Merge branch 'midstream-resize': mid-stream resolution resize

Lands the mid-stream resolution resize feature (client-driven Reconfigure so
the host's virtual display + encoder follow a resized client window without a
reconnect), all paths default OFF:

- host hardening H1-H5 + session-binary Match window (C1)
- Apple macOS/iPadOS Match-window trigger + settings (C3) and the resize
  overlay (blur + spinner) client UX
- Windows on-glass fixes: corrective-ack actual resolution + pf-vdisplay
  monitor re-arrival for out-of-list mid-stream modes
- Linux backend matrix + the live-reconfigure gate unit tests

Validated on-glass: Windows IDD-push (.173), Linux Mutter + KWin. Android
(C4) deferred; Apple full build pending on a Mac.

clients/apple/Sources/PunktfunkClient/ContentView.swift

@@ -327,12 +327,25 @@ struct ContentView: View {
         }()
         return ZStack {
             stream(captureEnabled: pendingFingerprint == nil)
-                .blur(radius: pendingFingerprint != nil ? 32 : 0)
+                // Blur the live stream during the trust prompt (heavy) and during a resize (lighter
+                // — the deliberate "hold on" while the host rebuilds its pipeline and the decoder
+                // re-inits on the new-mode IDR). Only the resize blur animates; the trust blur snaps
+                // as before (its own overlay handles the transition).
+                .blur(radius: pendingFingerprint != nil ? 32 : (model.resizing ? 16 : 0))
+                .animation(.easeInOut(duration: 0.22), value: model.resizing)
                 .overlay {
                     if pendingFingerprint != nil {
                         Color.black.opacity(0.45)
                     }
                 }
+                // The resize spinner rides over the (blurred) stream; suppressed under the trust
+                // prompt, which owns the screen. It never hit-tests, so window-drag resizes keep
+                // steering and the next click still reaches the stream.
+                .overlay {
+                    if pendingFingerprint == nil {
+                        ResizeIndicatorView(active: model.resizing)
+                    }
+                }
             if let fp = pendingFingerprint {
                 TrustCardView(
                     fingerprint: fp,
@@ -410,6 +423,16 @@ struct ContentView: View {
                     onSessionEnd: { [weak model] in
                         Task { @MainActor in model?.sessionEnded() }
                     },
+                    // Resize overlay START — the follower is main-actor, so this drives the blur
+                    // + spinner synchronously the instant the window differs from the live mode.
+                    onResizeTarget: { [weak model] w, h in
+                        model?.resizeTargeted(width: w, height: h)
+                    },
+                    // Resize overlay END — the coded dims of each new-mode IDR, reported from the
+                    // decode pump thread; hop to the main actor to clear the overlay.
+                    onDecodedSize: { [weak model] w, h in
+                        Task { @MainActor in model?.resizeDecoded(width: w, height: h) }
+                    },
                     endToEndMeter: model.endToEnd,
                     decodeMeter: model.decodeStage,
                     displayMeter: model.displayStage

