ios: experiment with inverted Agent transcript layout

ios/Packages/Sybil/Sources/Sybil/SybilAgentView.swift

@@ -45,25 +45,9 @@ private struct AgentTranscriptView: View {
         ScrollViewReader { proxy in
             ScrollView {
                 LazyVStack(alignment: .leading, spacing: 15) {
-                    if allMessages.count > displayed.count {
-                        Button("Load earlier messages") {
-                            // Loading older history may move the viewport as lazy
-                            // row estimates settle; do not chase the old position.
-                            atLatest = false
-                            historyLimit += 100
-                            historyStartID = allMessages[max(0, startIndex - 100)].id
-                        }
-                        .frame(maxWidth: .infinity)
-                        .padding(.vertical, 10)
-                    }
-                    if room.isLoading { ProgressView("Loading messages…").frame(maxWidth: .infinity) }
-                    ForEach(Array(displayed.enumerated()), id: \.element.id) { index, message in
-                        AgentTranscriptRow(message: message, room: room,
-                            startsDay: index == 0 || !Calendar.current.isDate(message.createdAt, inSameDayAs: displayed[index - 1].createdAt))
-                            .equatable()
-                            .modifier(AgentEntrance(animate: appeared && rendered.entranceIDs.contains(message.id), reduceMotion: reduceMotion))
-                            .id(message.id)
-                    }
+                    // The native scroll origin is the visual bottom. Keep model
+                    // and cursor order ascending; reverse only presentation.
+                    Color.clear.frame(height: 17).id(Self.bottomID)
                     if rendered.isTyping {
                         HStack(spacing: 9) {
                             AgentAvatar()
@@ -72,33 +56,49 @@ private struct AgentTranscriptView: View {
                         }
                         .foregroundStyle(SybilTheme.textMuted)
                         .accessibilityIdentifier("agent-typing")
+                        .scaleEffect(x: 1, y: -1)
+                    }
+                    ForEach(Array(displayed.enumerated().reversed()), id: \.element.id) { index, message in
+                        AgentTranscriptRow(message: message, room: room,
+                            startsDay: index == 0 || !Calendar.current.isDate(message.createdAt, inSameDayAs: displayed[index - 1].createdAt))
+                            .equatable()
+                            .modifier(AgentEntrance(animate: appeared && rendered.entranceIDs.contains(message.id), reduceMotion: reduceMotion))
+                            .scaleEffect(x: 1, y: -1)
+                            .id(message.id)
+                    }
+                    if room.isLoading {
+                        ProgressView("Loading messages…").frame(maxWidth: .infinity)
+                            .scaleEffect(x: 1, y: -1)
+                    }
+                    if allMessages.count > displayed.count {
+                        Button("Load earlier messages") {
+                            atLatest = false
+                            historyLimit += 100
+                            historyStartID = allMessages[max(0, startIndex - 100)].id
+                        }
+                        .frame(maxWidth: .infinity)
+                        .padding(.vertical, 10)
+                        .scaleEffect(x: 1, y: -1)
                     }
-                    // Include bottom padding in the target so Latest reaches
-                    // the actual content end before native keyboard avoidance.
-                    Color.clear.frame(height: 17).id(Self.bottomID)
                 }
                 // Keep native lazy-row targets without binding scroll position.
                 .scrollTargetLayout()
                 .padding(.horizontal, 16)
                 // Match normal chat: content clears the header, while the
                 // viewport extends beneath the shared navigation fade.
-                .padding(.top, 16 + topInset)
+                .padding(.bottom, 16 + topInset)
                 .frame(maxWidth: SybilLayout.webContentMaxWidth)
                 .frame(maxWidth: .infinity)
             }
+            .scaleEffect(x: 1, y: -1)
             .accessibilityIdentifier("agent-transcript")
-            .defaultScrollAnchor(.bottom, for: .initialOffset)
-            // Let SwiftUI follow size changes, including keyboard avoidance,
-            // without competing scrollTo calls from geometry updates.
-            .defaultScrollAnchor(atLatest ? .bottom : nil, for: .sizeChanges)
-            .defaultScrollAnchor(.bottom, for: .alignment)
             .scrollDismissesKeyboard(.interactively)
             .onScrollPhaseChange { _, phase in
                 scrollPhase = phase
             }
             .onScrollGeometryChange(for: Bool.self) { geometry in
                 geometry.containerSize.height > 0 &&
-                    geometry.contentSize.height + geometry.contentInsets.bottom - geometry.visibleRect.maxY <= 24
+                    geometry.contentOffset.y + geometry.contentInsets.top <= 24
             } action: { _, atBottom in
                 #if DEBUG
                 AgentRenderDiagnostics.record("scrollGeometry")
@@ -114,7 +114,7 @@ private struct AgentTranscriptView: View {
                 if !atLatest {
                     Button {
                         atLatest = true
-                        withAnimation(reduceMotion ? nil : .easeOut(duration: 0.24)) { proxy.scrollTo(Self.bottomID, anchor: .bottom) }
+                        withAnimation(reduceMotion ? nil : .easeOut(duration: 0.24)) { proxy.scrollTo(Self.bottomID, anchor: .top) }
                     } label: {
                         Label(room.unreadCount > 0 ? "\(room.unreadCount) unread" : "Latest", systemImage: "arrow.down")
                             .font(.sybil(.caption, weight: .semibold))
@@ -130,22 +130,17 @@ private struct AgentTranscriptView: View {
                 appeared = true
                 if !room.isLoading {
                     historyStartID = displayed.first?.id
-                    proxy.scrollTo(Self.bottomID, anchor: .bottom)
                 }
             }
             .onChange(of: room.isLoading) { _, loading in
                 if !loading && historyStartID == nil {
                     historyStartID = displayed.first?.id
-                    proxy.scrollTo(Self.bottomID, anchor: .bottom)
                 }
             }
-            .onChange(of: allMessages.count) { _, _ in
-                if atLatest { proxy.scrollTo(Self.bottomID, anchor: .bottom) }
-            }
             .onChange(of: latestRequest) { _, _ in
                 if !atLatest {
                     atLatest = true
-                    proxy.scrollTo(Self.bottomID, anchor: .bottom)
+                    proxy.scrollTo(Self.bottomID, anchor: .top)
                 }
             }
             .modifier(AgentReadAcknowledgement(room: room, tracking: scrollTracking,