feat: add autoFix hook integration helpers (Task 4)

Implements shouldRunAutoFix and buildAutoFixContext functions used by
the PostToolUse hook to determine when to run auto-fix and format
errors as AI-readable context for injection.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/services/autoFix/autoFixHook.test.ts

@@ -0,0 +1,63 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  shouldRunAutoFix,
+  buildAutoFixContext,
+} from './autoFixHook.js'
+
+describe('shouldRunAutoFix', () => {
+  test('returns true for file_edit tool when autoFix enabled', () => {
+    const config = { enabled: true, lint: 'eslint .', maxRetries: 3, timeout: 30000 }
+    expect(shouldRunAutoFix('file_edit', config)).toBe(true)
+  })
+
+  test('returns true for file_write tool when autoFix enabled', () => {
+    const config = { enabled: true, lint: 'eslint .', maxRetries: 3, timeout: 30000 }
+    expect(shouldRunAutoFix('file_write', config)).toBe(true)
+  })
+
+  test('returns false for bash tool', () => {
+    const config = { enabled: true, lint: 'eslint .', maxRetries: 3, timeout: 30000 }
+    expect(shouldRunAutoFix('bash', config)).toBe(false)
+  })
+
+  test('returns false for file_read tool', () => {
+    const config = { enabled: true, lint: 'eslint .', maxRetries: 3, timeout: 30000 }
+    expect(shouldRunAutoFix('file_read', config)).toBe(false)
+  })
+
+  test('returns false when config is null', () => {
+    expect(shouldRunAutoFix('file_edit', null)).toBe(false)
+  })
+})
+
+describe('buildAutoFixContext', () => {
+  test('formats lint errors as AI-readable context', () => {
+    const context = buildAutoFixContext({
+      hasErrors: true,
+      lintOutput: 'src/foo.ts:10:5 error no-unused-vars',
+      lintExitCode: 1,
+      errorSummary: 'Lint errors (exit code 1):\nsrc/foo.ts:10:5 error no-unused-vars',
+    })
+    expect(context).toContain('AUTO-FIX')
+    expect(context).toContain('no-unused-vars')
+    expect(context).toContain('Please fix')
+  })
+
+  test('returns null when no errors', () => {
+    const context = buildAutoFixContext({
+      hasErrors: false,
+    })
+    expect(context).toBeNull()
+  })
+
+  test('formats test failures as AI-readable context', () => {
+    const context = buildAutoFixContext({
+      hasErrors: true,
+      testOutput: 'FAIL src/foo.test.ts\n  expected true, got false',
+      testExitCode: 1,
+      errorSummary: 'Test failures (exit code 1):\nFAIL src/foo.test.ts',
+    })
+    expect(context).toContain('AUTO-FIX')
+    expect(context).toContain('FAIL')
+  })
+})

src/services/autoFix/autoFixHook.ts

@@ -0,0 +1,25 @@
+import type { AutoFixConfig } from './autoFixConfig.js'
+import type { AutoFixResult } from './autoFixRunner.js'
+
+const AUTO_FIX_TOOLS = new Set(['file_edit', 'file_write'])
+
+export function shouldRunAutoFix(
+  toolName: string,
+  config: AutoFixConfig | null,
+): boolean {
+  if (!config) return false
+  return AUTO_FIX_TOOLS.has(toolName)
+}
+
+export function buildAutoFixContext(result: AutoFixResult): string | null {
+  if (!result.hasErrors || !result.errorSummary) return null
+
+  return (
+    `<auto_fix_feedback>\n` +
+    `AUTO-FIX: The file you just edited has errors. Please fix them:\n\n` +
+    `${result.errorSummary}\n\n` +
+    `Please fix these errors in the files you just edited. ` +
+    `Do not ask the user — just apply the fix.\n` +
+    `</auto_fix_feedback>`
+  )
+}