feat(apple): explicit input-capture state machine — no more cursor grabs on window chrome

Capture used to engage whenever the app became active, so the click that activates the
window — on the title bar (a drag) or a resize edge — got the cursor warped away
mid-gesture, and raw deltas kept streaming to the host while the user fought the window.
Reworked Moonlight-style, with capture as a deliberate, reversible state owned by
StreamLayerView:

- Engage: automatically once when the stream starts / trust is confirmed (one-shot, can
  never fire surprisingly later), or by clicking into the video (that click's
  press/release are suppressed toward the host; acceptsFirstMouse makes it one click
  from another app). NEVER on app re-activation.
- Release: ⌘⎋ (toggles, key-window-scoped), focus loss — now including same-app window
  switches (⌘, / ⌘N / ⌘M resign key without resigning the app; previously the new
  window inherited a hidden frozen cursor and its typing was double-delivered to the
  host) — and disconnect.
- While released: nothing is forwarded (InputCapture.forwarding gates the GC handlers;
  held keys/buttons are flushed host-side so nothing sticks), the cursor is free, and
  the HUD (now showing the capture state) is clickable.
- The no-beep behavior moved from the NSEvent monitor to first-responder key
  consumption — swallowing at the monitor risked starving GC's own delivery (the
  "input broken altogether" report). The monitor now only intercepts ⌘⎋.
- Adversarial-review fixes: a second session preempts the previous one cleanly instead
  of leaving it captured with dead GC handlers (onPreempted); the engage click's
  suppression latch can't outlive the click (mouseUp backstop); ⌘⎋'s physical Esc can't
  type into the host in either toggle direction (suppressedVK latch + Esc-while-⌘
  guard); capture callbacks defer out of the SwiftUI update pass.

Validated live against the box: 16185 input datagrams injected during a captured
session (gamescope EIS), title-bar drag/resize free while released, and visible
cursor + typing on a streamed KWin desktop, all user-confirmed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/ContentView.swift

@@ -58,7 +58,7 @@ struct ContentView: View {
             return nil
         }()
         return ZStack {
-            stream(capturesCursor: pendingFingerprint == nil)
+            stream(captureEnabled: pendingFingerprint == nil)
                 .blur(radius: pendingFingerprint != nil ? 32 : 0)
                 .overlay {
                     if pendingFingerprint != nil {
@@ -257,19 +257,22 @@ struct ContentView: View {
 
     // MARK: - Stream
 
-    private func stream(capturesCursor: Bool) -> some View {
+    private func stream(captureEnabled: Bool) -> some View {
         Group {
             if let conn = model.connection {
                 StreamView(
                     connection: conn,
-                    capturesCursor: capturesCursor,
+                    captureEnabled: captureEnabled,
+                    onCaptureChange: { [weak model] captured in
+                        model?.mouseCaptured = captured
+                    },
                     onFrame: { [meter = model.meter] au in meter.note(byteCount: au.data.count) },
                     onSessionEnd: { [weak model] in
                         Task { @MainActor in model?.sessionEnded() }
                     }
                 )
                 .overlay(alignment: .topTrailing) {
-                    if capturesCursor { hud(conn) }
+                    if captureEnabled { hud(conn) }
                 }
             }
         }
@@ -279,8 +282,13 @@ struct ContentView: View {
         VStack(alignment: .trailing, spacing: 4) {
             Text("\(conn.width)×\(conn.height)@\(conn.refreshHz)  \(model.fps) fps  \(model.mbps, specifier: "%.1f") Mb/s")
                 .font(.system(.caption, design: .monospaced))
-            // ⌘D because the local cursor is hidden+frozen while streaming — the button
-            // can't be clicked. (Cmd+Tab away also frees the cursor.)
+            // While captured the cursor is hidden+frozen, so the button is keyboard-only
+            // (⌘⎋ or Cmd+Tab release the cursor; released, it's clickable again).
+            Text(model.mouseCaptured
+                ? "⌘⎋ releases the mouse"
+                : "Click the stream to capture input")
+                .font(.caption2)
+                .opacity(0.8)
             Button("Disconnect (⌘D)") { model.disconnect() }
                 .font(.caption)
                 .keyboardShortcut("d", modifiers: .command)

clients/apple/Sources/PunktfunkClient/SessionModel.swift

@@ -53,9 +53,11 @@ final class SessionModel: ObservableObject {
     @Published var fps = 0
     @Published var mbps = 0.0
     @Published var totalFrames = 0
+    /// Mirrors StreamView's capture state (it owns the input capture; this drives the
+    /// HUD's "click to capture" / "⌘⎋ releases" hint).
+    @Published var mouseCaptured = false
 
     let meter = FrameMeter()
-    private var inputCapture: InputCapture?
     private var statsTimer: Timer?
 
