feat: Track ACP token usage, improve chat scroll behavior, and show session costs

Add cumulative token tracking from ACP prompt results with fallback
display when DB has no data yet. Improve scroll-to-bottom reliability
with an external trigger for "Return to Active Session" and onAppear
auto-scroll. Show per-session cost in the dashboard session list.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scarf/scarf/Features/Chat/ViewModels/ChatViewModel.swift

@@ -187,6 +187,8 @@ final class ChatViewModel {
                 richChatViewModel.handleACPEvent(
                     .promptComplete(sessionId: sessionId, response: result)
                 )
+                // Re-fetch session from DB to pick up cost/token data Hermes may have written
+                await richChatViewModel.refreshSessionFromDB()
             } catch is CancellationError {
                 acpStatus = "Cancelled"
             } catch {

scarf/scarf/Features/Chat/ViewModels/RichChatViewModel.swift

@@ -32,9 +32,21 @@ final class RichChatViewModel {
     var messageGroups: [MessageGroup] = []
     var isAgentWorking = false
     var pendingPermission: PendingPermission?
+    /// Mutated to trigger a scroll-to-bottom in the message list.
+    var scrollTrigger = UUID()
+
+    // Cumulative ACP token tracking (ACP returns tokens per prompt but DB has none)
+    private(set) var acpInputTokens = 0
+    private(set) var acpOutputTokens = 0
+    private(set) var acpThoughtTokens = 0
+    private(set) var acpCachedReadTokens = 0
 
     var hasMessages: Bool { !messages.isEmpty }
 
+    func requestScrollToBottom() {
+        scrollTrigger = UUID()
+    }
+
     private(set) var sessionId: String?
     /// The original CLI session ID when resuming a CLI session via ACP.
     /// Used to combine old CLI messages with new ACP messages.
@@ -77,6 +89,10 @@ final class RichChatViewModel {
         streamingAssistantText = ""
         streamingThinkingText = ""
         streamingToolCalls = []
+        acpInputTokens = 0
+        acpOutputTokens = 0
+        acpThoughtTokens = 0
+        acpCachedReadTokens = 0
         pendingPermission = nil
     }
 
@@ -91,6 +107,17 @@ final class RichChatViewModel {
         await dataService.close()
     }
 
+    /// Re-fetch session metadata from DB to pick up cost/token updates.
+    func refreshSessionFromDB() async {
+        guard let sessionId else { return }
+        let opened = await dataService.open()
+        guard opened else { return }
+        if let session = await dataService.fetchSession(id: sessionId) {
+            currentSession = session
+        }
+        await dataService.close()
+    }
+
     // MARK: - ACP Event Handling
 
     /// Add a user message immediately (before DB write) for instant UI feedback.
@@ -136,8 +163,8 @@ final class RichChatViewModel {
                 kind: request.toolCallKind,
                 options: request.options
             )
-        case .promptComplete:
+        case .promptComplete(_, let response):
-            handlePromptComplete()
+            handlePromptComplete(response: response)
         case .connectionLost(let reason):
             handleConnectionLost(reason: reason)
         case .availableCommands, .unknown:
@@ -188,9 +215,13 @@ final class RichChatViewModel {
         buildMessageGroups()
     }
 
-    private func handlePromptComplete() {
+    private func handlePromptComplete(response: ACPPromptResult) {
-        // Finalize any remaining streaming content
         finalizeStreamingMessage()
+        // Accumulate token usage from this prompt
+        acpInputTokens += response.inputTokens
+        acpOutputTokens += response.outputTokens
+        acpThoughtTokens += response.thoughtTokens
+        acpCachedReadTokens += response.cachedReadTokens
         isAgentWorking = false
         buildMessageGroups()
     }

scarf/scarf/Features/Chat/Views/ChatView.swift

@@ -91,9 +91,8 @@ struct ChatView: View {
             Menu {
                 if viewModel.hasActiveProcess, let activeId = viewModel.richChatViewModel.sessionId {
                     Button("Return to Active Session (\(activeId.prefix(8))...)") {
-                        // Already active — just ensure we're showing it
+                        viewModel.richChatViewModel.requestScrollToBottom()
                     }
-                    .disabled(true)
                     Divider()
                 }
                 Button("New Session") {
@@ -105,6 +104,8 @@ struct ChatView: View {
                 if !viewModel.recentSessions.isEmpty {
                     Divider()
                     Text("Resume Session")
+                    let activeSessionId = viewModel.richChatViewModel.sessionId
+                    let originSessionId = viewModel.richChatViewModel.originSessionId
                     ForEach(viewModel.recentSessions) { session in
                         Button {
                             viewModel.resumeSession(session.id)
@@ -120,6 +121,7 @@ struct ChatView: View {
                                 }
                             }
                         }
+                        .disabled(session.id == activeSessionId || session.id == originSessionId)
                     }
                 }
             } label: {

scarf/scarf/Features/Chat/Views/RichChatMessageList.swift

@@ -3,6 +3,8 @@ import SwiftUI
 struct RichChatMessageList: View {
     let groups: [MessageGroup]
     let isWorking: Bool
+    /// External trigger to force a scroll-to-bottom (e.g., from "Return to Active Session").
+    var scrollTrigger: UUID = UUID()
 
