fix(napplet): sign as the account a surface was launched as

Requests resolved their signer through `sessionManager.loggedInAccount()`
— whichever account is active *right now* — with no binding to the
surface that asked. A full-screen host is a separate activity that an
account switch does not tear down, so:

- Open a site full-screen as A and log in via NIP-07: the page shows A.
- Switch to B in the main app.
- Return to that still-open surface and request a signature: the broker
  handed it **B's** key.

Confirmed on device before the fix. Worse than a mismatched prompt: B's
session was then written into **A's** WebView storage jar, so afterwards
even the embedded tab — which rebuilds correctly and had been verified
correct — displayed the wrong account. Per-account isolation held only
until a full-screen surface wrote a foreign session into a jar. And it
happened silently, because the ledger is per-account+origin and B had
already granted "always allow" for that origin from an earlier session.

`NappletLaunchRegistry.Session` now carries the account that minted the
token, and the broker resolves *that* account out of the cache. This
needs no new machinery to satisfy both halves of the rule: embedded
surfaces are torn down and re-minted on a switch, so they follow the
active account, while a full-screen surface keeps the account it was
opened with. It also extends an argument the code already made — the
sandbox can only act as the napplet it was launched as, because it holds
only its own token; now the same is true of the account.

Fails closed: if the launch account is no longer loaded, the request is
refused rather than falling back to whoever is signed in now.

The same live-account resolution existed on two adjacent paths, fixed
here too:

- Relay subscriptions took the account from a global supplier, so a
  full-screen surface's REQs would target the newly-active account's
  relays while its signatures came from the old one. The account is now
  passed per-open from the launch token.
- `identity.changed` streamed the app's active account, so a page bound
  to A could be told it had become B while signatures still returned A —
  the same desync inverted. It is now bound to the surface's own account
  and reports only that account going away.

Verified on device: with B active, a fresh identity read from a
full-screen surface launched as A returns **A**; the embedded tab still
follows B; both surfaces ran simultaneously under different accounts with
no cross-writes between jars.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

amethyst/src/main/java/com/vitorpamplona/amethyst/napplet/NappletBrokerService.kt

@@ -50,7 +50,7 @@ import com.vitorpamplona.amethyst.model.Account
 import com.vitorpamplona.amethyst.napplet.gateways.AccountNappletGateways
 import com.vitorpamplona.amethyst.napplethost.NappletIpc
 import com.vitorpamplona.amethyst.ui.MainActivity
-import com.vitorpamplona.amethyst.ui.screen.AccountState
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
@@ -93,17 +93,23 @@ class NappletBrokerService : Service() {
     // The broker for the current account, rebuilt only on account switch (see broker()).
     private var cachedBroker: Pair<Account, NappletBroker>? = null
 
-    // Live relay subscriptions, keyed by the applet's subId; reads the current account live.
-    private val liveSubscriptions = NappletLiveSubscriptions { Amethyst.instance.sessionManager.loggedInAccount() }
+    // Live relay subscriptions, keyed by the applet's subId. The account comes per-open from the
+    // requesting surface's launch token, so a surface's REQs always target the account it acts as.
+    private val liveSubscriptions = NappletLiveSubscriptions()
 
     // The app-wide inc pub/sub bus: routes inc.emit between live napplet sessions as inc.event pushes.
     private val incBus = NappletIncBus { replyTo, payload -> push(replyTo, payload) }
 
-    // Streams identity.changed pushes (account switch / connect / disconnect) to a watching applet.
+    // Streams identity.changed to a watching applet. Bound to the surface's LAUNCH account, not the
+    // app's active one: a surface acts as the account that opened it for its whole life, so switching
+    // accounts elsewhere is not an identity change *for it*. Announcing the newly-active pubkey here
+    // would tell a page it had become someone else while its signatures still came back as the
+    // original — the same desync the launch binding exists to prevent. What this does still report is
+    // that account going away (logout/removal), which emits "".
     private val identityWatch =
-        NappletIdentityWatch(scope) {
-            Amethyst.instance.sessionManager.accountContent
-                .map { (it as? AccountState.LoggedIn)?.account?.signer?.pubKey ?: "" }
+        NappletIdentityWatch(scope) { boundPubKey ->
+            Amethyst.instance.accountsCache.accounts
+                .map { loaded -> if (loaded.containsKey(boundPubKey)) boundPubKey else "" }
         }
 
