feat(demo): real testnet tx links + interactive buy-files flow

- Tx/explorer links open mempool.space/testnet/tx/<id>; the backend hydrates the
  wallet's transactions with REAL recent testnet txids at startup (best-effort,
  falls back to mock hashes offline). Mempool app + demo-external apps open in a
  new tab; deep-link paths are carried through.
- Add the content.* paid-download handlers the buy flow needs (owned-list,
  preview-peer, download-peer-{paid,invoice,onchain}, request-invoice,
  invoice-status, request-onchain, onchain-status) — every path resolves to a
  success state with testnet receive addresses / bolt11 invoices so visitors can
  walk the full buy → unlock journey.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

neode-ui/mock-backend.js

@@ -1869,6 +1869,54 @@ app.post('/rpc/v1', (req, res) => {
         return res.json({ result: { success: true } })
       }
 
+      // ── Demo paid-content / "buying files" flow ───────────────────────────
+      // Every payment path resolves to success so visitors can experience the
+      // full buy → unlock journey with testnet addresses and invoices.
+      case 'content.owned-list': {
+        return res.json({ result: { items: [] } })
+      }
+      case 'content.owned-get':
+      case 'content.preview-peer':
+      case 'content.download-peer-paid':
+      case 'content.download-peer-invoice':
+      case 'content.download-peer-onchain': {
+        const filename = params?.filename || 'demo-content'
+        const body = Buffer.from(
+          `Archipelago demo — "${filename}"\n\nThis is sample paid content delivered over the ` +
+          `node-to-node content market. On a real node this would be the actual file you purchased.\n`,
+          'utf-8'
+        ).toString('base64')
+        return res.json({ result: { data: body, mime_type: 'text/plain', ecash_backend: params?.method || 'cashu' } })
+      }
+      case 'content.request-invoice': {
+        const price = params?.price_sats || 500
+        return res.json({
+          result: {
+            bolt11: 'lntb' + price + '1p' + randomHex(50),
+            payment_hash: randomHex(32),
+            price_sats: price,
+          },
+        })
+      }
+      case 'content.invoice-status': {
+        // Settle after the first poll so the QR flow shows a realistic wait.
+        return res.json({ result: { paid: true } })
+      }
+      case 'content.request-onchain': {
+        const price = params?.price_sats || 500
+        return res.json({
+          result: {
+            address: 'tb1q' + randomHex(19),
+            amount_sats: price,
+            content_id: params?.content_id || '',
+            expires_at: new Date(Date.now() + 3600000).toISOString(),
+          },
+        })
+      }
+      case 'content.onchain-status': {
+        return res.json({ result: { paid: true, status: 'confirmed', confirmations: 1 } })
+      }
+
       case 'network.diagnostics': {
         return res.json({
           result: {
@@ -4087,11 +4135,33 @@ wss.on('connection', (ws, req) => {
   })
 })
 
+// Best-effort: pull a few REAL recent testnet txids so the wallet's transactions
+// deep-link to live mempool.space/testnet pages. Falls back to the mock hashes
+// (already set) if offline. Patches the pristine seed so every session inherits them.
+async function hydrateRealTestnetTxids() {
+  if (!DEMO) return
+  try {
+    const ctrl = new AbortController()
+    const t = setTimeout(() => ctrl.abort(), 4000)
+    const r = await fetch('https://mempool.space/testnet/api/mempool/recent', { signal: ctrl.signal })
+    clearTimeout(t)
+    if (!r.ok) return
+    const recent = await r.json()
+    const txids = (Array.isArray(recent) ? recent : []).map(x => x.txid).filter(Boolean)
+    if (!txids.length) return
+    SEED_WALLET.transactions.forEach((tx, i) => { if (txids[i]) tx.tx_hash = txids[i] })
+    // Also patch the already-built default store (sessions clone from SEED at creation).
+    defaultStore.walletState.transactions.forEach((tx, i) => { if (txids[i]) tx.tx_hash = txids[i] })
+    console.log(`[Demo] Hydrated ${Math.min(txids.length, SEED_WALLET.transactions.length)} real testnet txids`)
+  } catch { /* offline — keep mock hashes */ }
+}
+
 server.listen(PORT, '0.0.0.0', async () => {
   const runtime = await isContainerRuntimeAvailable()
 
   // Initialize package data from Docker
   await initializePackageData()
+  await hydrateRealTestnetTxids()
 
   console.log(`
 ╔════════════════════════════════════════════════════════════╗

neode-ui/src/views/AppSession.vue

@@ -109,6 +109,7 @@ import { useAppIdentity } from './appSession/useAppIdentity'
 import { useNostrBridge } from './appSession/useNostrBridge'
 import { openExternalUrl } from '@/utils/openExternal'
 import { useElectrsSync } from '@/composables/useElectrsSync'
+import { IS_DEMO, isDemoExternal } from '@/composables/useDemoIntro'
 
 const props = defineProps<{
   appIdProp?: string
@@ -157,7 +158,11 @@ const packageEntry = computed(() => store.data?.['package-data']?.[appId.value]
 const blockedReason = computed(() => launchBlockedReason(appId.value, packageEntry.value))
 const blockedTitle = computed(() => appId.value === 'fedimint' || appId.value === 'fedimintd' ? 'Waiting for Bitcoin sync' : 'App not ready')
 const isMobile = typeof window !== 'undefined' && window.innerWidth < 768
-const mustOpenNewTab = computed(() => NEW_TAB_APPS.has(appId.value))
+// In the demo, apps backed by a real external site that blocks iframing
+// (mempool.space) open in a new tab rather than the in-app session frame.
+const mustOpenNewTab = computed(() =>
+  NEW_TAB_APPS.has(appId.value) || (IS_DEMO && isDemoExternal(appId.value))
+)
 
 // ElectrumX shows a sync screen before its real UI (the Electrum server only
 // serves clients once its index is built). Poll /electrs-status while this is

neode-ui/src/views/appSession/appSessionConfig.ts

@@ -78,9 +78,12 @@ export const IFRAME_BLOCKED_APPS = new Set<string>([])
 /** Resolve app URL using direct port mapping (source of truth) */
 export function resolveAppUrl(id: string, routeQueryPath?: string, runtimeUrl?: string): string {
   // Demo: route to the app's mock UI or real external site (mempool.space,
-  // indee.tx1138.com). Non-demoable apps fall through to a generic notice page.
+  // indee.tx1138.com). Carry through a deep-link path (e.g. /tx/<hash> for
+  // mempool). Non-demoable apps fall through to a generic notice page.
   if (IS_DEMO) {
-    return demoAppUrl(id) || `/app/${id}/`
+    const base = demoAppUrl(id)
+    if (base) return routeQueryPath ? base + routeQueryPath : base
+    return `/app/${id}/`
   }
 
   // External HTTPS apps