fix(ui): clamp cursor to last char after all NORMAL mode deletes (#21973)

packages/cli/src/ui/components/shared/vim-buffer-actions.test.ts

@@ -572,6 +572,21 @@ describe('vim-buffer-actions', () => {
         const result = handleVimAction(state, action);
         expect(result).toHaveOnlyValidCharacters();
         expect(result.lines[0]).toBe('hel');
+        // Cursor clamps to last char of the shortened line (vim NORMAL mode
+        // cursor cannot rest past the final character).
+        expect(result.cursorCol).toBe(2);
+      });
+
+      it('should clamp cursor when deleting the last character on a line', () => {
+        const state = createTestState(['hello'], 0, 4);
+        const action = {
+          type: 'vim_delete_char' as const,
+          payload: { count: 1 },
+        };
+
+        const result = handleVimAction(state, action);
+        expect(result).toHaveOnlyValidCharacters();
+        expect(result.lines[0]).toBe('hell');
         expect(result.cursorCol).toBe(3);
       });
 
@@ -626,7 +641,7 @@ describe('vim-buffer-actions', () => {
         const result = handleVimAction(state, action);
         expect(result).toHaveOnlyValidCharacters();
         expect(result.lines[0]).toBe('hello ');
-        expect(result.cursorCol).toBe(6);
+        expect(result.cursorCol).toBe(5);
       });
 
       it('should delete only the word characters if it is the last word followed by whitespace', () => {
@@ -666,6 +681,55 @@ describe('vim-buffer-actions', () => {
         expect(result).toHaveOnlyValidCharacters();
         expect(result.lines[0]).toBe('foo    ');
       });
+
+      it('should clamp cursor when dW removes the last word leaving only a trailing space', () => {
+        // cursor on 'w' in 'hello world'; dW deletes 'world' → 'hello '
+        const state = createTestState(['hello world'], 0, 6);
+        const result = handleVimAction(state, {
+          type: 'vim_delete_big_word_forward' as const,
+          payload: { count: 1 },
+        });
+        expect(result.lines[0]).toBe('hello ');
+        // col 6 is past the new line end (len 6, max valid = 5)
+        expect(result.cursorCol).toBe(5);
+      });
+    });
+
+    describe('vim_delete_word_end', () => {
+      it('should clamp cursor when de removes the last word on a line', () => {
+        // cursor on 'w' in 'hello world'; de deletes through 'd' → 'hello '
+        const state = createTestState(['hello world'], 0, 6);
+        const result = handleVimAction(state, {
+          type: 'vim_delete_word_end' as const,
+          payload: { count: 1 },
+        });
+        expect(result.lines[0]).toBe('hello ');
+        expect(result.cursorCol).toBe(5);
+      });
+    });
+
+    describe('vim_delete_big_word_end', () => {
+      it('should delete from cursor to end of WORD (skipping punctuation)', () => {
+        // cursor on 'b' in 'foo bar.baz qux'; dE treats 'bar.baz' as one WORD
+        const state = createTestState(['foo bar.baz qux'], 0, 4);
+        const result = handleVimAction(state, {
+          type: 'vim_delete_big_word_end' as const,
+          payload: { count: 1 },
+        });
+        expect(result.lines[0]).toBe('foo  qux');
+        expect(result.cursorCol).toBe(4);
+      });
+
+      it('should clamp cursor when dE removes the last WORD on a line', () => {
+        // cursor on 'w' in 'hello world'; dE deletes through 'd' → 'hello '
+        const state = createTestState(['hello world'], 0, 6);
+        const result = handleVimAction(state, {
+          type: 'vim_delete_big_word_end' as const,
+          payload: { count: 1 },
+        });
+        expect(result.lines[0]).toBe('hello ');
+        expect(result.cursorCol).toBe(5);
+      });
     });
 
     describe('vim_delete_word_backward', () => {
@@ -751,7 +815,7 @@ describe('vim-buffer-actions', () => {
         const result = handleVimAction(state, action);
         expect(result).toHaveOnlyValidCharacters();
         expect(result.lines[0]).toBe('hello');
-        expect(result.cursorCol).toBe(5);
+        expect(result.cursorCol).toBe(4);
       });
 
       it('should do nothing at end of line', () => {
@@ -781,7 +845,7 @@ describe('vim-buffer-actions', () => {
         expect(result).toHaveOnlyValidCharacters();
         // 2D at position 5 on "line one" should delete "one" + entire "line two"
         expect(result.lines).toEqual(['line ', 'line three']);
-        expect(result.cursorCol).toBe(5);
+        expect(result.cursorCol).toBe(4);
       });
 
