feat(nip29): one-tap join from invite links carrying a code

An invite link's `?code=` now flows all the way to the join: tapping a
`wss://relay'id?code=…` card/link (or opening it as a deep link) opens the group
and, because the tap is itself the opt-in, fires the kind-9021 join with that
code once — no more re-typing it into the join dialog. Plain (code-less) group
links still just open the group for viewing.

- Route.RelayGroup gains inviteCode; threaded through AppNavigation →
  RelayGroupChatScreen → RelayGroupTopBar
- RelayGroupTopBar auto-joins once when a code is present and we're not already
  a member (reuses the optimistic "requested" state)
- RelayGroupCard / ClickableRelayGroupLink / uriToRoute carry the parsed code

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B5MLY4hq5LXJ2D5WeLRyXj

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/MainActivity.kt

@@ -337,5 +337,5 @@ private fun relayGroupDirectRoute(nip19: NAddress): Route? {
  */
 private fun relayGroupInviteRoute(uri: String): Route? {
     val link = GroupInviteLink.parse(uri.removePrefix(NOSTR_URI_PREFIX)) ?: return null
-    return Route.RelayGroup(link.groupId, link.relayUrl.url)
+    return Route.RelayGroup(link.groupId, link.relayUrl.url, inviteCode = link.code)
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/components/ClickableRelayGroupLink.kt

@@ -65,7 +65,7 @@ fun ClickableRelayGroupLink(
                         }
                     },
                     onClick = {
-                        nav.nav(Route.RelayGroup(invite.groupId, invite.relayUrl.url))
+                        nav.nav(Route.RelayGroup(invite.groupId, invite.relayUrl.url, inviteCode = invite.code))
                     },
                 )
         }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/components/RelayGroupCard.kt

@@ -46,7 +46,7 @@ import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
 import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.commons.model.nip29RelayGroups.RelayGroupChannel
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
-import com.vitorpamplona.amethyst.ui.navigation.routes.routeFor
+import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.relayGroup.LoadRelayGroupChannel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.relayGroup.datasource.RelayGroupPreviewSubscription
@@ -78,13 +78,14 @@ fun RelayGroupCard(
     val groupId = remember(invite) { invite.toGroupId() }
 
     LoadRelayGroupChannel(groupId, accountViewModel) { channel ->
-        RelayGroupCardContent(channel, accountViewModel, nav)
+        RelayGroupCardContent(channel, invite.code, accountViewModel, nav)
     }
 }
 
 @Composable
 private fun RelayGroupCardContent(
     baseChannel: RelayGroupChannel,
+    inviteCode: String?,
     accountViewModel: AccountViewModel,
     nav: INav,
 ) {
@@ -111,7 +112,11 @@ private fun RelayGroupCardContent(
         }
 
     OutlinedCard(
-        onClick = { nav.nav(routeFor(channel)) },
+        onClick = {
+            nav.nav(
+                Route.RelayGroup(channel.groupId.id, channel.groupId.relayUrl.url, inviteCode = inviteCode),
+            )
+        },
         modifier = Modifier.fillMaxWidth().padding(vertical = 4.dp),
     ) {
         Row(

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/AppNavigation.kt

@@ -568,6 +568,7 @@ fun BuildNavigation(
                 relayUrl = it.relayUrl,
                 draftId = it.draftId,
                 replyToId = it.replyTo,
+                inviteCode = it.inviteCode,
                 accountViewModel = accountViewModel,
                 nav = nav,
             )

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/routes/Routes.kt

@@ -642,6 +642,9 @@ sealed class Route {
         val relayUrl: String,
         val draftId: HexKey? = null,
         val replyTo: HexKey? = null,
+        // NIP-29 invite code from a `wss://relay'id?code=…` link — auto-joins a closed
+        // group when the screen opens. Null for a plain (view-only) group link.
+        val inviteCode: String? = null,
     ) : Route()
 
     @Serializable data class RelayGroupServer(

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

@@ -38,6 +38,7 @@ fun RelayGroupChatScreen(
     relayUrl: String,
     draftId: HexKey? = null,
     replyToId: HexKey? = null,
+    inviteCode: String? = null,
     accountViewModel: AccountViewModel,
     nav: INav,
 ) {
@@ -50,7 +51,7 @@ fun RelayGroupChatScreen(
         isInvertedLayout = true,
         topBar = {
             LoadRelayGroupChannel(channelId, accountViewModel) {
-                RelayGroupTopBar(it, accountViewModel, nav)
+                RelayGroupTopBar(it, inviteCode, accountViewModel, nav)
             }
         },
         accountViewModel = accountViewModel,

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

@@ -64,6 +64,7 @@ import com.vitorpamplona.quartz.nip01Core.relay.normalizer.displayUrl
 @Composable
 fun RelayGroupTopBar(
     baseChannel: RelayGroupChannel,
+    inviteCode: String? = null,
     accountViewModel: AccountViewModel,
     nav: INav,
 ) {
@@ -81,6 +82,19 @@ fun RelayGroupTopBar(
     LaunchedEffect(membership) {
         if (membership.isMember()) requested = false
     }
+
+    // Arrived via an invite link carrying a join code (`wss://relay'id?code=…`): the
+    // user already opted in by tapping it, so fire the kind-9021 join once (with the
+    // code) instead of making them re-enter it. Guarded to exactly once and skipped if
+    // the roster already shows us as a member.
+    var autoJoined by remember(channel.groupId) { mutableStateOf(false) }
+    LaunchedEffect(channel.groupId, inviteCode, membership) {
+        if (inviteCode != null && !autoJoined && !membership.isMember()) {
+            autoJoined = true
+            requested = true
+            accountViewModel.joinRelayGroup(channel, inviteCode)
+        }
+    }
     val displayMembership = if (!membership.isMember() && requested) RelayGroupMembership.PENDING else membership
 
     var menuOpen by remember { mutableStateOf(false) }