feat(live-chat): top zappers leaderboard above live stream chat

Add a horizontally-scrollable strip of pill chips showing the top
zappers on a live stream, placed above the goal header. Each chip has
an avatar, lightning icon, and compact sat total (K/M), matching
zap.stream's TopZappers look. Tapping a chip opens the zapper's
profile.

Aggregates zaps from two sources and dedupes by receipt id so a zap
that tags both #a=<stream> and #e=<goalId> doesn't double-count:
  - stream-scoped host-directed zaps already routed into the
    LiveActivitiesChannel cache via the existing #a subscription
  - goal-scoped zaps reachable through goalNote.zaps when a NIP-75
    goal is attached

Sorts contributors by total sats desc, takes top 10, hides the row
when there are none.

https://claude.ai/code/session_01WJA5PvDABegBYUu6h42YZi

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/nip53LiveActivities/ChannelView.kt

@@ -39,6 +39,7 @@ import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.feed.RefreshingChatro
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.dal.ChannelFeedViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.datasource.ChannelFilterAssemblerSubscription
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.nip53LiveActivities.header.LiveStreamGoalHeader
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.nip53LiveActivities.header.LiveStreamTopZappers
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.send.ChannelNewMessageViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.send.EditFieldRow
 import com.vitorpamplona.amethyst.ui.theme.DoubleVertSpacer
@@ -128,6 +129,7 @@ fun LiveActivityChannelView(
                     .weight(1f, true),
         ) {
             ShowVideoStreaming(channel, accountViewModel)
+            LiveStreamTopZappers(channel, accountViewModel, nav)
             LiveStreamGoalHeader(channel, accountViewModel, nav)
             RefreshingChatroomFeedView(
                 feedContentState = feedViewModel.feedState,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/nip53LiveActivities/header/LiveStreamTopZappers.kt

