feat: NIP-A4 compliance - add k tag to zap requests and enforce e tag prohibition

- Add KindTag to LnZapRequestEvent.create() when zapping events, as required
  by NIP-A4 ("NIP-57 zaps MUST include the k tag to 24")
- Enforce e tag prohibition in all PublicMessageEvent.build() methods by
  stripping any e tags from the tag builder output (NIP-A4: "e tags must not
  be used")
- Add comprehensive tests for both changes

https://claude.ai/code/session_019JsSsTTXivnNWiAtE5DE1R

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip57Zaps/LnZapRequestEvent.kt

@@ -34,6 +34,7 @@ import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
 import com.vitorpamplona.quartz.nip01Core.tags.aTag.ATag
 import com.vitorpamplona.quartz.nip01Core.tags.events.ETag
+import com.vitorpamplona.quartz.nip01Core.tags.kinds.KindTag
 import com.vitorpamplona.quartz.nip01Core.tags.people.PTag
 import com.vitorpamplona.quartz.nip31Alts.AltTag
 import com.vitorpamplona.quartz.utils.TimeUtils
@@ -101,6 +102,7 @@ class LnZapRequestEvent(
                     arrayOf("e", zappedEvent.id),
                     arrayOf("p", toUserPubHex ?: zappedEvent.pubKey),
                     arrayOf("relays") + relays.map { it.url },
+                    KindTag.assemble(zappedEvent.kind),
                     AltTag.assemble(ALT),
                 )
             if (zappedEvent is AddressableEvent) {

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipA4PublicMessages/PublicMessageEvent.kt

@@ -83,6 +83,7 @@ class PublicMessageEvent(
         ) = eventTemplate(KIND, "", createdAt) {
             alt(ALT_DESCRIPTION)
             initializer()
+            remove("e") // NIP-A4: e tags must not be used
         }
 
         fun build(
@@ -94,6 +95,7 @@ class PublicMessageEvent(
             alt(ALT_DESCRIPTION)
             toUser(to)
             initializer()
+            remove("e") // NIP-A4: e tags must not be used
         }
 
         fun build(
@@ -105,6 +107,7 @@ class PublicMessageEvent(
             alt(ALT_DESCRIPTION)
             toGroup(to)
             initializer()
+            remove("e") // NIP-A4: e tags must not be used
         }
     }
 }

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/experimental/publicMessages/PublicMessageEventTest.kt