     var isBusy: Bool { phase != .idle }
@@ -118,8 +120,6 @@ final class SessionModel: ObservableObject {
     }
 
     func disconnect() {
-        inputCapture?.stop()
-        inputCapture = nil
         statsTimer?.invalidate()
         statsTimer = nil
         if let conn = connection {
@@ -132,6 +132,7 @@ final class SessionModel: ObservableObject {
         phase = .idle
         fps = 0
         mbps = 0
+        mouseCaptured = false
     }
 
     /// Called (via the main actor) when the pump hits end-of-session.
@@ -143,11 +144,10 @@ final class SessionModel: ObservableObject {
     }
 
     private func beginStreaming() {
-        guard let conn = connection else { return }
+        guard connection != nil else { return }
+        // Input capture itself is owned by StreamView (engaged by the captureEnabled
+        // flip this phase change causes, released/re-engaged by the user from there).
         phase = .streaming
-        let capture = InputCapture(connection: conn)
-        capture.start()
-        inputCapture = capture
     }
 
     private func startStatsTimer() {

clients/apple/Sources/PunktfunkKit/InputCapture.swift

@@ -14,6 +14,11 @@
 // didResignActive and on stop(). All GC handlers and notifications fire on the main
 // queue (the framework default), so the mutable state here needs no locking.
 //
+// Forwarding is gated by `forwarding` (driven by StreamLayerView's capture state): the
+// handlers stay attached for the whole session, but while the user has released capture
+// (⌘⎋, focus loss) nothing reaches the host and key events travel the responder chain
+// normally. Everything held is flushed host-side on each transition to released.
+//
 // GCMouse.current/GCKeyboard.coalesced are process-global singletons with one handler
 // slot each: only one InputCapture can be live per process. `activeCapture` tracks
 // ownership so a stale capture's stop() can't clobber a newer one's handlers.
@@ -40,14 +45,66 @@ public final class InputCapture {
     private var residualScrollY: Float = 0
     private var pressedVKs: Set<UInt32> = []
     private var pressedButtons: Set<UInt32> = []
+    /// One-shot: the left click that engaged capture belongs to the local UI — GC sees
+    /// it at the HID layer regardless, so its press AND release are dropped here.
+    private var suppressedButton: UInt32?
+
+    /// One-shot twin of `suppressedButton` for the ⌘⎋ toggle: the physical Esc also
+    /// reaches GCKeyboard, racing the NSEvent monitor — latched here so it can't type
+    /// an Escape into the host in either toggle direction.
+    private var suppressedVK: UInt32?
+
+    /// While true, mouse/keyboard flow to the host and key NSEvents are swallowed
+    /// locally; while false the user is interacting with the local UI (dragging the
+    /// window, clicking the HUD) and nothing is forwarded. Main-queue only.
+    public private(set) var forwarding = false
+
+    /// Fired on ⌘⎋ (the capture toggle — detected here so it works in both states; the
+    /// event itself is swallowed). Main queue.
+    public var onToggleCapture: (() -> Void)?
+
+    /// Fired when a newer InputCapture takes the process-global GC handler slots (the
+    /// singletons hold ONE handler each): the preempted owner must drop its capture
+    /// state — its handlers are gone, so it would otherwise sit "captured" with dead
+    /// input. Main queue.
+    public var onPreempted: (() -> Void)?
 
     public init(connection: PunktfunkConnection) {
         self.connection = connection
     }
 
