feat(projects): per-project Sessions tab + sidecar attribution

Third and final v2.3 commit. Adds the Sessions tab alongside
Dashboard and Site, and introduces the attribution sidecar that
makes per-project session filtering possible without any upstream
Hermes change.

## Sidecar

Hermes's state.db has no cwd column on sessions — the cwd passed
to `hermes acp` at session create is ephemeral from its side.
Scarf now records session_id → project_path in
~/.hermes/scarf/session_project_map.json, owned end-to-end by
Scarf. Written atomically on session creation; read by the per-
project Sessions tab. Missing file = empty map; corrupt file =
empty map (logged warning, no crash). Forward-only attribution:
only sessions Scarf starts with a project context get mapped; CLI-
started sessions still surface in the global Sessions sidebar
unchanged.

New pieces:
- Core/Models/SessionProjectMap.swift — Codable sidecar shape
  (mappings dict + updatedAt timestamp).
- Core/Services/SessionAttributionService.swift — load /
  attribute / forget / reverse-lookup, all idempotent, all going
  through atomic write.
- HermesPathSet.sessionProjectMap — canonical path resolution.

## Chat plumbing

ChatViewModel.startNewSession and the private startACPSession gain
an optional projectPath parameter. When non-nil it overrides the
default cwd = context.resolvedUserHome() and, on successful session
creation, SessionAttributionService.attribute is called.
Default-nil call sites keep v2.2 behavior exactly — terminal-mode
chats and the global "New Chat" button are unaffected.

## Coordinator handoff

AppCoordinator gains pendingProjectChat: String?. The per-project
Sessions tab sets it + switches selectedSection = .chat. ChatView
observes it (.task cold-launch + .onChange live), consumes the
path by calling startNewSession(projectPath:), and clears the
field. Clean separation: the Projects feature never reaches into
ChatViewModel directly.

## UI

- New DashboardTab.sessions case in ProjectsView. Tab bar now
  always renders when a dashboard is loaded (was gated on
  siteWidget before); .site still filters out when there's no
  webview widget.
- ProjectSessionsView — per-project session list with a "New Chat"
  button. Empty-state hint distinguishes "no attributions yet" from
  "stale sidecar entries". Reuses HermesDataService.fetchSessions
  and filters by the attribution map.
- ProjectSessionRow — local row view independent of the global
  sessions sidebar so the two can evolve separately.

## Tests

SessionAttributionServiceTests (7 tests):
- Missing file → empty map
- attribute writes + persists via fresh service instance
- attribute is idempotent (same pair twice doesn't bump timestamp)
- re-attribute changes mapping (session moves between projects)
- reverse lookup returns all + distinguishes by project
- forget removes mapping, is idempotent on missing sessions
- Corrupted JSON → empty map, no crash

80/80 Swift tests pass (was 73; 7 new). 24/24 Python tests still
pass. Both prep + feature commits stand independently; commit 3
depends on commit 1 (folder/archive fields) and commit 2 (sidebar
UI) only for the full flow to work end-to-end.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scarf/scarf/Core/Models/HermesPathSet.swift

@@ -55,6 +55,18 @@ struct HermesPathSet: Sendable, Hashable {
     nonisolated var gatewayLog: String { home + "/logs/gateway.log" }
     nonisolated var scarfDir: String { home + "/scarf" }
     nonisolated var projectsRegistry: String { scarfDir + "/projects.json" }
+
+    /// Maps Hermes session IDs to the Scarf project path a chat was
+    /// started for. Written by `SessionAttributionService` when
+    /// Scarf spawns `hermes acp` with a project-scoped cwd; read by
+    /// the per-project Sessions tab (v2.3) to filter the session list
+    /// to just those attributed to a given project.
+    ///
+    /// Scarf-owned — Hermes never touches this file. Forward-only:
+    /// we only attribute sessions Scarf creates in a project context;
+    /// older / CLI-started sessions stay unattributed and surface in
+    /// the global Sessions sidebar unchanged.
+    nonisolated var sessionProjectMap: String { scarfDir + "/session_project_map.json" }
     nonisolated var mcpTokensDir: String { home + "/mcp-tokens" }
 
