feat(geohash-chat): opt-in "post as my real account"

Adds a per-session composer toggle (off by default) to post to a location channel
under the user's real Nostr identity instead of the anonymous per-geohash key —
trading location privacy for profile, reputation, and zaps. Enabling it requires
confirming a dialog that spells out the location-exposure trade-off. When on, the
message is signed with the account signer (and PoW mined for that pubkey); when
off, the anonymous identity is used as before.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0172JoMccseEKenyWan6txWV

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/geohashChat/GeohashChatScreen.kt

@@ -20,6 +20,8 @@
  */
 package com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.geohashChat
 
+import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxSize
@@ -29,6 +31,8 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.foundation.lazy.rememberLazyListState
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.DropdownMenu
 import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.FilterChip
@@ -37,6 +41,7 @@ import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
@@ -88,11 +93,35 @@ fun GeohashChatScreen(
     val relays by viewModel.relays.collectAsStateWithLifecycle()
     val myPubKey by viewModel.myPubKey.collectAsStateWithLifecycle()
     val teleporting by viewModel.teleported.collectAsStateWithLifecycle()
+    val postingAsSelf by viewModel.postAsSelf.collectAsStateWithLifecycle()
 
     var nickname by remember { mutableStateOf("") }
     var draft by remember { mutableStateOf("") }
+    var showPostAsSelfWarning by remember { mutableStateOf(false) }
     val listState = rememberLazyListState()
 
+    if (showPostAsSelfWarning) {
+        AlertDialog(
+            onDismissRequest = { showPostAsSelfWarning = false },
+            title = { Text("Post as your real account?") },
+            text = {
+                Text(
+                    "Location chat is anonymous by default. If you post as yourself, messages here are " +
+                        "signed with your Nostr identity and publicly reveal that you were at this location.",
+                )
+            },
+            confirmButton = {
+                TextButton(onClick = {
+                    viewModel.setPostAsSelf(true)
+                    showPostAsSelfWarning = false
+                }) { Text("Post as me") }
+            },
+            dismissButton = {
+                TextButton(onClick = { showPostAsSelfWarning = false }) { Text("Cancel") }
+            },
+        )
+    }
+
     Column(Modifier.fillMaxSize().imePadding()) {
         Column(Modifier.fillMaxWidth().padding(horizontal = 12.dp, vertical = 8.dp)) {
             Text("#$geohash", style = MaterialTheme.typography.titleMedium, fontWeight = FontWeight.Bold)
@@ -120,22 +149,28 @@ fun GeohashChatScreen(
         }
 
         HorizontalDivider()
+        OutlinedTextField(
+            value = nickname,
+            onValueChange = { nickname = it },
+            singleLine = true,
+            label = { Text("Nickname (optional)") },
+            modifier = Modifier.fillMaxWidth().padding(horizontal = 12.dp, vertical = 4.dp),
+        )
         Row(
-            Modifier.fillMaxWidth().padding(horizontal = 12.dp, vertical = 4.dp),
-            verticalAlignment = Alignment.CenterVertically,
+            Modifier.fillMaxWidth().horizontalScroll(rememberScrollState()).padding(horizontal = 12.dp),
+            horizontalArrangement = Arrangement.spacedBy(8.dp),
         ) {
-            OutlinedTextField(
-                value = nickname,
-                onValueChange = { nickname = it },
-                singleLine = true,
-                label = { Text("Nickname (optional)") },
-                modifier = Modifier.weight(1f),
-            )
             FilterChip(
                 selected = teleporting,
                 onClick = { viewModel.setTeleported(!teleporting) },
                 label = { Text("✈ Teleport") },
-                modifier = Modifier.padding(start = 8.dp),
+            )
+            FilterChip(
+                selected = postingAsSelf,
+                onClick = {
+                    if (postingAsSelf) viewModel.setPostAsSelf(false) else showPostAsSelfWarning = true
+                },
+                label = { Text("Post as me") },
             )
         }
         Row(

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/geohashChat/GeohashChatViewModel.kt

@@ -34,6 +34,7 @@ import com.vitorpamplona.quartz.nip01Core.relay.client.reqs.SubscriptionListener
 import com.vitorpamplona.quartz.nip01Core.relay.client.single.newSubId
 import com.vitorpamplona.quartz.nip01Core.relay.filters.Filter
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
 import com.vitorpamplona.quartz.nip13Pow.miner.PoWMiner
 import com.vitorpamplona.quartz.utils.TimeUtils
@@ -82,6 +83,13 @@ class GeohashChatViewModel : ViewModel() {
     private val _teleported = MutableStateFlow(false)
     val teleported: StateFlow<Boolean> = _teleported.asStateFlow()
 
+    /**
+     * When true, messages are signed with the user's REAL account key instead of the anonymous
+     * per-geohash identity — trading location privacy for profile/reputation/zaps. Off by default.
+     */
+    private val _postAsSelf = MutableStateFlow(false)
+    val postAsSelf: StateFlow<Boolean> = _postAsSelf.asStateFlow()
+
     private val seen = HashSet<String>()
     private val present = HashSet<String>()
     private val subId = newSubId()
@@ -105,6 +113,10 @@ class GeohashChatViewModel : ViewModel() {
         _teleported.value = value
     }
 
+    fun setPostAsSelf(value: Boolean) {
+        _postAsSelf.value = value
+    }
+
     private suspend fun start() {
         _myPubKey.value = withContext(Dispatchers.IO) { GeohashChatIdentity.keyPair(accountViewModel.account, geohash).pubKey.toHexKey() }
 
@@ -169,19 +181,29 @@ class GeohashChatViewModel : ViewModel() {
         if (relays.isEmpty()) return
 
         viewModelScope.launch {
-            val keyPair = withContext(Dispatchers.IO) { GeohashChatIdentity.keyPair(accountViewModel.account, geohash) }
-            val signer = NostrSignerInternal(keyPair)
+            val account = accountViewModel.account
+            // Anonymous per-geohash identity by default; the real account only when the user opts in.
+            val signer: NostrSigner
+            val pubKeyHex: String
+            if (_postAsSelf.value) {
+                signer = account.signer
+                pubKeyHex = account.signer.pubKey
+            } else {
+                val keyPair = withContext(Dispatchers.IO) { GeohashChatIdentity.keyPair(account, geohash) }
+                signer = NostrSignerInternal(keyPair)
+                pubKeyHex = keyPair.pubKey.toHexKey()
+            }
 
             var template = GeohashChatEvent.build(trimmed, geohash, nickname = nickname?.ifBlank { null }, teleported = _teleported.value)
             template =
                 withContext(Dispatchers.Default) {
                     val deadline = System.nanoTime() + POW_TIMEOUT_NANOS
                     runCatching {
-                        PoWMiner.mine(template, keyPair.pubKey.toHexKey(), POW_BITS, powThreads()) { System.nanoTime() < deadline }
+                        PoWMiner.mine(template, pubKeyHex, POW_BITS, powThreads()) { System.nanoTime() < deadline }
                     }.getOrDefault(template)
                 }
 
-            runCatching { accountViewModel.account.signWithAndSendPrivately(template, signer, relays) }
+            runCatching { account.signWithAndSendPrivately(template, signer, relays) }
         }
     }