Fix title-churn beachball in transcript adoption and sidebar rows

.github/swift-file-length-budget.tsv

@@ -3,7 +3,7 @@
 # Reduce counts as files shrink. CI fails if tracked files exceed this budget.
 34344	CLI/cmux.swift
 17606	Sources/AppDelegate.swift
-16021	Sources/ContentView.swift
+16038	Sources/ContentView.swift
 14100	Sources/TerminalController.swift
 12695	Sources/Workspace.swift
 12144	cmuxTests/AppDelegateShortcutRoutingTests.swift

Sources/AppDelegate.swift

@@ -2029,7 +2029,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate, UNUserNotificationCent
         auth.start()
         ensureMobileWorkspaceListObserver(for: tabManager)
         MobileTerminalRenderObserver.shared.start()
-        agentChatTranscriptService.start { TerminalController.shared.adoptDetectedAgentSessions(workspaceID: $0) }
+        agentChatTranscriptService.start { TerminalController.shared.adoptDetectedAgentSession(titleChange: $0) }
         installMobileHostSettingsObserver()
         scheduleGhosttyCrashBreadcrumbIfNeeded(notificationStore: notificationStore)
         startPaneMemoryGuardrailIfNeeded(notificationStore: notificationStore)

Sources/ContentView.swift

@@ -12112,7 +12112,6 @@ struct VerticalTabsSidebar: View {
             notificationStore: notificationStore,
             tab: tab,
             index: index,
-            isActive: tabManager.selectedTabId == tab.id,
             workspaceShortcutDigit: WorkspaceShortcutMapper.digitForWorkspace(
                 at: index,
                 workspaceCount: renderContext.workspaceCount
@@ -12914,7 +12913,6 @@ struct TabItemView: View, Equatable {
     nonisolated static func == (lhs: TabItemView, rhs: TabItemView) -> Bool {
         lhs.tab === rhs.tab &&
         lhs.index == rhs.index &&
-        lhs.isActive == rhs.isActive &&
         lhs.workspaceShortcutDigit == rhs.workspaceShortcutDigit &&
         lhs.workspaceShortcutModifierSymbol == rhs.workspaceShortcutModifierSymbol &&
         lhs.canCloseWorkspace == rhs.canCloseWorkspace &&
@@ -12943,7 +12941,6 @@ struct TabItemView: View, Equatable {
     @Environment(\.colorScheme) private var colorScheme
     let tab: Tab
     let index: Int
-    let isActive: Bool
     let workspaceShortcutDigit: Int?
     let workspaceShortcutModifierSymbol: String
     let canCloseWorkspace: Bool
@@ -12987,6 +12984,8 @@ struct TabItemView: View, Equatable {
     let onContextMenuAppear: () -> Void
     let onContextMenuDisappear: () -> Void
     @State private var workspaceSnapshotStorage: SidebarWorkspaceSnapshotBuilder.Snapshot?
+    // Row-local selection projection: selectedTabId changes update only rows whose boolean flips.
+    @State private var observedIsActive: Bool?
     @StateObject private var contextMenuState = SidebarTabItemContextMenuState()
     @State private var rowInteractionState = SidebarWorkspaceRowInteractionState()
     @State private var rowHeight: CGFloat = 1
@@ -13047,6 +13046,10 @@ struct TabItemView: View, Equatable {
         settings.activeTabIndicatorStyle
     }
 
+    private var isActive: Bool {
+        observedIsActive ?? (tabManager.selectedTabId == tab.id)
+    }
+
     private var sidebarSelectionColorHex: String? {
         settings.selectionColorHex
     }
@@ -13697,8 +13700,17 @@ struct TabItemView: View, Equatable {
             )
         }
         .onAppear {
+            updateObservedActiveState(tabManager.selectedTabId == tab.id)
             refreshWorkspaceSnapshot(force: true)
         }
+        .onReceive(
+            tabManager.selectedTabIdPublisher
+                .map { $0 == tab.id }
+                .removeDuplicates()
+                .receive(on: RunLoop.main)
+        ) { isSelected in
+            updateObservedActiveState(isSelected)
+        }
         .task(id: workspaceFinderDirectoryOpenRequest) {
             guard let request = workspaceFinderDirectoryOpenRequest else { return }
             await WorkspaceFinderDirectoryOpener.openInFinder(request.directoryURL)
@@ -13782,6 +13794,11 @@ struct TabItemView: View, Equatable {
         }
     }
 
+    private func updateObservedActiveState(_ isActive: Bool) {
+        guard observedIsActive != isActive else { return }
+        observedIsActive = isActive
+    }
+
     private func refreshWorkspaceSnapshot(force: Bool = false) {
         let nextSnapshot = makeWorkspaceSnapshot()
         let decision = SidebarWorkspaceSnapshotRefreshPolicy.decision(

Sources/Mobile/AgentChat/AgentChatSessionRegistry.swift

@@ -7,6 +7,7 @@ import Foundation
 @MainActor
 final class AgentChatSessionRegistry {
     private var records: [String: AgentChatSessionRecord] = [:]
+    private var liveSessionIDBySurfaceID: [String: String] = [:]
     private let hookStore: AgentChatHookSessionStore
 
     /// Called after a record mutation with the previous value (nil for a
@@ -59,6 +60,27 @@ final class AgentChatSessionRegistry {
         records[sessionID]
     }
 