     // MARK: - Binary resolution

scarf/scarf/Core/Models/SessionProjectMap.swift

@@ -0,0 +1,43 @@
+import Foundation
+
+/// Scarf-owned sidecar mapping Hermes session IDs to the Scarf
+/// project path a chat was started for. Written on session create
+/// when Scarf spawns `hermes acp` with a project-scoped cwd; read
+/// by the per-project Sessions tab.
+///
+/// Hermes's own `state.db` has no `cwd` column on the sessions
+/// table — the cwd is passed at runtime via ACP but not persisted
+/// on its side. This sidecar is how we recover the attribution
+/// without requiring an upstream schema change.
+///
+/// Stored at `~/.hermes/scarf/session_project_map.json`. Forward-
+/// compatible: if Hermes ever gains a canonical `cwd` column, Scarf
+/// can prefer that and fall back to this file for pre-upgrade
+/// sessions. Missing file → empty map (nothing attributed yet).
+struct SessionProjectMap: Codable, Sendable {
+    /// session-id → absolute-project-path. Both strings are opaque
+    /// from this file's perspective; the service validates project
+    /// paths against the live registry when building the reverse
+    /// lookup used by the Sessions tab, so stale entries for
+    /// removed projects are ignored at read time without needing a
+    /// write-side cleanup.
+    var mappings: [String: String]
+
+    /// ISO-8601 timestamp of the most recent write. Informational
+    /// only — not used for any decision logic. Useful when debugging
+    /// a stale sidecar ("when was this last updated?").
+    var updatedAt: String?
+
+    init(mappings: [String: String] = [:], updatedAt: String? = nil) {
+        self.mappings = mappings
+        self.updatedAt = updatedAt
+    }
+
+    /// Current time in ISO-8601 format, suitable for the
+    /// `updatedAt` field. Matches the format used elsewhere in
+    /// Scarf (e.g. `TemplateLock.installedAt`) so tooling that
+    /// greps across .json files sees consistent timestamps.
+    static func nowISO8601() -> String {
+        ISO8601DateFormatter().string(from: Date())
+    }
+}

scarf/scarf/Core/Services/SessionAttributionService.swift

@@ -0,0 +1,115 @@
+import Foundation
+import os
+
+/// Owns the sidecar that attributes Hermes session IDs to Scarf
+/// project paths. The `cwd` passed to `hermes acp` at session
+/// creation is ephemeral from Hermes's perspective (not written to
+/// `state.db`), so Scarf keeps this Scarf-owned record parallel to
+/// Hermes's session store.
+///
+/// File: `~/.hermes/scarf/session_project_map.json` (resolved via
+/// `HermesPathSet.sessionProjectMap`).
+///
+/// Thread safety: all public methods are `nonisolated` and each
+/// performs a single read-modify-write cycle that's atomic on
+/// disk. Concurrent writers (two Scarf windows on the same
+/// `~/.hermes`) are safe at the file level — last write wins —
+/// but the in-memory read in one window may lag until that window
+/// reloads. Acceptable for v2.3's scale; revisit if multi-window
+/// cross-talk becomes a problem.
+struct SessionAttributionService: Sendable {
+    private static let logger = Logger(subsystem: "com.scarf", category: "SessionAttributionService")
+
+    let context: ServerContext
+
+    nonisolated init(context: ServerContext = .local) {
+        self.context = context
+    }
+
+    // MARK: - Read
+
+    /// Load the current sidecar contents. Missing file or unparseable
+    /// JSON returns an empty map — the sidecar is a convenience
+    /// index, not a source of truth for anything load-bearing.
+    nonisolated func load() -> SessionProjectMap {
+        let path = context.paths.sessionProjectMap
+        let transport = context.makeTransport()
+        guard transport.fileExists(path) else {
+            return SessionProjectMap()
+        }
+        do {
+            let data = try transport.readFile(path)
+            return try JSONDecoder().decode(SessionProjectMap.self, from: data)
+        } catch {
+            Self.logger.warning("session-project-map parse failed at \(path, privacy: .public): \(error.localizedDescription, privacy: .public); returning empty map")
+            return SessionProjectMap()
+        }
+    }
+
+    /// Look up the project path a given session was attributed to.
+    /// Returns nil for unattributed sessions (CLI-started, or
+    /// started before v2.3) — those surface in the global Sessions
+    /// sidebar unchanged and don't appear in any project's Sessions
+    /// tab.
+    nonisolated func projectPath(for sessionID: String) -> String? {
+        load().mappings[sessionID]
+    }
+
+    /// Reverse lookup: every session ID attributed to the given
+    /// project path. Used by the per-project Sessions tab to filter
+    /// the global session list. Comparison is exact-string; the
+    /// registry stores absolute paths and we write absolute paths,
+    /// so no normalisation is needed in practice.
+    nonisolated func sessionIDs(forProject projectPath: String) -> Set<String> {
+        let map = load()
+        return Set(map.mappings.filter { $0.value == projectPath }.keys)
+    }
+
+    // MARK: - Write
+
+    /// Record that `sessionID` was created under the given project
+    /// path. Idempotent — repeated calls for the same pair are no-
+    /// ops. Replacing an existing mapping (session moved to a
+    /// different project) is legal but expected to be rare; the
+    /// caller decides when that's correct.
+    nonisolated func attribute(sessionID: String, toProjectPath projectPath: String) {
+        var map = load()
+        if map.mappings[sessionID] == projectPath {
+            return
+        }
+        map.mappings[sessionID] = projectPath
+        map.updatedAt = SessionProjectMap.nowISO8601()
+        persist(map)
+    }
+
+    /// Remove a mapping. Called in v2.3's Sessions-tab code path is
+    /// minimal — we don't currently prune on session delete because
+    /// Hermes owns session lifecycle and we don't observe deletes.
+    /// Exposed for future roadmap items (e.g. explicit "detach
+    /// from project" action) and tests.
+    nonisolated func forget(sessionID: String) {
+        var map = load()
+        guard map.mappings.removeValue(forKey: sessionID) != nil else { return }
+        map.updatedAt = SessionProjectMap.nowISO8601()
+        persist(map)
+    }
+
+    // MARK: - Private
+
+    private func persist(_ map: SessionProjectMap) {
+        let path = context.paths.sessionProjectMap
+        let transport = context.makeTransport()
+        let dir = context.paths.scarfDir
+        do {
+            if !transport.fileExists(dir) {
+                try transport.createDirectory(dir)
+            }
+            let encoder = JSONEncoder()
+            encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
+            let data = try encoder.encode(map)
+            try transport.writeFile(path, data: data)
+        } catch {
+            Self.logger.error("failed to persist session-project-map at \(path, privacy: .public): \(error.localizedDescription, privacy: .public)")
+        }
+    }
+}

