Optimize conversation restoration startup and reduce redundant sidebar recomputation

clients/macos/vellum-assistant/App/AppDelegate+Conversations.swift

@@ -113,7 +113,7 @@ extension AppDelegate {
                   let conversation = conversationManager.conversations.first(where: { $0.conversationId == conversationId }) else {
                 return false
             }
-            conversationManager.activeConversationId = conversation.id
+            conversationManager.activateConversation(conversation.id)
             // Switch the main content area to the chat so the user sees it
             // even if they were last viewing a panel, app, or other non-chat view.
             mainWindow?.windowState.selection = nil

clients/macos/vellum-assistant/App/AppDelegate+InputMonitors.swift

@@ -669,7 +669,7 @@ extension AppDelegate {
     func handleQuickInputSelectConversation(_ conversationId: UUID) {
         showMainWindow()
         guard let mainWindow else { return }
-        mainWindow.conversationManager.activeConversationId = conversationId
+        mainWindow.conversationManager.activateConversation(conversationId)
     }
 
     /// Tears down and re-registers the global "Open Vellum" hotkey based on

clients/macos/vellum-assistant/Features/MainWindow/ConversationManager.swift

@@ -109,9 +109,12 @@ final class ConversationManager: ConversationRestorerDelegate {
         selectionStore.restoreRecentConversations
     }
 
+    var lastActiveConversationIdString: String? {
+        selectionStore.lastActiveConversationIdString
+    }
+
     var activeConversationId: UUID? {
-        get { selectionStore.activeConversationId }
-        set { selectionStore.activeConversationId = newValue }
+        selectionStore.activeConversationId
     }
 
     var draftViewModel: ChatViewModel? {
@@ -303,7 +306,7 @@ final class ConversationManager: ConversationRestorerDelegate {
             vm.prepareForChannelRefresh()
         }
 
-        selectionStore.activeConversationId = id
+        selectionStore.performActivation(for: id)
 
         // Emit explicit seen signal for user-initiated conversation activation.
         // Skip during conversation restoration to avoid false "seen" signals on bootstrap.
@@ -472,7 +475,7 @@ final class ConversationManager: ConversationRestorerDelegate {
             self?.promoteDraft(fromUserSend: true)
         }
         selectionStore.draftViewModel = viewModel
-        selectionStore.activeConversationId = nil
+        selectionStore.performDeactivation()
         activityStore.observeActiveViewModel(viewModel.messageManager)
         log.info("Entered draft mode")
     }
@@ -508,7 +511,7 @@ final class ConversationManager: ConversationRestorerDelegate {
             self?.listStore.updateLastInteracted(conversationId: localId)
         }
 
-        selectionStore.activeConversationId = conversation.id
+        selectionStore.performActivation(for: conversation.id)
         listStore.updateLastInteracted(conversationId: conversation.id)
         log.info("Promoted draft to conversation \(conversation.id)")
     }
@@ -532,7 +535,7 @@ final class ConversationManager: ConversationRestorerDelegate {
         activityStore.observeInteractionState(for: conversation.id, messageManager: viewModel.messageManager, errorManager: viewModel.errorManager)
         selectionStore.touchVMAccessOrder(conversation.id)
         selectionStore.scheduleEvictionIfNeeded()
-        selectionStore.activeConversationId = conversation.id
+        selectionStore.performActivation(for: conversation.id)
         viewModel.createConversationIfNeeded(conversationType: "private")
         log.info("Created private conversation \(conversation.id)")
     }
@@ -631,9 +634,11 @@ final class ConversationManager: ConversationRestorerDelegate {
         ConversationSelectionStore.clearRenderCaches()
         if selectionStore.activeConversationId == id {
             if index < listStore.conversations.count {
-                selectionStore.activeConversationId = listStore.conversations[index].id
+                selectionStore.performActivation(for: listStore.conversations[index].id)
+            } else if let lastId = listStore.conversations.last?.id {
+                selectionStore.performActivation(for: lastId)
             } else {
-                selectionStore.activeConversationId = listStore.conversations.last?.id
+                selectionStore.performDeactivation()
             }
         }
         log.info("Closed conversation \(id)")
@@ -672,12 +677,12 @@ final class ConversationManager: ConversationRestorerDelegate {
         if listStore.visibleConversations.isEmpty {
             enterDraftMode()
         } else if selectionStore.activeConversationId == id {
-            let visibleAfter = listStore.conversations[index...].dropFirst().first(where: { !$0.isArchived })
-            let visibleBefore = listStore.conversations[..<index].last(where: { !$0.isArchived })
+            let visibleAfter = listStore.conversations[index...].dropFirst().first(where: { !$0.isArchived && $0.kind != .private })
+            let visibleBefore = listStore.conversations[..<index].last(where: { !$0.isArchived && $0.kind != .private })
             if let next = visibleAfter ?? visibleBefore {
-                selectionStore.activeConversationId = next.id
-            } else {
-                selectionStore.activeConversationId = listStore.visibleConversations.first?.id
+                selectionStore.performActivation(for: next.id)
+            } else if let firstVisibleId = listStore.visibleConversations.first?.id {
+                selectionStore.performActivation(for: firstVisibleId)
             }
         }
 