     /// Track the last group's assistant content length to detect streaming updates.
     private var scrollAnchor: String {
@@ -30,6 +32,14 @@ struct RichChatMessageList: View {
                 .padding()
             }
             .defaultScrollAnchor(.bottom)
+            // Scroll to bottom when view first appears with content
+            .onAppear {
+                if !groups.isEmpty {
+                    DispatchQueue.main.async {
+                        scrollToBottom(proxy: proxy, animated: false)
+                    }
+                }
+            }
             // Scroll on new groups
             .onChange(of: groups.count) {
                 scrollToBottom(proxy: proxy)
@@ -50,6 +60,10 @@ struct RichChatMessageList: View {
             .onChange(of: groups.last?.toolCallCount ?? 0) {
                 scrollToBottom(proxy: proxy)
             }
+            // Scroll on external trigger (e.g., "Return to Active Session" button)
+            .onChange(of: scrollTrigger) {
+                scrollToBottom(proxy: proxy)
+            }
         }
     }
 

scarf/scarf/Features/Chat/Views/RichChatView.swift

@@ -14,7 +14,10 @@ struct RichChatView: View {
         VStack(spacing: 0) {
             SessionInfoBar(
                 session: richChat.currentSession,
-                isWorking: richChat.isAgentWorking
+                isWorking: richChat.isAgentWorking,
+                acpInputTokens: richChat.acpInputTokens,
+                acpOutputTokens: richChat.acpOutputTokens,
+                acpThoughtTokens: richChat.acpThoughtTokens
             )
             Divider()
 
@@ -28,7 +31,8 @@ struct RichChatView: View {
             } else {
                 RichChatMessageList(
                     groups: richChat.messageGroups,
-                    isWorking: richChat.isAgentWorking
+                    isWorking: richChat.isAgentWorking,
+                    scrollTrigger: richChat.scrollTrigger
                 )
             }
 

scarf/scarf/Features/Chat/Views/SessionInfoBar.swift

@@ -3,6 +3,10 @@ import SwiftUI
 struct SessionInfoBar: View {
     let session: HermesSession?
     let isWorking: Bool
+    /// Fallback token counts from ACP prompt results (DB may have zeros for ACP sessions).
+    var acpInputTokens: Int = 0
+    var acpOutputTokens: Int = 0
+    var acpThoughtTokens: Int = 0
 
     var body: some View {
         HStack(spacing: 16) {
@@ -30,11 +34,14 @@ struct SessionInfoBar: View {
                     Label(model, systemImage: "cpu")
                 }
 
-                Label("\(formatTokens(session.inputTokens)) in / \(formatTokens(session.outputTokens)) out", systemImage: "number")
+                let inputToks = session.inputTokens > 0 ? session.inputTokens : acpInputTokens
+                let outputToks = session.outputTokens > 0 ? session.outputTokens : acpOutputTokens
+                Label("\(formatTokens(inputToks)) in / \(formatTokens(outputToks)) out", systemImage: "number")
                     .contentTransition(.numericText())
 
-                if session.reasoningTokens > 0 {
+                let reasonToks = session.reasoningTokens > 0 ? session.reasoningTokens : acpThoughtTokens
-                    Label("\(formatTokens(session.reasoningTokens)) reasoning", systemImage: "brain")
+                if reasonToks > 0 {
+                    Label("\(formatTokens(reasonToks)) reasoning", systemImage: "brain")
                 }
 
                 if let cost = session.displayCostUSD {

scarf/scarf/Features/Dashboard/Views/DashboardView.swift

@@ -164,6 +164,9 @@ struct SessionRow: View {
             HStack(spacing: 12) {
                 Label("\(session.messageCount)", systemImage: "bubble.left")
                 Label("\(session.toolCallCount)", systemImage: "wrench")
+                if let cost = session.displayCostUSD, cost > 0 {
+                    Label(String(format: "$%.4f", cost), systemImage: "dollarsign.circle")
+                }
             }
             .font(.caption)
             .foregroundStyle(.secondary)