+    /// Gate the forwarding without detaching the GC handlers. `suppressClick` marks the
+    /// transition as click-driven: that click's press/release are not forwarded. Every
+    /// transition to false flushes held keys/buttons host-side.
+    public func setForwarding(_ on: Bool, suppressClick: Bool = false) {
+        if on {
+            forwarding = true
+            suppressedButton = suppressClick ? 1 : nil
+        } else if forwarding {
+            releaseAll()
+            forwarding = false
+            suppressedButton = nil
+        }
+    }
+
+    /// The engage click is over (its NSEvent mouseUp processed) — stop suppressing.
+    /// Backstop for the GC-vs-NSEvent ordering where both halves of the click landed
+    /// before mouseDown armed the latch, which would otherwise eat the next real click.
+    public func endClickSuppression() {
+        suppressedButton = nil
+    }
+
     /// Begin forwarding the current (and future) mouse/keyboard to the host. Steals the
-    /// global GC handler slots from any previous capture (one live capture per process).
+    /// global GC handler slots from any previous capture (one live capture per process),
+    /// notifying it via `onPreempted` so its owner releases its capture state.
     public func start() {
+        if let previous = Self.activeCapture, previous !== self {
+            // Drop the previous owner's device lists first: its stop() must not be able
+            // to nil out the handler slots this capture is about to claim.
+            previous.mice.removeAll()
+            previous.keyboards.removeAll()
+            previous.onPreempted?()
+        }
         Self.activeCapture = self
         if let mouse = GCMouse.current { attach(mouse: mouse) }
         if let keyboard = GCKeyboard.coalesced { attach(keyboard: keyboard) }
@@ -67,15 +124,21 @@ public final class InputCapture {
         ) { [weak self] _ in
             self?.releaseAll()
         })
-        // GC reads the HID state directly — the NSEvents still travel the responder
-        // chain, where every unhandled keyDown makes NSWindow beep ("invalid input").
-        // Swallow key events while captured, EXCEPT ⌘-combos: those stay local (the
-        // HUD's ⌘D disconnect, ⌘Q, …) in addition to reaching the host via GC.
+        // ⌘⎋ — the capture toggle — is detected here so it works in both states. ONLY
+        // that one combo is intercepted: swallowing keys wholesale at the monitor level
+        // risks starving GC's own delivery, so the no-beep behavior lives in
+        // StreamLayerView (first responder consumes keyDown/keyUp while captured).
         keyEventMonitor = NSEvent.addLocalMonitorForEvents(
-            matching: [.keyDown, .keyUp]
-        ) { event in
-            event.modifierFlags.intersection(.deviceIndependentFlagsMask).contains(.command)
-                ? event : nil
+            matching: [.keyDown]
+        ) { [weak self] event in
+            guard let self else { return event }
+            let flags = event.modifierFlags.intersection(.deviceIndependentFlagsMask)
+            if event.keyCode == 53 /* Esc */, flags == .command {
+                self.suppressedVK = 0x1B // the same physical Esc is en route via GC
+                self.onToggleCapture?()
+                return nil
+            }
+            return event
         }
     }
 
@@ -126,6 +189,11 @@ public final class InputCapture {
     }
 
     private func sendButton(_ button: UInt32, pressed: Bool) {
+        guard forwarding else { return }
+        if button == suppressedButton {
+            if !pressed { suppressedButton = nil } // capture click over — stop suppressing
+            return
+        }
         if pressed {
             pressedButtons.insert(button)
         } else {
@@ -140,7 +208,7 @@ public final class InputCapture {
         else { return }
         mice.append(mouse)
         input.mouseMovedHandler = { [weak self] _, dx, dy in
-            guard let self else { return }
+            guard let self, self.forwarding else { return }
             // GC gives +y up; the host expects screen-space (+y down).
             let fx = dx + self.residualX
             let fy = -dy + self.residualY
@@ -170,7 +238,7 @@ public final class InputCapture {
             }
         }
         input.scroll.valueChangedHandler = { [weak self] _, x, y in
-            guard let self else { return }
+            guard let self, self.forwarding else { return }
             // WHEEL_DELTA(120) per notch; positive = up / right (Moonlight's convention).
             let fy = y * 120 + self.residualScrollY
             let fx = x * 120 + self.residualScrollX
@@ -188,6 +256,18 @@ public final class InputCapture {
         keyboards.append(keyboard)
         keyboard.keyboardInput?.keyChangedHandler = { [weak self] _, _, keyCode, pressed in
             guard let self, let vk = Self.hidToVK[keyCode.rawValue] else { return }
+            // The ⌘⎋ toggle's Esc — checked before the forwarding gate, because in the
+            // engage direction forwarding is already true when this fires.
+            if vk == self.suppressedVK {
+                if !pressed { self.suppressedVK = nil }
+                return
+            }
+            guard self.forwarding else { return }
+            // Release direction of the toggle: GC's Esc-down can beat the NSEvent
+            // monitor — never type Esc into the host while ⌘ is held (⌘⎋ is reserved).
+            if vk == 0x1B, self.pressedVKs.contains(0x5B) || self.pressedVKs.contains(0x5C) {
+                return
+            }
             if pressed {
                 self.pressedVKs.insert(vk)
             } else {

