feat(web): render write/edit tool output as a diff card

The write/edit tools already declare card:'diff' with applied hunks on
callView/resultView, but the Web client discarded it: a mutation landed on
GenericToolCard and the details panel flattened the result to a <pre>. Add
DiffBlock (ui-primitives), diff-card-model (the single callView/resultView
derivation), and FileMutationRow (keyed under write and edit), and make the
generic fallback row and the details panel diff-aware. The +/- block form,
per-file path header, same-file gap, and footer mirror the TUI diff card;
the chat row caps at CHAT_DIFF_MAX_LINES against the panel's full height.

packages/client/ui-primitives/tests/diff-block.spec.tsx

@@ -0,0 +1,162 @@
+// @vitest-environment jsdom
+// DiffBlock: the per-file hunk rows (path header, removed block, added block),
+// the same-file second-hunk gap separator, the `+A -R · N file(s)` footer and
+// its singular/plural, the head/tail height cap and its expand control, the
+// empty-diffs null render, and the copy control writing the prefixed diff text
+// on both the accepted and the refused clipboard paths. writeClipboard's own
+// return contract is pinned in terminal-block.spec.tsx (the shared seam), so
+// only its DOM consequence is asserted here.
+
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { act, cleanup, fireEvent, render, screen } from '@testing-library/react'
+import { DEFAULT_DIFF_MAX_LINES, DiffBlock, type DiffHunk } from '../src/index.ts'
+
+afterEach(cleanup)
+
+beforeEach(() => {
+  vi.useRealTimers()
+})
+
+/** The rendered body rows, one string per visible line (CSS-module class prefix). */
+function bodyRows(container: HTMLElement): string[] {
+  return [...container.querySelectorAll('[class*="_line_"]')].map(row => row.textContent ?? '')
+}
+
+/** Only the changed rows (add/del), excluding the path header and gap chrome. */
+function changeRows(container: HTMLElement): string[] {
+  return [...container.querySelectorAll('[class*="_del_"], [class*="_add_"]')].map(row => row.textContent ?? '')
+}
+
+/** `count` numbered added lines as one hunk's newText. */
+function added(count: number): string {
+  return Array.from({ length: count }, (_v, i) => `line ${i + 1}`).join('\n')
+}
+
+describe('DiffBlock structure', () => {
+  it('renders a create as a path header and an added block (no removed side)', () => {
+    const diffs: DiffHunk[] = [{ path: 'notes/new.txt', oldText: null, newText: 'hello\nworld' }]
+    const { container } = render(<DiffBlock diffs={diffs} />)
+    expect(screen.getByText('notes/new.txt')).toBeTruthy()
+    // No removed rows: both change lines are added.
+    expect(changeRows(container)).toEqual(['hello', 'world'])
+    expect(container.querySelectorAll('[class*="_del_"]').length).toBe(0)
+    expect(container.querySelectorAll('[class*="_add_"]').length).toBe(2)
+  })
+
+  it('renders an edit as a removed block above an added block', () => {
+    const diffs: DiffHunk[] = [{ path: 'a.ts', oldText: 'old', newText: 'new' }]
+    const { container } = render(<DiffBlock diffs={diffs} />)
+    expect(container.querySelectorAll('[class*="_del_"]').length).toBe(1)
+    expect(container.querySelectorAll('[class*="_add_"]').length).toBe(1)
+    expect(changeRows(container)).toEqual(['old', 'new'])
+  })
+
+  it('opens a same-file second hunk with a gap instead of repeating the path', () => {
+    const diffs: DiffHunk[] = [
+      { path: 'a.ts', oldText: 'x', newText: 'y' },
+      { path: 'a.ts', oldText: 'p', newText: 'q' },
+    ]
+    const { container } = render(<DiffBlock diffs={diffs} />)
+    // One path header, one gap row.
+    expect(container.querySelectorAll('[class*="_path_"]').length).toBe(1)
+    expect(container.querySelectorAll('[class*="_gap_"]').length).toBe(1)
+  })
+
+  it('opens a new file with its own path header', () => {
+    const diffs: DiffHunk[] = [
+      { path: 'a.ts', oldText: 'x', newText: 'y' },
+      { path: 'b.ts', oldText: 'p', newText: 'q' },
+    ]
+    const { container } = render(<DiffBlock diffs={diffs} />)
+    expect(container.querySelectorAll('[class*="_path_"]').length).toBe(2)
+    expect(container.querySelectorAll('[class*="_gap_"]').length).toBe(0)
