebuff |
 | 2.5b | Extract multiline editing handlers | ⬜ Not Started | - |
 | 2.6 | Simplify use-activity-query.ts | ⬜ Not Started | - |
 | 2.7 | Consolidate XML parsing | ⬜ Not Started | - |
@@ -395,22 +395,88 @@ During Commit 2.4 review, two pre-existing issues were identified and fixed:
 
 ---
 
-### Commit 2.5a: Extract Multiline Input Keyboard Navigation
+### Commit 2.5a: Extract Multiline Input Keyboard Navigation ✅ COMPLETE
 **Files:** `cli/src/components/multiline-input.tsx`  
 **Est. Time:** 3-4 hours  
-**Est. LOC Changed:** ~500-550
+**Actual Time:** ~5 hours (including stale closure bug discovery and fix)  
+**Est. LOC Changed:** ~500-550  
+**Actual LOC Changed:** 704 insertions, 563 deletions
 
 > ⚠️ **Corrected:** File is 1,102 lines, not 350-450. Split into two commits.
 
-| Task | Description |
-|------|-------------|
-| Create `useKeyboardNavigation` hook | Arrow keys, home/end |
-| Create `useKeyboardShortcuts` hook | Ctrl+C, Ctrl+D, etc. |
-| Update multiline-input | Delegate navigation to hooks |
+| Task | Description | Status |
+|------|-------------|--------|
+| Create `useKeyboardNavigation` hook | Arrow keys, home/end, word navigation, emacs bindings | ✅ |
+| Create `useKeyboardShortcuts` hook | Enter, deletion, Ctrl+C, Ctrl+D, etc. | ✅ |
+| Create `text-navigation.ts` utilities | findLineStart, findLineEnd, word boundary helpers | ✅ |
+| Create `keyboard-event-utils.ts` | isAltModifier, keyboard event helpers | ✅ |
+| Update multiline-input | Delegate navigation to hooks | ✅ |
+| Fix stale closure bug | Prevent stale state in rapid keypresses | ✅ |
+
+**New Files Created:**
+- `cli/src/hooks/use-keyboard-navigation.ts` (~210 lines) - Navigation key handling:
+  - Arrow key navigation (up/down/left/right)
+  - Word navigation (Alt+Left/Right, Alt+B/F)
+  - Line navigation (Home/End, Cmd+Left/Right, Ctrl+A/E)
+  - Document navigation (Cmd+Up/Down, Ctrl+Home/End)
+  - Emacs bindings (Ctrl+B, Ctrl+F)
+  - Sticky column handling for vertical navigation
+- `cli/src/hooks/use-keyboard-shortcuts.ts` (~280 lines) - Enter/deletion key handling:
+  - Enter handling (plain, shift, option, backslash)
+  - Deletion keys (backspace, delete, Ctrl+H, Ctrl+D)
+  - Word deletion (Alt+Backspace, Ctrl+W, Alt+Delete)
+  - Line deletion (Ctrl+U, Ctrl+K, Cmd+Delete)
+- `cli/src/utils/text-navigation.ts` (~50 lines) - Text boundary helpers:
+  - `findLineStart`, `findLineEnd`
+  - `findPreviousWordBoundary`, `findNextWordBoundary`
+- `cli/src/utils/keyboard-event-utils.ts` (~30 lines) - Keyboard event helpers:
+  - `isAltModifier` (handles escape sequences for Alt key)
+  - `isPrintableCharacterKey`
+
+**Component Size Reduction:**
+- `multiline-input.tsx`: ~1,102 → ~560 lines (-542 lines, -49%)
+
+**Stale Closure Bug Fix:**
+
+During tmux testing, a critical stale closure bug was discovered:
+
+| Issue | Problem | Solution |
+|-------|---------|----------|
+| **Stale state in callbacks** | Hooks captured `value` and `cursorPosition` at render time. Rapid keypresses (e.g., Left arrow then typing) used stale values | Created `stateRef` to hold current state, updated synchronously |
+| **React batching delay** | `onChange` updates state, but React may not re-render before next keypress | Created `onChangeWithRef` wrapper that updates `stateRef.current` immediately before calling `onChange` |
+
+**Implementation Pattern:**
+```typescript
+// State ref for real-time access (avoids stale closures)
+const stateRef = useRef({ value, cursorPosition })
+stateRef.current = { value, cursorPosition }
+
+// Wrapper that updates ref immediately before React state
+const onChangeWithRef = useCallback(
+  (newValue: string, newCursor: number) => {
+    stateRef.current = { value: newValue, cursorPosition: newCursor }
+    onChange(newValue, newCursor)
+  },
+  [onChange],
+)
+```
+
+**Test Results:**
+- 1,911 CLI tests pass
+- TypeScript compiles cleanly
+- Verified via tmux testing with character-by-character input
+
+**Review Findings (from 4 CLI agents):**
+- ✅ Extraction boundaries well-chosen with clear responsibilities
+- ✅ Keyboard behavior exactly preserved
+- ✅ No dead code or unused exports
+- ⚠️ Optional: Move `isPrintableCharacterKey` to keyboard-event-utils.ts
+- ⚠️ Optional: Remove verbose JSDoc/AI slop comments
 
 **Dependencies:** Commit 2.1 (use-send-message patterns)  
 **Risk:** Medium - User input handling  
-**Rollback:** Revert single commit
+**Rollback:** Revert single commit  
+**Commit:** `fc4a66569`
 
 ---