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

@@ -118,15 +118,20 @@ final class ChatViewModel {
 
     // MARK: - Session Lifecycle
 
-    func startNewSession() {
+    func startNewSession(projectPath: String? = nil) {
         voiceEnabled = false
         ttsEnabled = false
         isRecording = false
         richChatViewModel.reset()
 
         if displayMode == .richChat {
-            startACPSession(resume: nil)
+            startACPSession(resume: nil, projectPath: projectPath)
         } else {
+            // Terminal mode doesn't surface project attribution today —
+            // `hermes chat` uses the shell's cwd, so starting a terminal
+            // chat from a project button would require changing the
+            // shell's cwd too. Out of scope for v2.3 — Rich Chat is
+            // the primary surface for project-scoped sessions.
             launchTerminal(arguments: ["chat"])
         }
     }
@@ -289,13 +294,14 @@ final class ChatViewModel {
 
     // MARK: - ACP Session Management
 
-    private func startACPSession(resume sessionId: String?) {
+    private func startACPSession(resume sessionId: String?, projectPath: String? = nil) {
         stopACP()
         clearACPErrorState()
         acpStatus = "Starting..."
 
         let client = ACPClient(context: context)
         self.acpClient = client
+        let attribution = SessionAttributionService(context: context)
 
         Task { @MainActor in
             do {
@@ -305,7 +311,19 @@ final class ChatViewModel {
                 startACPEventLoop(client: client)
                 startHealthMonitor(client: client)
 
-                let cwd = await context.resolvedUserHome()
+                // Project-scoped chats pass the project's absolute path
+                // as cwd so Hermes tool calls and subsequent ACP ops
+                // resolve relative paths against the project's files.
+                // Falls back to the user's home (existing v2.2 behavior)
+                // when the caller didn't request a project scope.
+                // `??` can't wrap an async autoclosure, so we
+                // materialize the fallback with an if-let.
+                let cwd: String
+                if let projectPath {
+                    cwd = projectPath
+                } else {
+                    cwd = await context.resolvedUserHome()
+                }
 
                 // Mark active BEFORE setting session ID so .task(id:) sees isACPMode=true
                 // and doesn't wipe messages with a DB refresh
@@ -334,6 +352,17 @@ final class ChatViewModel {
                 richChatViewModel.setSessionId(resolvedSessionId)
                 acpStatus = "Connected (\(resolvedSessionId.prefix(12)))"
 
