fix(chat): return to the chat list from a chat opened by handle

Flipcash/Core/Screens/Main/Username/UsernameLookupScreen.swift

@@ -24,11 +24,12 @@ private let logger = Logger(label: "flipcash.username-lookup")
 /// verification screens use (`PhoneVerificationViewModel.swift:320-329`), and so
 /// is the push.
 ///
-/// This screen then drops out from under the chat, since a chat's Back belongs
-/// on the chat list. It goes while the push is still animating: the removal is a
-/// whole-path rewrite, which remounts the chat, and a freshly-mounted chat
-/// settles its layout a beat after it appears. Under the transition that settle
-/// is hidden — the same way it is on every other push into a chat.
+/// The route in then drops out from under the chat — this screen and the New
+/// Chat picker above the list — since a chat's Back belongs on the chat list. It
+/// goes while the push is still animating: the removal is a whole-path rewrite,
+/// which remounts the chat, and a freshly-mounted chat settles its layout a beat
+/// after it appears. Under the transition that settle is hidden — the same way
+/// it is on every other push into a chat.
 struct UsernameLookupScreen: View {
 
     @Environment(Container.self) private var container
@@ -158,6 +159,12 @@ struct UsernameLookupScreen: View {
                 lookupTask = nil
 
                 let chat = AppRouter.Destination.tipConversationForUser(userID)
+
+                // Measured rather than assumed: this screen is reached through
+                // the New Chat picker today and was reached straight off the
+                // chat list before it, so a fixed depth silently stops matching
+                // the moment a screen is added to or removed from the route.
+                let depthWithChat = router[.tips].count + 1
                 router.push(chat)
 
                 // Well inside the push transition, so the remounted chat settles
@@ -169,7 +176,7 @@ struct UsernameLookupScreen: View {
 
                 // Unless they went back while it landed: the lookup left with
                 // them, and rewriting the path would drag the chat back.
-                guard router[.tips].count == 2 else { return }
+                guard router[.tips].count == depthWithChat else { return }
 
                 // Unanimated, because nothing is arriving — only the entry
                 // underneath is leaving. Animated, SwiftUI stages the remount as

FlipcashTests/UsernameLookupRoutingTests.swift

@@ -79,6 +79,40 @@ struct UsernameLookupRoutingTests {
         #expect(ConversationContext.existing(chatID).resolvedContact(in: [contact]) != nil)
     }
 
+    // MARK: - Back stack -
+
+    @Test("The chat list is not a fixed number of screens below the lookup")
+    func backStack_routeInHasNoFixedDepth() {
+        // The lookup was pushed straight off the chat list until the New Chat
+        // picker went in between (#790). A screen that assumed the depth it had
+        // then is a screen that stops unwinding the moment the route changes.
+        let router = AppRouter()
+        router.activeTabStack = .tips
+
+        router.push(.newChat)
+        router.push(.usernameLookup)
+
+        #expect(router[.tips].count == 2)
+    }
+
+    @Test("Back from a chat opened by handle lands on the chat list")
+    func backStack_rewriteLeavesOnlyTheChat() {
+        let router = AppRouter()
+        router.activeTabStack = .tips
+        router.push(.newChat)
+        router.push(.usernameLookup)
+
+        let chat = AppRouter.Destination.tipConversationForUser(UUID())
+        let depthWithChat = router[.tips].count + 1
+        router.push(chat)
+        #expect(router[.tips].count == depthWithChat)
+
+        // What the screen does once the push has started: neither the picker
+        // nor the lookup is somewhere Back belongs, and the list is the root.
+        router.setPath([chat], on: .tips)
+        #expect(router[.tips].count == 1)
+    }
+
     // MARK: - Counterpart -
 
     @Test("The fetched profile supplies the name and handle the chat shows")