clients/apple/Sources/PunktfunkKit/StreamView.swift

@@ -5,6 +5,13 @@
 // zero-copy on Apple silicon. Stage 2 (explicit VTDecompressionSession + CAMetalLayer)
 // replaces this when we start tuning frame pacing / measuring glass-to-glass.
 //
+// The view also owns the input-capture state machine (Moonlight-style): capture is a
+// deliberate, reversible state — engaged when the stream starts and when the user clicks
+// into the video, released by ⌘⎋ or focus loss, and NEVER engaged by mere app
+// activation (the click that activates the window may be a title-bar drag or a resize —
+// warping the cursor there is exactly the intrusiveness this design removes). While
+// released, nothing is forwarded to the host and the local cursor is free.
+//
 // macOS-first (NSViewRepresentable); the iOS variant is the same layer under
 // UIViewRepresentable.
 
@@ -13,10 +20,10 @@ import AppKit
 import AVFoundation
 import SwiftUI
 
-/// Hides the LOCAL cursor while streaming. The host renders its own cursor, and the local
+/// Hides the LOCAL cursor while captured. The host renders its own cursor, and the local
 /// one both diverges from it (the host applies acceleration/clamping to our raw deltas)
-/// and can wander out of the window — a click there would focus another app. So while the
-/// stream has focus we do what Moonlight does: warp the cursor into the view, freeze it
+/// and can wander out of the window — a click there would focus another app. So while
+/// captured we do what Moonlight does: warp the cursor into the view, freeze it
 /// (`CGAssociateMouseAndMouseCursorPosition(false)` — GCMouse still delivers raw HID
 /// deltas), and hide it. hide/unhide and associate are balanced via `captured`.
 private final class CursorCapture {
@@ -44,34 +51,41 @@ private final class CursorCapture {
 
 public struct StreamView: NSViewRepresentable {
     private let connection: PunktfunkConnection
-    private let capturesCursor: Bool
+    private let captureEnabled: Bool
+    private let onCaptureChange: ((Bool) -> Void)?
     private let onFrame: (@Sendable (AccessUnit) -> Void)?
     private let onSessionEnd: (@Sendable () -> Void)?
 
     /// `onFrame`/`onSessionEnd` fire on the pump thread — hop to the main actor for UI.
-    /// `capturesCursor: false` keeps the local cursor usable while UI (e.g. a trust
-    /// prompt) is layered over the stream; flip it to true to enter capture.
+    /// `captureEnabled: false` disables input capture entirely while UI (e.g. a trust
+    /// prompt) is layered over the stream; flipping it to true auto-engages capture
+    /// once. `onCaptureChange` (main thread) reports engage/release — drive the HUD's
+    /// "click to capture" / "⌘⎋ releases" hint with it.
     public init(
         connection: PunktfunkConnection,
-        capturesCursor: Bool = true,
+        captureEnabled: Bool = true,
+        onCaptureChange: ((Bool) -> Void)? = nil,
         onFrame: (@Sendable (AccessUnit) -> Void)? = nil,
         onSessionEnd: (@Sendable () -> Void)? = nil
     ) {
         self.connection = connection
-        self.capturesCursor = capturesCursor
+        self.captureEnabled = captureEnabled
+        self.onCaptureChange = onCaptureChange
         self.onFrame = onFrame
         self.onSessionEnd = onSessionEnd
     }
 
     public func makeNSView(context: Context) -> StreamLayerView {
         let view = StreamLayerView()
-        view.capturesCursor = capturesCursor
+        view.onCaptureChange = onCaptureChange
+        view.captureEnabled = captureEnabled
         view.start(connection: connection, onFrame: onFrame, onSessionEnd: onSessionEnd)
         return view
     }
 
     public func updateNSView(_ view: StreamLayerView, context: Context) {
-        view.capturesCursor = capturesCursor
+        view.onCaptureChange = onCaptureChange
+        view.captureEnabled = captureEnabled
         // SwiftUI reuses the NSView across state changes — repoint the pump only when the
         // connection identity actually changed.
         if view.connection !== connection {
@@ -106,16 +120,30 @@ public final class StreamLayerView: NSView {
     private var token: PumpToken?
     public private(set) var connection: PunktfunkConnection?
     private let cursorCapture = CursorCapture()
+    private var inputCapture: InputCapture?
     private var appObservers: [NSObjectProtocol] = []
+    private var windowObservers: [NSObjectProtocol] = []
 
