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.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>`
+  )
+}