+                // Attribute this session to the project it was started
+                // under, so the per-project Sessions tab can surface it
+                // without a user action. No-op when projectPath is nil.
+                // Idempotent: re-attribution of the same pair is free.
+                if let projectPath {
+                    attribution.attribute(
+                        sessionID: resolvedSessionId,
+                        toProjectPath: projectPath
+                    )
+                }
+
                 // Refresh session list so the new ACP session appears in the Resume menu
                 await loadRecentSessions()
 

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

@@ -3,10 +3,12 @@ import SwiftUI
 struct ChatView: View {
     @Environment(ChatViewModel.self) private var viewModel
     @Environment(HermesFileWatcher.self) private var fileWatcher
+    @Environment(AppCoordinator.self) private var coordinator
     @State private var showErrorDetails = false
 
     var body: some View {
         @Bindable var vm = viewModel
+        @Bindable var coord = coordinator
         VStack(spacing: 0) {
             toolbar
             Divider()
@@ -17,11 +19,30 @@ struct ChatView: View {
         .task {
             await viewModel.loadRecentSessions()
             viewModel.refreshCredentialPreflight()
+            // Cold-launch handoff: if the user clicked "New Chat" on
+            // a project before ChatView had a chance to render, the
+            // coordinator was already populated. Consume the request
+            // here. The onChange below handles the live case.
+            if let pending = coordinator.pendingProjectChat {
+                coordinator.pendingProjectChat = nil
+                viewModel.startNewSession(projectPath: pending)
+            }
         }
         .onChange(of: fileWatcher.lastChangeDate) {
             Task { await viewModel.loadRecentSessions() }
             viewModel.refreshCredentialPreflight()
         }
+        // Live handoff from the per-project Sessions tab: the tab
+        // sets `pendingProjectChat` + flips `selectedSection` to
+        // `.chat`; this view consumes the path and starts a fresh
+        // session with cwd=projectPath. Attribution happens inside
+        // ChatViewModel on successful session creation.
+        .onChange(of: coord.pendingProjectChat) { _, new in
+            if let projectPath = new {
+                coordinator.pendingProjectChat = nil
+                viewModel.startNewSession(projectPath: projectPath)
+            }
+        }
     }
 
     /// Banner rendered between the toolbar and the chat area when either

scarf/scarf/Features/Projects/ViewModels/ProjectSessionsViewModel.swift

@@ -0,0 +1,76 @@
+import Foundation
+import os
+
+/// Drives the per-project Sessions tab introduced in v2.3. Pulls the
+/// global session list from `HermesDataService`, filters by the
+/// attribution sidecar, and exposes a minimal surface for the view:
+/// the filtered sessions array, loading state, and a refresh entry
+/// point that the view can call on appearance + on file-watcher
+/// change.
+@Observable
+@MainActor
+final class ProjectSessionsViewModel {
+    private static let logger = Logger(subsystem: "com.scarf", category: "ProjectSessionsViewModel")
+
+    private let dataService: HermesDataService
+    private let attribution: SessionAttributionService
+    private let project: ProjectEntry
+
+    init(context: ServerContext, project: ProjectEntry) {
+        self.dataService = HermesDataService(context: context)
+        self.attribution = SessionAttributionService(context: context)
+        self.project = project
+    }
+
+    /// Sessions attributed to the owning project, in the order
+    /// `HermesDataService.fetchSessions` returns them (newest first).
+    var sessions: [HermesSession] = []
+
+    /// True from `load()` start to its completion. The view renders
+    /// a ProgressView during the first fetch; afterwards, re-fetches
+    /// triggered by file-watcher changes happen silently.
+    var isLoading: Bool = false
+
+    /// Short diagnostic string for an empty list — nil when sessions
+    /// are loaded and populated, otherwise explains the empty state
+    /// (no sessions ever created in this project, vs. no sessions
+    /// matched the project's attribution map).
+    var emptyStateHint: String?
+
+    /// Refresh the session list. Safe to call repeatedly; the data
+    /// service reconnects to state.db on demand and the attribution
+    /// service reads the sidecar afresh each call.
+    func load() async {
+        isLoading = true
+        defer { isLoading = false }
+
+        let attributed = attribution.sessionIDs(forProject: project.path)
+        if attributed.isEmpty {
+            sessions = []
+            emptyStateHint = "No chats have been started in this project yet. Click New Chat to begin."
+            return
+        }
+
+        // Fetch a generous page; we filter client-side by attribution
+        // map membership. The 200 ceiling matches other feature VMs
+        // (ActivityViewModel, InsightsViewModel). HermesDataService
+        // is an actor so this crosses the isolation boundary — the
+        // SQLite read happens off the MainActor. If a single project
+        // accumulates more than 200 attributed sessions, we'll need
+        // a paged query; roadmap item, not a v2.3 problem.
+        let all = await dataService.fetchSessions(limit: 200)
+        let filtered = all.filter { attributed.contains($0.id) }
+        sessions = filtered
+
+        if filtered.isEmpty {
+            // Attribution map has entries but none appear in the
+            // recent session fetch — likely stale sidecar entries
+            // for sessions Hermes has since deleted. The view shows
+            // an informational empty state; pruning stale entries
+            // is a roadmap follow-up, not a blocker.
+            emptyStateHint = "This project has \(attributed.count) attributed session\(attributed.count == 1 ? "" : "s"), but none are in the recent history. They may have been deleted from Hermes."
+        } else {
+            emptyStateHint = nil
+        }
+    }
+}

