Re-tell the delivery key when a told peer writes unsealed

Mirror of the iOS change: the poll path un-marks a toldPeer whose
message arrived unsealed — their copy of our key is gone, and the next
send re-tells it. Same staleness class, and same cure, as the avatar
marker.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

client/src/main/kotlin/io/flamenet/client/Conversations.kt

@@ -613,6 +613,19 @@ class Conversations(
                 val fromUser = opened?.claimedFromUser ?: message.fromUser
                 val content = Content.parse(plaintext)
                 consumeControl(fromUser, content)
+                // 🔴 An UNSEALED message from a contact we have told our
+                // delivery key means their copy is gone — a reinstall wiped
+                // it. Sealing to us requires that key, and a peer who holds
+                // it seals everything. Un-mark them so the next send re-tells
+                // it; until then the relay sees their sender on every message
+                // they write us. Worst case: one redundant control envelope.
+                if (!sealed && fromUser != 0L) {
+                    vault.loadDelivery()?.let { d ->
+                        if (fromUser in d.toldPeers) {
+                            vault.saveDelivery(d.copy(toldPeers = d.toldPeers - fromUser))
+                        }
+                    }
+                }
                 out += Received(message.id, fromUser, fromDevice, content,
                                 sealed = sealed, at = message.createdAt)
             } catch (_: Exception) {