fix(cashu): show "discovering" state instead of empty-create CTA on first launch

NIP-60 wallets are portable — kind:17375 + 7375 + 7376 + 10019 are
stored on relays, so a wallet created in another client (cashu.me,
Boardwalk, etc.) should appear in Amethyst when the user signs in with
the same Nostr key. The plumbing already handles this: our
CashuWalletFilterAssembler subscribes to kinds=[17375, 7375, 7376,
7374, 10019] authored by us, and CashuWalletState.applyEvents() indexes
incoming events regardless of which client published them.

The UX bug: the wallet screen had two states (wallet event present /
absent). On first launch, before relays delivered the existing wallet
event, we rendered the "No Cashu wallet — Create" state. Tapping Create
there published a fresh kind:17375 which (being replaceable) clobbered
the remote wallet — destroying the P2PK key and orphaning any inbound
nutzaps locked to it.

Fix:

 * CashuWalletState gets a `discovering: StateFlow<Boolean>` set to
   true at start() until either a wallet event arrives (cleared from
   applyEvents) or DISCOVERY_TIMEOUT_MS (8 s) elapses, whichever first.
 * CashuWalletScreen renders a "Looking for your wallet…" pane with a
   spinner + explainer while discovering is true. Empty-create CTA only
   fires after timeout for genuinely wallet-less users.

playDebug + fdroidDebug compile clean; 24/24 jvm tests still pass.

https://claude.ai/code/session_01MdWddiar819f8XYt5N8BjP

amethyst/src/main/java/com/vitorpamplona/amethyst/model/nip60Cashu/CashuWalletState.kt

@@ -133,6 +133,24 @@ class CashuWalletState(
     private val _pendingQuotes = MutableStateFlow<List<CashuMintQuoteEvent>>(emptyList())
     val pendingQuotes: StateFlow<List<CashuMintQuoteEvent>> = _pendingQuotes.asStateFlow()
 
+    /**
+     * True while we're still waiting for relays to deliver an existing
+     * wallet event for this account.
+     *
+     * NIP-60 wallets are portable across clients — if the user previously
+     * created one in (say) Boardwalk or cashu.me, our subscription should
+     * pull the kind:17375 in within a few seconds of sign-in. The UI uses
+     * this flag to show a "Looking for your wallet…" state during that
+     * window instead of jumping straight to the "Create" CTA, which would
+     * overwrite the remote wallet (kind:17375 is replaceable).
+     *
+     * Cleared when:
+     *   - a wallet event arrives via cache backfill or live update, OR
+     *   - the discovery timeout elapses (~8 seconds), whichever first.
+     */
+    private val _discovering = MutableStateFlow(false)
+    val discovering: StateFlow<Boolean> = _discovering.asStateFlow()
+
     fun hasWallet(): Boolean = _walletEvent.value != null
 
     /** Read the wallet's P2PK pubkey (33-byte compressed hex). */
@@ -181,6 +199,21 @@ class CashuWalletState(
         started = true
         this.publish = publish
 
+        // Show the "discovering" state until either a wallet event lands
+        // (set inside applyEvents()) or the timeout below fires. Without
+        // this the UI would render the empty-wallet CTA the moment the
+        // screen opens — even for users whose wallet exists on relays but
+        // hasn't yet been delivered — and tapping Create there would
+        // overwrite the remote kind:17375.
+        if (_walletEvent.value == null) {
+            _discovering.value = true
+            jobs +=
+                scope.launch(Dispatchers.Default) {
+                    kotlinx.coroutines.delay(DISCOVERY_TIMEOUT_MS)
+                    _discovering.value = false
+                }
+        }
+
         // Backfill from cache once.
         scope.launch(Dispatchers.Default) {
             val initial = scanCacheForOwnEvents()
@@ -294,6 +327,9 @@ class CashuWalletState(
 
         if (dirtyWallet) {
             _walletEvent.value = walletEventInternal
+            // Any wallet event resolves the "discovering" state — whether it
+            // came from cache backfill or a fresh relay delivery.
+            _discovering.value = false
             walletEventInternal?.let { evt ->
                 _mints.value =
                     runCatching { evt.mints(signer) }
@@ -524,6 +560,16 @@ class CashuWalletState(
     private suspend fun publishEvent(event: Event) {
         publish(event)
     }
+
+    private companion object {
+        /**
+         * How long to remain in the "discovering" state before falling back
+         * to the empty-wallet CTA. Long enough that a typical relay round-
+         * trip on a cold start completes; short enough that genuinely
+         * wallet-less users don't stare at a spinner.
+         */
+        const val DISCOVERY_TIMEOUT_MS = 8_000L
+    }
 }
 
