fix(concord): seal rumors without a sig field

The envelope serialized the rumor with Event.toJson, which writes "sig": "".
A rumor is unsigned (NIP-59), and applesauce-based clients such as Accordion
read an object with a string sig as a signed event, fail its signature and
drop it, so Accordion never showed a single Concord message, Join or edition
we sent. Serialize through Rumor, as NIP-59 seals already do.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/concord/envelope/ConcordStreamEnvelope.kt

@@ -32,6 +32,7 @@ import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerSync
 import com.vitorpamplona.quartz.nip44Encryption.Nip44
 import com.vitorpamplona.quartz.nip44Encryption.Nip44v2
+import com.vitorpamplona.quartz.nip59Giftwrap.rumors.Rumor
 import com.vitorpamplona.quartz.utils.TimeUtils
 
 /**
@@ -78,11 +79,14 @@ object ConcordStreamEnvelope {
         authorSigner: NostrSigner,
         encrypted: Boolean,
     ): Event {
+        // A rumor is unsigned (NIP-59): serialize it without `sig`. applesauce clients read
+        // `"sig": ""` as a signed event with a bad signature and drop it.
+        val rumorJson = Rumor.toJson(Rumor.create(rumor))
         val content =
             if (encrypted) {
-                encryptChecked(rumor.toJson(), stream.conversationKey)
+                encryptChecked(rumorJson, stream.conversationKey)
             } else {
-                rumor.toJson()
+                rumorJson
             }
         val kind = if (encrypted) KIND_SEAL_ENCRYPTED else KIND_SEAL_PLAINTEXT
         return authorSigner.sign(rumor.createdAt, kind, EMPTY_TAGS, content)

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/concord/envelope/ConcordStreamEnvelopeTest.kt

@@ -28,8 +28,12 @@ import com.vitorpamplona.quartz.nip01Core.crypto.verify
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
 import com.vitorpamplona.quartz.nip59Giftwrap.rumors.RumorAssembler
 import kotlinx.coroutines.test.runTest
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
 import kotlin.test.assertNull
 import kotlin.test.assertTrue
 
@@ -69,6 +73,21 @@ class ConcordStreamEnvelopeTest {
             assertEquals(9, opened.rumor.kind)
         }
 
+    /**
+     * A rumor is unsigned (NIP-59): its JSON carries no `sig`. applesauce-based clients
+     * (Accordion) treat an object with `"sig": ""` as a signed event whose signature fails,
+     * and silently dropped every Concord message and Guestbook Join we sent.
+     */
+    @Test
+    fun sealedRumorJsonCarriesNoSig() =
+        runTest {
+            val seal = ConcordStreamEnvelope.seal(chatRumor("no sig"), stream, authorSigner, encrypted = false)
+            val rumorJson = Json.parseToJsonElement(seal.content).jsonObject
+
+            assertFalse("sig" in rumorJson, "rumor JSON must not carry a sig: ${seal.content}")
+            assertEquals(chatRumor("no sig").id, rumorJson["id"]?.jsonPrimitive?.content)
+        }
+
     @Test
     fun encryptedSealRoundTrips() =
         runTest {