@@ -0,0 +1,184 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.experimental.publicMessages
+
+import com.vitorpamplona.quartz.experimental.publicMessages.tags.ReceiverTag
+import com.vitorpamplona.quartz.nip01Core.tags.events.ETag
+import com.vitorpamplona.quartz.nip01Core.tags.events.eTag
+import com.vitorpamplona.quartz.utils.DeterministicSigner
+import com.vitorpamplona.quartz.utils.nsecToKeyPair
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class PublicMessageEventTest {
+    private val signer =
+        DeterministicSigner(
+            "nsec10g0wheggqn9dawlc0yuv6adnat6n09anr7eyykevw2dm8xa5fffs0wsdsr".nsecToKeyPair(),
+        )
+
+    private val receiverPubKey = "3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d"
+    private val receiverRelay = "wss://relay.example.com/"
+
+    @Test
+    fun `verify event kind is 24`() {
+        assertEquals(24, PublicMessageEvent.KIND)
+    }
+
+    @Test
+    fun `verify alt description`() {
+        assertEquals("Public Message", PublicMessageEvent.ALT_DESCRIPTION)
+    }
+
+    @Test
+    fun `build with single receiver`() {
+        val receiver = ReceiverTag(receiverPubKey, null)
+        val template = PublicMessageEvent.build(receiver, "Hello!")
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        assertEquals(24, event.kind)
+        assertEquals("Hello!", event.content)
+        assertTrue(event.tags.any { it[0] == "p" && it[1] == receiverPubKey })
+        assertTrue(event.tags.any { it[0] == "alt" && it[1] == "Public Message" })
+    }
+
+    @Test
+    fun `build with multiple receivers`() {
+        val receiver1 = ReceiverTag(receiverPubKey, null)
+        val receiver2PubKey = "32e1827635450ebb3c5a7d12c1f8e7b2b514439ac10a67eef3d9fd9c5c68e245"
+        val receiver2 = ReceiverTag(receiver2PubKey, null)
+
+        val template = PublicMessageEvent.build(listOf(receiver1, receiver2), "Group message")
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        assertEquals("Group message", event.content)
+        val pTags = event.tags.filter { it[0] == "p" }
+        assertEquals(2, pTags.size)
+        assertTrue(pTags.any { it[1] == receiverPubKey })
+        assertTrue(pTags.any { it[1] == receiver2PubKey })
+    }
+
+    @Test
+    fun `build with relay hint`() {
+        val receiver = ReceiverTag.parse(arrayOf("p", receiverPubKey, "wss://relay.example.com/"))!!
+        val template = PublicMessageEvent.build(receiver, "With relay hint")
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        val pTag = event.tags.first { it[0] == "p" && it[1] == receiverPubKey }
+        assertEquals("wss://relay.example.com/", pTag[2])
+    }
+
+    @Test
+    fun `e tags are stripped from build output`() {
+        val receiver = ReceiverTag(receiverPubKey, null)
+        val fakeEventId = "a".repeat(64)
+
+        val template =
+            PublicMessageEvent.build(receiver, "Test message") {
+                eTag(ETag(fakeEventId, null))
+            }
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        assertFalse(
+            event.tags.any { it[0] == "e" },
+            "NIP-A4 prohibits e tags in kind 24 events",
+        )
+    }
+
+    @Test
+    fun `e tags are stripped from empty build`() {
+        val fakeEventId = "b".repeat(64)
+
+        val template =
+            PublicMessageEvent.build {
+                eTag(ETag(fakeEventId, null))
+            }
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        assertFalse(
+            event.tags.any { it[0] == "e" },
+            "NIP-A4 prohibits e tags in kind 24 events",
+        )
+    }
+
+    @Test
+    fun `e tags are stripped from group build`() {
+        val receiver = ReceiverTag(receiverPubKey, null)
+        val fakeEventId = "c".repeat(64)
+
+        val template =
+            PublicMessageEvent.build(listOf(receiver), "Group test") {
+                eTag(ETag(fakeEventId, null))
+            }
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        assertFalse(
+            event.tags.any { it[0] == "e" },
+            "NIP-A4 prohibits e tags in kind 24 events",
+        )
+    }
+
+    @Test
+    fun `isIncluded checks receivers and author`() {
+        val receiver = ReceiverTag(receiverPubKey, null)
+        val template = PublicMessageEvent.build(receiver, "Test")
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        assertTrue(event.isIncluded(receiverPubKey))
+        assertTrue(event.isIncluded(event.pubKey))
+        assertFalse(event.isIncluded("0".repeat(64)))
+    }
+
+    @Test
+    fun `groupKeys includes author and receivers`() {
+        val receiver = ReceiverTag(receiverPubKey, null)
+        val template = PublicMessageEvent.build(receiver, "Test")
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        val keys = event.groupKeys()
+        assertTrue(keys.contains(event.pubKey))
+        assertTrue(keys.contains(receiverPubKey))
+    }
+
+    @Test
+    fun `groupKeySet returns unique keys`() {
+        val receiver = ReceiverTag(receiverPubKey, null)
+        val template = PublicMessageEvent.build(receiver, "Test")
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        val keySet = event.groupKeySet()
+        assertEquals(2, keySet.size)
+        assertTrue(keySet.contains(event.pubKey))
+        assertTrue(keySet.contains(receiverPubKey))
+    }
+
+    @Test
+    fun `chatroomKey excludes given user`() {
+        val receiver = ReceiverTag(receiverPubKey, null)
+        val template = PublicMessageEvent.build(receiver, "Test")
+        val event = signer.sign<PublicMessageEvent>(template)
+
+        val chatroomKey = event.chatroomKey(event.pubKey)
+        assertFalse(chatroomKey.contains(event.pubKey))
+        assertTrue(chatroomKey.contains(receiverPubKey))
+    }
+}

