nucleic-remote-ios/NucleicRemote/NucleicRemote/Models/RemoteStore.swift

import Foundation
import Network
import SwiftUI
import NucleicProtocol
import NucleicTailnet

/// On the phone there's no app-side `SessionSummary` view-model to collide with, so the wire
/// type *is* the model. Alias it under the host's name so the shared vocabulary reads the same.
typealias WireSessionSummary = NucleicProtocol.SessionSummary

/// The phone's single source of UI state — a pure projection of the host (UX_IOS §1.2). Owns
/// the `SyncClient`, reflects connectivity truth, and exposes the session list + the open
/// session's transcript/approvals. No canonical state is invented on-device.
@MainActor
final class RemoteStore: ObservableObject {
    enum Connectivity: Equatable {
        case unpaired
        case connecting
        case reconnecting
        case connected(SyncTransportHint)
        case hostOffline
        case failed(String)

        var label: String {
            switch self {
            case .unpaired: "Not paired"
            case .connecting: "Connecting…"
            case .reconnecting: "Reconnecting…"
            case .connected(let transport): "Connected · \(transport.label)"
            case .hostOffline: "Mac offline"
            case .failed(let m): m
            }
        }
        var isLive: Bool {
            if case .connected = self { return true }
            return false
        }
    }

    @Published private(set) var connectivity: Connectivity = .unpaired
    @Published private(set) var hostName: String = ""
    /// The paired Mac this connection currently reflects (mesh P3), by its `HostID` (fingerprint).
    /// `hostName`/`sessions`/etc. above are that host's projection; switching hosts re-points them
    /// (live: reconnect to a different paired Mac; demo: swap the mock host). `nil` until connected.
    @Published private(set) var activeHostID: String?
    @Published private(set) var sessions: [WireSessionSummary] = []
    @Published private(set) var capabilities = WireCapabilities(canModifyToolInput: false, allowAlwaysScopes: [])
    @Published private(set) var grantedScope: DeviceScope = .approve
    /// The host's model/effort catalog (SYNC §5.2), driving the composer + session-header pickers.
    /// `.empty` until `Welcome` arrives; the pickers fall back to the built-in effort list.
    @Published private(set) var modelCatalog: WireModelCatalog = .empty

    /// Home / Projects / To-Dos state — the dashboard projection.
    @Published private(set) var dashboard = DashboardSnapshot.empty

    /// The host's mesh peers (mesh P4), from `HostMsg.peerList`. Populated only when the host
    /// advertises `capabilities.canListPeers` and the client asks; drives the future mesh device
    /// list and session-transfer destination picker.
    @Published private(set) var meshPeers: [PeerSummary] = []

    // Open session projection.
    @Published private(set) var openSessionID: SessionID?
    @Published private(set) var openEvents: [AgentEvent] = []
    @Published private(set) var openApprovals: [ApprovalRequest] = []
    /// The open session's full diff (the Mac Diff tab's patch), fetched on demand when the
    /// user opens the Diff tab and the host advertises `canFetchDiff`. Nil until it arrives.
    @Published private(set) var openDiff: WireSessionDiff?
    @Published private(set) var diffLoading = false

    /// A transient host-reported error (the mobile echo of the Mac's last-error bubble):
    /// shown as a red bubble at the bottom of the screen, auto-dismissed after a few seconds.
    struct LastError: Equatable, Identifiable {
        let id = UUID()
        let message: String
        let sessionID: SessionID?
    }
    @Published var lastError: LastError?
    private var errorDismissTask: Task<Void, Never>?

    /// When each session was last opened on this device, for the green "finished while you
    /// weren't looking" wash on the session list (the Mac's unseen-completion marker; the wire
    /// doesn't carry the host's flag, so the phone tracks its own view locally).
    @Published private(set) var lastOpenedAt: [SessionID: Date] = RemoteStore.loadLastOpened()

    /// A navigation request from outside the view hierarchy (notification tap → this session).
    /// `RootView` switches to the Sessions tab; `SessionsView` pushes it and clears.
    @Published var pendingRoute: SessionID?

    /// Whether the app is foreground-active (scene phase), mirrored here so the store can
    /// decide which transitions deserve a notification.
    private(set) var isActive = true

    func setScenePhaseActive(_ active: Bool) { isActive = active }

    /// Route to a session from a notification tap (deep link).
    func route(to sessionID: SessionID) { pendingRoute = sessionID }

    /// An Allow/Deny straight from a notification action (UX_IOS §5.1). Requires a live
    /// channel; if the socket dropped while backgrounded, reconnect and send once ready —
    /// but only briefly (a stale queued approval must never fire minutes later; see
    /// UX_IOS §11.5, and the host dedupes/`alreadyResolved`s a lost race anyway).
    func respondFromNotification(_ id: ApprovalID, allow: Bool) {
        let decision: Decision = allow ? .allow(updatedInput: nil) : .deny(reason: nil)
        if connectivity.isLive {
            send(.approvalRespond(id, decision))
        } else {
            pendingNotificationDecision = (id, decision, Date())
            reconnect()
        }
    }

    /// At most one decision waits for reconnect, and it expires after 30s.
    private var pendingNotificationDecision: (ApprovalID, Decision, Date)?

    private func flushPendingNotificationDecision() {
        guard let (id, decision, at) = pendingNotificationDecision else { return }
        pendingNotificationDecision = nil
        guard Date().timeIntervalSince(at) < 30 else { return }  // stale — require the app
        send(.approvalRespond(id, decision))
    }

    private static let lastOpenedKey = "nucleic.lastOpenedAt"
    private static func loadLastOpened() -> [SessionID: Date] {
        guard let raw = UserDefaults.standard.dictionary(forKey: lastOpenedKey) else { return [:] }
        return raw.reduce(into: [:]) { result, entry in
            if let date = entry.value as? Date { result[SessionID(rawValue: entry.key)] = date }
        }
    }
    private func persistLastOpened() {
        let raw = lastOpenedAt.reduce(into: [String: Date]()) { $0[$1.key.rawValue] = $1.value }
        UserDefaults.standard.set(raw, forKey: Self.lastOpenedKey)
    }

    /// Whether `summary` completed its work after the user last looked at it on this device.
    func unseenCompletion(_ summary: WireSessionSummary) -> Bool {
        let done = summary.status == .finished
            || (summary.status == .awaitingInput && summary.disposition == .completed)
        guard done, summary.sessionID != openSessionID else { return false }
        guard let opened = lastOpenedAt[summary.sessionID] else { return true }
        return summary.updatedAt > opened
    }

    /// Non-archived sessions (archived chats are hidden, matching the Mac sidebar).
    var liveSessions: [WireSessionSummary] { sessions.filter { !$0.archived } }

    /// Sessions needing a human (drives the app-icon badge + NEEDS YOU section). Uses turn
    /// disposition so a finished-the-work session doesn't count, and excludes archived.
    var needsYouCount: Int {
        liveSessions.filter { $0.status.needsYou($0.disposition) }.count
    }

    var canControl: Bool { grantedScope >= .control }

    private let identity = IdentityStore.loadOrCreateIdentity()
    let discovery = LANDiscovery()
    private var client: SyncClient?
    private var eventTask: Task<Void, Never>?
    /// In-flight async connection setup (tailnet node start + dial); cancelled on teardown.
    private var connectTask: Task<Void, Never>?
    /// The pending reconnect backoff timer; cancelled on teardown so a stale retry can't
    /// tear down a newer in-flight attempt.
    private var retryTask: Task<Void, Never>?
    /// The transport the current connection attempt uses (drives the "Connected · …" chip).
    private var activeTransport: SyncTransportHint = .lan
    /// The phone's embedded Tailscale node state, for Settings (nil = not running).
    @Published private(set) var tailnetStatus: String?
    /// The Tailscale interactive-login URL while the node waits for a browser login (a
    /// first tailnet start with no auth key). Auto-opened; Settings shows a re-open button.
    @Published private(set) var tailnetLoginURL: URL?
    private var seenSeq: Set<UInt64> = []
    private var reconnectAttempts = 0

