Fix integration tests: correct vault derivation index and debug test failures

internal/vault/integration_version_test.go

@@ -1,3 +1,24 @@
+// Version Support Integration Tests
+//
+// Comprehensive integration tests for version functionality:
+//
+// - TestVersionIntegrationWorkflow: End-to-end workflow testing
+//   - Creating initial version with proper metadata
+//   - Creating multiple versions with timestamp updates
+//   - Retrieving specific versions by name
+//   - Promoting old versions to current
+//   - Testing version serial number limits (999/day)
+//   - Error cases and edge conditions
+//
+// - TestVersionConcurrency: Tests concurrent read operations
+//
+// - TestVersionCompatibility: Tests handling of legacy non-versioned secrets
+//
+// Test Environment:
+// - Uses in-memory filesystem (afero.MemMapFs)
+// - Consistent test mnemonic for reproducible keys
+// - Proper cleanup and isolation between tests
+
 package vault
 
 import (