-    /// Main-thread only. False = leave the local cursor alone (UI layered over the
-    /// stream); switching back to true re-enters capture immediately.
-    public var capturesCursor = true {
+    /// Whether input capture is currently engaged (cursor hidden+frozen, mouse/keyboard
+    /// forwarded). Main-thread only.
+    public private(set) var captured = false
+    /// One-shot auto-engage request (stream start, trust confirmed) — attempted as soon
+    /// as the view is in a window with real bounds, then dropped, so it can never fire
+    /// surprisingly later (e.g. on a resize).
+    private var pendingAutoCapture = false
+
+    /// Reports engage/release on the main thread.
+    public var onCaptureChange: ((Bool) -> Void)?
+
+    /// Main-thread only. False = input capture disabled outright (UI layered over the
+    /// stream); flipping to true auto-engages once.
+    public var captureEnabled = true {
         didSet {
-            if capturesCursor {
-                captureCursorIfStreaming()
+            guard captureEnabled != oldValue else { return }
+            if captureEnabled {
+                requestAutoCapture()
             } else {
-                cursorCapture.release()
+                releaseCapture()
             }
         }
     }
@@ -125,17 +153,13 @@ public final class StreamLayerView: NSView {
         displayLayer.videoGravity = .resizeAspect
         layer = displayLayer // layer-hosting: assign before wantsLayer
         wantsLayer = true
-        // The cursor comes back whenever the app loses focus (Cmd+Tab is the escape
-        // hatch) and is re-captured when the stream regains it.
+        // Focus loss releases capture. Becoming active does NOT re-engage: the click
+        // that activates the window may be on the title bar (a drag) or a resize edge —
+        // the user clicks into the video (or hits ⌘⎋) when they want capture back.
         appObservers.append(NotificationCenter.default.addObserver(
             forName: NSApplication.didResignActiveNotification, object: nil, queue: .main
         ) { [weak self] _ in
-            self?.cursorCapture.release()
-        })
-        appObservers.append(NotificationCenter.default.addObserver(
-            forName: NSApplication.didBecomeActiveNotification, object: nil, queue: .main
-        ) { [weak self] _ in
-            self?.captureCursorIfStreaming()
+            self?.releaseCapture()
         })
     }
 
@@ -143,18 +167,111 @@ public final class StreamLayerView: NSView {
 
     public override func viewDidMoveToWindow() {
         super.viewDidMoveToWindow()
-        if window == nil {
-            cursorCapture.release()
-        } else {
-            captureCursorIfStreaming()
+        windowObservers.forEach(NotificationCenter.default.removeObserver(_:))
+        windowObservers.removeAll()
+        guard let window else {
+            releaseCapture()
+            return
         }
+        // ⌘-key-equivalents stay live while captured, so Settings (⌘,), a new window
+        // (⌘N), or Minimize (⌘M) can take key status without the APP resigning active —
+        // capture must release then too, or the new window inherits a hidden, frozen
+        // cursor and its local typing is double-delivered to the host.
+        for name in [NSWindow.didResignKeyNotification, NSWindow.didMiniaturizeNotification] {
+            windowObservers.append(NotificationCenter.default.addObserver(
+                forName: name, object: window, queue: .main
+            ) { [weak self] _ in
+                self?.releaseCapture()
+            })
+        }
+        attemptPendingCapture()
     }
 
-    private func captureCursorIfStreaming() {
-        guard capturesCursor, token != nil, NSApp.isActive else { return }
-        cursorCapture.capture(in: self)
+    public override func layout() {
+        super.layout()
+        attemptPendingCapture() // bounds become real here on first presentation
     }
 
