Encrypt private media before BLE fragmentation (#1434)

Closes the last cleartext private-content path over BLE: private DM images/voice were sent as plaintext signed fileTransfer packets, TTL-relayed across the mesh, so every relay saw the full bytes. Now the complete BitchatFilePacket is encrypted as a single Noise AEAD message (inner type 0x20, matching Android) and the opaque ciphertext is fragmented. Adds an authenticated in-session capability proof (0x21 TLV: capabilities + Ed25519 key), TOFU-style downgrade pinning, a per-send consent dialog for the signed-cleartext fallback to legacy peers, and a cancellation/admission registry so cancel/delete cannot race a deferred cleartext send.

Android wire constants (0x20 / 0x21 / capability bit 8) confirmed shipping. The 256-fragment preflight cap applies only to the directed fileTransfer migration fallback; encrypted media to capable peers uses the full receiver ceiling.

Rebased over #1428/#1349: identity reads go through BLELocalIdentityStateStore; the session-bound authenticated signing-key check and the announce-path TOFU pin are kept as complementary checks. Full local suite green (1744+197 tests).

bitchat/Services/BLE/BLENoisePacketHandler.swift

@@ -7,6 +7,11 @@ struct BLENoiseHandshakeHandlingResult {
     let didEstablishAuthenticatedSession: Bool
 }
 
+struct BLENoiseDecryptionResult {
+    let plaintext: Data
+    let sessionGeneration: UUID
+}
+
 /// Narrow environment for `BLENoisePacketHandler`.
 ///
 /// All queue hops (collections barrier writes, main-actor UI notification)
@@ -35,9 +40,16 @@ struct BLENoisePacketHandlerEnvironment {
     /// Updates the registry last-seen timestamp for the peer (async barrier write).
     let updatePeerLastSeen: (PeerID) -> Void
     /// Decrypts an encrypted payload from the peer (crypto).
-    let decrypt: (_ payload: Data, _ peerID: PeerID) throws -> Data
+    let decrypt: (_ payload: Data, _ peerID: PeerID) throws -> BLENoiseDecryptionResult
     /// Clears the peer's Noise session after an unrecoverable decrypt failure (crypto).
     let clearSession: (PeerID) -> Void
+    /// Consumes session-authenticated protocol state inside the transport. It
+    /// must never escape to UI or Nostr payload dispatch.
+    let handleAuthenticatedPeerState: (
+        _ peerID: PeerID,
+        _ payload: Data,
+        _ sessionGeneration: UUID
+    ) -> Void
     /// Delivers `.noisePayloadReceived` to the UI as one main-actor hop.
     let deliverNoisePayload: (
         _ peerID: PeerID,
@@ -146,20 +158,30 @@ final class BLENoisePacketHandler {
         env.updatePeerLastSeen(peerID)
 
         do {
-            let decrypted = try env.decrypt(packet.payload, peerID)
+            let decryption = try env.decrypt(packet.payload, peerID)
+            let decrypted = decryption.plaintext
             guard decrypted.count > 0 else { return }
 
             // First byte indicates the payload type
             let payloadType = decrypted[0]
             let payloadData = decrypted.dropFirst()
 
-            guard let noisePayloadType = NoisePayloadType(rawValue: payloadType) else {
+            guard let noisePayloadType = NoisePayloadType.decoded(rawValue: payloadType) else {
                 SecureLogger.warning("⚠️ Unknown noise payload type: \(payloadType)")
                 return
             }
 
             SecureLogger.debug("🔐 Decrypted noise payload type \(noisePayloadType.description) from \(peerID.id.prefix(8))…", category: .session)
 
+            if noisePayloadType == .authenticatedPeerState {
+                env.handleAuthenticatedPeerState(
+                    peerID,
+                    Data(payloadData),
+                    decryption.sessionGeneration
+                )
+                return
+            }
+
             let ts = Date(timeIntervalSince1970: Double(packet.timestamp) / 1000)
             env.deliverNoisePayload(peerID, noisePayloadType, Data(payloadData), ts)
         } catch NoiseEncryptionError.sessionNotEstablished {