    /// Offline demo mode: seeds mock state and simulates the agent locally so every surface
    /// renders — and the core loops (send, approve, start chat, to-dos) actually respond —
    /// without a paired Mac. Reachable in two ways: the `NUCLEIC_DEMO=1` env var (dev /
    /// screenshots, forced on at launch) and a persisted in-app toggle
    /// (`enterDemo()` / `exitDemo()`) so an App Store reviewer with no Mac can exercise the app
    /// (App Review Guideline 2.1). `@Published` so the UI can show a DEMO indicator and the
    /// "Leave demo" affordance.
    private static let demoModeKey = "nucleic.demoMode"
    @Published private(set) var demoMode = ProcessInfo.processInfo.environment["NUCLEIC_DEMO"] == "1"
        || UserDefaults.standard.bool(forKey: RemoteStore.demoModeKey)
    /// In-flight simulated-run tasks (canned streaming), cancelled on `exitDemo()`.
    private var demoTasks: [Task<Void, Never>] = []

    // MARK: - Multi-host switching (mesh P3)

    /// One selectable Mac for the host switcher — the paired Macs (live) or the mock hosts (demo).
    struct HostChoice: Identifiable, Equatable {
        let id: String       // HostID (fingerprint), or a demo id
        let name: String
        let isActive: Bool
    }

    /// The Macs this phone can switch between. Live: the paired-host registry. Demo: the mock hosts.
    /// One entry ⇒ the switcher hides itself and the app reads single-host. Today the phone holds one
    /// *live* connection at a time (switching reconnects); simultaneous connections are the deferred
    /// multiplexer step.
    var hostChoices: [HostChoice] {
        if demoMode {
            return demoHosts.map { HostChoice(id: $0.id, name: $0.name, isActive: $0.id == activeHostID) }
        }
        return IdentityStore.pairedHosts().map {
            HostChoice(id: $0.fingerprint, name: $0.hostName, isActive: $0.fingerprint == activeHostID)
        }
    }

    /// Switch which paired Mac is active. Live: re-point the (single) connection via the existing
    /// reconnect machinery. Demo: swap the mock host's projection, preserving in-demo edits.
    func switchHost(to id: String) {
        guard id != activeHostID else { return }
        if demoMode {
            if let i = demoHosts.firstIndex(where: { $0.id == activeHostID }) {
                demoHosts[i].sessions = sessions   // keep any in-demo mutations
                demoHosts[i].dashboard = dashboard
            }
            guard let next = demoHosts.first(where: { $0.id == id }) else { return }
            applyDemoHost(next)
        } else {
            activeHostID = id
            reconnect()
        }
    }

    /// The paired Mac the live connection targets — the explicitly-active one, else the most-recent.
    private func activeHost() -> PairedHost? {
        if let id = activeHostID, let host = IdentityStore.pairedHost(id: id) { return host }
        return IdentityStore.pairedHosts().last
    }

    /// Mock hosts for the multi-host demo. Each carries its own name + sessions + dashboard;
    /// switching swaps the flat active-host projection. Empty outside demo.
    private struct DemoHost {
        let id: String
        let name: String
        var sessions: [WireSessionSummary]
        var dashboard: DashboardSnapshot
    }
    private var demoHosts: [DemoHost] = []

    /// Project a mock host onto the flat active-host state (demo host switch).
    private func applyDemoHost(_ host: DemoHost) {
        activeHostID = host.id
        hostName = host.name
        sessions = host.sessions
        dashboard = host.dashboard
        openSessionID = nil; openEvents = []; openApprovals = []; openDiff = nil
        LiveActivityManager.shared.sync(hostName: hostName, sessions: sessions)
        NotificationRouter.shared.updateBadge(needsYouCount)
    }

    var isPaired: Bool { demoMode || IdentityStore.loadPairedHost() != nil }
    var deviceFingerprint: String { identity.fingerprint }

    // MARK: - Lifecycle

    func onAppear() {
        if demoMode { seedDemo(); return }
        discovery.start()
        if isPaired { reconnect() }
    }

    private func seedDemo() {
        connectivity = .connected(.lan)
        hostName = "Andrew's Mac"
        grantedScope = .control
        capabilities = WireCapabilities(
            canModifyToolInput: true, allowAlwaysScopes: [.session, .toolName], canFetchDiff: true)
        modelCatalog = WireModelCatalog(
            groups: [
                [WireModelCatalog.Model(sku: "claude-opus-4-8[1m]", displayName: "Opus 4.8", backend: .claudeCode,
                                        contextBadge: "1M", contextWindow: 1_000_000,
                                        efforts: ["low", "medium", "high", "xhigh", "max"], effortNoun: "Effort"),
                 WireModelCatalog.Model(sku: "claude-sonnet-4-6", displayName: "Sonnet 4.6", backend: .claudeCode,
                                        contextBadge: nil, contextWindow: 200_000,
                                        efforts: ["low", "medium", "high", "xhigh", "max"], effortNoun: "Effort")],
                [WireModelCatalog.Model(sku: "gpt-5.5", displayName: "GPT-5.5", backend: .codex,
                                        contextBadge: nil, contextWindow: 350_000,
                                        efforts: ["low", "medium", "high", "xhigh"], effortNoun: "Reasoning")],
                [WireModelCatalog.Model(sku: "grok-build", displayName: "Grok Build", backend: .grok,
                                        contextBadge: nil, contextWindow: 256_000,
                                        efforts: ["auto"], effortNoun: "Reasoning")],
            ],
            effortDisplayNames: ["auto": "Auto", "orchestra": "Orchestra"],
            orchestraSentinel: "orchestra", orchestraRequiresControlNote: "Requires Nucleic Control",
            fallbackModel: "claude-opus-4-8[1m]", fallbackEffort: "high")
        let p1 = ProjectID(rawValue: "p1"), p2 = ProjectID(rawValue: "p2")
        func sum(_ id: String, _ project: ProjectID, _ name: String, _ title: String,
                 _ status: SessionStatus, _ disp: TurnDisposition? = nil, approvals: Int = 0,
                 fav: Bool = false, arch: Bool = false, add: Int = 0, rem: Int = 0) -> WireSessionSummary {
            WireSessionSummary(
                sessionID: SessionID(rawValue: id), projectID: project.rawValue, projectName: name,
                backend: .claudeCode, status: status, disposition: disp, title: title,
                branch: "nucleic/\(id)", lastSeq: 10,
                diffStat: add + rem > 0 ? DiffStat(filesChanged: 2, added: add, removed: rem) : nil,
                pendingApprovalCount: approvals, favorite: fav, archived: arch,
                updatedAt: Date())
        }
        let cal = Calendar.current
        let today = cal.startOfDay(for: Date())
        let activity = (0..<40).map { i -> ActivityDay in
            let count = (i * 7) % 6
            // Sample tokens roughly track messages so the preview grid shades by usage.
            return ActivityDay(day: cal.date(byAdding: .day, value: -i, to: today)!,
                               count: count, tokens: count * 8_500 + (i * 137) % 4_000)
        }
        // Host 1 — "Andrew's Mac".
        let host1Sessions = [
            sum("a1", p1, "nucleic", "auth-refactor", .awaitingApproval, approvals: 1, add: 312, rem: 40),
            sum("a2", p1, "nucleic", "flaky-tests", .running, add: 88, rem: 12),
            sum("a3", p2, "website", "graphql-migration", .awaitingInput, .awaitingInput, fav: true),
            sum("a4", p2, "website", "docs-pass", .awaitingInput, .completed, add: 20, rem: 4),
            sum("a5", p1, "nucleic", "old-experiment", .finished, arch: true),
        ]
        let host1Dashboard = DashboardSnapshot(
            counts: DashboardCounts(
                projects: 2, chats: 5, activeChats: 2, messages: 142, activeDays: 9, tokens: 1_284_000),
            activity: activity,
            projects: [
                WireProject(id: p1, name: "nucleic", defaultBranch: "main", sessionCount: 3, activeCount: 2),
                WireProject(id: p2, name: "website", defaultBranch: "main", sessionCount: 2, activeCount: 1),
            ],
            todos: [
                WireTodo(id: TodoID(rawValue: "t1"), text: "Add dark mode to settings", summary: "Dark mode in settings",
                         projectID: p2, projectName: "website", status: .open, dispatchedSessionID: nil,
                         triage: "high", updatedAt: Date()),
                WireTodo(id: TodoID(rawValue: "t2"), text: "Investigate the memory leak in the sync server", summary: "Sync server memory leak",
                         projectID: p1, projectName: "nucleic", status: .open, dispatchedSessionID: nil,
                         triage: "critical", updatedAt: Date()),
                WireTodo(id: TodoID(rawValue: "t3"), text: "Write release notes", summary: nil,
                         projectID: nil, projectName: nil, status: .open, dispatchedSessionID: nil,
                         triage: "low", updatedAt: Date()),
            ],
            usage: WireSubscriptionUsage(
                fiveHour: WireUsageWindow(utilization: 42, resetsAt: Date().addingTimeInterval(3 * 3600)),
                sevenDay: WireUsageWindow(utilization: 78, resetsAt: Date().addingTimeInterval(2.4 * 86_400))),
            statusFeeds: [
                WireStatusFeed(provider: "claude", providerName: "Claude", incidents: []),
                WireStatusFeed(provider: "openai", providerName: "OpenAI", incidents: [
                    WireStatusIncident(
                        id: "i1", title: "Elevated errors on Codex", url: URL(string: "https://status.openai.com"),
                        updatedAt: Date(), state: "Monitoring", isResolved: false, components: ["Codex"]),
                ]),
                WireStatusFeed(provider: "xai", providerName: "xAI", incidents: []),
            ])
        // Host 2 — "Studio Mac" (mesh P3: a second paired Mac, for the host switcher).
        let p3 = ProjectID(rawValue: "p3")
        let host2Sessions = [
            sum("b1", p3, "renderer", "shadow-mapping", .running, add: 140, rem: 22),
            sum("b2", p3, "renderer", "gpu-profiling", .awaitingApproval, approvals: 1),
            sum("b3", p1, "nucleic", "cloud-runtime", .awaitingInput, .completed, add: 60, rem: 8),
        ]
        let host2Dashboard = DashboardSnapshot(
            counts: DashboardCounts(
                projects: 1, chats: 3, activeChats: 2, messages: 61, activeDays: 5, tokens: 540_000),
            activity: activity,
            projects: [WireProject(id: p3, name: "renderer", defaultBranch: "main", sessionCount: 2, activeCount: 2)],
            todos: [
                WireTodo(id: TodoID(rawValue: "t4"), text: "Bake the light probes overnight", summary: "Bake light probes",
                         projectID: p3, projectName: "renderer", status: .open, dispatchedSessionID: nil,
                         triage: "medium", updatedAt: Date()),
            ],
            usage: WireSubscriptionUsage(
                fiveHour: WireUsageWindow(utilization: 18, resetsAt: Date().addingTimeInterval(2 * 3600)),
                sevenDay: WireUsageWindow(utilization: 40, resetsAt: nil)),
            statusFeeds: [])
        demoHosts = [
            DemoHost(id: "demo-1", name: "Andrew's Mac", sessions: host1Sessions, dashboard: host1Dashboard),
            DemoHost(id: "demo-2", name: "Studio Mac", sessions: host2Sessions, dashboard: host2Dashboard),
        ]
        applyDemoHost(demoHosts[0])
    }