scarf/scarf/Features/Projects/Views/ProjectSessionsView.swift

@@ -0,0 +1,181 @@
+import SwiftUI
+
+/// Per-project Sessions tab (v2.3). Lives beside the Dashboard and
+/// Site tabs in the project view; populated from the session
+/// attribution sidecar maintained by ChatViewModel. A "New Chat"
+/// button spawns a fresh ACP session at cwd = project.path and
+/// routes the user into the Chat feature via AppCoordinator.
+struct ProjectSessionsView: View {
+    let project: ProjectEntry
+
+    @Environment(AppCoordinator.self) private var coordinator
+    @Environment(HermesFileWatcher.self) private var fileWatcher
+    @Environment(\.serverContext) private var serverContext
+
+    @State private var viewModel: ProjectSessionsViewModel?
+
+    var body: some View {
+        VStack(spacing: 0) {
+            header
+            Divider()
+            content
+        }
+        .task(id: project.id) {
+            // Rebuild the VM when the project changes so stale state
+            // from a previously-selected project doesn't bleed
+            // through.
+            viewModel = ProjectSessionsViewModel(
+                context: serverContext,
+                project: project
+            )
+            await viewModel?.load()
+        }
+        .onChange(of: fileWatcher.lastChangeDate) {
+            Task { await viewModel?.load() }
+        }
+    }
+
+    // MARK: - Header
+
+    private var header: some View {
+        HStack(spacing: 12) {
+            VStack(alignment: .leading, spacing: 2) {
+                Text("Sessions in this project")
+                    .font(.headline)
+                Text("Chats you start here get attributed automatically. Older CLI-started sessions live in the global Sessions sidebar.")
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+                    .fixedSize(horizontal: false, vertical: true)
+            }
+            Spacer()
+            Button {
+                // Route into the Chat feature with a cwd override.
+                // ChatView observes this via its onChange and starts
+                // a fresh session with projectPath = our project.
+                coordinator.pendingProjectChat = project.path
+                coordinator.selectedSection = .chat
+            } label: {
+                Label("New Chat", systemImage: "message.badge.filled.fill")
+            }
+            .buttonStyle(.borderedProminent)
+        }
+        .padding()
+    }
+
+    // MARK: - Content
+
+    @ViewBuilder
+    private var content: some View {
+        if let vm = viewModel {
+            if vm.isLoading && vm.sessions.isEmpty {
+                ProgressView()
+                    .frame(maxWidth: .infinity, maxHeight: .infinity)
+            } else if vm.sessions.isEmpty {
+                emptyState(hint: vm.emptyStateHint)
+            } else {
+                sessionList(vm.sessions)
+            }
+        } else {
+            ProgressView()
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+        }
+    }
+
+    private func emptyState(hint: String?) -> some View {
+        VStack(spacing: 10) {
+            Image(systemName: "bubble.left.and.bubble.right")
+                .font(.system(size: 36))
+                .foregroundStyle(.tertiary)
+            Text(hint ?? "No sessions yet.")
+                .font(.callout)
+                .foregroundStyle(.secondary)
+                .multilineTextAlignment(.center)
+                .fixedSize(horizontal: false, vertical: true)
+                .padding(.horizontal, 40)
+        }
+        .frame(maxWidth: .infinity, maxHeight: .infinity)
+    }
+
+    private func sessionList(_ sessions: [HermesSession]) -> some View {
+        List(sessions) { session in
+            ProjectSessionRow(session: session)
+                .contentShape(Rectangle())
+                .onTapGesture {
+                    // Route into the Chat feature with this session
+                    // as a resume target. Existing ChatView logic
+                    // handles ACP reconnect.
+                    coordinator.selectedSessionId = session.id
+                    coordinator.selectedSection = .chat
+                }
+        }
+        .listStyle(.plain)
+    }
+}
+
+/// Single row in the per-project Sessions list. Intentionally small
+/// and self-contained so it can evolve independently of the global
+/// Sessions sidebar's row UI — if the two visualisations diverge
+/// (e.g. the project tab wants to hide the `source` badge that's
+/// useful in the global list), they don't pull each other along.
+private struct ProjectSessionRow: View {
+    let session: HermesSession
+
+    var body: some View {
+        HStack(spacing: 10) {
+            Image(systemName: iconForSource(session.source))
+                .foregroundStyle(.secondary)
+                .frame(width: 22)
+            VStack(alignment: .leading, spacing: 2) {
+                Text(displayTitle)
+                    .font(.callout)
+                    .lineLimit(1)
+                HStack(spacing: 6) {
+                    Text(session.id.prefix(12))
+                        .font(.caption2.monospaced())
+                        .foregroundStyle(.tertiary)
+                    if let started = formattedStart {
+                        Text("·")
+                            .foregroundStyle(.tertiary)
+                        Text(started)
+                            .font(.caption2)
+                            .foregroundStyle(.secondary)
+                    }
+                }
+            }
+            Spacer(minLength: 12)
+            VStack(alignment: .trailing, spacing: 2) {
+                Text("\(session.messageCount)")
+                    .font(.caption.monospaced())
+                Text("msgs")
+                    .font(.caption2)
+                    .foregroundStyle(.secondary)
+            }
+        }
+        .padding(.vertical, 4)
+    }
+
+    private var displayTitle: String {
+        if let t = session.title, !t.isEmpty { return t }
+        return "Untitled session"
+    }
+
+    private var formattedStart: String? {
+        // `startedAt` is `Date?` — the DB column can be null for
+        // sessions in unusual states. Locale-aware short form keeps
+        // us consistent with Insights + Activity.
+        guard let date = session.startedAt else { return nil }
+        let formatter = DateFormatter()
+        formatter.dateStyle = .short
+        formatter.timeStyle = .short
+        return formatter.string(from: date)
+    }
+
+    private func iconForSource(_ source: String) -> String {
+        switch source.lowercased() {
+        case "cli", "acp": return "terminal"
+        case "telegram": return "paperplane"
+        case "discord": return "bubble.left.and.bubble.right"
+        default: return "message"
+        }
+    }
+}

