fix(infra): enforce one open request

新增 V8 部分唯一索引 uq_req_open：(REQ_TYPE, OPERATION_DAY, SENDER) 仅在 PENDING/SENT 唯一；建索引前用 DO 块检测存量重复组并以带业务键的异常中止迁移，禁止静默删数据。保留 idx_req_open 服务含关闭态的查询；不引入运行时协调器（归 US-08）。

验证：全量 ./gradlew test 126 tests / 0 fail；索引与拒绝第二条开放请求的断言在 FlywayMigrationTest（需真实 PG，本机无 Docker 时按既有 assumeTrue 跳过）。

src/main/resources/db/migration/V8__req_track_open_unique.sql

@@ -0,0 +1,34 @@
+-- =====================================================================
+-- V8：REQ_TRACK 开放态部分唯一约束
+-- ---------------------------------------------------------------------
+-- 只动自有 PostgreSQL；共享 MySQL 不建表、不改结构。
+--
+-- design「记录模型」：同一 (REQ_TYPE, OPERATION_DAY, SENDER) 只允许一个开放请求，
+-- 且仅对开放状态（PENDING / SENT）生效。这里只建立数据库防线；「新请求原子过期旧请求
+-- 并登记自身」的运行时流程仍归 US-08 协调器（[G-REQ-TRACK]）。
+--
+-- 存量若已有重复开放组，不静默删数据：带业务键的诊断直接让迁移失败，由人工处置。
+-- 保留既有普通索引 idx_req_open（仍服务含关闭态的查询）。
+-- =====================================================================
+
+DO $$
+DECLARE offenders text;
+BEGIN
+    SELECT string_agg(format('%s/%s/%s', req_type, operation_day, sender), ', ')
+      INTO offenders
+      FROM (
+            SELECT req_type, operation_day, sender
+              FROM req_track
+             WHERE state IN ('PENDING', 'SENT')
+             GROUP BY req_type, operation_day, sender
+            HAVING count(*) > 1
+             LIMIT 20
+           ) dup;
+    IF offenders IS NOT NULL THEN
+        RAISE EXCEPTION 'V8 aborted: duplicate open REQ_TRACK rows for (req_type/operation_day/sender): %', offenders;
+    END IF;
+END $$;
+
+CREATE UNIQUE INDEX uq_req_open
+    ON req_track (req_type, operation_day, sender)
+ WHERE state IN ('PENDING', 'SENT');

src/test/kotlin/com/gzzn/omms/msgexchange/infra/persistence/jdbc/FlywayMigrationTest.kt

@@ -3,6 +3,7 @@ package com.gzzn.omms.msgexchange.infra.persistence.jdbc
 import com.gzzn.omms.msgexchange.support.PgTestSupport
 import org.flywaydb.core.Flyway
 import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertThrows
 import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Assumptions.assumeTrue
 import org.junit.jupiter.api.Test
@@ -48,7 +49,7 @@ class FlywayMigrationTest {
                     while (rs.next()) {
                         records.add(Triple(rs.getString("version"), rs.getString("script"), rs.getBoolean("success")))
                     }
-                    assertTrue(records.size >= 7, "flyway_schema_history must record all migrations")
+                    assertTrue(records.size >= 8, "flyway_schema_history must record all migrations")
                     assertEquals("1", records[0].first)
                     assertEquals("V1__flight_state_baseline.sql", records[0].second)
                     assertEquals("2", records[1].first)
@@ -63,6 +64,8 @@ class FlywayMigrationTest {
                     assertEquals("V6__enqueued_at.sql", records[5].second)
                     assertEquals("7", records[6].first)
                     assertEquals("V7__drop_processing_started_at.sql", records[6].second)
+                    assertEquals("8", records[7].first)
+                    assertEquals("V8__req_track_open_unique.sql", records[7].second)
                     assertTrue(records.all { it.third })
                 }
 
@@ -114,6 +117,37 @@ class FlywayMigrationTest {
                     assertEquals(0, rs.getInt(1), "V7 必须已删除 PROCESSING_STARTED_AT")
                 }
 
+                // V8：REQ_TRACK 开放态部分唯一约束（仅 PENDING/SENT；关闭态可并存）
+                stmt.executeQuery(
+                    "SELECT indexdef FROM pg_indexes WHERE tablename = 'req_track' AND indexname = 'uq_req_open'",
+                ).use { rs ->
+                    assertTrue(rs.next(), "V8 必须建立开放态唯一索引 uq_req_open")
+                    val indexDef = rs.getString(1)
+                    assertTrue(indexDef.contains("UNIQUE"), "uq_req_open 必须是唯一索引：$indexDef")
+                    assertTrue(indexDef.contains("WHERE"), "uq_req_open 必须是仅约束开放态的部分索引：$indexDef")
+                }
+                stmt.executeUpdate(
+                    "INSERT INTO req_track (req_type, operation_day, sender, state, created_at) " +
+                        "VALUES ('RQFD-NONE', DATE '2026-09-12', 'RMS', 'PENDING', now())",
+                )
+                stmt.executeUpdate(
+                    "INSERT INTO req_track (req_type, operation_day, sender, state, created_at) " +
+                        "VALUES ('RQFD-NONE', DATE '2026-09-12', 'RMS', 'DONE', now())",
+                )
+                assertThrows(java.sql.SQLException::class.java) {
+                    stmt.executeUpdate(
+                        "INSERT INTO req_track (req_type, operation_day, sender, state, created_at) " +
+                            "VALUES ('RQFD-NONE', DATE '2026-09-12', 'RMS', 'SENT', now())",
+                    )
+                }
+                stmt.executeUpdate(
+                    "UPDATE req_track SET state = 'DONE' WHERE req_type = 'RQFD-NONE' AND state = 'PENDING'",
+                )
+                stmt.executeUpdate(
+                    "INSERT INTO req_track (req_type, operation_day, sender, state, created_at) " +
+                        "VALUES ('RQFD-NONE', DATE '2026-09-12', 'RMS', 'PENDING', now())",
+                )
+
                 // V6：入队时间是超期判据 R 的比较对象，必须非空（received_at 则允许为 NULL）
                 stmt.executeQuery(
                     "SELECT is_nullable FROM information_schema.columns " +