feat(clink): make offer payments zappable

When a noffer is rendered in someone's note, paying it now attaches a NIP-57
zap request so the offer service issues a zappable invoice and publishes a zap
receipt — turning the payment into a real zap on the author instead of a silent
invoice:
- ClinkOfferPayer.requestInvoice forwards a serialized zap request via
  OfferClient's existing zap field.
- ClinkOfferPreview builds the 9734 from the threaded authorPubKey using the
  account's default zap type (skipped for NONZAP), at the resolved amount.
- RichTextViewer threads authorPubKey into the offer-segment renderers; the
  markdown/secret paths default to null (plain invoice, no target).

Falls back to a plain invoice when there's no author or the user opted out of
zaps. :amethyst compiles; the round-trip and receipt remain untested end-to-end.

amethyst/src/main/java/com/vitorpamplona/amethyst/service/ClinkOfferPayer.kt

@@ -52,13 +52,14 @@ object ClinkOfferPayer {
         account: Account,
         offer: NOffer,
         amountSats: Long? = null,
+        zap: String? = null,
         timeoutMs: Long = DEFAULT_TIMEOUT_MS,
     ): OfferResponse? {
         val relays = offer.relays.toSet()
         if (relays.isEmpty()) return null
 
         val client = OfferClient(offer, account.signer)
-        val request = client.requestInvoice(amountSats)
+        val request = client.requestInvoice(amountSats = amountSats, zap = zap)
 
         val reply = CompletableDeferred<OfferEvent>()
         val subId = "clink-offer-${request.id}"

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

@@ -368,6 +368,7 @@ private fun RenderRegular(
                         callbackUri,
                         accountViewModel,
                         nav,
+                        authorPubKey,
                     )
                 }
             }
@@ -381,6 +382,7 @@ private fun RenderRegular(
                     backgroundColor,
                     accountViewModel,
                     nav,
+                    authorPubKey,
                 )
             }
         }
@@ -476,6 +478,7 @@ private fun RenderWordWithoutPreview(
     backgroundColor: MutableState<Color>,
     accountViewModel: AccountViewModel,
     nav: INav,
+    authorPubKey: String? = null,
 ) {
     when (word) {
         // Don't preview Images
@@ -510,7 +513,7 @@ private fun RenderWordWithoutPreview(
 
         // Decoding is local and the network round-trip only fires on the Pay tap,
         // so the offer card is safe to render even in the no-preview path.
-        is ClinkOfferSegment -> ClinkOfferPreview(word.offer, accountViewModel)
+        is ClinkOfferSegment -> ClinkOfferPreview(word.offer, accountViewModel, authorPubKey)
 
         is EmailSegment -> ClickableEmail(word.segmentText)
 
@@ -547,6 +550,7 @@ private fun RenderWordWithPreview(
     callbackUri: String? = null,
     accountViewModel: AccountViewModel,
     nav: INav,
+    authorPubKey: String? = null,
 ) {
     when (word) {
         is ImageSegment -> ZoomableContentView(word.segmentText, state, accountViewModel)
@@ -558,7 +562,7 @@ private fun RenderWordWithPreview(
         is InvoiceSegment -> MayBeInvoicePreview(word.segmentText, accountViewModel)
         is WithdrawSegment -> MayBeWithdrawal(word.segmentText, accountViewModel)
         is CashuSegment -> CashuPreview(word.segmentText, accountViewModel)
-        is ClinkOfferSegment -> ClinkOfferPreview(word.offer, accountViewModel)
+        is ClinkOfferSegment -> ClinkOfferPreview(word.offer, accountViewModel, authorPubKey)
         is EmailSegment -> ClickableEmail(word.segmentText)
         is SecretEmoji -> DisplaySecretEmoji(word, state, callbackUri, true, quotesLeft, backgroundColor, accountViewModel, nav)
         is MathSegment -> LatexEquation(word.latex, word.displayMode, word.leading, word.trailing)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/creators/invoice/ClinkOfferPreview.kt

@@ -63,6 +63,7 @@ import com.vitorpamplona.quartz.experimental.clink.common.SatRange
 import com.vitorpamplona.quartz.experimental.clink.offers.OfferErrorCode
 import com.vitorpamplona.quartz.experimental.clink.pointers.NOffer
 import com.vitorpamplona.quartz.experimental.clink.pointers.OfferPriceType
+import com.vitorpamplona.quartz.nip57Zaps.LnZapEvent
 import kotlinx.coroutines.launch
 
 /**
@@ -70,11 +71,18 @@ import kotlinx.coroutines.launch
  * runs the offer round-trip ([ClinkOfferPayer]) to fetch a fresh BOLT-11 over Nostr,
  * then pays it through the user's default payment source (confirmed for in-app wallets,
  * see [InvoicePaymentDispatcher]).
+ *
+ * When [authorPubKey] is known (the offer appears in someone's note) and the user's
+ * default zap type isn't NONZAP, the request carries a NIP-57 zap request so the offer
+ * service issues a zappable invoice and publishes a zap receipt — making the payment a
+ * real zap on the author rather than a silent invoice. With no author it falls back to
+ * a plain invoice.
  */
 @Composable
 fun ClinkOfferPreview(
     offer: NOffer,
     accountViewModel: AccountViewModel,
+    authorPubKey: String? = null,
 ) {
     val context = LocalContext.current
     val scope = rememberCoroutineScope()
@@ -191,8 +199,26 @@ fun ClinkOfferPreview(
                 onClick = {
                     requesting = true
                     scope.launch {
-                        val amount = if (amountRequired) amountInput.toLongOrNull() else null
-                        val response = ClinkOfferPayer.requestInvoice(accountViewModel.account, offer, amountSats = amount)
+                        val amount = if (amountRequired) amountInput.toLongOrNull() else offer.price?.toLong()
+
+                        // Attach a NIP-57 zap request so paying the offer becomes a real zap
+                        // on the author (skipped when there's no author or the user opted out
+                        // of zaps via a NONZAP default).
+                        val zapType = accountViewModel.defaultZapType()
+                        val zapRequest =
+                            if (authorPubKey != null && zapType != LnZapEvent.ZapType.NONZAP) {
+                                val author = accountViewModel.account.cache.getOrCreateUser(authorPubKey)
+                                accountViewModel.account
+                                    .createZapRequestFor(
+                                        user = author,
+                                        zapType = zapType,
+                                        amountMillisats = amount?.times(1000),
+                                    ).toJson()
+                            } else {
+                                null
+                            }
+
+                        val response = ClinkOfferPayer.requestInvoice(accountViewModel.account, offer, amountSats = amount, zap = zapRequest)
                         requesting = false
 
                         val bolt11 = response?.bolt11