clients/apple/Sources/PunktfunkClient/Session/ResizeIndicatorView.swift

@@ -0,0 +1,41 @@
+// The resize overlay (design/midstream-resolution-resize.md — client resize UX). A Match-window
+// resize renegotiates the host's virtual display + encoder and re-inits the local VideoToolbox
+// decoder on the first new-mode IDR — an unavoidable sub-second gap where the last frame lingers,
+// briefly freezes, or the picture pops to the new geometry. Rather than let that read as a stutter,
+// we make it DELIBERATE: the caller blurs the live stream and this centered spinner + caption
+// acknowledges the transition. It clears the instant a frame at the requested size decodes (the
+// `onDecodedSize` END signal) or on the follower's safety timeout — see `SessionModel.resizing`.
+//
+// Floating overlay, never a hit-test target: input keeps flowing to the stream underneath so a
+// resize the user triggers by dragging the window never swallows their next click.
+
+import PunktfunkKit
+import SwiftUI
+
+struct ResizeIndicatorView: View {
+    /// Mirrors `SessionModel.resizing`; the fade in/out is driven off this.
+    let active: Bool
+
+    var body: some View {
+        ZStack {
+            if active {
+                VStack(spacing: 12) {
+                    ProgressView().controlSize(.large).tint(.white)
+                    Text("Resizing…")
+                        .font(.geist(15, .medium, relativeTo: .callout))
+                        .foregroundStyle(.white.opacity(0.85))
+                }
+                .padding(.horizontal, 30)
+                .padding(.vertical, 24)
+                .glassBackground(RoundedRectangle(cornerRadius: 20, style: .continuous))
+                .overlay(
+                    RoundedRectangle(cornerRadius: 20, style: .continuous)
+                        .strokeBorder(.white.opacity(0.12), lineWidth: 1))
+                .transition(.opacity.combined(with: .scale(scale: 0.92)))
+            }
+        }
+        .environment(\.colorScheme, .dark) // the spinner + glass read over any frame
+        .animation(.easeInOut(duration: 0.22), value: active)
+        .allowsHitTesting(false) // the stream keeps receiving input the whole time
+    }
+}

clients/apple/Sources/PunktfunkClient/Session/SessionModel.swift

@@ -109,6 +109,16 @@ final class SessionModel: ObservableObject {
     /// Mirrors StreamView's capture state (it owns the input capture; this drives the
     /// HUD's "click to capture" / "⌘⎋ releases" hint).
     @Published var mouseCaptured = false
+    /// Resize overlay (design/midstream-resolution-resize.md — client resize UX): true from the
+    /// instant a Match-window resize starts steering toward a new size until a frame at that size
+    /// decodes (or a safety timeout). Drives the blur+spinner so the unavoidable host-rebuild delay
+    /// reads as a deliberate, acknowledged transition instead of a stutter. Pure state lives in
+    /// `ResizeIndicator`; this mirrors its `active` for SwiftUI.
+    @Published private(set) var resizing = false
+    /// START = follower steering (main actor), END = a new-mode IDR's coded dims (decode pump,
+    /// hopped to main), TIMEOUT = safety net for a rejected/capped switch that never yields a
+    /// differently-sized frame. Ticked from the 1 Hz stats timer.
+    private var resizeIndicator = ResizeIndicator()
 
     let meter = FrameMeter()
     /// Capture→received (the host+network stage), fed per AU at receipt by the stream view's
@@ -364,6 +374,8 @@ final class SessionModel: ObservableObject {
         lostFrames = 0
         lostPct = 0
         mouseCaptured = false
+        resizing = false
+        resizeIndicator = ResizeIndicator() // no stale target/timer into the next session
     }
 
     /// Called (via the main actor) when the pump hits end-of-session.
@@ -374,6 +386,23 @@ final class SessionModel: ObservableObject {
         errorMessage = "Session ended by \(name)."
     }
 
+    /// Resize overlay START (main actor — from the Match-window follower's `onResizeTarget`): the
+    /// window began differing from the live mode, so a `Reconfigure` toward `(width, height)` is
+    /// imminent. Show the blur+spinner immediately, before the debounced request even leaves.
+    func resizeTargeted(width: UInt32, height: UInt32) {
+        resizeIndicator.steering(
+            width: width, height: height, now: Date().timeIntervalSinceReferenceDate)
+        resizing = resizeIndicator.active
+    }
+
+    /// Resize overlay END (main actor — hopped from the decode pump's `onDecodedSize`): a new-mode
+    /// IDR decoded at `(width, height)`. Clears the overlay only when that matches the size we're
+    /// steering to (a same-size loss-recovery IDR, or the initial connect IDR, is a no-op).
+    func resizeDecoded(width: Int, height: Int) {
+        resizeIndicator.decoded(width: UInt32(max(width, 0)), height: UInt32(max(height, 0)))
+        resizing = resizeIndicator.active
+    }
+
     private func beginStreaming() {
         guard let conn = connection else { return }
         // Input capture itself is owned by StreamView (engaged by the captureEnabled
@@ -417,6 +446,11 @@ final class SessionModel: ObservableObject {
         let timer = Timer(timeInterval: 1.0, repeats: true) { [weak self] _ in
             guard let self else { return }
             Task { @MainActor in
+                // Resize-overlay safety net: clear a stuck overlay when a targeted size never
+                // decodes (a rejected/capped switch). The decoded-frame END clears it promptly on
+                // success; this only fires after the timeout.
+                self.resizeIndicator.tick(now: Date().timeIntervalSinceReferenceDate)
+                self.resizing = self.resizeIndicator.active
                 let (frames, bytes, total) = self.meter.drain()
                 self.fps = frames
                 self.mbps = Double(bytes) * 8 / 1_000_000