     // Binding is restricted to our own UID by exported=false in the manifest, enforced by the OS.
@@ -241,7 +247,10 @@ class NappletBrokerService : Service() {
             val replyTo = msg.replyTo ?: return true
             val origin = data.getString(NappletIpc.KEY_BROWSER_ORIGIN)?.takeIf { it.isNotBlank() } ?: return true
             val identity = NappletIdentity(authorPubKey = BROWSER_IDENTITY_AUTHOR, identifier = origin)
-            val token = NappletLaunchRegistry.register(identity, setOf(NappletCapability.IDENTITY, NappletCapability.RELAY))
+            // Bind to the account active at mint time: a browser token minted for one account must
+            // never sign as another if the user switches while the page is still open.
+            val mintAccount = Amethyst.instance.sessionManager.loggedInAccount() ?: return true
+            val token = NappletLaunchRegistry.register(identity, setOf(NappletCapability.IDENTITY, NappletCapability.RELAY), mintAccount.pubKey)
             val response =
                 Message.obtain(null, NappletIpc.MSG_BROWSER_TOKEN).apply {
                     this.data =
@@ -278,17 +287,20 @@ class NappletBrokerService : Service() {
             // The shared, host-agnostic router owns decode → broker → encode and the subscribe-vs-reply
             // decision (it stays wire-identical with the future desktop host). This service only supplies
             // the broker, the Messenger transport, and the live relay subscription each Outcome implies.
-            val broker = broker()
+            // The launch token decides whose key signs — not the active account. A surface opened by
+            // one account can never be handed another's signer, even while it stays open across a switch.
+            val broker = brokerFor(session.accountPubKey)
             if (broker == null) {
-                reply(replyTo, requestId, NappletProtocolJson.encodeResponse(requestType, NappletResponse.Failed("No account is signed in.")))
+                reply(replyTo, requestId, NappletProtocolJson.encodeResponse(requestType, NappletResponse.Failed("That account is no longer signed in.")))
                 return@launch
             }
             when (val outcome = NappletRequestRouter.route(broker, identity, declared, payload)) {
                 is NappletRequestRouter.Outcome.Ignore -> {}
                 is NappletRequestRouter.Outcome.Reply -> reply(replyTo, requestId, outcome.payload)
-                is NappletRequestRouter.Outcome.OpenSubscription -> liveSubscriptions.open(outcome.subId, outcome.filters) { push(replyTo, it) }
+                is NappletRequestRouter.Outcome.OpenSubscription ->
+                    liveSubscriptions.open(outcome.subId, outcome.filters, accountFor(session.accountPubKey)) { push(replyTo, it) }
                 is NappletRequestRouter.Outcome.CloseSubscription -> liveSubscriptions.close(outcome.subId)
-                is NappletRequestRouter.Outcome.WatchIdentity -> identityWatch.start { push(replyTo, it) }
+                is NappletRequestRouter.Outcome.WatchIdentity -> identityWatch.start(session.accountPubKey) { push(replyTo, it) }
                 is NappletRequestRouter.Outcome.UnwatchIdentity -> identityWatch.stop()
                 is NappletRequestRouter.Outcome.Push -> outcome.payloads.forEach { push(replyTo, it) }
                 is NappletRequestRouter.Outcome.SubscribeInc -> incBus.subscribe(replyTo, outcome.topic)
@@ -327,14 +339,29 @@ class NappletBrokerService : Service() {
             }
     }
 
+    /** The launched-as account, or null once it is no longer loaded. */
+    private fun accountFor(accountPubKey: HexKey): Account? = Amethyst.instance.accountsCache.accounts.value[accountPubKey]
+
     /**
-     * The broker for the *currently* signed-in account, cached and rebuilt only when the account
-     * changes (reference identity). The gateways capture the account and read its flows live, so a
-     * cached broker stays correct across requests without per-request allocation.
+     * The broker for the account a surface was LAUNCHED as — [NappletLaunchRegistry.Session.accountPubKey],
+     * never whichever account is active right now.
+     *
+     * Resolving live was wrong in a way that defeated per-account isolation: a full-screen host is a
+     * separate activity that an account switch does not tear down, so its WebView kept account A's
+     * cookies while requests were signed by B. The page displayed one identity while another signed,
+     * and B's session was written into A's storage jar — after which even the embedded tab, which is
+     * rebuilt correctly, showed the wrong account.
+     *
+     * Binding to the launch account satisfies both halves of the rule with no extra machinery:
+     * embedded surfaces are torn down and re-minted on a switch, so they follow the active account,
+     * while a full-screen surface stays on the account it was opened with.
+     *
+     * Returns null when that account is no longer loaded (logged out), so requests fail closed
+     * rather than silently falling back to someone else's key.
      */
     @Synchronized
-    private fun broker(): NappletBroker? {
-        val account = Amethyst.instance.sessionManager.loggedInAccount() ?: return null
+    private fun brokerFor(accountPubKey: HexKey): NappletBroker? {
+        val account = accountFor(accountPubKey) ?: return null
         cachedBroker?.let { (acc, broker) -> if (acc === account) return broker }
         val broker =
             AccountNappletGateways(

amethyst/src/main/java/com/vitorpamplona/amethyst/napplet/NappletIdentityWatch.kt

@@ -39,15 +39,18 @@ import kotlinx.coroutines.launch
  */
 class NappletIdentityWatch(
     private val scope: CoroutineScope,
-    private val pubKey: () -> Flow<String>,
+    private val pubKey: (boundPubKey: String) -> Flow<String>,
 ) {
     private var job: Job? = null
 
