diff --git a/composeApp/src/jvmTest/kotlin/press/mantra/compose/database/dao/MarmotOutboundDaoJvmTest.kt b/composeApp/src/jvmTest/kotlin/press/mantra/compose/database/dao/MarmotOutboundDaoJvmTest.kt
new file mode 100644
index 00000000..1d0ac995
--- /dev/null
+++ b/composeApp/src/jvmTest/kotlin/press/mantra/compose/database/dao/MarmotOutboundDaoJvmTest.kt
@@ -0,0 +1,154 @@
+package press.mantra.compose.database.dao
+
+import androidx.room3.Room
+import com.vitorpamplona.quartz.nip01Core.core.toHexKey
+import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
+import kotlinx.coroutines.runBlocking
+import press.mantra.compose.database.MantraDatabase
+import press.mantra.compose.database.builder.getRoomDatabase
+import press.mantra.compose.database.model.ChatRoom
+import press.mantra.compose.database.model.MarmotKeyPackage
+import press.mantra.compose.database.model.NostrEvent
+import press.mantra.compose.database.model.Profile
+import press.mantra.compose.database.model.intermdiate.LocalChatRoom
+import press.mantra.compose.exceptions.MarmotMissingChatGroupException
+import kotlin.test.AfterTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+/**
+ * The membership guards on [MarmotOutboundDao].
+ *
+ * Both entry points that change a group's membership begin by restoring the MLS state off the
+ * ChatRoom row, and a room restored from an inbound gift wrap has none -- there is nothing to
+ * add a member to. The comment on `inviteMemberToChatRoom` says the point of the throw is to
+ * "say so instead of silently doing nothing and letting the caller report success", which is a
+ * claim about behaviour and therefore testable: a guard that returned quietly would still
+ * compile, still look like it worked, and leave a room whose members believe someone was
+ * invited.
+ *
+ * These cover the paths that need no MLS material. Everything past the guard -- the commit, the
+ * Welcome, the epoch advance and its persistence -- needs a real peer key package to exercise,
+ * which means an MLS fixture this test file deliberately does not build. Those paths are worth
+ * covering and are not covered here.
+ */
+class MarmotOutboundDaoJvmTest {
+
+    private val db: MantraDatabase = getRoomDatabase(
+        Room.inMemoryDatabaseBuilder<MantraDatabase>()
+    )
+
+    @AfterTest
+    fun closeDb() = db.close()
+
+    private val user = KeyPair().pubKey.toHexKey()
+    private val peer = KeyPair().pubKey.toHexKey()
+    private val roomId = "b".repeat(64)
+
+    /**
+     * A room with `mlsGroupState = null` -- exactly the shape a room restored from an inbound
+     * gift wrap has, which is the case the guard exists for.
+     */
+    private suspend fun seedStatelessRoom(): LocalChatRoom {
+        val nostrEventId = "c".repeat(64)
+        db.nostrEventDao().upsert(
+            NostrEvent(
+                id = nostrEventId,
+                pubKey = user,
+                kind = 0,
+                tags = emptyArray(),
+                content = "{}",
+                sig = "0".repeat(128),
+            )
+        )
+        db.profileDao().upsert(Profile(publicKey = user, userName = "user", nostrEventId = nostrEventId))
+        val chatRoom = ChatRoom(
+            id = roomId,
+            userPublicKey = user,
+            subject = "a restored room",
+            description = null,
+            mlsGroupState = null,
+        )
+        db.chatRoomDao().upsert(chatRoom)
+        return LocalChatRoom(chatRoom = chatRoom)
+    }
+
+    /**
+     * Never decoded: the guard throws before any of these tests reach the MLS layer, so the
+     * bytes only have to exist. A test that got past the guard would need a real key package.
+     */
+    private fun keyPackage() = MarmotKeyPackage(
+        id = "d".repeat(64),
+        publicKey = peer,
+        tlsEncodedMarmotKeyPackage = ByteArray(0),
+    )
+
+    @Test
+    fun `inviting into a room with no mls state is refused rather than ignored`() = runBlocking<Unit> {
+        val localChatRoom = seedStatelessRoom()
+
+        assertFailsWith<MarmotMissingChatGroupException> {
+            db.marmotOutboundDao().inviteMemberToChatRoom(
+                localChatRoom = localChatRoom,
+                peerPublicKey = peer,
+                peerKeyPackage = keyPackage(),
+            )
+        }
+    }
+
+    /**
+     * The guard has to come before the Participant write, not after. `sealGiftWrapPayload`
+     * walks a room's participants to decide who to wrap a Welcome for, so a participant row
+     * left behind by a failed invite would make the room look like it has a member that no MLS
+     * group knows about.
+     */
+    @Test
+    fun `a refused invite leaves no participant behind`() = runBlocking {
+        val localChatRoom = seedStatelessRoom()
+
+        runCatching {
+            db.marmotOutboundDao().inviteMemberToChatRoom(
+                localChatRoom = localChatRoom,
+                peerPublicKey = peer,
+                peerKeyPackage = keyPackage(),
+            )
+        }
+
+        val participants = db.participantDao().findParticipantsByChatRoomId(roomId)
+        assertTrue(
+            participants.none { it.participantPublicKey == peer },
+            "the invitee was persisted despite the invite being refused",
+        )
+    }
+
+    @Test
+    fun `adding members to a room with no mls state is refused`() = runBlocking<Unit> {
+        val localChatRoom = seedStatelessRoom()
+
+        assertFailsWith<MarmotMissingChatGroupException> {
+            db.marmotOutboundDao().addMembersToChatRoom(
+                localChatRoom = localChatRoom,
+                peers = listOf(peer to keyPackage()),
+            )
+        }
+    }
+
+    /**
+     * The empty-batch guard returns before the MLS state is even looked at, so it must not
+     * throw on the same stateless room the two tests above reject. Adding nobody is not a
+     * failure to add somebody.
+     */
+    @Test
+    fun `adding no members is not an error even without mls state`() = runBlocking {
+        val localChatRoom = seedStatelessRoom()
+
+        val failed = db.marmotOutboundDao().addMembersToChatRoom(
+            localChatRoom = localChatRoom,
+            peers = emptyList(),
+        )
+
+        assertEquals(emptyList(), failed)
+    }
+}