fix: refuse an ambiguous nickname instead of picking the first peer

bitchat/Services/UnifiedPeerService.swift

@@ -251,17 +251,21 @@ final class UnifiedPeerService: ObservableObject, TransportPeerEventsDelegate {
         return peerIndex[peerID]
     }
 
-    /// Get peer ID for nickname
+    /// Get peer ID for nickname.
+    ///
+    /// An unsuffixed name is accepted only when it identifies exactly one peer.
+    /// Colliding nicknames must be disambiguated with the people-list `#xxxx`
+    /// suffix (first four hex characters of the peer ID).
     func getPeerID(for nickname: String) -> PeerID? {
-        // Normalize both sides: the query may come from typed content and
-        // stored names may predate NFC-at-ingest (e.g. persisted favorites).
-        let target = nickname.normalizedNickname
-        for peer in peers {
-            if peer.displayName.normalizedNickname == target || peer.nickname.normalizedNickname == target {
-                return peer.peerID
+        guard let id = NicknameLookup.uniquePeerIDString(
+            for: nickname,
+            peers: peers.map { peer in
+                (id: peer.peerID.id, nickname: peer.nickname, displayName: peer.displayName)
             }
+        ) else {
+            return nil
         }
-        return nil
+        return peers.first(where: { $0.peerID.id == id })?.peerID
     }
 
     /// Check if peer is blocked

bitchat/Utils/NicknameLookup.swift

@@ -0,0 +1,29 @@
+import Foundation
+
+/// Resolve a typed nickname to a peer ID string.
+///
+/// An unsuffixed name is accepted only when it identifies exactly one peer.
+/// Colliding nicknames must be disambiguated with the people-list `#xxxx`
+/// suffix (first four hex characters of the peer ID).
+enum NicknameLookup {
+    static func uniquePeerIDString(
+        for query: String,
+        peers: [(id: String, nickname: String, displayName: String)]
+    ) -> String? {
+        let target = query.normalizedNickname
+        var matches: [String] = []
+        for peer in peers {
+            let nick = peer.nickname.normalizedNickname
+            let display = peer.displayName.normalizedNickname
+            let prefix = String(peer.id.prefix(4))
+            let suffixedNick = (nick + "#" + prefix).normalizedNickname
+            let suffixedDisplay = (display + "#" + prefix).normalizedNickname
+            if display == target || nick == target || suffixedNick == target || suffixedDisplay == target {
+                if !matches.contains(peer.id) {
+                    matches.append(peer.id)
+                }
+            }
+        }
+        return matches.count == 1 ? matches.first : nil
+    }
+}

bitchat/ViewModels/ChatPeerIdentityCoordinator.swift

@@ -518,24 +518,31 @@ final class ChatPeerIdentityCoordinator {
         let nickname = nickname.normalizedNickname
         switch context.activeChannel {
         case .location:
-            if nickname.contains("#"),
-               let person = context.visibleGeohashPeople()
-                .first(where: { $0.displayName == nickname }) {
-                let conversationKey = PeerID(nostr_: person.id)
-                context.registerNostrKeyMapping(person.id, for: conversationKey)
-                return conversationKey
+            if nickname.contains("#") {
+                let people = context.visibleGeohashPeople().filter {
+                    $0.displayName.normalizedNickname == nickname
+                }
+                if people.count == 1, let person = people.first {
+                    let conversationKey = PeerID(nostr_: person.id)
+                    context.registerNostrKeyMapping(person.id, for: conversationKey)
+                    return conversationKey
+                }
             }
 
             let base = nickname
                 .split(separator: "#", maxSplits: 1, omittingEmptySubsequences: false)
                 .first
                 .map(String.init)?
                 .lowercased() ?? nickname.lowercased()
-            if let pubkey = context.geoNicknames.first(where: { $0.value.lowercased() == base })?.key {
+            let geoMatches = context.geoNicknames.filter { $0.value.lowercased() == base }
+            if geoMatches.count == 1, let pubkey = geoMatches.keys.first {
                 let conversationKey = PeerID(nostr_: pubkey)
                 context.registerNostrKeyMapping(pubkey, for: conversationKey)
                 return conversationKey
             }
+            if geoMatches.count > 1 {
+                return nil
+            }
 
