diff --git a/backend/internal/repository/auth_identity_compat_backfill_integration_test.go b/backend/internal/repository/auth_identity_compat_backfill_integration_test.go
new file mode 100644
index 00000000..56b37512
--- /dev/null
+++ b/backend/internal/repository/auth_identity_compat_backfill_integration_test.go
@@ -0,0 +1,73 @@
+//go:build integration
+
+package repository
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAuthIdentityCompatBackfillMigration_AllowsLongReportTypes(t *testing.T) {
+	tx := testTx(t)
+	ctx := context.Background()
+
+	migration108Path := filepath.Join("..", "..", "migrations", "108_auth_identity_foundation_core.sql")
+	migration108SQL, err := os.ReadFile(migration108Path)
+	require.NoError(t, err)
+
+	migration109Path := filepath.Join("..", "..", "migrations", "109_auth_identity_compat_backfill.sql")
+	migration109SQL, err := os.ReadFile(migration109Path)
+	require.NoError(t, err)
+
+	_, err = tx.ExecContext(ctx, `
+DROP TABLE IF EXISTS auth_identity_migration_reports CASCADE;
+DROP TABLE IF EXISTS auth_identity_channels CASCADE;
+DROP TABLE IF EXISTS identity_adoption_decisions CASCADE;
+DROP TABLE IF EXISTS pending_auth_sessions CASCADE;
+DROP TABLE IF EXISTS auth_identities CASCADE;
+
+ALTER TABLE users
+	DROP COLUMN IF EXISTS signup_source,
+	DROP COLUMN IF EXISTS last_login_at,
+	DROP COLUMN IF EXISTS last_active_at;
+`)
+	require.NoError(t, err)
+
+	_, err = tx.ExecContext(ctx, string(migration108SQL))
+	require.NoError(t, err)
+
+	var userID int64
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO users (email, password_hash, role, status, balance, concurrency)
+VALUES ('oidc-demo-subject@oidc-connect.invalid', 'hash', 'user', 'active', 0, 1)
+RETURNING id`).Scan(&userID))
+
+	_, err = tx.ExecContext(ctx, string(migration109SQL))
+	require.NoError(t, err)
+
+	var reportCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identity_migration_reports
+WHERE report_type = 'oidc_synthetic_email_requires_manual_recovery'
+  AND report_key = $1
+`, strconv.FormatInt(userID, 10)).Scan(&reportCount))
+	require.Equal(t, 1, reportCount)
+
+	var reportTypeLimit int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT character_maximum_length
+FROM information_schema.columns
+WHERE table_schema = 'public'
+  AND table_name = 'auth_identity_migration_reports'
+  AND column_name = 'report_type'
+`).Scan(&reportTypeLimit))
+	require.GreaterOrEqual(t, reportTypeLimit, 45)
+
+	require.NotZero(t, userID)
+}
diff --git a/backend/internal/repository/migrations_runner.go b/backend/internal/repository/migrations_runner.go
index 9cf3b392..5a2e6677 100644
--- a/backend/internal/repository/migrations_runner.go
+++ b/backend/internal/repository/migrations_runner.go
@@ -73,6 +73,12 @@ var migrationChecksumCompatibilityRules = map[string]migrationChecksumCompatibil
 			"222b4a09c797c22e5922b6b172327c824f5463aaa8760e4f621bc5c22e2be0f3": {},
 		},
 	},
+	"109_auth_identity_compat_backfill.sql": {
+		fileChecksum: "551e498aa5616d2d91096e9d72cf9fb36e418ee22eacc557f8811cadbc9e20ee",
+		acceptedDBChecksum: map[string]struct{}{
+			"2b380305e73ff0c13aa8c811e45897f2b36ca4a438f7b3e8f98e19ecb6bae0b3": {},
+		},
+	},
 }
 
 // ApplyMigrations 将嵌入的 SQL 迁移文件应用到指定的数据库。
diff --git a/backend/internal/repository/migrations_runner_checksum_test.go b/backend/internal/repository/migrations_runner_checksum_test.go
index 6c3ad725..6030991b 100644
--- a/backend/internal/repository/migrations_runner_checksum_test.go
+++ b/backend/internal/repository/migrations_runner_checksum_test.go
@@ -51,4 +51,13 @@ func TestIsMigrationChecksumCompatible(t *testing.T) {
 		)
 		require.False(t, ok)
 	})
+
+	t.Run("109历史checksum可兼容", func(t *testing.T) {
+		ok := isMigrationChecksumCompatible(
+			"109_auth_identity_compat_backfill.sql",
+			"2b380305e73ff0c13aa8c811e45897f2b36ca4a438f7b3e8f98e19ecb6bae0b3",
+			"551e498aa5616d2d91096e9d72cf9fb36e418ee22eacc557f8811cadbc9e20ee",
+		)
+		require.True(t, ok)
+	})
 }
diff --git a/backend/migrations/109_auth_identity_compat_backfill.sql b/backend/migrations/109_auth_identity_compat_backfill.sql
index ddbbedbc..5147ae45 100644
--- a/backend/migrations/109_auth_identity_compat_backfill.sql
+++ b/backend/migrations/109_auth_identity_compat_backfill.sql
@@ -1,3 +1,6 @@
+ALTER TABLE auth_identity_migration_reports
+ALTER COLUMN report_type TYPE VARCHAR(80);
+
 INSERT INTO auth_identities (
     user_id,
     provider_type,