Merge pull request #3732 from vitorpamplona/fix/buzz-forum-post-only-in-forum-channels

fix(buzz): only offer "new thread" where a forum post belongs

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/buzz/BuzzCanvasScreen.kt

@@ -63,6 +63,7 @@ import com.vitorpamplona.amethyst.ui.navigation.topbars.TopBarExtensibleWithBack
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.quartz.buzz.stream.CanvasEvent
+import com.vitorpamplona.quartz.buzz.workspace.isBuzzDm
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
 import com.vitorpamplona.quartz.nip29RelayGroups.GroupId
 import kotlinx.coroutines.Dispatchers
@@ -95,14 +96,21 @@ fun BuzzCanvasScreen(
     val canvas = remember(version) { state.canvasNote }
     val content = canvas?.event?.content
 
-    // The channel this canvas belongs to, for the subtitle. Null until its kind-39000 lands, which
-    // only costs the subtitle — the canvas itself is keyed by the raw channel id.
-    val channelName =
+    // The channel this canvas belongs to, for the subtitle and the edit gate. Null until its
+    // kind-39000 lands, which only costs the subtitle — the canvas itself is keyed by the raw id.
+    val channel =
         remember(channelId, relayUrl) {
             RelayUrlNormalizer.normalizeOrNull(relayUrl)?.let { relay ->
-                LocalCache.getRelayGroupChannelIfExists(GroupId(channelId, relay))?.toBestDisplayName()
+                LocalCache.getRelayGroupChannelIfExists(GroupId(channelId, relay))
             }
         }
+    val channelName = channel?.toBestDisplayName()
+
+    // Buzz never lets a DM's canvas be written: its editor's `canEdit` is `canEditNarrative`, which
+    // excludes `channelType === "dm"` outright. A DM reaching this screen at all means a canvas
+    // already exists (see the top bar's gate), so render it read-only rather than offering an edit
+    // that Buzz's own client would never show.
+    val canEdit = channel?.event?.isBuzzDm() != true
 
     var editing by remember { mutableStateOf(false) }
 
@@ -145,8 +153,10 @@ fun BuzzCanvasScreen(
             )
         },
         floatingActionButton = {
-            FloatingActionButton(onClick = { editing = true }) {
-                Icon(symbol = MaterialSymbols.Edit, contentDescription = stringRes(R.string.buzz_canvas_edit))
+            if (canEdit) {
+                FloatingActionButton(onClick = { editing = true }) {
+                    Icon(symbol = MaterialSymbols.Edit, contentDescription = stringRes(R.string.buzz_canvas_edit))
+                }
             }
         },
     ) { padding ->

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/RelayGroupThreadsScreen.kt

@@ -70,6 +70,8 @@ import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.relayG
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.theme.Size35dp
 import com.vitorpamplona.quartz.buzz.forum.ForumPostEvent
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_FORUM
+import com.vitorpamplona.quartz.buzz.workspace.buzzChannelType
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
 import com.vitorpamplona.quartz.nip29RelayGroups.GroupId
@@ -99,6 +101,26 @@ fun RelayGroupThreadsScreen(
     }
 }
 
+/**
+ * Whether *starting* a thread belongs on this channel, given its Buzz `t` [channelType] (null on a
+ * relay that doesn't declare one) and whether its host speaks the Buzz dialect.
+ *
+ * On a Buzz relay the compose FAB writes a kind-45001 forum post, and Buzz only ever puts those in a
+ * `t=forum` channel — its own client mounts the forum view for `channelType === "forum"` alone, so a
+ * 45001 in a `t=stream` chat channel is a post nobody outside Amethyst can see. The relay itself
+ * accepts it (nothing there gates 45001 by channel type), which is exactly why the client has to.
+ *
+ * A Buzz channel whose kind-39000 hasn't landed yet reads as null and is treated as not-a-forum: the
+ * FAB appearing a moment later is a smaller error than publishing into the wrong channel.
+ *
+ * This gates writing only. Reading stays open on every channel — an existing thread is worth showing
+ * wherever it came from — and non-Buzz relays are untouched, where the FAB writes a NIP-7D kind-11.
+ */
+fun canStartThreadHere(
+    channelType: String?,
+    isBuzzRelay: Boolean,
+): Boolean = !isBuzzRelay || channelType == BUZZ_CHANNEL_TYPE_FORUM
+
 @Composable
 private fun RelayGroupThreads(
     channel: RelayGroupChannel,
@@ -121,7 +143,10 @@ private fun RelayGroupThreads(
 