       it('should handle count exceeding available lines', () => {
@@ -2094,6 +2158,18 @@ describe('vim-buffer-actions', () => {
       });
       expect(result.undoStack.length).toBeGreaterThan(0);
     });
+
+    it('df: clamps cursor when deleting through the last char on the line', () => {
+      // cursor at 1 in 'hello'; dfo finds 'o' at col 4 and deletes [1,4] → 'h'
+      const state = createTestState(['hello'], 0, 1);
+      const result = handleVimAction(state, {
+        type: 'vim_delete_to_char_forward' as const,
+        payload: { char: 'o', count: 1, till: false },
+      });
+      expect(result.lines[0]).toBe('h');
+      // cursor was at col 1, new line has only col 0 valid
+      expect(result.cursorCol).toBe(0);
+    });
   });
 
   describe('vim_delete_to_char_backward (dF/dT)', () => {
@@ -2138,5 +2214,17 @@ describe('vim-buffer-actions', () => {
       });
       expect(result.undoStack.length).toBeGreaterThan(0);
     });
+
+    it('dF: clamps cursor when deletion removes chars up to end of line', () => {
+      // 'hello', cursor on last char 'o' (col 4), dFe finds 'e' at col 1
+      // deletes [1, 5) → 'h'; without clamp cursor would be at col 1 (past end)
+      const state = createTestState(['hello'], 0, 4);
+      const result = handleVimAction(state, {
+        type: 'vim_delete_to_char_backward' as const,
+        payload: { char: 'e', count: 1, till: false },
+      });
+      expect(result.lines[0]).toBe('h');
+      expect(result.cursorCol).toBe(0);
+    });
   });
 });

packages/cli/src/ui/components/shared/vim-buffer-actions.ts

@@ -109,6 +109,20 @@ function findCharInLine(
   return found;
 }
 
+/**
+ * In NORMAL mode the cursor can never rest past the last character of a line.
+ * Call this after any delete action that stays in NORMAL mode to enforce that
+ * invariant. Change actions must NOT use this — they immediately enter INSERT
+ * mode where the cursor is allowed to sit at the end of the line.
+ */
+function clampNormalCursor(state: TextBufferState): TextBufferState {
+  const line = state.lines[state.cursorRow] || '';
+  const len = cpLen(line);
+  const maxCol = Math.max(0, len - 1);
+  if (state.cursorCol <= maxCol) return state;
+  return { ...state, cursorCol: maxCol };
+}
+
 export function handleVimAction(
   state: TextBufferState,
   action: VimAction,
@@ -143,7 +157,7 @@ export function handleVimAction(
 
       if (endRow !== cursorRow || endCol !== cursorCol) {
         const nextState = detachExpandedPaste(pushUndo(state));
-        return replaceRangeInternal(
+        const newState = replaceRangeInternal(
           nextState,
           cursorRow,
           cursorCol,
@@ -151,6 +165,9 @@ export function handleVimAction(
           endCol,
           '',
         );
+        return action.type === 'vim_delete_word_forward'
+          ? clampNormalCursor(newState)
+          : newState;
       }
       return state;
     }
@@ -185,7 +202,7 @@ export function handleVimAction(
 
       if (endRow !== cursorRow || endCol !== cursorCol) {
         const nextState = pushUndo(state);
-        return replaceRangeInternal(
+        const newState = replaceRangeInternal(
           nextState,
           cursorRow,
           cursorCol,
@@ -193,6 +210,9 @@ export function handleVimAction(
           endCol,
           '',
         );
+        return action.type === 'vim_delete_big_word_forward'
+          ? clampNormalCursor(newState)
+          : newState;
       }
       return state;
     }
@@ -298,7 +318,7 @@ export function handleVimAction(
 
       if (endRow !== cursorRow || endCol !== cursorCol) {
         const nextState = detachExpandedPaste(pushUndo(state));
-        return replaceRangeInternal(
+        const newState = replaceRangeInternal(
           nextState,
           cursorRow,
           cursorCol,
@@ -306,6 +326,9 @@ export function handleVimAction(
           endCol,
           '',
         );
+        return action.type === 'vim_delete_word_end'
+          ? clampNormalCursor(newState)
+          : newState;
       }
       return state;
     }
@@ -351,7 +374,7 @@ export function handleVimAction(
 