         case .mesh:
             break

bitchatTests/ChatPeerIdentityCoordinatorContextTests.swift

@@ -446,6 +446,27 @@ struct ChatPeerIdentityCoordinatorContextTests {
         context.peerIDsByNickname["carol"] = meshPeer
         #expect(coordinator.getPeerIDForNickname("carol") == meshPeer)
     }
+
+    @Test @MainActor
+    func getPeerIDForNickname_inGeohashChannel_refusesAmbiguousBaseName() async {
+        let context = MockChatPeerIdentityContext()
+        let coordinator = ChatPeerIdentityCoordinator(context: context)
+        let aliceA = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+        let aliceB = "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
+        context.activeChannel = .location(GeohashChannel(level: .city, geohash: "u4pruy"))
+        context.geohashPeople = [
+            GeoPerson(id: aliceA, displayName: "alice#aaaa", lastSeen: Date()),
+            GeoPerson(id: aliceB, displayName: "alice#bbbb", lastSeen: Date())
+        ]
+        context.geoNicknames[aliceA] = "alice"
+        context.geoNicknames[aliceB] = "alice"
+        context.peerIDsByNickname["alice"] = PeerID(str: "1122334455667788")
+
+        #expect(coordinator.getPeerIDForNickname("alice") == nil)
+        #expect(coordinator.getPeerIDForNickname("alice#aaaa") == PeerID(nostr_: aliceA))
+        #expect(coordinator.getPeerIDForNickname("alice#bbbb") == PeerID(nostr_: aliceB))
+    }
+
     @Test @MainActor
     func toggleFavorite_forNoiseKeyPeer_usesInjectedFavoritesStore() async {
         let context = MockChatPeerIdentityContext()

bitchatTests/Services/UnifiedPeerServiceTests.swift

@@ -27,6 +27,38 @@ struct UnifiedPeerServiceTests {
         #expect(fingerprint == "fp-1")
     }
 
+    @Test @MainActor
+    func getPeerID_acceptsAUniqueNickname() async {
+        let transport = MockTransport()
+        let identity = TestIdentityManager()
+        let idBridge = NostrIdentityBridge(keychain: MockKeychainHelper())
+        let service = UnifiedPeerService(meshService: transport, idBridge: idBridge, identityManager: identity)
+
+        let alice = PeerID(str: "1111111111111111")
+        transport.simulateConnect(alice, nickname: "alice")
+        service.didUpdatePeerSnapshots(transport.currentPeerSnapshots())
+
+        #expect(service.getPeerID(for: "alice") == alice)
+    }
+
+    @Test @MainActor
+    func getPeerID_refusesAmbiguousNicknameUnlessSuffixed() async {
+        let transport = MockTransport()
+        let identity = TestIdentityManager()
+        let idBridge = NostrIdentityBridge(keychain: MockKeychainHelper())
+        let service = UnifiedPeerService(meshService: transport, idBridge: idBridge, identityManager: identity)
+
+        let aliceA = PeerID(str: "1111111111111111")
+        let aliceB = PeerID(str: "2222222222222222")
+        transport.simulateConnect(aliceA, nickname: "alice")
+        transport.simulateConnect(aliceB, nickname: "alice")
+        service.didUpdatePeerSnapshots(transport.currentPeerSnapshots())
+
+        #expect(service.getPeerID(for: "alice") == nil)
+        #expect(service.getPeerID(for: "alice#1111") == aliceA)
+        #expect(service.getPeerID(for: "alice#2222") == aliceB)
+    }
+
     @Test @MainActor
     func isBlocked_usesSocialIdentity() async {
         let transport = MockTransport()