     // Hide the compose FAB where the relay would reject the kind-11: on membership-gated groups
     // that don't list me. Open Buzz channels accept any authenticated member. See [RelayGroupChannel.canPost].
-    val canPost = channel.canPost(accountViewModel.userProfile().pubkeyHex)
+    val isBuzz = remember(channel.groupId.relayUrl) { BuzzRelayDialect.isBuzz(channel.groupId.relayUrl) }
+    val canPost =
+        channel.canPost(accountViewModel.userProfile().pubkeyHex) &&
+            canStartThreadHere(channel.event?.buzzChannelType(), isBuzz)
 
     Scaffold(
         topBar = {
@@ -153,7 +178,7 @@ private fun RelayGroupThreads(
                         // On a Buzz workspace, "new thread" is a Buzz forum post (kind 45001);
                         // vanilla NIP-29 relays use a kind-11 thread. Buzz relays reject
                         // unknown kinds, so a kind-11 thread would be refused there.
-                        if (BuzzRelayDialect.isBuzz(channel.groupId.relayUrl)) {
+                        if (isBuzz) {
                             nav.nav(Route.BuzzForumPost(channel.groupId.id, channel.groupId.relayUrl.url))
                         } else {
                             nav.nav(
@@ -178,7 +203,12 @@ private fun RelayGroupThreads(
         if (threads.isEmpty()) {
             Box(Modifier.fillMaxSize().padding(padding), contentAlignment = Alignment.Center) {
                 Text(
-                    text = stringRes(R.string.relay_group_threads_empty),
+                    text =
+                        if (canPost) {
+                            stringRes(R.string.relay_group_threads_empty)
+                        } else {
+                            stringRes(R.string.relay_group_threads_empty_read_only)
+                        },
                     style = MaterialTheme.typography.bodyMedium,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
                     modifier = Modifier.padding(32.dp),

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/RelayGroupTopBar.kt

@@ -37,6 +37,7 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.State
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -47,10 +48,12 @@ import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
 import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.commons.model.buzz.BuzzRelayDialect
+import com.vitorpamplona.amethyst.commons.model.buzz.BuzzWorkspaceStates
 import com.vitorpamplona.amethyst.commons.model.nip29RelayGroups.RelayGroupChannel
 import com.vitorpamplona.amethyst.commons.model.nip29RelayGroups.RelayGroupMembership
 import com.vitorpamplona.amethyst.model.LocalCache
@@ -170,11 +173,17 @@ fun RelayGroupTopBar(
             }
         },
         actions = {
-            // Buzz workspace canvas (kind 40100): shown on any Buzz-dialect relay so a member can
-            // open the shared markdown doc — or create one when the channel has none yet. The only
-            // affordance that stays an icon: it is this channel's shared document, i.e. content, while
-            // Threads and Share are navigation the reader needs once in a while.
-            if (BuzzRelayDialect.isBuzz(channel.groupId.relayUrl)) {
+            // Buzz canvas (kind 40100): shown on any Buzz-dialect relay so a member can open the
+            // channel's shared markdown doc — or create one when it has none yet. The only affordance
+            // that stays an icon: it is this channel's shared document, i.e. content, while Threads and
+            // Share are navigation the reader needs once in a while.
+            //
+            // Except on a DM, where Buzz itself never offers to *write* one: its canvas entry needs
+            // `hasCanvas || canEditNarrative`, and `canEditNarrative` excludes `channelType === "dm"`
+            // outright. So a DM shows the icon only when a canvas already exists — which is also what
+            // keeps us from advertising "start a shared doc" in a two-person conversation.
+            val hasCanvas by observeBuzzCanvas(channel.groupId.id)
+            if (BuzzRelayDialect.isBuzz(channel.groupId.relayUrl) && (!isDm || hasCanvas)) {
                 IconButton(onClick = { nav.nav(Route.BuzzCanvas(channel.groupId.id, channel.groupId.relayUrl.url)) }) {
                     Icon(
                         symbol = MaterialSymbols.Dashboard,
@@ -372,3 +381,18 @@ private fun RoleBadge(membership: RelayGroupMembership) {
         )
     }
 }
+
+/**
+ * Whether this Buzz channel has a canvas (kind 40100) in cache, recomposing when one lands.
+ *
+ * Only the top bar's DM case needs this: a DM gets the canvas affordance solely when a document
+ * already exists, mirroring Buzz's own `hasCanvas || canEditNarrative` where `canEditNarrative`
+ * excludes DMs. Reads the same [BuzzWorkspaceStates] registry the canvas screen renders from, so the
+ * icon appears the moment the document arrives rather than on the next visit.
+ */
+@Composable
+private fun observeBuzzCanvas(channelId: String): State<Boolean> {
+    val state = remember(channelId) { BuzzWorkspaceStates.getOrCreate(channelId) }
+    val version by state.canvasUpdates.collectAsStateWithLifecycle()
+    return remember(channelId, version) { mutableStateOf(state.canvasNote != null) }
+}