       if (endRow !== cursorRow || endCol !== cursorCol) {
         const nextState = pushUndo(state);
-        return replaceRangeInternal(
+        const newState = replaceRangeInternal(
           nextState,
           cursorRow,
           cursorCol,
@@ -359,6 +382,9 @@ export function handleVimAction(
           endCol,
           '',
         );
+        return action.type === 'vim_delete_big_word_end'
+          ? clampNormalCursor(newState)
+          : newState;
       }
       return state;
     }
@@ -432,12 +458,13 @@ export function handleVimAction(
       const { count } = action.payload;
       const currentLine = lines[cursorRow] || '';
       const totalLines = lines.length;
+      const isDelete = action.type === 'vim_delete_to_end_of_line';
 
       if (count === 1) {
         // Single line: delete from cursor to end of current line
         if (cursorCol < cpLen(currentLine)) {
           const nextState = detachExpandedPaste(pushUndo(state));
-          return replaceRangeInternal(
+          const newState = replaceRangeInternal(
             nextState,
             cursorRow,
             cursorCol,
@@ -445,6 +472,7 @@ export function handleVimAction(
             cpLen(currentLine),
             '',
           );
+          return isDelete ? clampNormalCursor(newState) : newState;
         }
         return state;
       } else {
@@ -457,7 +485,7 @@ export function handleVimAction(
           // No additional lines to delete, just delete to EOL
           if (cursorCol < cpLen(currentLine)) {
             const nextState = detachExpandedPaste(pushUndo(state));
-            return replaceRangeInternal(
+            const newState = replaceRangeInternal(
               nextState,
               cursorRow,
               cursorCol,
@@ -465,6 +493,7 @@ export function handleVimAction(
               cpLen(currentLine),
               '',
             );
+            return isDelete ? clampNormalCursor(newState) : newState;
           }
           return state;
         }
@@ -472,7 +501,7 @@ export function handleVimAction(
         // Delete from cursor position to end of endRow (including newlines)
         const nextState = detachExpandedPaste(pushUndo(state));
         const endLine = lines[endRow] || '';
-        return replaceRangeInternal(
+        const newState = replaceRangeInternal(
           nextState,
           cursorRow,
           cursorCol,
@@ -480,6 +509,7 @@ export function handleVimAction(
           cpLen(endLine),
           '',
         );
+        return isDelete ? clampNormalCursor(newState) : newState;
       }
     }
 
@@ -1035,7 +1065,7 @@ export function handleVimAction(
       if (cursorCol < lineLength) {
         const deleteCount = Math.min(count, lineLength - cursorCol);
         const nextState = detachExpandedPaste(pushUndo(state));
-        return replaceRangeInternal(
+        const newState = replaceRangeInternal(
           nextState,
           cursorRow,
           cursorCol,
@@ -1043,6 +1073,7 @@ export function handleVimAction(
           cursorCol + deleteCount,
           '',
         );
+        return clampNormalCursor(newState);
       }
       return state;
     }
@@ -1298,13 +1329,15 @@ export function handleVimAction(
       if (found === -1) return state;
       const endCol = till ? found : found + 1;
       const nextState = detachExpandedPaste(pushUndo(state));
-      return replaceRangeInternal(
-        nextState,
-        cursorRow,
-        cursorCol,
-        cursorRow,
-        endCol,
-        '',
+      return clampNormalCursor(
+        replaceRangeInternal(
+          nextState,
+          cursorRow,
+          cursorCol,
+          cursorRow,
+          endCol,
+          '',
+        ),
       );
     }
 
@@ -1331,7 +1364,11 @@ export function handleVimAction(
         endCol,
         '',
       );
-      return { ...resultState, cursorCol: startCol, preferredCol: null };
+      return clampNormalCursor({
+        ...resultState,
+        cursorCol: startCol,
+        preferredCol: null,
+      });
     }
 
     case 'vim_find_char_forward': {

packages/cli/src/ui/hooks/vim.test.tsx

@@ -1044,9 +1044,10 @@ describe('useVim hook', () => {
         });
 
         // Should delete "world" (no trailing space at end), leaving "hello "
+        // Cursor clamps to last valid index in NORMAL mode (col 5 = trailing space)
         expect(result.lines).toEqual(['hello ']);
         expect(result.cursorRow).toBe(0);
-        expect(result.cursorCol).toBe(6);
+        expect(result.cursorCol).toBe(5);
       });
 
       it('should delete multiple words with count', () => {
@@ -1726,7 +1727,8 @@ describe('useVim hook', () => {
         count: 1,
         expectedLines: ['hello '],
         expectedCursorRow: 0,
-        expectedCursorCol: 6,
+        // Cursor clamps to last valid index in NORMAL mode (col 5 = trailing space)
+        expectedCursorCol: 5,
       },
       {
         command: 'D',