diff --git a/src/main/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodec.kt b/src/main/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodec.kt
index 2b7248a..a310bf2 100644
--- a/src/main/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodec.kt
+++ b/src/main/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodec.kt
@@ -1,6 +1,7 @@
 package com.gzzn.omms.msgexchange.codec
 
 import com.fasterxml.jackson.databind.DeserializationFeature
+import com.fasterxml.jackson.databind.JsonMappingException
 import com.fasterxml.jackson.module.kotlin.registerKotlinModule
 import com.fasterxml.jackson.dataformat.xml.XmlFactory
 import com.fasterxml.jackson.dataformat.xml.XmlMapper
@@ -34,6 +35,14 @@ class JacksonXmlCodec : XmlCodec {
         }
         val msg = try {
             mapper.readValue(trimmed, SisMessageXml::class.java)
+        } catch (e: JsonMappingException) {
+            // META 层绑定失败=发送方违反必填契约（MALFORMED）；体层（SCHD/FLOP）结构不匹配
+            // =wire 结构超出编解码器当前绑定能力（CODEC_ERROR：退避重试，修复后可重放，design §2.3）。
+            val first = e.path.firstOrNull()?.fieldName ?: ""
+            if (first.equals("meta", ignoreCase = true)) {
+                return DecodeResult.Err(DecodeFailure(ErrorClass.MALFORMED, "xml-meta:${e.originalMessage.take(200)}"))
+            }
+            return DecodeResult.Err(DecodeFailure(ErrorClass.CODEC_ERROR, "xml-mapping:${e.originalMessage.take(200)}"))
         } catch (e: Exception) {
             return DecodeResult.Err(
                 DecodeFailure(ErrorClass.MALFORMED, "xml-parse:${e.message?.take(200) ?: e.javaClass.simpleName}"),
diff --git a/src/test/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodecTest.kt b/src/test/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodecTest.kt
index 386a61e..259187b 100644
--- a/src/test/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodecTest.kt
+++ b/src/test/kotlin/com/gzzn/omms/msgexchange/codec/JacksonXmlCodecTest.kt
@@ -94,6 +94,26 @@ class JacksonXmlCodecTest {
         assertTrue(err.failure.detail.contains("empty-or-non-xml"))
     }
 
+    @Test
+    fun `body shape beyond binding capability is CODEC_ERROR while meta violations stay MALFORMED`() {
+        val meta = "<META><SNDR>AODB</SNDR><SEQN>1</SEQN><DTTM>20021010090311</DTTM><TYPE>SCHD</TYPE><STYP>DNLD</STYP></META>"
+        val recsAsText = "<MSG>$meta<SCHD><RECS>not-a-number</RECS></SCHD></MSG>"
+        val bodyErr = codec.decode(recsAsText) as DecodeResult.Err
+        assertEquals(com.gzzn.omms.msgexchange.domain.ErrorClass.CODEC_ERROR, bodyErr.failure.errorClass)
+        assertTrue(bodyErr.failure.detail.startsWith("xml-mapping"))
+
+        val badSeqn = "<MSG><META><SNDR>AODB</SNDR><SEQN>abc</SEQN><DTTM>20021010090311</DTTM><TYPE>SCHD</TYPE><STYP>DNLD</STYP></META></MSG>"
+        val metaErr = codec.decode(badSeqn) as DecodeResult.Err
+        assertEquals(com.gzzn.omms.msgexchange.domain.ErrorClass.MALFORMED, metaErr.failure.errorClass)
+    }
+
+    @Test
+    fun `broken token stream stays MALFORMED`() {
+        val err = codec.decode("<MSG><META>") as DecodeResult.Err
+        assertEquals(com.gzzn.omms.msgexchange.domain.ErrorClass.MALFORMED, err.failure.errorClass)
+        assertTrue(err.failure.detail.startsWith("xml-parse"))
+    }
+
     @Test
     fun `SIS documented attributes and mixed DELY text become typed payload`() {
         val raw = """