    /// Offline diff fixture (NUCLEIC_DEMO) so the full-patch Diff tab renders without a host.
    private func demoDiff(_ sessionID: SessionID) -> WireSessionDiff {
        WireSessionDiff(
            sessionID: sessionID,
            stat: DiffStat(filesChanged: 2, added: 312, removed: 40),
            files: [
                WireFileDiff(path: "auth/middleware.ts", oldPath: nil, status: "modified", added: 290, removed: 38),
                WireFileDiff(path: "auth/session.ts", oldPath: nil, status: "added", added: 22, removed: 2),
            ],
            patch: """
            diff --git a/auth/middleware.ts b/auth/middleware.ts
            --- a/auth/middleware.ts
            +++ b/auth/middleware.ts
            @@ -10,7 +10,9 @@ export function requireSession(req: Request) {
            -  const token = req.headers.get("x-auth")
            +  const header = req.headers.get("authorization") ?? ""
            +  const token = header.replace(/^Bearer /, "")
            +  if (!token) throw new AuthError("missing bearer token")
               return verify(token)
             }
            diff --git a/auth/session.ts b/auth/session.ts
            new file mode 100644
            --- /dev/null
            +++ b/auth/session.ts
            @@ -0,0 +1,6 @@
            +export interface Session {
            +  userId: string
            +  issuedAt: number
            +}
            +
            +export const SESSION_TTL = 3600
            """)
    }

    /// One dialable way to reach the Mac. A connect builds an ordered candidate list — LAN
    /// first (cheapest when reachable), then the tailnet (SYNC §3.2's LAN-then-fallback
    /// ordering) — and `attempt` walks it until one carries a session.
    private enum TransportAttempt {
        case lan(NWEndpoint)
        case tailnet(host: String, port: UInt16)
    }

    /// The in-progress connect: remaining candidates plus everything needed to start a
    /// client on whichever one succeeds. Cleared on `.ready` (chain done) and by teardown.
    private struct ConnectPlan {
        var remaining: [TransportAttempt]
        let hostStaticKey: Data
        let mode: SyncClient.Mode
        let deviceID: String
        let pairingPayload: PairingPayload?
    }
    private var connectPlan: ConnectPlan?
    /// Kills a LAN attempt whose TCP connect just hangs (stale IP hint) so the chain can
    /// move on — NWConnection's own timeout is far too slow for a fallback decision.
    private var lanConnectTimeout: Task<Void, Never>?

    /// Pair from a scanned QR (SYNC §4.2): try the QR's transports in order (LAN hint or
    /// Bonjour first, then the Mac's tailnet IP via the phone's embedded node), run XXpsk0,
    /// and on success pin the host key for future IK reconnects.
    func pair(with payload: PairingPayload) {
        teardown()
        connectivity = .connecting
        hostName = payload.hostName
        activeHostID = payload.hostStaticKey.fingerprintHex
        guard let hint = payload.transportHint else {
            connectivity = .failed("This pairing code needs a newer version of Nucleic Remote.")
            return
        }
        guard hint != .relay else {
            connectivity = .failed("Relay connections aren't supported yet.")
            return
        }
        let candidates = buildCandidates(
            fingerprint: payload.hostStaticKey.fingerprintHex,
            lanHost: payload.lanHost, lanPort: payload.lanPort,
            tailnet: hint == .tailnet ? (payload.tailnetHost, payload.tailnetPort) : nil)
        guard !candidates.isEmpty else {
            connectivity = .failed(hint == .tailnet && !TailnetSupport.isBuiltIn
                ? TailnetError.notBuiltIn.errorDescription ?? "Tailscale support isn't built in"
                : "No Mac found on this network")
            return
        }
        connectPlan = ConnectPlan(
            remaining: candidates, hostStaticKey: payload.hostStaticKey,
            mode: .pair(secret: payload.pairingSecret), deviceID: IdentityStore.deviceID(),
            pairingPayload: payload)
        _ = tryNextCandidate()
    }

    /// Reconnect to the already-paired host using IK against the pinned static key: LAN
    /// when reachable, else the pairing's tailnet hint — so a phone that leaves the Mac's
    /// Wi‑Fi rolls over to the tailnet and rolls back when it returns.
    func reconnect() {
        guard let host = activeHost() else { connectivity = .unpaired; return }
        teardown()
        activeHostID = host.fingerprint
        connectivity = reconnectAttempts == 0 ? .connecting : .reconnecting
        hostName = host.hostName
        guard host.transportHint != .relay else {
            connectivity = .failed("Relay connections aren't supported yet.")
            return
        }
        let candidates = buildCandidates(
            fingerprint: host.fingerprint,
            lanHost: host.lanHost, lanPort: host.lanPort,
            tailnet: host.transportHint == .tailnet ? (host.tailnetHost, host.tailnetPort) : nil)
        guard !candidates.isEmpty else {
            connectivity = .hostOffline
            scheduleRetry()
            return
        }
        connectPlan = ConnectPlan(
            remaining: candidates, hostStaticKey: host.hostStaticKey,
            mode: .reconnect, deviceID: host.deviceID, pairingPayload: nil)
        _ = tryNextCandidate()
    }