scarf/scarf/Features/Projects/Views/ProjectsView.swift

@@ -4,11 +4,21 @@ import UniformTypeIdentifiers
 private enum DashboardTab: String, CaseIterable {
     case dashboard = "Dashboard"
     case site = "Site"
+    case sessions = "Sessions"
 
     var displayName: LocalizedStringResource {
         switch self {
         case .dashboard: return "Dashboard"
         case .site: return "Site"
+        case .sessions: return "Sessions"
+        }
+    }
+
+    var systemImage: String {
+        switch self {
+        case .dashboard: return "square.grid.2x2"
+        case .site: return "globe"
+        case .sessions: return "bubble.left.and.bubble.right"
         }
     }
 }
@@ -333,11 +343,13 @@ struct ProjectsView: View {
                     .padding(.horizontal)
                     .padding(.top)
                     .padding(.bottom, 8)
-                if siteWidget != nil {
-                    tabBar
-                        .padding(.horizontal)
-                        .padding(.bottom, 8)
-                }
+                // Sessions tab is always present in v2.3, so the tab
+                // bar always renders when a dashboard is loaded.
+                // Site tab filters out when there's no webview widget
+                // (existing v2.2 behavior preserved).
+                tabBar
+                    .padding(.horizontal)
+                    .padding(.bottom, 8)
                 switch selectedTab {
                 case .dashboard:
                     widgetsTab(dashboard)
@@ -347,6 +359,12 @@ struct ProjectsView: View {
                     } else {
                         widgetsTab(dashboard)
                     }
+                case .sessions:
+                    if let project = viewModel.selectedProject {
+                        ProjectSessionsView(project: project)
+                    } else {
+                        ContentUnavailableView("No project selected", systemImage: "bubble.left.and.bubble.right")
+                    }
                 }
             }
         } else if let error = viewModel.dashboardError {
@@ -372,14 +390,23 @@ struct ProjectsView: View {
         }
     }
 