clients/apple/Sources/PunktfunkClient/Settings/SettingsView+Sections.swift

@@ -13,6 +13,11 @@ extension SettingsView {
     // failed exactly one slice: the iOS archive (macOS/tvOS never compile that branch).
     @ViewBuilder var streamModeSection: some View {
         Section {
+            #if os(iOS) || os(macOS)
+            // Match-window (design/midstream-resolution-resize.md D1): follow the session
+            // window/scene, renegotiating the host mode on a resize. Off → the explicit mode below.
+            Toggle("Match window", isOn: $matchWindow)
+            #endif
             #if os(iOS)
             iosResolutionWheel
             iosRefreshRows
@@ -35,8 +40,11 @@ extension SettingsView {
         } header: {
             Text("Stream mode")
         } footer: {
-            Text("The host creates a virtual output at exactly this mode — "
-                + "native resolution, no scaling. \(Self.bitrateFooter)")
+            Text(matchWindow
+                ? "The stream follows this window — the host resizes its virtual output to match "
+                    + "as you resize, no scaling. \(Self.bitrateFooter)"
+                : "The host creates a virtual output at exactly this mode — "
+                    + "native resolution, no scaling. \(Self.bitrateFooter)")
                 .font(.geist(12, relativeTo: .caption))
                 .foregroundStyle(.secondary)
         }

clients/apple/Sources/PunktfunkClient/Settings/SettingsView.swift

@@ -21,6 +21,7 @@ struct SettingsView: View {
     @AppStorage(DefaultsKey.streamWidth) var width = 1920
     @AppStorage(DefaultsKey.streamHeight) var height = 1080
     @AppStorage(DefaultsKey.streamHz) var hz = 60
+    @AppStorage(DefaultsKey.matchWindow) var matchWindow = false
     @AppStorage(DefaultsKey.compositor) var compositor = 0
     @AppStorage(DefaultsKey.gamepadType) var gamepadType = 0
     @AppStorage(DefaultsKey.bitrateKbps) var bitrateKbps = 0

clients/apple/Sources/PunktfunkKit/Support/DefaultsKeys.swift

@@ -11,6 +11,15 @@ public enum DefaultsKey {
     public static let streamWidth = "punktfunk.width"
     public static let streamHeight = "punktfunk.height"
     public static let streamHz = "punktfunk.hz"
+    /// Match-window resolution policy (design/midstream-resolution-resize.md D1/D2): when on, the
+    /// stream mode FOLLOWS the session view — the connect asks for the view's pixel size and a
+    /// mid-session resize (a windowed macOS window, an iPad Stage Manager / Split View scene)
+    /// renegotiates the host's virtual display + encoder (`PunktfunkConnection.requestMode`), so a
+    /// windowed session streams native-resolution pixels instead of scaling. Off (default): the
+    /// explicit `streamWidth`/`streamHeight` are used and never auto-resized (a fullscreen session
+    /// is native either way, so this degenerates to Auto-native there). Read per session by the
+    /// stream views' `MatchWindowFollower`.
+    public static let matchWindow = "punktfunk.matchWindow"
     public static let compositor = "punktfunk.compositor"
     public static let gamepadType = "punktfunk.gamepadType"
     public static let gamepadID = "punktfunk.gamepadID"

