fix: fall back to observed relays when public chat declares an empty relay list

PublicChatChannel.relays() was `info.relays?.toSet() ?: super.relays()`.
An empty (non-null) declared-relay list — `emptyList()?.toSet()` — yields an
empty set and short-circuits the elvis, so the channel reported zero relays
instead of falling back to the relays it was actually observed on. Both the
message-send path and the broadcast path (computeRelaysForChannels /
wantsBroadcastRelays) read relays(), so the message was published to nowhere
while a manual broadcast still reached the user's personal relays — matching
the reported symptom.

Treat an empty declared list like "no declared relays" via ifEmpty, so it
falls back to observed relays. Adds PublicChatChannelRelayTest covering the
declared-relay round-trip, message->channel resolution, and the empty-list
fallback regression.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AYtHYEob2THu74inTxZxCh

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/nip28PublicChats/PublicChatChannel.kt

@@ -49,7 +49,11 @@ class PublicChatChannel(
     var infoTags = EmptyTagList
     var updatedMetadataAt: Long = 0
 
-    override fun relays() = info.relays?.toSet() ?: super.relays()
+    // An empty declared-relay list must behave like "no declared relays" and fall
+    // back to the relays the channel was actually observed on. Without ifEmpty,
+    // `emptyList()?.toSet()` short-circuits the elvis to an empty set, so the
+    // channel reports zero relays and messages get published to nowhere.
+    override fun relays() = info.relays?.ifEmpty { null }?.toSet() ?: super.relays()
 
     fun relayHintUrls() = relays().take(3)
 

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/model/PublicChatChannelRelayTest.kt

@@ -0,0 +1,97 @@
+/*
+ * 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.amethyst.commons.model
+
+import com.vitorpamplona.amethyst.commons.model.nip28PublicChats.PublicChatChannel
+import com.vitorpamplona.quartz.nip01Core.hints.EventHintBundle
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
+import com.vitorpamplona.quartz.nip28PublicChat.admin.ChannelCreateEvent
+import com.vitorpamplona.quartz.nip28PublicChat.message.ChannelMessageEvent
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+/**
+ * Reproduces the "public chat message not sent to the channel-declared relay" report.
+ *
+ * Walks the exact protocol path the app uses:
+ *  1. build a kind-40 ChannelCreate carrying a declared relay in its content,
+ *  2. feed it to a PublicChatChannel via updateChannelInfo (what LocalCache does),
+ *  3. assert channel.relays() returns the declared relay (what both the send path
+ *     and computeRelaysForChannels/broadcast read),
+ *  4. build a kind-42 message for that channel and assert channelId() resolves back
+ *     to the channel id (what getAnyChannel uses to find the channel at broadcast).
+ */
+class PublicChatChannelRelayTest {
+    private val authorKey = "e".repeat(64)
+    private val channelId = "a".repeat(64)
+    private val msgId = "b".repeat(64)
+    private val sig = "f".repeat(128)
+
+    private val declaredRelay = RelayUrlNormalizer.normalizeOrNull("wss://relay.example.com")!!
+
+    private fun createEvent(relays: List<NormalizedRelayUrl>?): ChannelCreateEvent {
+        val template = ChannelCreateEvent.build("My Channel", "about", null, relays)
+        return ChannelCreateEvent(channelId, authorKey, template.createdAt, template.tags, template.content, sig)
+    }
+
+    @Test
+    fun channelRelaysContainsDeclaredRelay() {
+        val create = createEvent(listOf(declaredRelay))
+
+        // sanity: the relay survives the content round-trip
+        assertEquals(listOf(declaredRelay), create.channelInfo().relays)
+
+        val channel = PublicChatChannel(channelId)
+        channel.info = create.channelInfo() // exactly what updateChannelInfo does
+
+        assertTrue(channel.relays().contains(declaredRelay), "channel.relays() must contain the declared relay")
+    }
+
+    @Test
+    fun messageResolvesBackToChannel() {
+        val create = createEvent(listOf(declaredRelay))
+
+        val template = ChannelMessageEvent.message("hello", EventHintBundle(create, declaredRelay))
+        val message = ChannelMessageEvent(msgId, authorKey, template.createdAt, template.tags, template.content, sig)
+
+        assertEquals(channelId, message.channelId(), "message must resolve to the channel id (getAnyChannel)")
+    }
+
+    @Test
+    fun emptyDeclaredRelayListFallsThroughToObservedRelays() {
+        // Regression: info.relays = [] (empty, not null) must NOT short-circuit to an
+        // empty set. It has to fall back to the relays the channel was observed on,
+        // otherwise messages are published to nowhere.
+        val create = createEvent(emptyList())
+
+        val channel = PublicChatChannel(channelId)
+        channel.addRelaySync(declaredRelay) // observed relay
+        channel.info = create.channelInfo() // exactly what updateChannelInfo does
+
+        assertTrue(channel.info.relays!!.isEmpty(), "precondition: declared relay list is empty")
+        assertTrue(
+            channel.relays().contains(declaredRelay),
+            "relays() must fall back to observed relays when the declared list is empty",
+        )
+    }
+}