task-201: 迁移演练 runbook（docs/flyway-migration-drill.md：clean migrate/validate/验证SQL/回滚/锁窗口/校验和/幂等重跑/不动历史）+ 8 条测试

on-DB 的 migrate 执行需在副本库按 runbook 进行（本环境无数据库，仓库内以静态检查+清单兜底）

backend-java/src/test/java/com/nanri/aiimage/config/FlywayMigrationDrillDocTest.java

@@ -0,0 +1,66 @@
+package com.nanri.aiimage.config;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * task-201：迁移演练 runbook 契约。
+ * docs/flyway-migration-drill.md 固化演练步骤：干净迁移/validate/验证 SQL/回滚/锁窗口/校验和/
+ * 幂等重跑/不动历史；on-DB 步骤由运维在副本库按 runbook 执行（本环境无库）。
+ */
+class FlywayMigrationDrillDocTest {
+
+    private static final String DOC = "docs/flyway-migration-drill.md";
+
+    private String doc() throws IOException {
+        return Files.readString(Path.of(System.getProperty("user.dir"), DOC));
+    }
+
+    @Test
+    void drillDocExists() {
+        assertTrue(Files.exists(Path.of(System.getProperty("user.dir"), DOC)), "演练 runbook 应存在");
+    }
+
+    @Test
+    void cleanMigrateStepDescribed() throws IOException {
+        assertTrue(doc().contains("migrate"), "应描述干净迁移步骤");
+    }
+
+    @Test
+    void validateStepDescribed() throws IOException {
+        assertTrue(doc().contains("validate"), "应包含 validate 校验历史 checksum 步骤");
+    }
+
+    @Test
+    void validationSqlStepDescribed() throws IOException {
+        assertTrue(doc().contains("验证 SQL"), "应包含验证 SQL 步骤");
+    }
+
+    @Test
+    void rollbackStepDescribed() throws IOException {
+        assertTrue(doc().contains("回滚"), "应包含回滚验证步骤");
+    }
+
+    @Test
+    void lockWindowEstimatedStepDescribed() throws IOException {
+        assertTrue(doc().contains("锁窗口"), "应包含锁窗口估算步骤");
+    }
+
+    @Test
+    void checksumAndIdempotentRerunDescribed() throws IOException {
+        String text = doc();
+        assertTrue(text.contains("checksum") || text.contains("校验和"), "应包含校验和检查");
+        assertTrue(text.contains("幂等重跑") || text.contains("idempotent"), "应包含幂等重跑");
+    }
+
+    @Test
+    void noLegacyTouchGuarded() throws IOException {
+        assertTrue(doc().contains("历史") && (doc().contains("未被动") || doc().contains("未被改动")),
+                "应明确演练不动历史迁移");
+    }
+}