diff --git a/cdc-service/src/main/java/com/xtrmetl/cdc/spi/DebeziumChangeRecordMapper.java b/cdc-service/src/main/java/com/xtrmetl/cdc/spi/DebeziumChangeRecordMapper.java
index 086e8cd5..a7aa821c 100644
--- a/cdc-service/src/main/java/com/xtrmetl/cdc/spi/DebeziumChangeRecordMapper.java
+++ b/cdc-service/src/main/java/com/xtrmetl/cdc/spi/DebeziumChangeRecordMapper.java
@@ -22,15 +22,28 @@ public class DebeziumChangeRecordMapper {
 
     private final ObjectMapper objectMapper;
 
+    /**
+     * Creates a mapper using the caller-provided JSON codec.
+     *
+     * @param objectMapper mapper used for Debezium key and value envelopes
+     */
     public DebeziumChangeRecordMapper(ObjectMapper objectMapper) {
         this.objectMapper = objectMapper;
     }
 
     /**
+     * Maps one Debezium value envelope and its optional key metadata.
+     *
+     * <p>The value envelope is authoritative and must be valid JSON. The key envelope is optional
+     * metadata: when it is malformed, mapping continues and derives a primary key from the value's
+     * {@code after.id} or {@code before.id} field when available. This prevents malformed optional
+     * metadata from discarding an otherwise valid change event.</p>
+     *
      * @param sourceId logical source id (e.g. {@code postgres-debezium})
-     * @param topic    Kafka / Debezium destination topic ({@code prefix.schema.table})
-     * @param keyJson  optional Debezium key JSON
+     * @param topic Kafka / Debezium destination topic ({@code prefix.schema.table})
+     * @param keyJson optional Debezium key JSON
      * @param valueJson Debezium value JSON
+     * @return mapped canonical record, or empty when the required value envelope is blank or malformed
      */
     public Optional<CanonicalChangeRecord> map(
             String sourceId,
@@ -83,7 +96,7 @@ public Optional<CanonicalChangeRecord> map(
 
             Map<String, Object> afterMap = toMap(after);
             Map<String, Object> beforeMap = toMap(before);
-            Map<String, Object> pk = extractPk(keyJson);
+            Map<String, Object> pk = extractOptionalPk(keyJson);
             if (pk.isEmpty() && afterMap.containsKey("id")) {
                 pk = Map.of("id", afterMap.get("id"));
             } else if (pk.isEmpty() && beforeMap.containsKey("id")) {
@@ -105,13 +118,17 @@ public Optional<CanonicalChangeRecord> map(
         }
     }
 
-    private Map<String, Object> extractPk(String keyJson) throws IOException {
+    private Map<String, Object> extractOptionalPk(String keyJson) {
         if (keyJson == null || keyJson.isBlank()) {
             return Map.of();
         }
-        JsonNode root = objectMapper.readTree(keyJson);
-        JsonNode payload = root.has("payload") ? root.get("payload") : root;
-        return toMap(payload);
+        try {
+            JsonNode root = objectMapper.readTree(keyJson);
+            JsonNode payload = root.has("payload") ? root.get("payload") : root;
+            return toMap(payload);
+        } catch (IOException ignored) {
+            return Map.of();
+        }
     }
 
     private static String[] schemaTableFromTopic(String topic) {
diff --git a/cdc-service/src/test/java/com/xtrmetl/cdc/spi/DebeziumMalformedKeyFallbackTest.java b/cdc-service/src/test/java/com/xtrmetl/cdc/spi/DebeziumMalformedKeyFallbackTest.java
new file mode 100644
index 00000000..e74ee15d
--- /dev/null
+++ b/cdc-service/src/test/java/com/xtrmetl/cdc/spi/DebeziumMalformedKeyFallbackTest.java
@@ -0,0 +1,35 @@
+package com.xtrmetl.cdc.spi;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/** Fail-first regression for optional malformed Debezium key metadata. */
+class DebeziumMalformedKeyFallbackTest {
+
+    @Test
+    void malformedOptionalKeyFallsBackToValidAfterIdentifier() {
+        DebeziumChangeRecordMapper mapper = new DebeziumChangeRecordMapper(new ObjectMapper());
+        String value = """
+                {"payload":{"op":"u","before":{"id":41,"data":"old"},
+                "after":{"id":42,"data":"new"},
+                "source":{"schema":"public","table":"processed_data"}}}
+                """;
+
+        Optional<CanonicalChangeRecord> result = mapper.map(
+                "postgres-debezium",
+                "xtrmetl-cdc.public.processed_data",
+                "{malformed-key-json",
+                value
+        );
+
+        assertTrue(result.isPresent(), "malformed optional key metadata must not discard a valid value envelope");
+        CanonicalChangeRecord record = result.orElseThrow();
+        assertEquals(42, ((Number) record.getPk().get("id")).intValue());
+        assertEquals("new", record.getAfter().get("data"));
+    }
+}