Add readline-like keybindings to the input prompts. (#354)

New keybindings in the main input prompt (when auto-suggestions are not active):

  - `Ctrl+L`: Clears the entire screen.
  - `Ctrl+A`: Moves the cursor to the beginning of the current input line.
  - `Ctrl+E`: Moves the cursor to the end of the current input line.
  - `Ctrl+P`: Navigates to the previous command in the input history.
  - `Ctrl+N`: Navigates to the next command in the input history.

In the multiline text editor (e.g., when editing a previous message):
   - `Ctrl+K`: Deletes text from the current cursor position to the end of the line ("kill line right").

2 files changed, 82 insertions, 4 deletions

diff --git a/packages/cli/src/ui/components/shared/multiline-editor.tsx b/packages/cli/src/ui/components/shared/multiline-editor.tsx
index bd49efcb..e1e21fff 100644
--- a/packages/cli/src/ui/components/shared/multiline-editor.tsx
+++ b/packages/cli/src/ui/components/shared/multiline-editor.tsx
@@ -43,7 +43,12 @@ export interface MultilineTextEditorProps {
 
   // Called on all key events to allow the caller. Returns true if the
   // event was handled and should not be passed to the editor.
-  readonly inputPreprocessor?: (input: string, key: Key) => boolean;
+  readonly inputPreprocessor?: (
+    input: string,
+    key: Key,
+    currentText: string,
+    cursorOffset: number,
+  ) => boolean;
 
   // Optional initial cursor position (character offset)
   readonly initialCursorOffset?: number;
@@ -92,7 +97,24 @@ export const MultilineTextEditor = ({
         return;
       }
 
-      if (inputPreprocessor?.(input, key) === true) {
+      // Calculate cursorOffset for inputPreprocessor
+      let charOffset = 0;
+      for (let i = 0; i < buffer.cursor[0]; i++) {
+        charOffset += buffer.lines[i].length + 1; // +1 for newline
+      }
+      charOffset += buffer.cursor[1];
+
+      if (inputPreprocessor?.(input, key, buffer.text, charOffset) === true) {
+        return;
+      }
+
+      if (key.ctrl && input === 'k') {
+        buffer.killLineRight();
+        return;
+      }
+
+      if (key.ctrl && input === 'u') {
+        buffer.killLineLeft();
         return;
       }
 
diff --git a/packages/cli/src/ui/components/shared/text-buffer.ts b/packages/cli/src/ui/components/shared/text-buffer.ts
index f2cb1ae2..661df70c 100644
--- a/packages/cli/src/ui/components/shared/text-buffer.ts
+++ b/packages/cli/src/ui/components/shared/text-buffer.ts
@@ -372,9 +372,9 @@ export function useTextBuffer({
     pushUndo,
     cursorRow,
     cursorCol,
-    lines,
     currentLine,
     currentLineLen,
+    lines.length,
     setPreferredCol,
   ]);
 
@@ -521,12 +521,58 @@ export function useTextBuffer({
     pushUndo,
     cursorRow,
     cursorCol,
-    lines,
     currentLine,
     del,
+    lines.length,
     setPreferredCol,
   ]);
 
+  const killLineRight = useCallback((): void => {
+    const lineContent = currentLine(cursorRow);
+    if (cursorCol < currentLineLen(cursorRow)) {
+      // Cursor is before the end of the line's content, delete text to the right
+      pushUndo();
+      setLines((prevLines) => {
+        const newLines = [...prevLines];
+        newLines[cursorRow] = cpSlice(lineContent, 0, cursorCol);
+        return newLines;
+      });
+      // Cursor position and preferredCol do not change in this case
+    } else if (
+      cursorCol === currentLineLen(cursorRow) &&
+      cursorRow < lines.length - 1
+    ) {
+      // Cursor is at the end of the line's content (or line is empty),
+      // and it's not the last line. Delete the newline.
+      // `del()` handles pushUndo and setPreferredCol.
+      del();
+    }
+    // If cursor is at the end of the line and it's the last line, do nothing.
+  }, [
+    pushUndo,
+    cursorRow,
+    cursorCol,
+    currentLine,
+    currentLineLen,
+    lines.length,
+    del,
+  ]);
+
+  const killLineLeft = useCallback((): void => {
+    const lineContent = currentLine(cursorRow);
+    // Only act if the cursor is not at the beginning of the line
+    if (cursorCol > 0) {
+      pushUndo();
+      setLines((prevLines) => {
+        const newLines = [...prevLines];
+        newLines[cursorRow] = cpSlice(lineContent, cursorCol);
+        return newLines;
+      });
+      setCursorCol(0);
+      setPreferredCol(null);
+    }
+  }, [pushUndo, cursorRow, cursorCol, currentLine, setPreferredCol]);
+
   const move = useCallback(
     (dir: Direction): void => {
       const before = [cursorRow, cursorCol];
@@ -772,6 +818,8 @@ export function useTextBuffer({
     replaceRange,
     deleteWordLeft,
     deleteWordRight,
+    killLineRight,
+    killLineLeft,
     handleInput,
     openInExternalEditor,
 
@@ -873,6 +921,14 @@ export interface TextBuffer {
    */
   deleteWordRight: () => void;
   /**
+   * Deletes text from the cursor to the end of the current line.
+   */
+  killLineRight: () => void;
+  /**
+   * Deletes text from the start of the current line to the cursor.
+   */
+  killLineLeft: () => void;
+  /**
    * High level "handleInput" – receives what Ink gives us.
    */
   handleInput: (