    /// LAN first (explicit hint, else a Bonjour match), tailnet second when the pairing
    /// carries one and this build can dial it.
    private func buildCandidates(
        fingerprint: String?, lanHost: String?, lanPort: UInt16?,
        tailnet: (host: String?, port: UInt16?)?
    ) -> [TransportAttempt] {
        var candidates: [TransportAttempt] = []
        if let endpoint = resolveEndpoint(fingerprint: fingerprint, lanHost: lanHost, lanPort: lanPort) {
            candidates.append(.lan(endpoint))
        }
        if let tailnet, let host = tailnet.host, let port = tailnet.port, TailnetSupport.isBuiltIn {
            candidates.append(.tailnet(host: host, port: port))
        }
        return candidates
    }

    /// Pop and dial the next candidate. False when the plan is exhausted (or gone) — the
    /// caller then applies its terminal failure handling.
    private func tryNextCandidate() -> Bool {
        guard var plan = connectPlan, !plan.remaining.isEmpty else { return false }
        let next = plan.remaining.removeFirst()
        connectPlan = plan
        attempt(next, plan: plan)
        return true
    }

    private func attempt(_ candidate: TransportAttempt, plan: ConnectPlan) {
        teardownClient()
        switch candidate {
        case .lan(let endpoint):
            activeTransport = .lan
            let channel = makeChannel(endpoint)
            // Close the channel if TCP isn't up within the window (a stale IP hint would
            // otherwise hang the chain on NWConnection's slow timeout); the finished stream
            // then advances to the next candidate. The timer checks readiness itself — it's
            // bound to exactly this channel, so a stale timer can never hit a later attempt.
            lanConnectTimeout?.cancel()
            lanConnectTimeout = Task { [weak channel] in
                try? await Task.sleep(for: .seconds(4))
                guard !Task.isCancelled, let channel, !channel.isReady else { return }
                channel.close()
            }
            startClient(
                channel: channel, hostStaticKey: plan.hostStaticKey,
                mode: plan.mode, deviceID: plan.deviceID, pairingPayload: plan.pairingPayload)
        case .tailnet(let host, let port):
            activeTransport = .tailnet
            connectTask = Task { [weak self] in
                guard let self else { return }
                do {
                    let channel = try await self.tailnetChannel(host: host, port: port)
                    guard !Task.isCancelled else { channel.close(); return }
                    self.startClient(
                        channel: channel, hostStaticKey: plan.hostStaticKey,
                        mode: plan.mode, deviceID: plan.deviceID, pairingPayload: plan.pairingPayload)
                } catch {
                    guard !Task.isCancelled else { return }
                    self.tailnetAttemptFailed(error, isPairing: plan.pairingPayload != nil)
                }
            }
        }
    }

    /// The tailnet is always the last candidate, so its failure ends the chain: terminal
    /// for pairing and for anything retrying can't fix; otherwise offline + backoff.
    private func tailnetAttemptFailed(_ error: Error, isPairing: Bool) {
        if tryNextCandidate() { return }
        if isPairing {
            connectivity = .failed(error.localizedDescription)
            return
        }
        switch error {
        case TailnetError.notBuiltIn, TailnetError.notConfigured:
            connectivity = .failed(error.localizedDescription)
        default:
            connectivity = .hostOffline
            scheduleRetry()
        }
    }


    /// Create the `SyncClient` on an established channel and start consuming its events —
    /// the tail of every connect path, LAN or tailnet, pair or reconnect.
    private func startClient(
        channel: any FrameChannel, hostStaticKey: Data, mode: SyncClient.Mode,
        deviceID: String, pairingPayload: PairingPayload?
    ) {
        let client = SyncClient(
            channel: channel, identity: identity, hostStaticKey: hostStaticKey,
            mode: mode, deviceID: deviceID,
            deviceLabel: UIDevice.current.name, pushToken: PushRegistrar.shared.tokenHex,
            releaseChannel: BuildInfo.current.channel.releaseChannel)
        self.client = client
        consume(client, pairingPayload: pairingPayload)
    }

    /// Bring the phone's embedded Tailscale node up (first run needs the auth key from
    /// Settings ▸ Tailscale; afterwards the on-disk state carries the registration) and dial
    /// the Mac's tailnet address.
    private func tailnetChannel(host: String, port: UInt16) async throws -> FDFrameChannel {
        guard TailnetSupport.isBuiltIn else { throw TailnetError.notBuiltIn }
        let config = Self.phoneTailnetConfig()
        tailnetStatus = "Starting…"
        // Mirror node status while the start is in flight. A first start with no auth key
        // goes through the interactive browser login; pairing usually runs from the scanner
        // sheet — not Settings — so take the user straight to the approval page.
        let watcher = Task { [weak self] in
            for await status in await TailnetNode.shared.statusStream() {
                guard let self, !Task.isCancelled else { break }
                self.tailnetStatus = status.label
                if case .needsLogin(let url) = status, let loginURL = URL(string: url) {
                    if self.tailnetLoginURL != loginURL {
                        self.tailnetLoginURL = loginURL
                        // Eject to Safari only for user-initiated pairing — the user is
                        // actively watching. A routine reconnect that suddenly needs a
                        // login (node revoked, state wiped) must not yank them out of the
                        // app; Settings ▸ Tailscale carries the login link instead.
                        if self.connectPlan?.pairingPayload != nil {
                            UIApplication.shared.open(loginURL, options: [:], completionHandler: nil)
                        }
                    }
                } else {
                    self.tailnetLoginURL = nil
                }
            }
        }
        defer {
            watcher.cancel()
            tailnetLoginURL = nil
        }
        do {
            try await TailnetNode.shared.ensureRunning(config: config)
        } catch TailnetError.timedOut(let message) {
            // A login/auth timeout won't fix itself — retrying would just block per lap.
            // Rethrow as .notConfigured so reconnect() treats it as terminal, not offline.
            tailnetStatus = await TailnetNode.shared.status.label
            throw TailnetError.notConfigured(message)
        } catch {
            tailnetStatus = await TailnetNode.shared.status.label
            throw error
        }
        tailnetStatus = await TailnetNode.shared.status.label
        return try await TailnetNode.shared.dial(host: host, port: port)
    }

    /// The phone's embedded-node config. State lives in this app's sandboxed Application
    /// Support (no cross-channel collision — each channel is its own app container).
    private static func phoneTailnetConfig() -> TailnetConfig {
        let base = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)[0]
            .appendingPathComponent("Nucleic", isDirectory: true)
            .appendingPathComponent("tailnet", isDirectory: true)
        return TailnetConfig(
            hostName: TailnetConfig.nodeName(for: UIDevice.current.name),
            stateDirectory: base,
            authKey: TailnetAuthStore.loadAuthKey())
    }

    func unpair() {
        teardown()
        // Forget the *active* Mac specifically (the switcher may have made it not the last).
        if let id = activeHostID { IdentityStore.removePairedHost(id: id) } else { IdentityStore.clearPairedHost() }
        activeHostID = nil
        // Mesh P3: if other Macs remain paired, switch to one rather than going fully unpaired.
        if IdentityStore.pairedHosts().last != nil {
            reconnect()
            return
        }
        connectivity = .unpaired
        sessions = []
        // Nothing left to dial — spin the embedded Tailscale node down if it was running.
        Task { await TailnetNode.shared.stop() }
        tailnetStatus = nil
        LiveActivityManager.shared.end()
        NotificationRouter.shared.updateBadge(0)
    }

    /// Enter the in-app demo (the "Explore a demo" button): drop any live connection, persist the
    /// flag so it survives relaunch (a reviewer may relaunch), and seed the mock world. `isPaired`
    /// then returns true, so `RootView` shows the full TabView.
    func enterDemo() {
        teardown()
        demoMode = true
        UserDefaults.standard.set(true, forKey: Self.demoModeKey)
        reconnectAttempts = 0
        seedDemo()
    }