clients/apple/Sources/PunktfunkKit/Video/MatchWindowFollower.swift

@@ -0,0 +1,153 @@
+// Match-window resize follower (design/midstream-resolution-resize.md D1/D2, client C3).
+//
+// The presenting view feeds this its PHYSICAL-PIXEL size on every layout; it debounces to
+// resize-end, spaces requests ≥ 1 s apart, and asks the connection to switch the host's virtual
+// display + encoder to match (`PunktfunkConnection.requestMode`) — so a windowed macOS session or
+// an iPad Stage Manager / Split View scene streams native-resolution pixels instead of scaling.
+// The decode/present side needs nothing: VideoToolbox recreates its session on the keyframe-derived
+// format-description change (the first new-mode AU is an IDR with fresh parameter sets).
+//
+// The trigger discipline is the shared cross-client one (mirrors the session binary's
+// `resize_decision`): physical pixels rounded DOWN to even (the host rejects odd dimensions) and
+// clamped ≥ 320×200; debounce to resize-end; ≥ 1 s between requests; skip a size equal to the live
+// mode; and request each distinct size at most once — which both stops re-asking a rejected size
+// and keeps a host-side rollback (accepted, rebuild failed, corrective ack restored the old mode)
+// from looping request → rollback → request.
+
+import Foundation
+
+/// The pure, side-effect-free core of the Match-window trigger — so the normalize/skip discipline
+/// is unit-tested without a live connection or a UI (`MatchWindowTests`).
+public enum MatchWindow {
+    /// Even-floor + clamp a physical-pixel size to a host-valid mode dimension: the host's
+    /// `validate_dimensions` rejects odd sizes, and we never ask below 320×200.
+    public static func normalize(widthPx: Int, heightPx: Int) -> (width: UInt32, height: UInt32) {
+        let evenClamp: (Int, UInt32) -> UInt32 = { px, minimum in
+            let even = UInt32(max(px, 0)) / 2 * 2
+            return max(even, minimum)
+        }
+        return (evenClamp(widthPx, 320), evenClamp(heightPx, 200))
+    }
+
+    /// Whether to request `target` now (the debounce has already settled; spacing is the caller's
+    /// timer): `nil` to skip — equal to the live mode, or already requested once (a rejected size /
+    /// a host rollback must not loop). `target` is expected already-[normalize]d.
+    public static func request(
+        target: (width: UInt32, height: UInt32),
+        current: (width: UInt32, height: UInt32),
+        lastRequested: (width: UInt32, height: UInt32)?
+    ) -> (width: UInt32, height: UInt32)? {
+        if target.width == current.width, target.height == current.height { return nil }
+        if let lr = lastRequested, lr.width == target.width, lr.height == target.height { return nil }
+        return target
+    }
+}
+
+/// Owns the debounce timer + serialization state and drives `PunktfunkConnection.requestMode` from
+/// the stream view's layout callbacks. Main-actor: the views feed it on the main thread and it reads
+/// the connection's live mode there. Enabled per session from the `matchWindow` setting.
+@MainActor
+public final class MatchWindowFollower {
+    private weak var connection: PunktfunkConnection?
+    private let debounce: TimeInterval
+    private let minSpacing: TimeInterval
+    private var enabled: Bool
+
+    private var work: DispatchWorkItem?
+    private var pendingSize: (width: Int, height: Int)?
+    private var lastRequested: (width: UInt32, height: UInt32)?
+    private var lastRequestAt: Date?
+    /// The last size we reported via [`onResizeTarget`] — dedups the per-layout stream of a drag so
+    /// the UI is notified once per distinct target, and reset to `nil` when the window is back in
+    /// sync with the live mode (so a later resize re-reports).
+    private var lastSteered: (width: UInt32, height: UInt32)?
+
+    /// Fired (on the main actor) the instant the window starts differing from the live mode — i.e.
