Count the sealed-to-unsealed fallback, and offer to refuse it

Android half of ios#16. `Sent.sealed` already reported each send's
outcome, but nothing accumulated, so nobody could answer "how often does
this happen to me".

🔴 The copy distinguishes sender from content, with tests asserting it.
An unsealed send is still end-to-end encrypted; what the relay learns is
who sent it. Somebody who reads "sealed" as "encrypted" makes the wrong
decision in both directions.

⚠️ Aggregate only. Per-contact counts would be more useful and would also
build a record of who this account talks to and how often — the precise
thing sealing exists to keep off a server.

Refusing is offered and off by default: it turns a metadata leak into an
undelivered message, which for most people is the worse outcome. It has
its own exception type so the refusal can explain itself.

⚠️ Refusing spends nothing. `sealed` is false exactly when neither a
capability nor a key was found, so `takePeerToken` returned null and
there is no token to hand back — my first cut had a line handing one
back, which was unreachable.

⚠️ The policy and the counter are injected as lambdas, since `client` and
the engine have no Android dependency, and both are wired in one helper.
Two sign-in paths build a session, and only one of them applying the
policy is how a setting silently stops working on half the app.

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

app/src/main/kotlin/io/flamenet/messenger/app/ChatScreens.kt

@@ -737,6 +737,8 @@ fun ColumnScope.AccountScreen(
     SettingsSection { PresencePicker(model, phase.presence) }
 
     SectionBand()
+    // ios#16 — beside the other privacy settings.
+    SettingsSection { SealingSection(model) }
     SettingsSection { StoryAudienceSection(model, phase) }
     // ios#54 — beside the audience setting, because both answer "what happens
     // to my stories".
@@ -1174,6 +1176,45 @@ fun ColumnScope.StoryArchiveSection(
     }
 }
 
+/**
+ * The fallback from sealed to unsealed, which used to happen silently (ios#16).
+ *
+ * 🔴 Names exactly what sealing protects, and what it does not. Somebody who
+ * reads "sealed" as "encrypted" makes the wrong decision here in both
+ * directions — relaxed when it is off, and alarmed when it degrades on a
+ * message that was never readable by the server anyway.
+ */
+@Composable
+fun ColumnScope.SealingSection(model: MessengerViewModel) {
+    val context = LocalContext.current
+    val settings = remember { MediaSettings(context) }
+    var refuse by remember { mutableStateOf(settings.requireSealedSending) }
+    val record = remember(refuse) { settings.sealingRecord }
+
+    Text("Who the server can see is sending", style = MaterialTheme.typography.titleMedium)
+    Row(
+        modifier = Modifier.fillMaxWidth().padding(vertical = Space.sm),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        Text("Refuse to send if it can't be sealed", modifier = Modifier.weight(1f))
+        androidx.compose.material3.Switch(
+            checked = refuse,
+            onCheckedChange = { settings.requireSealedSending = it; refuse = it },
+            modifier = Modifier.testTag("require-sealed"),
+        )
+    }
+    Text(record.summary, fontSize = 12.sp, color = Palette.SecondaryText)
+    Spacer(Modifier.size(Space.sm))
+    Text(
+        "Your messages are always end-to-end encrypted. Sealing hides something " +
+            "further: which account sent them. It needs a key your contact's device " +
+            "supplies, so it can't always be done — usually before they have replied " +
+            "to you for the first time. Refusing means those messages don't go at all.",
+        fontSize = 12.sp,
+        color = Palette.SecondaryText,
+    )
+}
+
 @Composable
 private fun ColumnScope.StoryAudienceSection(
     model: MessengerViewModel,

app/src/main/kotlin/io/flamenet/messenger/app/MediaSettings.kt

@@ -61,6 +61,33 @@ class MediaSettings(context: Context) {
         get() = prefs.getBoolean("stories.archiveEnabled", false)
         set(value) { prefs.edit().putBoolean("stories.archiveEnabled", value).apply() }
 