    /// Leave the demo (Settings ▸ Leave demo): cancel any simulated runs, clear the mock world,
    /// and return to the real state — reconnect if a Mac is actually paired, else the pairing intro.
    func exitDemo() {
        demoMode = false
        UserDefaults.standard.set(false, forKey: Self.demoModeKey)
        demoTasks.forEach { $0.cancel() }
        demoTasks.removeAll()
        demoHosts = []
        activeHostID = nil
        openSessionID = nil
        openEvents = []
        openApprovals = []
        openDiff = nil
        diffLoading = false
        sessions = []
        dashboard = .empty
        LiveActivityManager.shared.end()
        NotificationRouter.shared.updateBadge(0)
        if IdentityStore.loadPairedHost() != nil {
            reconnect()
        } else {
            connectivity = .unpaired
        }
    }

    // MARK: - Intents (UX_IOS §9)

    func open(_ sessionID: SessionID) {
        openSessionID = sessionID
        openEvents = []
        openApprovals = []
        openDiff = nil
        diffLoading = false
        seenSeq.removeAll()
        markOpened(sessionID)
        if demoMode { seedDemoTranscript(sessionID); return }
        send(.subscribe(Subscribe(sessionID: sessionID, sinceSeq: nil, verbosity: .full)))
    }

    /// Ask the host for the open session's full patch (Diff tab). No-op when the host
    /// doesn't advertise the capability — the view falls back to the diffstat summary.
    func fetchDiff(_ sessionID: SessionID) {
        if demoMode { openDiff = demoDiff(sessionID); return }
        guard capabilities.canFetchDiff else { return }
        diffLoading = openDiff == nil
        send(.fetchDiff(sessionID))
    }

    /// Record that the user looked at this session now (clears its unseen-completion wash).
    func markOpened(_ sessionID: SessionID) {
        lastOpenedAt[sessionID] = Date()
        persistLastOpened()
    }

    /// Offline transcript fixture (NUCLEIC_DEMO) so the richer transcript surfaces — grouped
    /// tools, Orchestra card, usage/cost, file changes, run outcome — render without a host.
    private func seedDemoTranscript(_ sessionID: SessionID) {
        func event(_ seq: UInt64, _ kind: AgentEvent.Kind) -> AgentEvent {
            AgentEvent(sessionID: sessionID, seq: seq, at: Date(), backend: .claudeCode,
                       nativeType: nil, kind: kind)
        }
        // A realistic `git commit` (heredoc message) so the transcript's structured commit card
        // is exercisable offline: expand the Bash call to see the subject + Markdown body.
        let demoCommitCommand = "git commit -F - <<'EOF'\nfix: harden auth middleware\n\nRequire a Bearer token and reject a missing or blank one.\n\n- extract `requireSession`\n- add a `Bearer` prefix check\nEOF"
        // A multi-step, destructive shell pipeline so the transcript's step list (with the delete
        // flagged in red) is exercisable offline: expand the Bash call to see the breakdown.
        let demoCleanupCommand = "cd ~/code/nucleic && rm -rf .worktrees/auth-old && git worktree prune && git branch -D nucleic/auth-old"
        openEvents = [
            event(1, .sessionStarted(SessionStarted(
                backendSessionID: "demo", model: "claude-opus-4-8[1m]", cwd: "~/code/nucleic", toolNames: []))),
            event(2, .userText(TextChunk(messageID: "u1", text: "Refactor the auth middleware and run the tests.", isPartial: false))),
            event(3, .assistantText(TextChunk(messageID: "a1", text: "I'll update the auth middleware, then run the suite.\n\n**Plan:**\n- extract `requireSession`\n- add a `Bearer` check", isPartial: false))),
            event(4, .toolCallStarted(ToolCall(toolCallID: "t1", name: "Edit", input: ["file_path": "auth/middleware.ts"]))),
            event(5, .toolCallCompleted(ToolCall(toolCallID: "t1", name: "Edit", input: ["file_path": "auth/middleware.ts"]))),
            event(6, .fileChange(FileChange(path: "auth/middleware.ts", kind: .update, toolCallID: "t1"))),
            event(7, .toolResult(ToolResult(toolCallID: "t1", content: "Applied 2 edits to auth/middleware.ts", isError: false))),
            event(8, .toolCallStarted(ToolCall(toolCallID: "t2", name: "Bash", input: ["command": "npm test"]))),
            event(9, .toolCallCompleted(ToolCall(toolCallID: "t2", name: "Bash", input: ["command": "npm test"]))),
            event(10, .toolResult(ToolResult(toolCallID: "t2", content: "42 passing\n0 failing", isError: false))),
            event(11, .toolCallStarted(ToolCall(toolCallID: "t3", name: "Task", input: ["description": "Audit other call sites", "prompt": "Find every caller of the old auth API."]))),
            event(12, .toolCallCompleted(ToolCall(toolCallID: "t3", name: "Task", input: ["description": "Audit other call sites"]))),
            event(13, .toolResult(ToolResult(toolCallID: "t3", content: "Checked 7 files; 1 stale caller updated.", isError: false))),
            event(14, .toolCallStarted(ToolCall(toolCallID: "t4", name: "Bash", input: ["command": .string(demoCommitCommand)]))),
            event(15, .toolCallCompleted(ToolCall(toolCallID: "t4", name: "Bash", input: ["command": .string(demoCommitCommand)]))),
            event(16, .toolResult(ToolResult(toolCallID: "t4", content: "[nucleic/auth-refactor 1a2b3c4] fix: harden auth middleware\n 2 files changed, 312 insertions(+), 40 deletions(-)", isError: false))),
            event(17, .toolCallStarted(ToolCall(toolCallID: "t5", name: "Bash", input: ["command": .string(demoCleanupCommand)]))),
            event(18, .toolCallCompleted(ToolCall(toolCallID: "t5", name: "Bash", input: ["command": .string(demoCleanupCommand)]))),
            event(19, .toolResult(ToolResult(toolCallID: "t5", content: "Removed 1 worktree; deleted branch nucleic/auth-old.", isError: false))),
            event(20, .usage(Usage(inputTokens: 84_300, outputTokens: 2_140, costUSD: 0.0421, contextInputTokens: 84_300))),
            event(21, .runFinished(RunFinished(outcome: .completed, finalText: "Done."))),
        ]
        // If this session is blocked on a human, surface a real approval card so the
        // Allow/Deny loop is exercisable in the demo (the seeded `a1` session).
        if sessions.first(where: { $0.sessionID == sessionID })?.status == .awaitingApproval {
            openApprovals = [ApprovalRequest(
                id: Self.demoApprovalID(for: sessionID),
                sessionID: sessionID, toolCallID: "t-appr", toolName: "Bash",
                input: ["command": "npm run deploy"], title: "Run npm run deploy",
                risk: .execute, createdAt: Date())]
        }
    }

    /// Deterministic approval id for a demo session's seeded approval, so re-opening the same
    /// session doesn't stack duplicate cards.
    private static func demoApprovalID(for sessionID: SessionID) -> ApprovalID {
        ApprovalID(rawValue: "demo-appr-\(sessionID.rawValue)")
    }

    /// Close a session's live subscription. `id` names *which* session is closing — the detail
    /// view passes its own. On iPad's split view, switching session A→B can mount B (which calls
    /// `open(B)`, setting `openSessionID = B`) *before* A's detail disappears; so we always
    /// unsubscribe the named session but only tear down the shared open-state when it still
    /// belongs to that session — otherwise we'd wipe B's freshly-loaded transcript. Called with
    /// no argument it closes whatever is currently open (the iPhone push/pop path, unchanged).
    func closeOpen(_ id: SessionID? = nil) {
        guard let target = id ?? openSessionID else { return }
        send(.unsubscribe(target))
        markOpened(target)  // everything up to now has been seen
        guard openSessionID == target else { return }
        openSessionID = nil
        openEvents = []
        openApprovals = []
        openDiff = nil
        diffLoading = false
    }

    func respond(_ approval: ApprovalRequest, _ decision: Decision) {
        send(.approvalRespond(approval.id, decision))
        openApprovals.removeAll { $0.id == approval.id }  // optimistic dismiss; host confirms
    }

    func sendInput(_ text: String, to sessionID: SessionID) {
        let trimmed = text.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return }
        send(.sendInput(sessionID, AgentInput(text: trimmed)))
    }

    func refreshSessions() { send(.listSessions); send(.listDashboard) }

    // MARK: - Control intents (control scope; the same actions the Mac can take)

