perf(web-read-card): lazy-load read grammars and guard empty-window copy

Only TypeScript, shell, and JSON grammars load at Web boot; the read card's
wider langFromPath extension set loads through dynamic imports on first use,
so a session that never opens a read card in one of those languages avoids
~1.6 MB of grammar modules and their synchronous init. ReadBlock/CodeBlock
re-render on grammar-load via useSyncExternalStore, picking up highlighting
once the grammar registers. ReadBlock hides the copy control on an empty
window (a successful read of an empty file settles to lines: [] with
card:'read'), matching TerminalBlock so it cannot wipe the clipboard.

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

@@ -31,6 +31,24 @@ describe('highlightToHtml', () => {
     expect(highlightToHtml('x', 'cobol')).toBeUndefined()
     expect(highlightToHtml('x', undefined)).toBeUndefined()
   })
+
+  // Every read-tool language hint whose grammar loads lazily (the boot set —
+  // ts/js/bash/sh/json — is covered above). Touching each one drives its own
+  // dynamic import thunk, so the whole LAZY_GRAMMARS table is exercised.
+  const LAZY_ALIASES = [
+    'py', 'rb', 'go', 'rs', 'java', 'c', 'cpp', 'cs', 'kotlin', 'swift', 'php',
+    'yaml', 'toml', 'ini', 'md', 'mdx', 'html', 'css', 'scss', 'less', 'sql',
+    'xml', 'lua',
+  ]
+
+  it('lazily loads every read-card grammar: plain first, highlighted after load', async () => {
+    // First touch returns the plain fallback (undefined) and starts the import.
+    for (const alias of LAZY_ALIASES) expect(highlightToHtml('x', alias)).toBeUndefined()
+    // Once every grammar has registered, the same call highlights.
+    await vi.waitFor(() => {
+      for (const alias of LAZY_ALIASES) expect(highlightToHtml('x', alias)).toContain('shiki')
+    })
+  })
 })
 
 describe('CodeBlock', () => {

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

@@ -10,7 +10,7 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { act, cleanup, fireEvent, render, screen } from '@testing-library/react'
 import { DEFAULT_READ_MAX_LINES, ReadBlock, type ReadBlockLine } from '../src/index.ts'
-import { highlightLines } from '../src/markdown/highlight.ts'
+import { grammarLoadCount, highlightLines, subscribeGrammarLoaded } from '../src/markdown/highlight.ts'
 
 afterEach(cleanup)
 
@@ -71,6 +71,25 @@ describe('highlightLines', () => {
     expect(highlightLines('x', 'cobol')).toBeUndefined()
     expect(highlightLines('x', undefined)).toBeUndefined()
   })
+
+  it('loads a lazy grammar on first use: plain first, highlighted after it registers', async () => {
+    // A boot grammar (ts) is ready synchronously; a lazy grammar (python) is
+    // not, so the first call renders plain and imports the grammar, and a
+    // subscriber fires once it registers, after which the same call highlights.
+    let notified = 0
+    const stop = subscribeGrammarLoaded(() => { notified += 1 })
+    // First touch: grammar not loaded yet, so plain fallback while it imports.
+    expect(highlightLines('def f(): pass', 'py')).toBeUndefined()
+    // The import + loadLanguageSync resolve on a microtask; wait for the notify.
+    await vi.waitFor(() => { expect(notified).toBeGreaterThan(0) })
+    expect(grammarLoadCount()).toBeGreaterThan(0)
+    const result = highlightLines('def f(): pass', 'py')
+    expect(result).not.toBeUndefined()
+    // `def` is a python keyword and carries a --shiki-* color once highlighted.
+    const keyword = result!.flat().find(span => span.text === 'def')
+    expect(keyword?.style?.color).toContain('var(--shiki-')
+    stop()
+  })
 })
 
 describe('ReadBlock rows', () => {
@@ -212,4 +231,11 @@ describe('ReadBlock copy', () => {
     const view = render(<ReadBlock className="x" label="a" lines={lines(1)} totalLines={1} />)
     expect(view.container.firstElementChild?.classList.contains('x')).toBe(true)
   })
+
+  it('hides the copy control for an empty window so it cannot wipe the clipboard', () => {
+    // A successful read of an empty file settles to lines: [] with card:'read',
+    // so this branch is reachable; copying then would clear the clipboard.
+    const view = render(<ReadBlock label="empty.ts" lines={[]} totalLines={0} />)
+    expect(view.queryByRole('button', { name: '复制' })).toBeNull()
+  })
 })