+    /**
+     * Refuse to send at all when the send cannot be sealed (§14.5, ios#16).
+     *
+     * 🔴 **Off by default, and that is the honest default rather than the lazy
+     * one.** An unsealed send is still end-to-end encrypted; what leaks is that
+     * this account sent something to that one. Refusing turns a metadata leak
+     * into an undelivered message, which for most people is the worse outcome
+     * — so the default degrades and SAYS SO.
+     */
+    var requireSealedSending: Boolean
+        get() = prefs.getBoolean("privacy.requireSealed", false)
+        set(value) { prefs.edit().putBoolean("privacy.requireSealed", value).apply() }
+
+    /** Counters for how often sealing degraded (ios#16). */
+    var sealingRecord: io.flamenet.e2e.SealingRecord
+        get() = io.flamenet.e2e.SealingRecord(
+            sealed = prefs.getInt("privacy.sealing.sealed", 0),
+            unsealed = prefs.getInt("privacy.sealing.unsealed", 0),
+            lastUnsealedAt = prefs.getLong("privacy.sealing.lastUnsealedAt", 0L))
+        set(value) {
+            prefs.edit()
+                .putInt("privacy.sealing.sealed", value.sealed)
+                .putInt("privacy.sealing.unsealed", value.unsealed)
+                .putLong("privacy.sealing.lastUnsealedAt", value.lastUnsealedAt)
+                .apply()
+        }
+
     /**
      * Refuse to send unless the relay can prove the recipient's keys appear in
      * the log it publishes.

app/src/main/kotlin/io/flamenet/messenger/app/MessengerViewModel.kt

@@ -370,6 +370,7 @@ class MessengerViewModel(app: Application) : AndroidViewModel(app) {
                         it.archiveEnabled = {
                             MediaSettings(getApplication()).storyArchiveEnabled
                         }
+                        wireSealingPolicy(it)
                     }
                     val fetchedBuddies = runCatching { session!!.roster() }
                     val fetchedGroups = runCatching { session!!.namedGroups() }
@@ -582,6 +583,7 @@ class MessengerViewModel(app: Application) : AndroidViewModel(app) {
             api = io.flamenet.client.MessengerApi(config.baseUrl, account.username, credential),
         ).also {
             it.archiveEnabled = { MediaSettings(getApplication()).storyArchiveEnabled }
+            wireSealingPolicy(it)
         }
 
         // 🔴 **Our return address, before the first federated send.** A relay
@@ -2125,6 +2127,21 @@ class MessengerViewModel(app: Application) : AndroidViewModel(app) {
         update { it.copy(error = message) }
     }
 
+    /**
+     * Wire the sealing policy and counters into a fresh session (ios#16).
+     *
+     * ⚠️ In one place, because two call sites building a `Session` and only
+     * one of them applying the policy is how a setting silently stops working
+     * on one of the two sign-in paths.
+     */
+    private fun wireSealingPolicy(session: Session) {
+        val settings = MediaSettings(getApplication())
+        session.conversations.requireSealed = { settings.requireSealedSending }
+        session.onSendSealed = { wasSealed, at ->
+            settings.sealingRecord = settings.sealingRecord.recording(wasSealed, at)
+        }
+    }
+
     /** Change who may see this account's stories. */
     fun setStoryAudience(audience: Session.StoryAudience) = viewModelScope.launch {
         val current = session ?: return@launch

app/src/main/kotlin/io/flamenet/messenger/app/Session.kt

@@ -360,6 +360,11 @@ class Session(
         // 🔴 The sender's own copy expires too. A timer that only cleared the
         // recipient's phone would be the opposite of the promise: the person
         // who set it would be the one still holding the message.
+
+        // ios#16 — every send's outcome, not just this one's. `Sent.sealed`
+        // answers "was that sealed"; the record answers "how often does this
+        // happen to me", which nobody could ask before.
+        onSendSealed(sent.sealed, at)
         record(Vault.threadForUser(peerUserId), text, mine = true, at = at,
                link = link, lifetimeSeconds = lifetimeSeconds,
                delivery = if (sent.reachedSomeone) Delivery.DELIVERED else Delivery.PENDING)
@@ -1228,6 +1233,14 @@ class Session(
         )
     }
 
+    /**
+     * Told after every 1:1 send whether it was sealed (ios#16).
+     *
+     * ⚠️ Injected: the counters live in Android preferences and this layer has
+     * no Android dependency.
+     */
+    var onSendSealed: (Boolean, Long) -> Unit = { _, _ -> }
+
     /**
      * Members of a group we are in, or null if the relay does not list it for
      * us (audit H1). Cached for a short window: a poll pass can carry many