    func startChat(in projectID: ProjectID, message: String, model: String? = nil,
                   effort: String? = nil, baseBranch: String? = nil,
                   useWorktree: Bool = true, auto: Bool? = nil) {
        let text = message.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !text.isEmpty else { return }
        send(.startChat(StartChatRequest(
            projectID: projectID, message: text, model: model, effort: effort,
            baseBranch: baseBranch, useWorktree: useWorktree, auto: auto)))
    }

    func captureTodo(_ text: String, projectID: ProjectID?) {
        let trimmed = text.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return }
        send(.captureTodo(CaptureTodoRequest(text: trimmed, projectID: projectID)))
    }

    func dispatchTodo(_ id: TodoID, in projectID: ProjectID) { send(.dispatchTodo(id, projectID)) }
    func completeTodo(_ id: TodoID) { send(.setTodoStatus(id, .done)) }
    func deleteTodo(_ id: TodoID) { send(.deleteTodo(id)) }

    func renameSession(_ id: SessionID, to title: String) {
        let trimmed = title.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return }
        send(.renameSession(id, trimmed))
    }
    func setFavorite(_ id: SessionID, _ favorite: Bool) { send(.setFavorite(id, favorite)) }
    func setArchived(_ id: SessionID, _ archived: Bool) { send(.setArchived(id, archived)) }
    func deleteSession(_ id: SessionID) {
        send(.deleteSession(id))
        if id == openSessionID { closeOpen() }
    }
    func integrate(_ id: SessionID, _ mode: IntegrationMode) { send(.integrate(id, mode)) }
    /// Throw away the session's branch/worktree without landing it (the Mac's Discard…).
    func discard(_ id: SessionID) { send(.discard(id)) }
    func interrupt(_ id: SessionID) { send(.interrupt(id)) }
    /// Cancel one queued (not-yet-sent) follow-up by id — the phone's per-message ✕.
    func cancelQueuedMessage(_ id: SessionID, _ messageID: UUID) { send(.cancelQueuedMessage(id, messageID)) }

    // Mid-session model / reasoning / automation — the same affordances the Mac header exposes.
    // `nil` model/effort resets the session to the host/app default.
    func setSessionModel(_ id: SessionID, _ model: String?) { send(.setSessionModel(id, model)) }
    func setSessionEffort(_ id: SessionID, _ effort: String?) { send(.setSessionEffort(id, effort)) }
    func setSessionAuto(_ id: SessionID, _ auto: Bool) { send(.setSessionAuto(id, auto)) }
    func setSessionAutoShip(_ id: SessionID, _ autoShip: Bool) { send(.setSessionAutoShip(id, autoShip)) }
    func setSessionShipBranch(_ id: SessionID, _ branch: String?) { send(.setSessionShipBranch(id, branch)) }

    // MARK: - Plumbing

    private func send(_ msg: ClientMsg) {
        if demoMode { demoHandle(msg); return }
        guard let client else { return }
        Task { await client.send(msg) }
    }

    // MARK: - Demo simulator (offline, interactive)
    //
    // In demo mode there's no host, so writes can't go over the wire. Instead they mutate the
    // already-`@Published` projection directly and (for the agent loop) stream a short canned run,
    // so a reviewer can send messages, approve actions, start chats, and manage to-dos and see the
    // UI respond — the read-only fixtures (`seedDemo`/`seedDemoTranscript`/`demoDiff`) already
    // cover the passive surfaces.

    private func demoHandle(_ msg: ClientMsg) {
        switch msg {
        case .sendInput(let id, let input):
            demoRun(id, userText: input.plainText ?? "")
        case .startChat(let req):
            demoStartChat(req)
        case .approvalRespond(let id, let decision):
            demoResolveApproval(id, decision)
        case .captureTodo(let req):
            demoCaptureTodo(req)
        case .setTodoStatus(let id, let status):
            demoSetTodoStatus(id, status)
        case .deleteTodo(let id):
            demoMutateTodos { $0.filter { $0.id != id } }
        case .dispatchTodo(let id, _):
            demoSetTodoStatus(id, .dispatched)
        case .renameSession(let id, let title):
            demoUpdateSession(id) { $0.demoCopy(title: title) }
        case .setFavorite(let id, let favorite):
            demoUpdateSession(id) { $0.demoCopy(favorite: favorite) }
        case .setArchived(let id, let archived):
            demoUpdateSession(id) { $0.demoCopy(archived: archived) }
        case .deleteSession(let id):
            sessions.removeAll { $0.sessionID == id }
            NotificationRouter.shared.updateBadge(needsYouCount)
            LiveActivityManager.shared.sync(hostName: hostName, sessions: sessions)
        case .discard(let id):
            sessions.removeAll { $0.sessionID == id }
            NotificationRouter.shared.updateBadge(needsYouCount)
        case .interrupt(let id):
            demoUpdateSession(id) { $0.demoCopy(status: .interrupted, disposition: .some(nil)) }
        case .integrate(let id, _):
            demoAppend(id, .note(NoteEvent(text: "nvrsion: Landed to trunk.", icon: "arrow.triangle.branch")))
            demoUpdateSession(id) { $0.demoCopy(status: .finished, disposition: .some(.completed)) }
        case .setSessionModel(let id, let model):
            demoUpdateSession(id) { $0.demoCopy(model: .some(model)) }
        case .setSessionEffort(let id, let effort):
            demoUpdateSession(id) { $0.demoCopy(effort: .some(effort)) }
        case .setSessionAuto(let id, let auto):
            demoUpdateSession(id) { $0.demoCopy(auto: auto) }
        case .setSessionAutoShip(let id, let autoShip):
            demoUpdateSession(id) { $0.demoCopy(autoShip: autoShip) }
        case .setSessionShipBranch(let id, let branch):
            demoUpdateSession(id) { $0.demoCopy(shipBranch: .some(branch)) }
        case .hello, .listSessions, .listDashboard, .subscribe, .unsubscribe,
             .ping, .cancelQueuedMessage, .fetchDiff, .listPeers, .addressUpdate,
             // Session transfer (mesh P5) is a Mac↔Mac flow — the phone never originates these,
             // and demo has no peer Macs, so they're inert here.
             .transferOffer, .transferChunk, .transferCommit, .transferCancel:
            break  // passive / already handled by the seeded fixtures (demo has no mesh peers)
        }
    }

    /// Append a transcript event to the open session (no-op if it isn't the one on screen).
    private func demoAppend(_ sessionID: SessionID, _ kind: AgentEvent.Kind) {
        guard sessionID == openSessionID else { return }
        let seq = (openEvents.map(\.seq).max() ?? 0) + 1
        let backend = sessions.first { $0.sessionID == sessionID }?.backend ?? .claudeCode
        openEvents.append(AgentEvent(
            sessionID: sessionID, seq: seq, at: Date(), backend: backend, nativeType: nil, kind: kind))
    }

    /// Replace a session summary in the list, keeping the badge / Live Activity in sync.
    private func demoUpdateSession(_ id: SessionID, _ transform: (WireSessionSummary) -> WireSessionSummary) {
        guard let i = sessions.firstIndex(where: { $0.sessionID == id }) else { return }
        sessions[i] = transform(sessions[i])
        NotificationRouter.shared.updateBadge(needsYouCount)
        LiveActivityManager.shared.sync(hostName: hostName, sessions: sessions)
    }

