fix(delivery): msg 队头失败或退避只暂停同 FLID，不阻塞其他航班（ACM2-95）

- drainKafkaMsg 按分区键维护本轮暂停集：队头失败/退避未到期仅停该 FLID（D2）
- 同一 FLID 内仍严格按 EVENT_ID 保序不越队
- 补三条用例：失败仅停同 FLID、退避未到期仅停同 FLID、同 FLID 跨轮保序（TestClocks 无 sleep）

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

@@ -214,6 +214,82 @@ class DispatcherTickTest {
         d.tick()
         assertEquals(1, port.sent.count { it.topic == "msg" && it.key == "F9" })
     }
+
+    @Test
+    fun `msg head failure pauses only the same FLID while other flights deliver in the same tick`() {
+        val repo = StubMsgEvents()
+        val port = FailingMsgKeyPort("F1")
+        val d = dispatcher(repo, port)
+        repo.insertAll(
+            listOf(
+                ev(1, Targets.KAFKA_MSG, "F1", """{"flid":"F1","v":1}"""),
+                ev(2, Targets.KAFKA_MSG, "F2", """{"flid":"F2","v":1}"""),
+                ev(3, Targets.KAFKA_MSG, "F1", """{"flid":"F1","v":2}"""),
+            ),
+        )
+
+        d.tick()
+
+        // D2：F1 队头失败只暂停 F1（含 id=3 的后续），F2 照常发出
+        assertEquals(1, port.sent.count { it.topic == "msg" && it.key == "F2" })
+        assertEquals(0, port.sent.count { it.topic == "msg" && it.key == "F1" })
+        val f1Rows = repo.rows.values.filter { it.partitionKey == "F1" }
+        assertEquals(2, f1Rows.size)
+        assertTrue(f1Rows.all { it.state == EventStatus.PENDING })
+    }
+
+    @Test
+    fun `msg head backoff not yet due pauses only the same FLID`() {
+        val repo = StubMsgEvents()
+        val port = StubDeliveryPort()
+        val d = dispatcher(repo, port)
+        repo.insertAll(
+            listOf(
+                ev(1, Targets.KAFKA_MSG, "F1", """{"flid":"F1","v":1}"""),
+                ev(2, Targets.KAFKA_MSG, "F2", """{"flid":"F2","v":1}"""),
+            ),
+        )
+        repo.scheduleRetry(1, clock.instant().plusSeconds(60), 1)   // F1 队头退避未到期
+
+        d.tick()
+
+        assertEquals(1, port.sent.count { it.topic == "msg" && it.key == "F2" })
+        val f1 = repo.rows.values.single { it.partitionKey == "F1" }
+        assertEquals(EventStatus.PENDING, f1.state)
+        assertEquals(1, f1.attempts)
+    }
+
+    @Test
+    fun `same FLID msg events keep strict order across ticks`() {
+        val repo = StubMsgEvents()
+        val port = StubDeliveryPort()
+        val d = dispatcher(repo, port)
+        repo.insertAll(
+            listOf(
+                ev(1, Targets.KAFKA_MSG, "F1", """{"v":1}"""),
+                ev(2, Targets.KAFKA_MSG, "F1", """{"v":2}"""),
+                ev(3, Targets.KAFKA_MSG, "F1", """{"v":3}"""),
+            ),
+        )
+
+        d.tick()
+
+        val f1Keys = port.sent.filter { it.topic == "msg" }.map { it.payload }
+        assertEquals(listOf("""{"v":1}""", """{"v":2}""", """{"v":3}"""), f1Keys)   // 同 FLID 不越队
+    }
+}
+
+/** KAFKA:msg 对指定 FLID 的发送永远失败，其他 FLID 照常记录，用来验证按 FLID 暂停。 */
+private class FailingMsgKeyPort(private val failingKey: String) : DeliveryPort {
+    val sent = mutableListOf<StubDeliveryPort.Sent>()
+
+    override fun sendKafka(topic: String, key: String, payloadJson: String) {
+        if (key == failingKey) throw IllegalStateException("broker-down:$key")
+        sent.add(StubDeliveryPort.Sent(topic, key, payloadJson))
+    }
+
+    override fun sendKafkaSchd(topic: String, key: String, payloadJson: String) = Unit
+    override fun sendKafkaNull(topic: String, key: String) = Unit
 }
 
 /** KAFKA_SCHD 发送永远失败的投递端口，用来验证退避重试和最终转死信的闭环。 */