 /** Mint + recipient pubkey resolved from a kind:10019. */

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/wallet/CashuWalletScreen.kt

@@ -96,6 +96,7 @@ fun CashuWalletScreen(
     viewModel.init(accountViewModel)
 
     val walletEvent by viewModel.walletEvent.collectAsState()
+    val discovering by viewModel.discovering.collectAsState()
     val mints by viewModel.mints.collectAsState()
     val balanceSats by viewModel.balanceSats.collectAsState()
     val history by viewModel.history.collectAsState()
@@ -139,23 +140,33 @@ fun CashuWalletScreen(
             )
         },
     ) { padding ->
-        if (walletEvent == null) {
-            EmptyCashuWallet(
-                modifier = Modifier.padding(padding),
-                onCreate = { nav.nav(Route.WalletAddCashu) },
-            )
-        } else {
-            CashuWalletContent(
-                modifier = Modifier.padding(padding),
-                balanceSats = balanceSats,
-                mints = mints,
-                history = history,
-                onReceive = { receiveOpen = true },
-                onSendLn = { sendLnOpen = true },
-                onSendToken = { sendTokenOpen = true },
-                onRedeem = { redeemOpen = true },
-                onRecommendMint = { viewModel.recommendMint(it) },
-            )
+        when {
+            walletEvent != null ->
+                CashuWalletContent(
+                    modifier = Modifier.padding(padding),
+                    balanceSats = balanceSats,
+                    mints = mints,
+                    history = history,
+                    onReceive = { receiveOpen = true },
+                    onSendLn = { sendLnOpen = true },
+                    onSendToken = { sendTokenOpen = true },
+                    onRedeem = { redeemOpen = true },
+                    onRecommendMint = { viewModel.recommendMint(it) },
+                )
+
+            // NIP-60 wallets are portable across clients — show a "looking
+            // for your wallet" state until the relay subscription returns
+            // anything (or times out). Without this, a user who created
+            // their wallet in another app would see the Create CTA on
+            // first launch and would clobber the remote kind:17375.
+            discovering ->
+                DiscoveringCashuWallet(modifier = Modifier.padding(padding))
+
+            else ->
+                EmptyCashuWallet(
+                    modifier = Modifier.padding(padding),
+                    onCreate = { nav.nav(Route.WalletAddCashu) },
+                )
         }
     }
 
@@ -200,6 +211,33 @@ fun CashuWalletScreen(
     }
 }
 
+@Composable
+private fun DiscoveringCashuWallet(modifier: Modifier) {
+    Column(
+        modifier =
+            modifier
+                .fillMaxSize()
+                .padding(32.dp),
+        horizontalAlignment = Alignment.CenterHorizontally,
+        verticalArrangement = Arrangement.Center,
+    ) {
+        CircularProgressIndicator(modifier = Modifier.size(36.dp), strokeWidth = 3.dp)
+        Spacer(modifier = Modifier.height(16.dp))
+        Text(
+            text = stringRes(R.string.cashu_discovering),
+            style = MaterialTheme.typography.titleMedium,
+            fontWeight = FontWeight.SemiBold,
+        )
+        Spacer(modifier = Modifier.height(8.dp))
+        Text(
+            text = stringRes(R.string.cashu_discovering_description),
+            style = MaterialTheme.typography.bodySmall,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            textAlign = androidx.compose.ui.text.style.TextAlign.Center,
+        )
+    }
+}
+
 @Composable
 private fun EmptyCashuWallet(
     modifier: Modifier,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/wallet/CashuWalletViewModel.kt

@@ -145,6 +145,7 @@ class CashuWalletViewModel : ViewModel() {
     val tokenEntries: StateFlow<List<TokenEntry>> get() = state.tokenEntries
     val history get() = state.history
     val pendingQuotes get() = state.pendingQuotes
+    val discovering get() = state.discovering
 
     private val _createState = MutableStateFlow<CashuWalletCreateState>(CashuWalletCreateState.Idle)
     val createState = _createState.asStateFlow()

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

@@ -1876,6 +1876,8 @@
     <string name="cashu_wallet_title">Cashu Wallet</string>
     <string name="cashu_no_wallet">No Cashu wallet yet</string>
     <string name="cashu_no_wallet_description">Create a Cashu wallet to hold ecash tokens and receive nutzaps.</string>
+    <string name="cashu_discovering">Looking for your wallet…</string>
+    <string name="cashu_discovering_description">NIP-60 wallets sync across clients. If you created one in another app under this Nostr key, it should appear in a few seconds.</string>
     <string name="cashu_balance">Balance</string>
     <string name="cashu_mints">Mints</string>
     <string name="cashu_mint_url">Mint URL</string>