feat(app): add @ workspace file autocomplete in agent chat

packages/app/src/utils/file-mention-autocomplete.test.ts

@@ -0,0 +1,61 @@
+import { describe, expect, it } from 'vitest'
+import { applyFileMentionReplacement, findActiveFileMention } from './file-mention-autocomplete'
+
+describe('findActiveFileMention', () => {
+  it('detects mentions at the start of input', () => {
+    const mention = findActiveFileMention({
+      text: '@src/components',
+      cursorIndex: '@src/components'.length,
+    })
+    expect(mention).toEqual({
+      start: 0,
+      end: '@src/components'.length,
+      query: 'src/components',
+    })
+  })
+
+  it('detects mentions in the middle of input using cursor position', () => {
+    const text = 'read "@src/com" before merging'
+    const cursorIndex = text.indexOf('"') + 9
+    const mention = findActiveFileMention({
+      text,
+      cursorIndex,
+    })
+    expect(mention).toEqual({
+      start: text.indexOf('@'),
+      end: cursorIndex,
+      query: 'src/com',
+    })
+  })
+
+  it('returns null when cursor is outside the mention token', () => {
+    const text = 'please review @src/components now'
+    const mention = findActiveFileMention({
+      text,
+      cursorIndex: text.length,
+    })
+    expect(mention).toBeNull()
+  })
+})
+
+describe('applyFileMentionReplacement', () => {
+  it('replaces only the active @query segment with a quoted relative path', () => {
+    const text = 'open @src/com next'
+    const next = applyFileMentionReplacement({
+      text,
+      mention: { start: 5, end: 13, query: 'src/com' },
+      relativePath: 'src/components/chat.tsx',
+    })
+    expect(next).toBe('open "src/components/chat.tsx" next')
+  })
+
+  it('escapes double quotes in replacement path', () => {
+    const text = '@foo'
+    const next = applyFileMentionReplacement({
+      text,
+      mention: { start: 0, end: 4, query: 'foo' },
+      relativePath: 'src/"quoted".ts',
+    })
+    expect(next).toBe('"src/\\"quoted\\".ts"')
+  })
+})