Number diff lines, render task lists, and add word navigation

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

test/diff.test.tsx

@@ -50,6 +50,45 @@ test('the rendered diff marks additions and removals and counts them', () => {
   app.unmount();
 });
 
+test('changed lines carry their line numbers, old and new', () => {
+  const before = ['one', 'two', 'three'].join('\n');
+  const after = ['one', 'TWO', 'three'].join('\n');
+  const app = render(<Diff before={before} after={after} />);
+
+  const frame = app.lastFrame() ?? '';
+  // `two` was line 2 before and `TWO` is line 2 after: a diff without numbers
+  // forces the reader to count them, which is exactly what the panel is for.
+  expect(frame).toMatch(/2.*- two/);
+  expect(frame).toMatch(/2.*\+ TWO/);
+  app.unmount();
+});
+
+test('a gap names the line range it hides, so the reader can jump there', () => {
+  const lines = Array.from({ length: 40 }, (_, i) => `line ${i + 1}`).join('\n');
+  const app = render(<Diff before={lines} after={lines.replace('line 30', 'CHANGED')} />);
+
+  const frame = app.lastFrame() ?? '';
+  expect(frame).toContain('CHANGED');
+  // "27 unchanged lines" says how much; "lines 1-27" says where, which is what a
+  // reader needs to open the file at the right place.
+  expect(frame).toMatch(/lines \d+-\d+/);
+  app.unmount();
+});
+
+test('added and removed lines count up separately through one diff', () => {
+  const before = ['a', 'b'].join('\n');
+  const after = ['a', 'B', 'c', 'd'].join('\n');
+  const app = render(<Diff before={before} after={after} path="src/x.ts" />);
+
+  // The header is the part a reader scans for: +3 -1 answers "how big was this"
+  // before the lines are read at all.
+  const frame = app.lastFrame() ?? '';
+  expect(frame).toContain('+3');
+  expect(frame).toContain('-1');
+  expect(frame).toContain('src/x.ts');
+  app.unmount();
+});
+
 test('a very large diff is truncated with a notice', () => {
   const before = Array.from({ length: 200 }, (_, i) => `line ${i}`).join('\n');
   const after = Array.from({ length: 200 }, (_, i) => `changed ${i}`).join('\n');

test/input.test.tsx

@@ -134,6 +134,73 @@ test('ctrl-u clears to the start of the line', async () => {
   app.unmount();
 }, 20_000);
 
+// Word-wise motion: the escape sequences a shell sends for ctrl-left/right.
+const CTRL_LEFT = '\u001B[1;5D';
+const CTRL_RIGHT = '\u001B[1;5C';
+
+test('ctrl-left jumps the cursor back one word', async () => {
+  const { app, session } = mount();
+  await wait(150);
+  await type(app, 'one two');
+  await press(app, CTRL_LEFT);
+  await type(app, 'X ');
+  await press(app, '\r', 500);
+  // Cursor was after "two"; a word jump puts it before it, so the X lands between.
+  expect(session.messages[0]?.content).toBe('one X two');
+  app.unmount();
+}, 20_000);
+
+test('ctrl-right jumps the cursor forward one word over a gap', async () => {
+  const { app, session } = mount();
+  await wait(150);
+  await press(app, 'one two', 150);
+  // Back before "one", then one word forward: the jump crosses the word and stops
+  // at its end, not one character along.
+  await press(app, CTRL_LEFT);
+  await press(app, CTRL_LEFT);
+  await press(app, CTRL_RIGHT);
+  await type(app, 'X');
+  await press(app, '\r', 500);
+  expect(session.messages[0]?.content).toBe('oneX two');
+  app.unmount();
+}, 20_000);
+
+test('a word jump over the line edge stays put', async () => {
+  const { app, session } = mount();
+  await wait(150);
+  await type(app, 'abc');
+  // Three jumps past the start: the cursor must clamp, not walk off the string.
+  await press(app, CTRL_LEFT);
+  await press(app, CTRL_LEFT);
+  await type(app, 'X');
+  await press(app, '\r', 500);
+  expect(session.messages[0]?.content).toBe('Xabc');
+  app.unmount();
+}, 20_000);
+
+test('ctrl-d deletes forward from the cursor', async () => {
+  const { app, session } = mount();
+  await wait(150);
+  await type(app, 'abcd');
+  // Back to the start, then delete two characters forward.
+  await press(app, '\u0001');
+  await press(app, '\u0004');
+  await press(app, '\u0004');
+  await press(app, '\r', 500);
+  expect(session.messages[0]?.content).toBe('cd');
+  app.unmount();
+}, 20_000);
+
+test('ctrl-d at the end of the line deletes nothing', async () => {
+  const { app, session } = mount();
+  await wait(150);
+  await type(app, 'end');
+  await press(app, '\u0004');
+  await press(app, '\r', 500);
+  expect(session.messages[0]?.content).toBe('end');
+  app.unmount();
+}, 20_000);
+
 test('a pasted multi-character chunk is inserted whole', async () => {
   const { app, session } = mount();
   await wait(150);

test/ui-panels.test.tsx

@@ -20,6 +20,24 @@ test('markdown renders headings, bullets, and code distinctly', () => {
   app.unmount();
 });
 
+test('a task list renders as checkboxes, not as literal brackets', () => {
+  // Models write progress as markdown task lists. Rendering "- [x] done" literally
+  // turns a status report into markup noise.
+  const app = render(<Markdown text={'- [x] first\n- [ ] second'} />);
+  const frame = app.lastFrame() ?? '';
+  expect(frame).toContain('[x] first');
+  expect(frame).toContain('[ ] second');
+  app.unmount();
+});
+
+test('an ordered list keeps its numbers rather than becoming dashes', () => {
+  const app = render(<Markdown text={'1. first step\n2. second step'} />);
+  const frame = app.lastFrame() ?? '';
+  expect(frame).toContain('1. first step');
+  expect(frame).toContain('2. second step');
+  app.unmount();
+});
+
 test('markdown strips the markup characters from the rendered output', () => {
   const app = render(<Markdown text={'Use **bold** and `code` here.'} />);
   const frame = app.lastFrame() ?? '';