diff --git a/apps/server/src/main/kotlin/com/correx/apps/server/bridge/DomainEventMapper.kt b/apps/server/src/main/kotlin/com/correx/apps/server/bridge/DomainEventMapper.kt
index f0e81ca0..4aaf83cf 100644
--- a/apps/server/src/main/kotlin/com/correx/apps/server/bridge/DomainEventMapper.kt
+++ b/apps/server/src/main/kotlin/com/correx/apps/server/bridge/DomainEventMapper.kt
@@ -21,6 +21,9 @@ import com.correx.core.events.events.TransitionExecutedEvent
 import com.correx.core.events.events.WorkflowCompletedEvent
 import com.correx.core.events.events.WorkflowFailedEvent
 import com.correx.core.events.types.ArtifactId
+import org.slf4j.LoggerFactory
+
+private val log = LoggerFactory.getLogger("DomainEventMapper")
 
 class DomainEventMapper(private val artifactStore: ArtifactStore = NoopArtifactStore) {
     suspend fun map(event: StoredEvent): ServerMessage? =
@@ -138,7 +141,15 @@ suspend fun domainEventToServerMessage(
         )
 
         is ApprovalRequestedEvent -> mapApprovalRequested(p, seq, sessionSequence)
-        else -> null
+        else -> {
+            log.debug(
+                "DomainEventMapper: unmapped payload type={} sessionId={} sequence={}",
+                p::class.simpleName,
+                event.metadata.sessionId,
+                event.sequence,
+            )
+            null
+        }
     }
 }
 
diff --git a/apps/server/src/test/kotlin/com/correx/apps/server/bridge/DomainEventMapperTest.kt b/apps/server/src/test/kotlin/com/correx/apps/server/bridge/DomainEventMapperTest.kt
index 3a48976d..13d1945c 100644
--- a/apps/server/src/test/kotlin/com/correx/apps/server/bridge/DomainEventMapperTest.kt
+++ b/apps/server/src/test/kotlin/com/correx/apps/server/bridge/DomainEventMapperTest.kt
@@ -37,8 +37,15 @@ import com.correx.core.events.types.ValidationReportId
 import com.correx.core.inference.TokenUsage
 import kotlinx.coroutines.test.runTest
 import kotlinx.datetime.Instant
+import org.apache.logging.log4j.Level
+import org.apache.logging.log4j.LogManager
+import org.apache.logging.log4j.core.LogEvent
+import org.apache.logging.log4j.core.LoggerContext
+import org.apache.logging.log4j.core.appender.AbstractAppender
+import org.apache.logging.log4j.core.config.Property
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Assertions.assertNull
+import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Test
 
 class DomainEventMapperTest {
@@ -368,4 +375,33 @@ class DomainEventMapperTest {
         val result = domainEventToServerMessage(event, noopStore, sessionSequence = 0L)
         assertNull(result)
     }
+
+    private class TestAppender : AbstractAppender("TestCapture", null, null, true, Property.EMPTY_ARRAY) {
+        val events = mutableListOf<LogEvent>()
+        override fun append(event: LogEvent) {
+            events.add(event.toImmutable())
+        }
+    }
+
+    @Test
+    fun `unmapped event emits debug log`(): Unit = runTest {
+        val ctx = LogManager.getContext(false) as LoggerContext
+        val logger = ctx.getLogger("DomainEventMapper")
+        val appender = TestAppender().also { it.start() }
+        logger.addAppender(appender)
+        val origLevel = logger.level
+        logger.level = Level.DEBUG
+        try {
+            val event = storedEvent(SessionStartedEvent(sessionId = sessionId))
+            val result = domainEventToServerMessage(event, noopStore, sessionSequence = 0L)
+            assertNull(result)
+            assertEquals(1, appender.events.size)
+            assertEquals(Level.DEBUG, appender.events[0].level)
+            assertTrue(appender.events[0].message.formattedMessage.contains("SessionStartedEvent"))
+        } finally {
+            logger.removeAppender(appender)
+            appender.stop()
+            logger.level = origLevel
+        }
+    }
 }