@@ -0,0 +1,208 @@
+/*
+ * 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.nip53LiveActivities.header
+
+import androidx.compose.foundation.BorderStroke
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.lazy.LazyRow
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import com.vitorpamplona.amethyst.commons.model.nip53LiveActivities.LiveActivitiesChannel
+import com.vitorpamplona.amethyst.model.Note
+import com.vitorpamplona.amethyst.service.relayClient.reqCommand.event.observeNoteZaps
+import com.vitorpamplona.amethyst.ui.navigation.navs.INav
+import com.vitorpamplona.amethyst.ui.navigation.routes.Route
+import com.vitorpamplona.amethyst.ui.note.UserPicture
+import com.vitorpamplona.amethyst.ui.note.ZapIcon
+import com.vitorpamplona.amethyst.ui.note.showAmountInteger
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
+import com.vitorpamplona.amethyst.ui.theme.BitcoinOrange
+import com.vitorpamplona.amethyst.ui.theme.Size16Modifier
+import com.vitorpamplona.amethyst.ui.theme.Size24dp
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip57Zaps.LnZapEvent
+import com.vitorpamplona.quartz.nip57Zaps.LnZapRequestEvent
+import java.math.BigDecimal
+
+private const val TOP_ZAPPERS_LIMIT = 10
+
+private data class TopZapperEntry(
+    val zapperPubKey: HexKey,
+    val totalSats: BigDecimal,
+)
+
+/**
+ * Horizontally-scrollable leaderboard of the top zappers on a live stream.
+ * Aggregates zaps from both the stream's #a subscription and the attached
+ * NIP-75 zap goal (if any), de-duplicating by zap-receipt id. Matches
+ * zap.stream's TopZappers UX: pill chips with avatar + lightning + sats.
+ */
+@Composable
+fun LiveStreamTopZappers(
+    channel: LiveActivitiesChannel,
+    accountViewModel: AccountViewModel,
+    nav: INav,
+) {
+    val goalId = channel.info?.goalEventId()
+
+    if (goalId != null) {
+        var goalNote by remember(goalId) { mutableStateOf(accountViewModel.getNoteIfExists(goalId)) }
+        if (goalNote == null) {
+            LaunchedEffect(goalId) {
+                goalNote = accountViewModel.checkGetOrCreateNote(goalId)
+            }
+        }
+        TopZappersStrip(channel, goalNote, accountViewModel, nav)
+    } else {
+        TopZappersStrip(channel, null, accountViewModel, nav)
+    }
+}
+
+@Composable
+private fun TopZappersStrip(
+    channel: LiveActivitiesChannel,
+    goalNote: Note?,
+    accountViewModel: AccountViewModel,
+    nav: INav,
+) {
+    // Trigger recomposition whenever a new zap lands in the channel cache.
+    val channelTick by channel.changesFlow().collectAsStateWithLifecycle(initialValue = null)
+
+    // Trigger recomposition when zaps arrive for the goal note.
+    val goalZapsState =
+        if (goalNote != null) {
+            observeNoteZaps(goalNote, accountViewModel).value
+        } else {
+            null
+        }
+
+    val entries =
+        remember(channel, channelTick, goalNote, goalZapsState) {
+            aggregateTopZappers(channel, goalNote)
+        }
+
+    if (entries.isEmpty()) return
+
+    LazyRow(
+        modifier = Modifier.fillMaxWidth().padding(horizontal = 8.dp, vertical = 4.dp),
+        horizontalArrangement = Arrangement.spacedBy(6.dp),
+        contentPadding = PaddingValues(horizontal = 4.dp),
+    ) {
+        items(entries, key = { it.zapperPubKey }) { entry ->
+            ZapperPill(entry, accountViewModel, nav)
+        }
+    }
+}
+
+@Composable
+private fun ZapperPill(
+    entry: TopZapperEntry,
+    accountViewModel: AccountViewModel,
+    nav: INav,
+) {
+    Surface(
+        shape = CircleShape,
+        color = MaterialTheme.colorScheme.surface,
+        border = BorderStroke(1.dp, MaterialTheme.colorScheme.outlineVariant),
+        modifier =
+            Modifier.clickable {
+                nav.nav(Route.Profile(entry.zapperPubKey))
+            },
+    ) {
+        Row(
+            modifier = Modifier.padding(horizontal = 6.dp, vertical = 2.dp),
+            verticalAlignment = Alignment.CenterVertically,
+            horizontalArrangement = Arrangement.spacedBy(4.dp),
+        ) {
+            UserPicture(
+                userHex = entry.zapperPubKey,
+                size = Size24dp,
+                accountViewModel = accountViewModel,
+                nav = nav,
+            )
+            ZapIcon(Size16Modifier, BitcoinOrange)
+            Text(
+                text = showAmountInteger(entry.totalSats),
+                style = MaterialTheme.typography.labelMedium,
+            )
+            Spacer(Modifier.padding(start = 2.dp))
+        }
+    }
+}
+
+private fun aggregateTopZappers(
+    channel: LiveActivitiesChannel,
+    goalNote: Note?,
+): List<TopZapperEntry> {
+    // receiptId -> (zapperPubKey, sats) — dedupes a zap that appears via both #a and #e.
+    val byReceipt = HashMap<HexKey, Pair<HexKey, BigDecimal>>()
+
+    // Stream-level zaps routed to the channel cache.
+    channel.notes.forEach { _, note ->
+        val ev = note.event
+        if (ev is LnZapEvent) {
+            val zapper = ev.zapRequest?.pubKey ?: return@forEach
+            val sats = ev.amount() ?: return@forEach
+            byReceipt[note.idHex] = zapper to sats
+        }
+    }
+
+    // Goal-scoped zaps attached to the goal note via #e.
+    goalNote?.zaps?.forEach { (zapRequestNote, receiptNote) ->
+        val receiptEv = receiptNote?.event as? LnZapEvent ?: return@forEach
+        val zapper = (zapRequestNote.event as? LnZapRequestEvent)?.pubKey ?: return@forEach
+        val sats = receiptEv.amount() ?: return@forEach
+        byReceipt[receiptNote.idHex] = zapper to sats
+    }
+
+    if (byReceipt.isEmpty()) return emptyList()
+
+    val totals = HashMap<HexKey, BigDecimal>(byReceipt.size)
+    byReceipt.values.forEach { (pk, sats) ->
+        totals[pk] = (totals[pk] ?: BigDecimal.ZERO) + sats
+    }
+
+    return totals.entries
+        .asSequence()
+        .sortedByDescending { it.value }
+        .take(TOP_ZAPPERS_LIMIT)
+        .map { TopZapperEntry(it.key, it.value) }
+        .toList()
+}