Courier: deposit in parallel when the only route is a send queue (#1368)

* Deposit with couriers in parallel when the only route is a send queue

The courier path was nearly unreachable: NostrTransport claims any
favorite with a known npub as "reachable" regardless of connectivity,
and the mesh favorite exchange shares npubs, so for essentially every
courier-eligible recipient the router picked Nostr's reachable branch.
With no internet the message just sat in the relay send queue — in the
flagship scenario (internet shutdown, mutual friend standing right
there) the courier walked away carrying nothing.

Add Transport.canDeliverPromptly(to:), defaulting to reachability for
radio-backed transports; NostrTransport answers honestly by mirroring
the relay manager's connection state (fail-closed behind Tor). When the
chosen transport can't hand the message off promptly, the router now
also deposits a sealed copy with connected couriers. Double delivery is
harmless: receivers dedup by message ID, and delivered/read acks never
downgrade the carried status. When relays are up, sends are trusted and
no courier quota is spent.

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

* Track DM-relay connectivity, not any-relay, for prompt delivery

Codex review: NostrRelayManager.isConnected is true when any relay is
up, including geohash/custom relays — but private messages target the
default (gift-wrap-capable) relay set and queue when none of those are
connected. A lone geohash relay would have suppressed the parallel
courier deposit while the DM sat in the queue. Publish a DM-scoped
connectivity flag and drive canDeliverPromptly from it.

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

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

bitchat/Services/NostrTransport.swift

@@ -14,7 +14,13 @@ final class NostrTransport: Transport, @unchecked Sendable {
         let registerPendingGiftWrap: @MainActor (String) -> Void
         let sendEvent: @MainActor (NostrEvent) -> Void
         let scheduleAfter: @Sendable (TimeInterval, @escaping @Sendable () -> Void) -> Void
+        /// Emits whether a relay that carries private messages is up
+        /// (fail-closed behind Tor). A connected geohash/custom relay alone
+        /// doesn't count: DM sends target the default relay set and would
+        /// still queue.
+        let relayConnectivity: @MainActor () -> AnyPublisher<Bool, Never>
 
+        @MainActor
         static func live(idBridge: NostrIdentityBridge) -> Dependencies {
             Dependencies(
                 notificationCenter: .default,
@@ -26,7 +32,8 @@ final class NostrTransport: Transport, @unchecked Sendable {
                 sendEvent: { NostrRelayManager.shared.sendEvent($0) },
                 scheduleAfter: { delay, action in
                     DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: action)
-                }
+                },
+                relayConnectivity: { NostrRelayManager.shared.$isDMRelayConnected.eraseToAnyPublisher() }
             )
         }
     }
@@ -49,6 +56,10 @@ final class NostrTransport: Transport, @unchecked Sendable {
 
     // Reachability Cache (thread-safe)
     private var reachablePeers: Set<PeerID> = []
+    // Mirror of the relay manager's connection state, cached here because
+    // canDeliverPromptly is called synchronously off the main actor.
+    private var relaysConnected = false
+    private var relayConnectivityCancellable: AnyCancellable?
     private let queue = DispatchQueue(label: "nostr.transport.state", attributes: .concurrent)
 
     @MainActor
@@ -72,6 +83,12 @@ final class NostrTransport: Transport, @unchecked Sendable {
         queue.sync(flags: .barrier) {
             self.reachablePeers = Set(reachable)
         }
+
+        relayConnectivityCancellable = self.dependencies.relayConnectivity()
+            .sink { [weak self] connected in
+                guard let self else { return }
+                self.queue.async(flags: .barrier) { self.relaysConnected = connected }
+            }
     }
 
     deinit {
@@ -133,6 +150,14 @@ final class NostrTransport: Transport, @unchecked Sendable {
             return reachablePeers.contains(where: { $0.toShort() == short })
         }
     }
+
+    func canDeliverPromptly(to peerID: PeerID) -> Bool {
+        // A known npub makes a peer "reachable", but with no relay
+        // connection a send only joins the local queue. Answering honestly
+        // here lets the router hand a sealed copy to a courier in parallel
+        // instead of waiting for internet that may never come.
+        isPeerReachable(peerID) && queue.sync { relaysConnected }
+    }
     
     func peerNickname(peerID: PeerID) -> String? { nil }
     func getPeerNicknames() -> [PeerID: String] { [:] }