@@ -723,7 +728,7 @@ final class ConversationManager: ConversationRestorerDelegate {
             vm.prepareForChannelRefresh()
         }
 
-        selectionStore.activeConversationId = id
+        selectionStore.performActivation(for: id)
 
         if id != previousActiveId {
             listStore.markConversationSeen(conversationId: id)
@@ -935,7 +940,9 @@ final class ConversationManager: ConversationRestorerDelegate {
             if listStore.visibleConversations.isEmpty {
                 enterDraftMode()
             } else {
-                selectionStore.activeConversationId = listStore.visibleConversations.first?.id
+                if let firstVisibleId = listStore.visibleConversations.first?.id {
+                    selectionStore.performActivation(for: firstVisibleId)
+                }
             }
         } else if listStore.visibleConversations.isEmpty {
             enterDraftMode()
@@ -1090,13 +1097,15 @@ final class ConversationManager: ConversationRestorerDelegate {
     func handleNotificationIntentForExistingConversation(daemonConversationId: String) {
         guard let idx = listStore.conversations.firstIndex(where: { $0.conversationId == daemonConversationId }) else { return }
         let localId = listStore.conversations[idx].id
-        listStore.conversations[idx].lastInteractedAt = Date()
+        var conversation = listStore.conversations[idx]
+        conversation.lastInteractedAt = Date()
 
         if localId != selectionStore.activeConversationId {
-            listStore.conversations[idx].hasUnseenLatestAssistantMessage = true
-            listStore.conversations[idx].latestAssistantMessageAt = Date()
+            conversation.hasUnseenLatestAssistantMessage = true
+            conversation.latestAssistantMessageAt = Date()
             listStore.pendingSeenConversationIds.removeAll { $0 == daemonConversationId }
         }
+        listStore.conversations[idx] = conversation
 
         if let vm = selectionStore.chatViewModels[localId], !vm.isThinking, !vm.isSending {
             pendingNotificationCatchUpIds.remove(daemonConversationId)
@@ -1263,21 +1272,25 @@ final class ConversationManager: ConversationRestorerDelegate {
         if isNewMessage && !listStore.conversations[index].isBackgroundConversation {
             listStore.updateLastInteracted(conversationId: conversationId)
         }
-        if listStore.conversations[index].latestAssistantMessageAt == nil || isNewMessage {
-            listStore.conversations[index].latestAssistantMessageAt = Date()
+        var conversation = listStore.conversations[index]
+        if conversation.latestAssistantMessageAt == nil || isNewMessage {
+            conversation.latestAssistantMessageAt = Date()
         }
+        var shouldEmitSeenSignal = false
         if conversationId == selectionStore.activeConversationId {
-            if listStore.conversations[index].hasUnseenLatestAssistantMessage {
-                listStore.conversations[index].hasUnseenLatestAssistantMessage = false
+            if conversation.hasUnseenLatestAssistantMessage {
+                conversation.hasUnseenLatestAssistantMessage = false
             }
             let streamingJustCompleted = previousSnapshot?.isStreaming == true && !currentSnapshot.isStreaming
             if isNewMessage || streamingJustCompleted {
-                if let conversationId = listStore.conversations[index].conversationId {
-                    listStore.emitConversationSeenSignal(conversationId: conversationId)
-                }
+                shouldEmitSeenSignal = true
             }
-        } else if !listStore.conversations[index].hasUnseenLatestAssistantMessage {
-            listStore.conversations[index].hasUnseenLatestAssistantMessage = true
+        } else if !conversation.hasUnseenLatestAssistantMessage {
+            conversation.hasUnseenLatestAssistantMessage = true
+        }
+        listStore.conversations[index] = conversation
+        if shouldEmitSeenSignal, let daemonId = conversation.conversationId {
+            listStore.emitConversationSeenSignal(conversationId: daemonId)
         }
     }
 

clients/macos/vellum-assistant/Features/MainWindow/ConversationRestorer.swift

@@ -1,5 +1,6 @@
 import Combine
 import Foundation
+import SwiftUI
 import VellumAssistantShared
 import os
 