+    // MARK: - Capture state machine
+
+    /// Clicking into the video engages capture; that click is local (engagement), so
+    /// InputCapture suppresses its press/release toward the host. Clicks while captured
+    /// are the host's (GC forwards them) — nothing to do here.
+    public override func mouseDown(with event: NSEvent) {
+        if captureEnabled, !captured {
+            engageCapture(fromClick: true)
+            return
+        }
+        super.mouseDown(with: event)
+    }
+
+    /// A click from another app counts (one click into the video captures, not two).
+    public override func acceptsFirstMouse(for event: NSEvent?) -> Bool { true }
+
+    /// The engage click is complete — drop its suppression latch (see InputCapture;
+    /// guards against GC delivering both halves of the click before our mouseDown).
+    public override func mouseUp(with event: NSEvent) {
+        inputCapture?.endClickSuppression()
+        super.mouseUp(with: event)
+    }
+
+    // While captured, the view is first responder and consumes key events — GC delivers
+    // them to the host independently, and consuming here stops the responder chain's
+    // "unhandled keyDown" beep without touching the event stream GC may rely on.
+    // ⌘-combos arrive via performKeyEquivalent instead and stay fully functional (⌘D).
+    public override var acceptsFirstResponder: Bool { true }
+    public override func keyDown(with event: NSEvent) {
+        if captured { return }
+        super.keyDown(with: event)
+    }
+    public override func keyUp(with event: NSEvent) {
+        if captured { return }
+        super.keyUp(with: event)
+    }
+
+    private func requestAutoCapture() {
+        pendingAutoCapture = true
+        attemptPendingCapture()
+    }
+
+    private func attemptPendingCapture() {
+        guard pendingAutoCapture, window != nil, bounds.width > 0 else { return }
+        pendingAutoCapture = false // one shot, even if the engage below is refused
+        engageCapture(fromClick: false)
+    }
+
+    private func engageCapture(fromClick: Bool) {
+        // A click is explicit intent AND may arrive mid-activation (acceptsFirstMouse:
+        // NSApp.isActive / isKeyWindow are still false for the click coming in from
+        // another app) — only the auto-engage paths require already-held key status.
+        guard captureEnabled, !captured, token != nil, window != nil,
+              fromClick || (NSApp.isActive && window?.isKeyWindow == true)
+        else { return }
+        cursorCapture.capture(in: self)
+        inputCapture?.setForwarding(true, suppressClick: fromClick)
+        captured = true
+        window?.makeFirstResponder(self)
+        notifyCaptureChange(true)
+    }
+
+    private func releaseCapture() {
+        guard captured else { return }
+        cursorCapture.release()
+        inputCapture?.setForwarding(false)
+        captured = false
+        notifyCaptureChange(false)
+    }
+
+    /// Engage/release can run inside a SwiftUI update pass (captureEnabled flips in
+    /// updateNSView; release in dismantleNSView) — publishing model state synchronously
+    /// there is undefined behavior, so the callback is deferred a runloop turn.
+    private func notifyCaptureChange(_ captured: Bool) {
+        guard let onCaptureChange else { return }
+        DispatchQueue.main.async { onCaptureChange(captured) }
+    }
+
+    // MARK: - Pump
+
     /// Pump thread: pull AUs from the connection, wrap, enqueue. The first IDR yields the
     /// format description; non-IDR AUs before it are dropped (the host opens with an IDR).
     public func start(
@@ -169,6 +286,27 @@ public final class StreamLayerView: NSView {
         let layer = displayLayer
         layer.flush() // drop any frames a previous connection left queued
 
+        // The view owns the session's input capture: handlers attach now, but nothing is
+        // forwarded until capture engages (captureEnabled + auto-engage or a click).
+        let capture = InputCapture(connection: connection)
+        capture.onToggleCapture = { [weak self] in
+            // The ⌘⎋ monitor is app-wide — only the key window's stream owns the toggle
+            // (two stream windows would otherwise flip each other's capture).
+            guard let self, self.window?.isKeyWindow == true else { return }
+            if self.captured {
+                self.releaseCapture()
+            } else {
+                self.engageCapture(fromClick: false)
+            }
+        }
+        capture.onPreempted = { [weak self] in
+            // A newer session took the GC handler slots — staying "captured" here would
+            // be a cursor trap with dead input.
+            self?.releaseCapture()
+        }
+        capture.start()
+        inputCapture = capture
+
         let thread = Thread {
             var format: CMVideoFormatDescription?
             while token.isLive {
@@ -203,13 +341,15 @@ public final class StreamLayerView: NSView {
         thread.name = "punktfunk-pump"
         thread.qualityOfService = .userInteractive
         thread.start()
-        captureCursorIfStreaming()
+        requestAutoCapture() // entering a session is the deliberate "capture me" moment
     }
 
     /// Stop pumping (≤ one poll timeout). Does not close the connection — that stays with
     /// whoever owns it (PunktfunkConnection.close() is safe alongside a draining pump).
     public func stop() {
-        cursorCapture.release()
+        releaseCapture()
+        inputCapture?.stop()
+        inputCapture = nil
         token?.cancel()
         token = nil
         connection = nil
@@ -217,6 +357,7 @@ public final class StreamLayerView: NSView {
 
     deinit {
         appObservers.forEach(NotificationCenter.default.removeObserver(_:))
+        windowObservers.forEach(NotificationCenter.default.removeObserver(_:))
         token?.cancel()
     }
 }