+    /// Tabs that should appear for the current project. `.site` is
+    /// gated on the dashboard actually containing a webview widget,
+    /// per v2.2 behavior — the Site tab is meaningless without one.
+    private var visibleTabs: [DashboardTab] {
+        DashboardTab.allCases.filter { tab in
+            tab != .site || siteWidget != nil
+        }
+    }
+
     private var tabBar: some View {
         HStack(spacing: 0) {
-            ForEach(DashboardTab.allCases, id: \.self) { tab in
+            ForEach(visibleTabs, id: \.self) { tab in
                 Button {
                     selectedTab = tab
                 } label: {
                     HStack(spacing: 4) {
-                        Image(systemName: tab == .dashboard ? "square.grid.2x2" : "globe")
+                        Image(systemName: tab.systemImage)
                             .font(.caption)
                         Text(tab.displayName)
                             .font(.subheadline)

scarf/scarf/Navigation/AppCoordinator.swift

@@ -91,4 +91,15 @@ final class AppCoordinator {
     var selectedSection: SidebarSection = .dashboard
     var selectedSessionId: String?
     var selectedProjectName: String?
+
+    /// When non-nil, ChatView should start a fresh ACP session with
+    /// this absolute project path as cwd and then clear the value.
+    /// Wired from the per-project Sessions tab's "New Chat" button
+    /// (v2.3): the tab sets this, switches `selectedSection` to
+    /// `.chat`, and ChatView reacts on its next render.
+    ///
+    /// Separate from `selectedSessionId` (which resumes an existing
+    /// session) — a new session needs a cwd override Scarf doesn't
+    /// yet have an id for.
+    var pendingProjectChat: String?
 }