+  })
+
+  it('renders nothing for empty diffs', () => {
+    const { container } = render(<DiffBlock diffs={[]} />)
+    expect(container.firstChild).toBeNull()
+  })
+})
+
+describe('DiffBlock footer', () => {
+  it('counts added and removed lines and one file', () => {
+    const diffs: DiffHunk[] = [{ path: 'a.ts', oldText: 'a\nb', newText: 'c' }]
+    render(<DiffBlock diffs={diffs} />)
+    expect(screen.getByText('└ +1 -2 · 1 file')).toBeTruthy()
+  })
+
+  it('pluralizes the distinct-file count', () => {
+    const diffs: DiffHunk[] = [
+      { path: 'a.ts', oldText: null, newText: 'x' },
+      { path: 'b.ts', oldText: null, newText: 'y' },
+    ]
+    render(<DiffBlock diffs={diffs} />)
+    expect(screen.getByText('└ +2 -0 · 2 files')).toBeTruthy()
+  })
+})
+
+describe('DiffBlock height cap', () => {
+  it('shows head and tail with an expand control past the cap, then all lines expanded', () => {
+    // One added line over the default cap forces the collapse.
+    const diffs: DiffHunk[] = [{ path: 'a.ts', oldText: null, newText: added(DEFAULT_DIFF_MAX_LINES) }]
+    // The path header counts as a row, so a body of maxLines added lines plus
+    // the header is one over the cap.
+    const { container } = render(<DiffBlock diffs={diffs} />)
+    const toggle = screen.getByRole('button', { name: /展开其余/ })
+    expect(toggle.getAttribute('aria-expanded')).toBe('false')
+    // Collapsed shows fewer rows than the full body.
+    const collapsedCount = bodyRows(container).length
+    expect(collapsedCount).toBeLessThan(DEFAULT_DIFF_MAX_LINES + 1)
+    fireEvent.click(toggle)
+    expect(screen.getByRole('button', { name: '收起差异' }).getAttribute('aria-expanded')).toBe('true')
+    expect(bodyRows(container).length).toBeGreaterThan(collapsedCount)
+  })
+
+  it('shows no expand control at or under the cap', () => {
+    const diffs: DiffHunk[] = [{ path: 'a.ts', oldText: null, newText: added(4) }]
+    render(<DiffBlock diffs={diffs} maxLines={16} />)
+    expect(screen.queryByRole('button', { name: /展开其余|收起差异/ })).toBeNull()
+  })
+})
+
+describe('DiffBlock copy', () => {
+  it('copies the prefixed diff text and flips the label on success', async () => {
+    vi.useFakeTimers()
+    const writeText = vi.fn().mockResolvedValue(undefined)
+    Object.defineProperty(navigator, 'clipboard', { configurable: true, value: { writeText } })
+    const diffs: DiffHunk[] = [
+      { path: 'a.ts', oldText: 'old', newText: 'new' },
+      { path: 'a.ts', oldText: 'p', newText: 'q' },
+    ]
+    render(<DiffBlock diffs={diffs} />)
+    const copy = screen.getByRole('button', { name: '复制' })
+    await act(async () => { fireEvent.click(copy) })
+    // Path header, del/add prefixes, and the same-file gap all reach the clipboard.
+    expect(writeText).toHaveBeenCalledWith('a.ts\n- old\n+ new\n⋯\n- p\n+ q')
+    expect(screen.getByRole('button', { name: '复制成功' })).toBeTruthy()
+    await act(async () => { await vi.advanceTimersByTimeAsync(1000) })
+    expect(screen.getByRole('button', { name: '复制' })).toBeTruthy()
+  })
+
+  it('keeps the label on a refused clipboard write', async () => {
+    Object.defineProperty(navigator, 'clipboard', {
+      configurable: true,
+      value: { writeText: vi.fn().mockRejectedValue(new Error('denied')) },
+    })
+    render(<DiffBlock diffs={[{ path: 'a.ts', oldText: null, newText: 'x' }]} />)
+    const copy = screen.getByRole('button', { name: '复制' })
+    await act(async () => { fireEvent.click(copy) })
+    expect(screen.getByRole('button', { name: '复制' })).toBeTruthy()
+  })
+
+  it('ignores a second click while the copied label is showing', async () => {
+    vi.useFakeTimers()
+    const writeText = vi.fn().mockResolvedValue(undefined)
+    Object.defineProperty(navigator, 'clipboard', { configurable: true, value: { writeText } })
+    render(<DiffBlock diffs={[{ path: 'a.ts', oldText: null, newText: 'x' }]} />)
+    const copy = screen.getByRole('button', { name: '复制' })
+    await act(async () => { fireEvent.click(copy) })
+    await act(async () => { fireEvent.click(screen.getByRole('button', { name: '复制成功' })) })
+    expect(writeText).toHaveBeenCalledTimes(1)
+  })
+})