Improve mesh relaying, presence, and DM robustness; signed public msgs; reachability UI; quicker announces; store-and-forward (#527)

* Sign public broadcasts; verify relayed messages via persisted signing keys; keep scheduled relays in sparse graphs and speed their jitter; persist announce signing key for offline auth; add short backoff after disconnect errors to reduce reconnect thrash

* Add connected vs reachable model: retain peers after link drop, expire after reachability window; expose all peers in snapshots; compute isReachable in UI; add meshReachable state and sorting; avoid removing peers on link events; notify UI on stale removals

* ContentView: handle new .meshReachable connection state in header icon switch (exhaustive switch fix)

* Logs: tag relayed announces as 'Reachable via mesh' and annotate public message logs with (direct|mesh) path for easier field analysis

* Fix syntax error: remove stray else/log inserted into writeOrEnqueue; keep logs clean

* UI: use 'point.3.connected.trianglepath.dotted' for mesh-reachable; change people count to include connected+reachable (exclude Nostr-only)

* UI: switch to 'point.3.filled.connected.trianglepath.dotted' for mesh-reachable icons in list and header

* Reachability: reduce retention to 21s for all peers (verified and unverified) to minimize stale presence

* mesh DMs/acks: route to reachable peers; queue READ/DELIVERED until handshake; add Transport.isPeerReachable; UI: hide offline non-mutuals; DM header: better name fallback + show transport + encryption icons; fix NostrTransport conformance

* Verification sheet: compute encryption status and fingerprint using short mesh ID mapping (fix 'not encrypted/handshake' for DMs with stable key)

* Announce cadence: faster discovery (4s), sparse 15±4s, dense 30±8s; initial 0.6s; post-subscribe 50ms; min-force 150ms; maintenance 5s; proactive announces on handshake + recent-traffic nudge

* Relay: increase broadcast TTL cap in sparse graphs to 6; tighten jitter for handshake (10–35ms) and directed (20–60ms) relays

* Range/robustness: store-and-forward for directed packets (15s) with flush on new links + periodic; announces: no subset + afterglow re-announce on first-seen; adaptive scanning: force ON when <=2 neighbors or recent traffic

* Fix warnings: remove unused msgID and unused mutable var in directed spool flush

* Announces: TTL 7 (sparse only) via RelayController; no fanout subset for announces; neighbor-change rebroadcast of last 2–3 announces. Fragments: faster pacing (5ms global, 4ms directed).

* Peer list: real-time icon updates by publishing snapshots on connectivity checks; add unread message indicator (envelope) next to peers with unread DMs

* UI: unread envelope uses orange; hasUnreadMessages checks Nostr conv key for peers with known Nostr pubkeys (geohash DM consistency)

* Logs/robustness: debounce disconnect notifications (1.5s), debounce 'reconnected' logs (2s), add weak-link cooldown after timeouts on very weak RSSI (<= -90)

* Peer icons: faster, accurate reachability\n\n- Run connectivity checks every maintenance tick (5s)\n- Publish peer snapshots on central unsubscribe for instant UI refresh\n- Lower inactivity timeout to 8s and disconnect debounce to 0.9s\n- Gate reachability on mesh-attached (>=1 direct link); no links => no reachable peers\n- Keep 21s retention for verified/unverified, but only when attached to mesh\n\nImproves list responsiveness when walking out of range and prevents stale 'reachable' states when isolated.

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/ViewModels/ChatViewModel.swift

@@ -935,6 +935,13 @@ class ChatViewModel: ObservableObject, BitchatDelegate {
             if unreadPrivateMessages.contains(noiseKeyHex) {
                 return true
             }
+            // Also check for geohash (Nostr) DM conv key if this peer has a known Nostr pubkey
+            if let nostrHex = peer.nostrPublicKey {
+                let convKey = "nostr_" + String(nostrHex.prefix(TransportConfig.nostrConvKeyPrefixLength))
+                if unreadPrivateMessages.contains(convKey) {
+                    return true
+                }
+            }
         }
         
         // Get the peer's nickname to check for temporary Nostr peer IDs
@@ -1874,6 +1881,7 @@ class ChatViewModel: ObservableObject, BitchatDelegate {
         // Determine routing method and recipient nickname
         guard let noiseKey = Data(hexString: peerID) else { return }
         let isConnected = meshService.isPeerConnected(peerID)
+        let isReachable = meshService.isPeerReachable(peerID)
         let favoriteStatus = FavoritesPersistenceService.shared.getFavoriteStatus(for: noiseKey)
         let isMutualFavorite = favoriteStatus?.isMutual ?? false
         let hasNostrKey = favoriteStatus?.peerNostrPublicKey != nil
@@ -1913,8 +1921,8 @@ class ChatViewModel: ObservableObject, BitchatDelegate {
         // Trigger UI update for sent message
         objectWillChange.send()
         
-        // Send via appropriate transport (BLE if connected, else Nostr when possible)
-        if isConnected || (isMutualFavorite && hasNostrKey) {
+        // Send via appropriate transport (BLE if connected/reachable, else Nostr when possible)
+        if isConnected || isReachable || (isMutualFavorite && hasNostrKey) {
             messageRouter.sendPrivate(content, to: peerID, recipientNickname: recipientNickname ?? "user", messageID: messageID)
             // Optimistically mark as sent for both transports; delivery/read will update subsequently
             if let idx = privateChats[peerID]?.firstIndex(where: { $0.id == messageID }) {
@@ -2542,16 +2550,12 @@ class ChatViewModel: ObservableObject, BitchatDelegate {
             }
         }
         
-        // If we know the original transport, use it for the read receipt
+        // If this originated over Nostr, skip (handled by Nostr code paths)
         if originalTransport == "nostr" {
-            // Skip read receipts for Nostr messages - unnecessary complexity
-            // The radical simplification plan says to accept occasional loss
-        } else if meshService.peerNickname(peerID: actualPeerID) != nil {
-            // Use mesh for connected peers (default behavior)
-            messageRouter.sendReadReceipt(receipt, to: actualPeerID)
-        } else {
-            // Skip read receipts for offline peers - fire and forget principle
+            return
         }
+        // Use router to decide (mesh if reachable, else Nostr if available)
+        messageRouter.sendReadReceipt(receipt, to: actualPeerID)
     }
     
     @MainActor