-    fun start(push: (String) -> Unit) {
+    fun start(
+        boundPubKey: String,
+        push: (String) -> Unit,
+    ) {
         stop()
         job =
             scope.launch {
-                pubKey()
+                pubKey(boundPubKey)
                     .distinctUntilChanged()
                     .drop(1)
                     .collect { push(NappletProtocolJson.encodeIdentityChanged(it)) }

amethyst/src/main/java/com/vitorpamplona/amethyst/napplet/NappletLaunchRegistry.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.amethyst.napplet
 
 import com.vitorpamplona.amethyst.commons.napplet.NappletCapability
 import com.vitorpamplona.amethyst.commons.napplet.NappletIdentity
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.core.toHexKey
 import java.security.SecureRandom
 
@@ -45,6 +46,18 @@ object NappletLaunchRegistry {
     data class Session(
         val identity: NappletIdentity,
         val declared: Set<NappletCapability>,
+        /**
+         * The account this surface was launched as. Requests resolve their signer through THIS, not
+         * through whichever account happens to be active when they arrive.
+         *
+         * A full-screen host is a separate activity that an account switch does not tear down, so
+         * resolving live meant its WebView kept account A's cookies while the broker signed as B —
+         * a page showing one identity while another signed, and B's session written into A's
+         * storage jar. Binding here gives both halves of the rule for free: embedded surfaces are
+         * rebuilt on a switch, so they re-mint and follow the active account, while a full-screen
+         * surface keeps the account it was opened with.
+         */
+        val accountPubKey: HexKey,
     )
 
     // Access-ordered + capped so tokens from long-closed napplets can't accumulate without bound. The
@@ -60,9 +73,10 @@ object NappletLaunchRegistry {
     fun register(
         identity: NappletIdentity,
         declared: Set<NappletCapability>,
+        accountPubKey: HexKey,
     ): String {
         val token = ByteArray(32).also(secureRandom::nextBytes).toHexKey()
-        sessions[token] = Session(identity, declared)
+        sessions[token] = Session(identity, declared, accountPubKey)
         return token
     }
 

amethyst/src/main/java/com/vitorpamplona/amethyst/napplet/NappletLauncher.kt

@@ -120,7 +120,16 @@ object NappletLauncher {
         // requests back to THIS identity + declared set, regardless of anything the sandbox sends.
         val identity = NappletIdentity(authorPubKey = authorPubKey, identifier = identifier, aggregateHash = aggregateHash)
         val declared = profile.declaredCapabilities(requires)
-        val launchToken = NappletLaunchRegistry.register(identity, declared)
+        // Bound to the account launching it, so the surface keeps signing as that account even if the
+        // user switches while it is open (an embedded surface is rebuilt on a switch and re-mints).
+        // An empty key can never match a loaded account, so a launch with nobody signed in fails
+        // closed at the broker rather than falling back to whoever signs in later.
+        val launchAccountPubKey =
+            Amethyst.instance.sessionManager
+                .loggedInAccount()
+                ?.pubKey
+                .orEmpty()
+        val launchToken = NappletLaunchRegistry.register(identity, declared, launchAccountPubKey)
 
         // Resolve the per-site network choice (Tor default; a site can be opted out to the open web).
         // Locked napplets always keep Tor for their blob fetches — only nSites expose the toggle.

amethyst/src/main/java/com/vitorpamplona/amethyst/napplet/NappletLiveSubscriptions.kt

@@ -38,12 +38,13 @@ import java.util.concurrent.atomic.AtomicInteger
  * `relay.eose`. Encodes the `relay.event`/`relay.eose`/`relay.closed` pushes and hands them to the
  * caller-supplied sink — it never touches the transport itself.
  *
- * [account] is read live (so it always targets the currently signed-in account); [open] is reached
- * only after the broker authorized the subscription (RELAY consent).
+ * The account is supplied per [open] by the caller, which resolves it from the requesting surface's
+ * LAUNCH account — not from whoever is signed in at the time. A full-screen surface survives an
+ * account switch, and reading live would have pointed its REQs at the new account's relays while its
+ * signatures still came from the old one. [open] is reached only after the broker authorized the
+ * subscription (RELAY consent).
  */
-class NappletLiveSubscriptions(
-    private val account: () -> Account?,
-) {
+class NappletLiveSubscriptions {
     private val liveSubs = ConcurrentHashMap<String, LiveSub>()
     private val liveSeq = AtomicInteger(0)
 
@@ -62,9 +63,9 @@ class NappletLiveSubscriptions(
     fun open(
         nappletSubId: String,
         filters: List<Filter>,
+        account: Account?,
         push: (String) -> Unit,
     ) {
-        val account = account()
         val relays = account?.homeRelays?.flow?.value ?: emptySet()
         if (account == null || filters.isEmpty() || relays.isEmpty()) {
             push(NappletProtocolJson.encodeRelayEose(nappletSubId))