    /// Stream a short, believable canned turn for a session: assistant prose, a tool call +
    /// result, usage, and a finish — flipping the summary running → awaiting-input. Each step
    /// re-checks demo mode and cancellation so `exitDemo()` stops it cleanly. Runs entirely on the
    /// main actor (the store is `@MainActor`, and a `Task` in an isolated method inherits it).
    private func demoRun(_ sessionID: SessionID, userText: String?) {
        if let userText, !userText.isEmpty {
            demoAppend(sessionID, .userText(TextChunk(messageID: UUID().uuidString, text: userText, isPartial: false)))
        }
        demoUpdateSession(sessionID) { $0.demoCopy(status: .running, disposition: .some(nil)) }
        let toolID = UUID().uuidString
        let task = Task { [weak self] in
            guard let self else { return }
            @MainActor func pause(_ ms: Int) async -> Bool {
                try? await Task.sleep(for: .milliseconds(ms))
                if Task.isCancelled { return false }
                return self.demoMode
            }
            guard await pause(600) else { return }
            self.demoAppend(sessionID, .assistantText(TextChunk(
                messageID: UUID().uuidString, text: "On it — let me take a look.", isPartial: false)))
            guard await pause(700) else { return }
            self.demoAppend(sessionID, .toolCallStarted(ToolCall(
                toolCallID: toolID, name: "Bash", input: ["command": "npm test"])))
            guard await pause(900) else { return }
            self.demoAppend(sessionID, .toolResult(ToolResult(
                toolCallID: toolID, content: "42 passing\n0 failing", isError: false)))
            guard await pause(700) else { return }
            self.demoAppend(sessionID, .assistantText(TextChunk(
                messageID: UUID().uuidString,
                text: "All green — tests pass and the change is in place. Anything else?",
                isPartial: false)))
            self.demoAppend(sessionID, .usage(Usage(
                inputTokens: 12_400, outputTokens: 640, costUSD: 0.0088, contextInputTokens: 12_400)))
            self.demoAppend(sessionID, .runFinished(RunFinished(outcome: .completed, finalText: "Done.")))
            self.demoUpdateSession(sessionID) {
                $0.demoCopy(status: .awaitingInput, disposition: .some(.completed))
            }
        }
        demoTasks.append(task)
    }

    private func demoStartChat(_ req: StartChatRequest) {
        let project = dashboard.projects.first { $0.id == req.projectID }
        let id = SessionID(rawValue: "demo-\(UUID().uuidString.prefix(8))")
        let title = String(req.message.prefix(48))
        let summary = WireSessionSummary(
            sessionID: id, projectID: req.projectID.rawValue,
            projectName: project?.name ?? "project", backend: BackendID.forModel(req.model) ?? .claudeCode,
            status: .running, disposition: nil, title: title.isEmpty ? "New chat" : title,
            branch: "nucleic/\(id.rawValue)", lastSeq: 0, diffStat: nil,
            pendingApprovalCount: 0, favorite: false, archived: false,
            model: req.model, effort: req.effort, auto: req.auto ?? false,
            updatedAt: Date())
        sessions.insert(summary, at: 0)
        LiveActivityManager.shared.sync(hostName: hostName, sessions: sessions)
        demoRun(id, userText: req.message)
    }

    private func demoResolveApproval(_ id: ApprovalID, _ decision: Decision) {
        openApprovals.removeAll { $0.id == id }
        NotificationRouter.shared.withdrawApproval(id)
        guard let sessionID = openSessionID else { return }
        switch decision {
        case .deny, .cancelRun:
            demoAppend(sessionID, .note(NoteEvent(text: "You denied the command.", icon: "hand.raised")))
            demoUpdateSession(sessionID) {
                $0.demoCopy(status: .awaitingInput, disposition: .some(.awaitingInput), pendingApprovalCount: 0)
            }
        case .allow, .allowAlways:
            demoAppend(sessionID, .toolResult(ToolResult(
                toolCallID: "t-appr", content: "Deployed successfully.", isError: false)))
            demoUpdateSession(sessionID) { $0.demoCopy(pendingApprovalCount: 0) }
            demoRun(sessionID, userText: nil)  // wrap up the turn after the approved tool runs
        }
    }

    private func demoCaptureTodo(_ req: CaptureTodoRequest) {
        let project = req.projectID.flatMap { pid in dashboard.projects.first { $0.id == pid } }
        let todo = WireTodo(
            id: .generate(), text: req.text, summary: nil, projectID: req.projectID,
            projectName: project?.name, status: .open, dispatchedSessionID: nil,
            triage: nil, updatedAt: Date())
        demoMutateTodos { [todo] + $0 }
    }

    private func demoSetTodoStatus(_ id: TodoID, _ status: TodoStatus) {
        demoMutateTodos { todos in
            todos.map { todo in
                todo.id == id
                    ? WireTodo(id: todo.id, text: todo.text, summary: todo.summary,
                               projectID: todo.projectID, projectName: todo.projectName,
                               status: status, dispatchedSessionID: todo.dispatchedSessionID,
                               triage: todo.triage, updatedAt: Date())
                    : todo
            }
        }
    }

    /// Rebuild the dashboard with a transformed to-do list (its fields are `let`).
    private func demoMutateTodos(_ transform: ([WireTodo]) -> [WireTodo]) {
        dashboard = DashboardSnapshot(
            counts: dashboard.counts, activity: dashboard.activity, projects: dashboard.projects,
            todos: transform(dashboard.todos), usage: dashboard.usage, statusFeeds: dashboard.statusFeeds)
    }

    private func makeChannel(_ endpoint: NWEndpoint) -> NWFrameChannel {
        let channel = NWFrameChannel(endpoint: endpoint)
        // Surface a transport-level failure with an actionable message. Without this, a refused
        // connection or a denied local-network permission finished the frame stream and only
        // showed up as a generic "handshake closed" — hiding the real (usually fixable) cause.
        channel.onFailed = { [weak self] error in
            Task { @MainActor in self?.handleTransportFailure(error) }
        }
        return channel
    }

    /// Map an `NWConnection` failure to a connectivity state the pairing/onboarding UI can act on.
    /// Only meaningful while we're still establishing the link; once connected, a drop is the
    /// normal `.closed` → reconnect path's job. And only when the connect chain has nothing
    /// left to try — a failed LAN probe about to fall back to the tailnet is routine, not news.
    private func handleTransportFailure(_ error: String) {
        guard !connectivity.isLive else { return }
        guard connectPlan?.remaining.isEmpty != false else { return }
        connectivity = .failed(Self.friendlyTransportError(error))
    }

    /// Turn a raw `NWError` string into a short, fixable hint. The common onboarding failures are
    /// a denied Local Network permission (EPERM / -65555) and the Mac not listening (refused).
    private static func friendlyTransportError(_ error: String) -> String {
        let lower = error.lowercased()
        if lower.contains("denied") || lower.contains("not permitted") || lower.contains("65555") {
            return "Can't reach the local network. In Settings ▸ Nucleic, allow Local Network access, then try again."
        }
        if lower.contains("refused") {
            return "Your Mac refused the connection. Check that remote access is still on in Nucleic ▸ Settings."
        }
        return "Couldn't connect to your Mac — make sure it's on the same Wi‑Fi and remote access is on."
    }

    private func resolveEndpoint(fingerprint: String?, lanHost: String?, lanPort: UInt16?) -> NWEndpoint? {
        discovery.endpoint(forFingerprint: fingerprint, lanHost: lanHost, lanPort: lanPort)
    }

    private func consume(_ client: SyncClient, pairingPayload: PairingPayload?) {
        eventTask = Task { [weak self] in
            let stream = await client.start()
            for await event in stream {
                // A replaced client's tail events (`.failed` is always chased by `.closed`)
                // must not leak into the new attempt — they'd advance the candidate chain
                // or schedule retries against a connection that no longer exists.
                guard let self, self.client === client else { break }
                await self.handle(event, pairingPayload: pairingPayload)
            }
        }
    }