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip57Zaps/LnZapRequestKindTagTest.kt

@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.nip57Zaps
+
+import com.vitorpamplona.quartz.experimental.publicMessages.PublicMessageEvent
+import com.vitorpamplona.quartz.experimental.publicMessages.tags.ReceiverTag
+import com.vitorpamplona.quartz.nip01Core.core.Event
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
+import com.vitorpamplona.quartz.utils.DeterministicSigner
+import com.vitorpamplona.quartz.utils.nsecToKeyPair
+import kotlinx.coroutines.test.runTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class LnZapRequestKindTagTest {
+    private val signer =
+        DeterministicSigner(
+            "nsec10g0wheggqn9dawlc0yuv6adnat6n09anr7eyykevw2dm8xa5fffs0wsdsr".nsecToKeyPair(),
+        )
+
+    private val nostrSigner = NostrSignerInternal(signer.key)
+
+    private val receiverPubKey = "3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d"
+
+    @Test
+    fun `zap request for kind 24 event includes k tag`() =
+        runTest {
+            val receiver = ReceiverTag(receiverPubKey, null)
+            val template = PublicMessageEvent.build(receiver, "Test message")
+            val publicMsg = signer.sign<PublicMessageEvent>(template)
+
+            val relays = setOf(NormalizedRelayUrl("wss://relay.example.com/"))
+
+            val zapRequest =
+                LnZapRequestEvent.create(
+                    zappedEvent = publicMsg,
+                    relays = relays,
+                    signer = nostrSigner,
+                    pollOption = null,
+                    message = "",
+                    zapType = LnZapEvent.ZapType.PUBLIC,
+                    toUserPubHex = null,
+                )
+
+            val kTag = zapRequest.tags.firstOrNull { it[0] == "k" }
+            assertTrue(kTag != null, "Zap request must include k tag per NIP-A4")
+            assertEquals("24", kTag[1], "k tag must contain the zapped event's kind")
+        }
+
+    @Test
+    fun `zap request for kind 1 event includes k tag`() =
+        runTest {
+            val kind1Event =
+                Event(
+                    id = "a".repeat(64),
+                    pubKey = receiverPubKey,
+                    createdAt = 1000L,
+                    kind = 1,
+                    tags = emptyArray(),
+                    content = "Hello world",
+                    sig = "b".repeat(128),
+                )
+
+            val relays = setOf(NormalizedRelayUrl("wss://relay.example.com/"))
+
+            val zapRequest =
+                LnZapRequestEvent.create(
+                    zappedEvent = kind1Event,
+                    relays = relays,
+                    signer = nostrSigner,
+                    pollOption = null,
+                    message = "",
+                    zapType = LnZapEvent.ZapType.PUBLIC,
+                    toUserPubHex = null,
+                )
+
+            val kTag = zapRequest.tags.firstOrNull { it[0] == "k" }
+            assertTrue(kTag != null, "Zap request should include k tag")
+            assertEquals("1", kTag[1], "k tag should contain the zapped event's kind")
+        }
+
+    @Test
+    fun `zap request for user only has no k tag`() =
+        runTest {
+            val relays = setOf(NormalizedRelayUrl("wss://relay.example.com/"))
+
+            val zapRequest =
+                LnZapRequestEvent.create(
+                    userHex = receiverPubKey,
+                    relays = relays,
+                    signer = nostrSigner,
+                    message = "",
+                    zapType = LnZapEvent.ZapType.PUBLIC,
+                )
+
+            val kTag = zapRequest.tags.firstOrNull { it[0] == "k" }
+            assertEquals(null, kTag, "User-only zap should not have k tag")
+        }
+}