@@ -13,6 +14,8 @@ protocol ConversationRestorerDelegate: AnyObject {
     var groups: [ConversationGroup] { get set }
     var daemonSupportsGroups: Bool { get set }
     var restoreRecentConversations: Bool { get }
+    /// The persisted last-active conversation UUID string (UserDefaults-backed).
+    var lastActiveConversationIdString: String? { get }
     var isLoadingMoreConversations: Bool { get set }
     var hasMoreConversations: Bool { get set }
     var serverOffset: Int { get set }
@@ -206,14 +209,22 @@ final class ConversationRestorer {
         // Seed groups from the response if available, otherwise fall back to system defaults.
         // This must run before the restoreRecentConversations guard so that users who
         // disable restore still get groups initialized for the session.
+        // Wrapped in an animation-suppressing transaction so SwiftUI doesn't
+        // compute diffing/animation for the groups-only update.
+        var groupTransaction = Transaction()
+        groupTransaction.disablesAnimations = true
         let daemonSupportsGroups: Bool
         if let responseGroups = response.groups, !responseGroups.isEmpty {
-            delegate.groups = responseGroups.map { ConversationGroup(from: $0) }
+            withTransaction(groupTransaction) {
+                delegate.groups = responseGroups.map { ConversationGroup(from: $0) }
+            }
             delegate.daemonSupportsGroups = true
             daemonSupportsGroups = true
         } else {
             if delegate.groups.isEmpty {
-                delegate.groups = [ConversationGroup.pinned, ConversationGroup.scheduled, ConversationGroup.background]
+                withTransaction(groupTransaction) {
+                    delegate.groups = [ConversationGroup.pinned, ConversationGroup.scheduled, ConversationGroup.background]
+                }
             }
             delegate.daemonSupportsGroups = false
             daemonSupportsGroups = false
@@ -254,9 +265,16 @@ final class ConversationRestorer {
             // createNotificationConversation before the session list response arrived),
             // merge server pin/order metadata into it instead of creating a duplicate.
             if let existingIdx = delegate.conversations.firstIndex(where: { $0.conversationId == session.id }) {
-                delegate.conversations[existingIdx].groupId = groupId
-                delegate.conversations[existingIdx].displayOrder = session.displayOrder.map { Int($0) }
-                delegate.conversations[existingIdx].forkParent = session.forkParent
+                // Copy-modify-writeback for non-attention fields: write back once
+                // so conversations.didSet fires once instead of per-field.
+                var existing = delegate.conversations[existingIdx]
+                existing.groupId = groupId
+                existing.displayOrder = session.displayOrder.map { Int($0) }
+                existing.forkParent = session.forkParent
+                delegate.conversations[existingIdx] = existing
+                // Attention merge must go through mergeAssistantAttention so that
+                // pendingAttentionOverrides are reconciled (e.g. a notification
+                // conversation the user already opened before the list arrived).
                 delegate.mergeAssistantAttention(from: session, intoConversationAt: existingIdx)
                 continue
             }
@@ -298,26 +316,51 @@ final class ConversationRestorer {
             restoredConversations.append(conversation)
         }
 
-        if defaultConversationIsEmpty {
-            if let defaultConversation = delegate.conversations.first {
-                delegate.removeChatViewModel(for: defaultConversation.id)
+        // Suppress animations during bulk list assignment. Without this,
+        // SwiftUI computes before/after diffing and animation interpolation
+        // for every row — expensive when restoring ~50 conversations at once.
+        var transaction = Transaction()
+        transaction.disablesAnimations = true
+        withTransaction(transaction) {
+            if defaultConversationIsEmpty {
+                if let defaultConversation = delegate.conversations.first {
+                    delegate.removeChatViewModel(for: defaultConversation.id)
+                }
+                delegate.conversations = restoredConversations
+            } else {
+                delegate.conversations = restoredConversations + delegate.conversations
             }
-            delegate.conversations = restoredConversations
-        } else {
-            delegate.conversations = restoredConversations + delegate.conversations
         }
 
-        if let firstVisible = restoredConversations.first(where: { !$0.isArchived }) {
-            delegate.activateConversation(firstVisible.id)
+        if let hasMore = response.hasMore {
+            delegate.hasMoreConversations = hasMore
+        }
+
+        // Determine the activation target once up front.
+        // Priority: saved last-active > first visible restored > new conversation.
+        let activationTarget: UUID? = {
+            // Try the user's last active conversation first.
+            if delegate.restoreRecentConversations,
+               let savedString = delegate.lastActiveConversationIdString,
+               let savedUUID = UUID(uuidString: savedString),
+               delegate.conversations.contains(where: { $0.id == savedUUID && !$0.isArchived }) {
+                return savedUUID
+            }
+            // Fall back to the first visible restored conversation.
+            if let firstVisible = restoredConversations.first(where: { !$0.isArchived }) {
+                return firstVisible.id
+            }
+            return nil
+        }()
+
+        if let target = activationTarget {
+            delegate.activateConversation(target)
         } else if defaultConversationIsEmpty {
             // All restored conversations are archived and the default conversation was removed,
             // so create a new empty conversation to avoid a blank window.
             delegate.createConversation()
         }
 
-        if let hasMore = response.hasMore {
-            delegate.hasMoreConversations = hasMore
-        }
         // serverOffset is set by fetchConversationList before merging foreground +
         // background, so it reflects foreground-only count for correct pagination.
         log.info("Restored \(restoredConversations.count) conversations from daemon (hasMore: \(response.hasMore ?? false))")