fix(delivery): drop redundant schd event index

V9 追加删除已无消费者的 idx_evt_flid（读端不再按 (PARTITION_KEY, STATE_VERSION) 合并），并在最终 schema 断言其不存在；新增用例覆盖 schd DEAD 行被更高合法代次替换为单行 PENDING、错误字段清空、旧代次不得复活。

验证：./gradlew test 130 tests / 0 fail。

src/main/resources/db/migration/V9__schd_single_row.sql

@@ -22,3 +22,6 @@ DELETE FROM msg_event a
 CREATE UNIQUE INDEX uq_schd_event
     ON msg_event (target, partition_key)
  WHERE target = 'KAFKA:schd';
+
+-- 读端不再按 (PARTITION_KEY, STATE_VERSION) 合并（单行化 + 条件确认），idx_evt_flid 已无消费者。
+DROP INDEX IF EXISTS idx_evt_flid;

src/test/kotlin/com/gzzn/omms/msgexchange/delivery/DispatcherTickTest.kt

@@ -2,6 +2,7 @@ package com.gzzn.omms.msgexchange.delivery
 
 import com.gzzn.omms.msgexchange.MutableClock
 import com.gzzn.omms.msgexchange.config.PipelineProps
+import com.gzzn.omms.msgexchange.domain.ErrorClass
 import com.gzzn.omms.msgexchange.domain.EventStatus
 import com.gzzn.omms.msgexchange.domain.EventType
 import com.gzzn.omms.msgexchange.domain.MsgEvent
@@ -181,6 +182,27 @@ class DispatcherTickTest {
         assertEquals(EventStatus.PENDING, row.state)   // 旧代次的确认影响 0 行，不把新内容带走
     }
 
+    @Test
+    fun `a higher generation replaces a dead schd row and clears the old error`() {
+        val repo = StubMsgEvents()
+        repo.insertAll(listOf(ev(1, Targets.KAFKA_SCHD, "F1", """{"v":"v1"}""", 1)))
+        val deadId = repo.rows.values.single().eventId!!
+        repo.markDead(deadId, ErrorClass.EXHAUSTED, "broker-down", attempts = 5)
+
+        repo.insertAll(listOf(ev(2, Targets.KAFKA_SCHD, "F1", """{"v":"v2"}""", 2)))
+
+        val row = repo.rows.values.single()   // 仍是一行；DEAD 只保留到下一合法代次
+        assertEquals(EventStatus.PENDING, row.state)
+        assertEquals(2, row.stateVersion)
+        assertEquals(0, row.attempts)
+        assertNull(row.errorClass)
+        assertNull(row.lastError)
+        assertTrue(row.eventId != deadId, "接受新代次必须以新的 EVENT_ID 替换行主键")
+
+        repo.insertAll(listOf(ev(3, Targets.KAFKA_SCHD, "F1", """{"v":"v1-late"}""", 1)))
+        assertEquals(2, repo.rows.values.single().stateVersion)   // 不被接受的旧代次不得复活该行
+    }
+
     @Test
     fun `KAFKA msg delivery unaffected while schd batch is retrying`() {
         val repo = StubMsgEvents()

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

@@ -177,6 +177,12 @@ class FlywayMigrationTest {
                     "INSERT INTO msg_event (target, partition_key, event_type, state_version, payload_json, state, attempts, created_at) " +
                         "VALUES ('KAFKA:msg', 'F1', 'UPSERT', 2, '{}', 'PENDING', 0, now())",
                 )
+                stmt.executeQuery(
+                    "SELECT count(*) FROM pg_indexes WHERE tablename = 'msg_event' AND indexname = 'idx_evt_flid'",
+                ).use { rs ->
+                    assertTrue(rs.next())
+                    assertEquals(0, rs.getInt(1), "V9 必须删除已无消费者的 idx_evt_flid")
+                }
 
                 // 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(