+    /// The current live session bound to a terminal surface, if any.
+    ///
+    /// - Parameter surfaceID: Terminal surface UUID string.
+    /// - Returns: A non-ended record bound to the surface, or `nil`.
+    func liveSession(surfaceID: String) -> AgentChatSessionRecord? {
+        while let sessionID = liveSessionIDBySurfaceID[surfaceID] {
+            guard let record = records[sessionID],
+                  record.surfaceID == surfaceID,
+                  record.state != .ended else {
+                liveSessionIDBySurfaceID.removeValue(forKey: surfaceID)
+                return nil
+            }
+            if let pid = record.pid, processIsDead(pid) {
+                update(sessionID: sessionID) { $0.state = .ended }
+                continue
+            }
+            return record
+        }
+        return nil
+    }
+
     /// Every session id the registry already tracks. Title-detected adoption
     /// passes this to the transcript resolver so a second hook-bypassed claude
     /// in the same directory resolves to a *different* (unclaimed) transcript
@@ -98,6 +120,7 @@ final class AgentChatSessionRegistry {
         var record = previous
         mutate(&record)
         records[sessionID] = record
+        updateLiveSessionIndex(previous: previous, current: record)
         onRecordChanged?(record, previous)
     }
 
@@ -127,7 +150,7 @@ final class AgentChatSessionRegistry {
             for entry in hookStore.entries(agentSource: source) {
                 guard records[entry.sessionID] == nil else { continue }
                 let alive = entry.pid.map { kill(pid_t($0), 0) == 0 } ?? false
-                records[entry.sessionID] = AgentChatSessionRecord(
+                let record = AgentChatSessionRecord(
                     sessionID: entry.sessionID,
                     agentKind: kind,
                     workspaceID: entry.workspaceID,
@@ -139,6 +162,8 @@ final class AgentChatSessionRegistry {
                     title: nil,
                     pid: entry.pid
                 )
+                records[entry.sessionID] = record
+                updateLiveSessionIndex(previous: nil, current: record)
             }
         }
     }
@@ -168,7 +193,7 @@ final class AgentChatSessionRegistry {
         at timestamp: Date
     ) -> AgentChatSessionRecord {
         if let existing = records[sessionID] { return existing }
-        if let bound = records.values.first(where: { $0.surfaceID == surfaceID && $0.state != .ended }) {
+        if let bound = liveSession(surfaceID: surfaceID) {
             return bound
         }
         let record = AgentChatSessionRecord(
@@ -184,6 +209,7 @@ final class AgentChatSessionRegistry {
             pid: nil
         )
         records[sessionID] = record
+        updateLiveSessionIndex(previous: nil, current: record)
         onRecordChanged?(record, nil)
         return record
     }
@@ -249,10 +275,58 @@ final class AgentChatSessionRegistry {
         let previous = records[sessionID]
         record.state = Self.nextState(previous: record.state, event: event)
         records[sessionID] = record
+        updateLiveSessionIndex(previous: previous, current: record)
         onRecordChanged?(record, previous)
         return record
     }
 
+    private func updateLiveSessionIndex(
+        previous: AgentChatSessionRecord?,
+        current: AgentChatSessionRecord
+    ) {
+        let previousSurfaceID = Self.liveSurfaceID(previous)
+        let currentSurfaceID = Self.liveSurfaceID(current)
+        if let previousSurfaceID,
+           previousSurfaceID != currentSurfaceID,
+           liveSessionIDBySurfaceID[previousSurfaceID] == previous?.sessionID {
+            liveSessionIDBySurfaceID.removeValue(forKey: previousSurfaceID)
+            rebuildLiveSessionIndex(surfaceID: previousSurfaceID)
+        }
+        guard let currentSurfaceID else { return }
+        guard let indexedSessionID = liveSessionIDBySurfaceID[currentSurfaceID],
+              let indexed = records[indexedSessionID],
+              indexed.surfaceID == currentSurfaceID,
+              indexed.state != .ended else {
+            liveSessionIDBySurfaceID[currentSurfaceID] = current.sessionID
+            return
+        }
+        if indexed.sessionID == current.sessionID || current.lastActivityAt >= indexed.lastActivityAt {
+            liveSessionIDBySurfaceID[currentSurfaceID] = current.sessionID
+        }
+    }
+
+    private func rebuildLiveSessionIndex(surfaceID: String?) {
+        guard let surfaceID else { return }
+        if let newest = records.values
+            .filter({ $0.surfaceID == surfaceID && $0.state != .ended })
+            .max(by: { $0.lastActivityAt < $1.lastActivityAt }) {
+            liveSessionIDBySurfaceID[surfaceID] = newest.sessionID
+        } else {
+            liveSessionIDBySurfaceID.removeValue(forKey: surfaceID)
+        }
+    }
+
+    private static func liveSurfaceID(_ record: AgentChatSessionRecord?) -> String? {
+        guard let record, record.state != .ended else {
+            return nil
+        }
+        return record.surfaceID
+    }
+
+    private func processIsDead(_ pid: Int) -> Bool {
+        kill(pid_t(pid), 0) != 0 && errno == ESRCH
+    }
+
     /// Strips an agent-name prefix from prefixed workstream ids
     /// (`claude-<uuid>`); raw hook ids pass through.
     private static func normalizedSessionID(_ id: String, source: String) -> String {