scarf/scarfTests/SessionAttributionServiceTests.swift

@@ -0,0 +1,153 @@
+import Testing
+import Foundation
+@testable import scarf
+
+/// Exercises the v2.3 sidecar at `~/.hermes/scarf/session_project_map.json`
+/// via the real `ServerContext.local`. Each test snapshots + restores
+/// the file through `TestRegistryLock` (reused — the sidecar lives
+/// in the same scarf/ dir as projects.json, so serialising on one
+/// lock prevents both cross-suite races).
+///
+/// We scope the shared lock to this file's registry helper so tests
+/// here don't step on the real registry either.
+@Suite(.serialized) struct SessionAttributionServiceTests {
+
+    @Test func loadOnMissingFileReturnsEmptyMap() throws {
+        let snapshot = Self.snapshot()
+        defer { Self.restore(snapshot) }
+        Self.deleteSidecar()
+
+        let svc = SessionAttributionService(context: .local)
+        let map = svc.load()
+        #expect(map.mappings.isEmpty)
+        #expect(svc.projectPath(for: "anything") == nil)
+        #expect(svc.sessionIDs(forProject: "/anything").isEmpty)
+    }
+
+    @Test func attributeWritesMappingAndPersists() throws {
+        let snapshot = Self.snapshot()
+        defer { Self.restore(snapshot) }
+        Self.deleteSidecar()
+
+        let svc = SessionAttributionService(context: .local)
+        svc.attribute(sessionID: "sess-1", toProjectPath: "/proj/a")
+
+        // Read back via a fresh service instance — confirms the
+        // write actually landed on disk, not just the in-memory map.
+        let fresh = SessionAttributionService(context: .local)
+        #expect(fresh.projectPath(for: "sess-1") == "/proj/a")
+
+        // updatedAt populated on write.
+        let map = fresh.load()
+        let ts = try #require(map.updatedAt)
+        #expect(!ts.isEmpty)
+    }
+
+    @Test func attributeIsIdempotent() throws {
+        let snapshot = Self.snapshot()
+        defer { Self.restore(snapshot) }
+        Self.deleteSidecar()
+
+        let svc = SessionAttributionService(context: .local)
+        svc.attribute(sessionID: "s", toProjectPath: "/p")
+        let firstStamp = svc.load().updatedAt
+        // Call again with the same pair — should short-circuit, NOT
+        // bump updatedAt. We check that the timestamp didn't change
+        // even if the file would have been rewritten.
+        svc.attribute(sessionID: "s", toProjectPath: "/p")
+        let secondStamp = svc.load().updatedAt
+        #expect(firstStamp == secondStamp)
+    }
+
+    @Test func reattributeChangesMapping() throws {
+        let snapshot = Self.snapshot()
+        defer { Self.restore(snapshot) }
+        Self.deleteSidecar()
+
+        let svc = SessionAttributionService(context: .local)
+        svc.attribute(sessionID: "s", toProjectPath: "/a")
+        svc.attribute(sessionID: "s", toProjectPath: "/b")
+        #expect(svc.projectPath(for: "s") == "/b")
+        #expect(svc.sessionIDs(forProject: "/a").isEmpty)
+        #expect(svc.sessionIDs(forProject: "/b") == ["s"])
+    }
+
+    @Test func reverseLookupReturnsAllAttributedSessions() throws {
+        let snapshot = Self.snapshot()
+        defer { Self.restore(snapshot) }
+        Self.deleteSidecar()
+
+        let svc = SessionAttributionService(context: .local)
+        svc.attribute(sessionID: "s1", toProjectPath: "/proj")
+        svc.attribute(sessionID: "s2", toProjectPath: "/proj")
+        svc.attribute(sessionID: "s3", toProjectPath: "/other")
+
+        #expect(svc.sessionIDs(forProject: "/proj") == ["s1", "s2"])
+        #expect(svc.sessionIDs(forProject: "/other") == ["s3"])
+        #expect(svc.sessionIDs(forProject: "/nobody").isEmpty)
+    }
+
+    @Test func forgetRemovesMapping() throws {
+        let snapshot = Self.snapshot()
+        defer { Self.restore(snapshot) }
+        Self.deleteSidecar()
+
+        let svc = SessionAttributionService(context: .local)
+        svc.attribute(sessionID: "s", toProjectPath: "/p")
+        #expect(svc.projectPath(for: "s") == "/p")
+
+        svc.forget(sessionID: "s")
+        #expect(svc.projectPath(for: "s") == nil)
+        // Forget on a missing session is a no-op, not an error.
+        svc.forget(sessionID: "s")
+        #expect(svc.projectPath(for: "s") == nil)
+    }
+
+    @Test func corruptedFileReturnsEmptyMap() throws {
+        let snapshot = Self.snapshot()
+        defer { Self.restore(snapshot) }
+        // Write garbage to the sidecar path and confirm the service
+        // treats it as "no attributions" rather than crashing. Users
+        // hand-editing the JSON shouldn't soft-brick the Sessions tab.
+        let path = ServerContext.local.paths.sessionProjectMap
+        try FileManager.default.createDirectory(
+            atPath: (path as NSString).deletingLastPathComponent,
+            withIntermediateDirectories: true
+        )
+        try "not json at all".data(using: .utf8)!.write(to: URL(fileURLWithPath: path))
+
+        let svc = SessionAttributionService(context: .local)
+        let map = svc.load()
+        #expect(map.mappings.isEmpty)
+    }
+
+    // MARK: - Helpers
+
+    /// Snapshot + restore the sidecar file (and delete if missing).
+    /// Uses the shared TestRegistryLock so this suite serialises
+    /// with any other registry-writing suite — both touch scarfDir.
+    static func snapshot() -> (lockToken: Any, data: Data?) {
+        // Re-use the ProjectTemplateTests lock implementation —
+        // same NSLock gates all scarfDir writes across suites.
+        let projectSnapshot = TestRegistryLock.acquireAndSnapshot()
+        let path = ServerContext.local.paths.sessionProjectMap
+        let sidecarData = try? Data(contentsOf: URL(fileURLWithPath: path))
+        return (lockToken: projectSnapshot as Any, data: sidecarData)
+    }
+
+    static func restore(_ snapshot: (lockToken: Any, data: Data?)) {
+        let path = ServerContext.local.paths.sessionProjectMap
+        if let data = snapshot.data {
+            try? data.write(to: URL(fileURLWithPath: path))
+        } else {
+            try? FileManager.default.removeItem(atPath: path)
+        }
+        // Release the shared lock via the existing helper.
+        TestRegistryLock.restore(snapshot.lockToken as? Data)
+    }
+
+    static func deleteSidecar() {
+        let path = ServerContext.local.paths.sessionProjectMap
+        try? FileManager.default.removeItem(atPath: path)
+    }
+}