    private func handle(_ event: SyncClient.Event, pairingPayload: PairingPayload?) async {
        switch event {
        case .connecting:
            break
        case .ready(let welcome):
            reconnectAttempts = 0
            connectPlan = nil  // the chain found its transport
            connectivity = .connected(activeTransport)
            hostName = welcome.host.hostName
            capabilities = welcome.capabilities
            grantedScope = welcome.grantedScope
            modelCatalog = welcome.modelCatalog
            if let payload = pairingPayload, let hostKey = await client?.hostKey() {
                IdentityStore.savePairedHost(PairedHost(
                    deviceID: IdentityStore.deviceID(), hostName: welcome.host.hostName,
                    hostStaticKey: hostKey, fingerprint: hostKey.fingerprintHex,
                    lanHost: payload.lanHost, lanPort: payload.lanPort,
                    transport: payload.transport, tailnetHost: payload.tailnetHost,
                    tailnetPort: payload.tailnetPort))
            }
            send(.listSessions)
            send(.listDashboard)
            if let id = openSessionID { send(.subscribe(Subscribe(sessionID: id, sinceSeq: nil, verbosity: .full))) }
            flushPendingNotificationDecision()
        case .sessionList(let list):
            sessions = list
            NotificationRouter.shared.updateBadge(needsYouCount)
            LiveActivityManager.shared.sync(hostName: hostName, sessions: sessions)
        case .sessionUpdated(let summary):
            let previous: WireSessionSummary?
            if let i = sessions.firstIndex(where: { $0.sessionID == summary.sessionID }) {
                previous = sessions[i]
                sessions[i] = summary
            } else {
                previous = nil
                sessions.append(summary)
            }
            // Notify on the transition into "waiting on you" / "finished" — only when the
            // app isn't foreground-active (in-app, the list's washes and badges carry it).
            let becameWaiting = summary.status == .awaitingInput
                && previous?.status != .awaitingInput
            if becameWaiting, !isActive, !summary.archived {
                NotificationRouter.shared.postSessionUpdate(summary)
            }
            NotificationRouter.shared.updateBadge(needsYouCount)
            LiveActivityManager.shared.sync(hostName: hostName, sessions: sessions)
        case .dashboard(let snapshot):
            dashboard = snapshot
        case .snapshot(let snapshot):
            guard snapshot.summary.sessionID == openSessionID else { break }
            seenSeq = Set(snapshot.recentEvents.map(\.seq))
            openEvents = snapshot.recentEvents
            openApprovals = snapshot.pendingApprovals
        case .events(let batch):
            guard batch.sessionID == openSessionID else { break }
            for e in batch.events where !seenSeq.contains(e.seq) {
                seenSeq.insert(e.seq)
                openEvents.append(e)
            }
        case .approvalRequested(let req):
            if req.sessionID == openSessionID, !openApprovals.contains(where: { $0.id == req.id }) {
                openApprovals.append(req)
            }
            // Always post; the router suppresses the banner when the user is already
            // looking at this session, and resolution (any device) withdraws it.
            let title = sessions.first { $0.sessionID == req.sessionID }?.title ?? "Approval"
            NotificationRouter.shared.postApproval(req, sessionTitle: title)
        case .approvalResolved(let resolved):
            openApprovals.removeAll { $0.id == resolved.id }
            NotificationRouter.shared.withdrawApproval(resolved.id)
        case .sessionDiff(let diff):
            guard diff.sessionID == openSessionID else { break }
            openDiff = diff
            diffLoading = false
        case .peerList(let peers):
            // Mesh P4: the host's known peers, for the (future) mesh device list and transfer
            // picker. Recorded now so multi-host UI can render it; single-host builds ignore it.
            meshPeers = peers
        case .transferAccept, .transferReject, .transferReady, .transferCommitted, .transferChunkAck:
            // Session-transfer replies (mesh P5) only reach a *source* Mac driving a transfer; a
            // phone is never a transfer source, so these are inert here.
            break
        case .wireError(let error):
            // A channel mismatch means the host and this remote were built from incompatible
            // release channels. Surface it as a persistent failure with a clear message rather
            // than a transient bubble; the follow-on `.closed` still schedules a backoff retry,
            // so the connection recovers on its own once either side is updated to a matching
            // channel.
            if error.code == .channelMismatch {
                connectivity = .failed(error.message)
                break
            }
            // Not fatal — surface as a transient bubble (the Mac's last-error overlay).
            // Losing an approval race isn't an error worth interrupting for; the card
            // collapses on the matching `approvalResolved`.
            guard error.code != .alreadyResolved else { break }
            // While the connect chain is still resolving a transport, a pre-ready error
            // (e.g. "handshake closed" from a LAN probe about to fall back to tailnet) is
            // routine, not news — the follow-on `.closed` advances the chain silently.
            guard connectPlan == nil else { break }
            showError(error.message, sessionID: error.sessionID)
        case .failed(let message):
            // Another candidate may still carry the session (e.g. LAN died → tailnet).
            if tryNextCandidate() { break }
            connectPlan = nil
            // The channel's onFailed may have just surfaced a friendlier transport-level
            // cause (denied Local Network, connection refused) — don't clobber it.
            if case .failed = connectivity {} else { connectivity = .failed(message) }
            scheduleRetry()
        case .closed:
            if !connectivity.isLive, tryNextCandidate() { break }
            if connectivity.isLive {
                connectivity = .reconnecting
            } else if connectPlan?.pairingPayload != nil {
                // A pairing chain died silently (every candidate closed pre-welcome).
                // There's no retry loop before a pairing succeeds, so without a terminal
                // state this would sit on "Connecting…" forever. Keep a friendlier
                // transport-level failure if one was already surfaced.
                if case .failed = connectivity {} else {
                    connectivity = .failed("Couldn't connect to your Mac — check that it's reachable, then scan again.")
                }
            }
            connectPlan = nil
            scheduleRetry()
        }
    }

    /// Show a transient error bubble, replacing any current one; auto-dismisses after 6s
    /// (matching the Mac's last-error overlay cadence).
    private func showError(_ message: String, sessionID: SessionID?) {
        let error = LastError(message: message, sessionID: sessionID)
        lastError = error
        errorDismissTask?.cancel()
        errorDismissTask = Task { [weak self] in
            try? await Task.sleep(for: .seconds(6))
            guard let self, self.lastError == error else { return }
            self.lastError = nil
        }
    }

    func dismissError() {
        errorDismissTask?.cancel()
        lastError = nil
    }

    private func scheduleRetry() {
        guard isPaired else { return }
        reconnectAttempts += 1
        let delay = min(Double(reconnectAttempts) * 1.5, 10)
        retryTask?.cancel()
        retryTask = Task { [weak self] in
            // `try?` swallows the sleep's CancellationError, so check explicitly.
            try? await Task.sleep(for: .seconds(delay))
            guard !Task.isCancelled, let self, !self.connectivity.isLive else { return }
            self.reconnect()
        }
    }

    private func teardown() {
        retryTask?.cancel()
        retryTask = nil
        connectTask?.cancel()
        connectTask = nil
        connectPlan = nil
        teardownClient()
    }

    /// Drop just the current client/channel — what moving to the next transport candidate
    /// needs, without discarding the rest of the plan.
    private func teardownClient() {
        lanConnectTimeout?.cancel()
        lanConnectTimeout = nil
        eventTask?.cancel()
        eventTask = nil
        if let client { Task { await client.disconnect() } }
        client = nil
    }
}

extension Data {
    /// Same fingerprint scheme as `DeviceIdentity.fingerprint` (first 8 bytes of SHA-256).
    var fingerprintHex: String {
        DeviceIdentity.fingerprint(ofStaticKey: self)
    }
}

extension WireSessionSummary {
    /// A copy with selected fields overridden — the demo simulator's only way to "mutate" a
    /// summary, whose stored properties are all `let`. Nullable fields use a double optional so a
    /// caller can distinguish "keep" (omit) from "set to nil" (`.some(nil)`). `updatedAt` bumps
    /// to now unless given. Only the fields the simulator touches are exposed.
    func demoCopy(
        status: SessionStatus? = nil,
        disposition: TurnDisposition?? = nil,
        title: String? = nil,
        favorite: Bool? = nil,
        archived: Bool? = nil,
        pendingApprovalCount: Int? = nil,
        diffStat: DiffStat?? = nil,
        model: String?? = nil,
        effort: String?? = nil,
        auto: Bool? = nil,
        autoShip: Bool? = nil,
        shipBranch: String?? = nil,
        updatedAt: Date? = nil
    ) -> WireSessionSummary {
        WireSessionSummary(
            sessionID: sessionID, projectID: projectID, projectName: projectName, backend: backend,
            status: status ?? self.status,
            disposition: disposition ?? self.disposition,
            title: title ?? self.title, branch: branch, lastSeq: lastSeq,
            diffStat: diffStat ?? self.diffStat,
            pendingApprovalCount: pendingApprovalCount ?? self.pendingApprovalCount,
            favorite: favorite ?? self.favorite,
            archived: archived ?? self.archived,
            queuedMessage: queuedMessage, queuedMessages: queuedMessages,
            model: model ?? self.model, effort: effort ?? self.effort,
            auto: auto ?? self.auto, autoShip: autoShip ?? self.autoShip,
            shipBranch: shipBranch ?? self.shipBranch,
            contextInputTokens: contextInputTokens,
            updatedAt: updatedAt ?? Date(),
            movedTo: movedTo, arrivedFrom: arrivedFrom)
    }
}