amethyst/src/main/res/values/strings.xml

@@ -2636,6 +2636,8 @@
     <string name="relay_group_discovery_empty_filtered">No groups found for this filter yet.</string>
     <string name="relay_group_favorite_relay">Favorite this relay</string>
     <string name="relay_group_threads_empty">No threads yet. Start one with the + button.</string>
+    <!-- Same, where this viewer cannot start one: not a member, or a Buzz chat channel (forum posts belong to forum channels). -->
+    <string name="relay_group_threads_empty_read_only">No threads yet.</string>
     <string name="relay_group_threads_loading_older">Loading older threads…</string>
     <string name="relay_group_threads_all_caught_up">No older threads</string>
     <string name="relay_group_thread_new">New thread</string>

amethyst/src/test/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/CanStartThreadHereTest.kt

@@ -0,0 +1,68 @@
+/*
+ * 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.ui.screen.loggedIn.chats.publicChannels.relayGroup
+
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_DM
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_FORUM
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_STREAM
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Which channels may *start* a thread. The Threads screen's compose FAB writes a Buzz kind-45001
+ * forum post on a Buzz relay and a NIP-7D kind-11 everywhere else, so the gate has to key on the
+ * channel's declared type — not just on whether the relay would accept the event, which it does.
+ *
+ * The forum case is here rather than on-device because no relay we can reach in a manual pass
+ * currently exposes a `t=forum` channel, and the allow-path is the half that must not regress: a
+ * gate that only ever denies is indistinguishable from deleting the feature.
+ */
+class CanStartThreadHereTest {
+    @Test
+    fun buzzForumChannelCanStartAThread() {
+        assertTrue(canStartThreadHere(BUZZ_CHANNEL_TYPE_FORUM, isBuzzRelay = true))
+    }
+
+    @Test
+    fun buzzChatAndDmChannelsCannot() {
+        // A 45001 here is accepted by the relay and then rendered by nobody — Buzz's own client
+        // mounts its forum view for `channelType === "forum"` alone.
+        assertFalse(canStartThreadHere(BUZZ_CHANNEL_TYPE_STREAM, isBuzzRelay = true))
+        assertFalse(canStartThreadHere(BUZZ_CHANNEL_TYPE_DM, isBuzzRelay = true))
+    }
+
+    @Test
+    fun buzzChannelWithUnknownOrUnloadedTypeCannot() {
+        // kind-39000 not in yet, or a type this version predates: fail closed rather than publish
+        // into a channel that may not be a forum.
+        assertFalse(canStartThreadHere(null, isBuzzRelay = true))
+        assertFalse(canStartThreadHere("workflow", isBuzzRelay = true))
+    }
+
+    @Test
+    fun nonBuzzRelaysAreUntouchedWhateverTheTypeSays() {
+        // Vanilla NIP-29: the FAB writes a kind-11 thread, which is valid in any group, and these
+        // relays declare no `t` at all.
+        assertTrue(canStartThreadHere(null, isBuzzRelay = false))
+        assertTrue(canStartThreadHere(BUZZ_CHANNEL_TYPE_STREAM, isBuzzRelay = false))
+    }
+}