+    /// a resize is under way and a `Reconfigure` for `(width, height)` is imminent. Drives the
+    /// resize overlay's INSTANT feedback (blur + spinner) BEFORE the debounced request leaves; the
+    /// overlay clears when a decoded frame reaches this size (or on a timeout). Deduped per target.
+    public var onResizeTarget: ((_ width: UInt32, _ height: UInt32) -> Void)?
+
+    /// `debounce` = quiet time after the last size event before requesting (Win32 gets
+    /// `WM_EXITSIZEMOVE` for free; we debounce). `minSpacing` = floor between accepted requests
+    /// (a full host pipeline rebuild each). Defaults match the other clients.
+    public init(
+        connection: PunktfunkConnection,
+        enabled: Bool,
+        debounce: TimeInterval = 0.4,
+        minSpacing: TimeInterval = 1.0
+    ) {
+        self.connection = connection
+        self.enabled = enabled
+        self.debounce = debounce
+        self.minSpacing = minSpacing
+    }
+
+    /// Turn following on/off live (a mid-session settings change; off cancels a pending request).
+    public func setEnabled(_ on: Bool) {
+        enabled = on
+        if !on {
+            work?.cancel()
+            work = nil
+            pendingSize = nil
+            lastSteered = nil
+        }
+    }
+
+    /// Feed the presenting view's current PHYSICAL-PIXEL size (its `bounds` × the backing/display
+    /// scale). Called from every layout pass; coalesced by the debounce so a drag-resize sends one
+    /// request at its end, never one per frame.
+    public func noteSize(widthPx: Int, heightPx: Int) {
+        guard enabled else { return }
+        pendingSize = (widthPx, heightPx)
+        schedule()
+        reportSteering(widthPx: widthPx, heightPx: heightPx)
+    }
+
+    /// Report the resize overlay's START signal (deduped): the moment the normalized window size
+    /// differs from the live mode we're steering toward a new size. No connection / no negotiated
+    /// mode yet → nothing to compare against, skip.
+    private func reportSteering(widthPx: Int, heightPx: Int) {
+        guard let connection else { return }
+        let target = MatchWindow.normalize(widthPx: widthPx, heightPx: heightPx)
+        let mode = connection.currentMode()
+        guard mode.width > 0, mode.height > 0 else { return }
+        if target.width == mode.width, target.height == mode.height {
+            lastSteered = nil // back in sync — a later change re-reports
+            return
+        }
+        if lastSteered?.width == target.width, lastSteered?.height == target.height { return }
+        lastSteered = target
+        onResizeTarget?(target.width, target.height)
+    }
+
+    private func schedule() {
+        work?.cancel()
+        let item = DispatchWorkItem { [weak self] in self?.fire() }
+        work = item
+        DispatchQueue.main.asyncAfter(deadline: .now() + debounce, execute: item)
+    }
+
+    private func fire() {
+        guard enabled, let connection, let size = pendingSize else { return }
+        // ≥ 1 s spacing: a request went out recently → re-arm the debounce and retry later rather
+        // than fire early (keeps at most ~one request outstanding — the accept ack round-trips in
+        // milliseconds, ahead of the host's rebuild).
+        if let last = lastRequestAt, Date().timeIntervalSince(last) < minSpacing {
+            schedule()
+            return
+        }
+        let target = MatchWindow.normalize(widthPx: size.width, heightPx: size.height)
+        let mode = connection.currentMode()
+        pendingSize = nil
+        guard let req = MatchWindow.request(
+            target: target,
+            current: (mode.width, mode.height),
+            lastRequested: lastRequested
+        ) else { return }
+        // Keep the current refresh — Match-window follows SIZE, not rate.
+        connection.requestMode(width: req.width, height: req.height, refreshHz: mode.refreshHz)
+        lastRequested = req
+        lastRequestAt = Date()
+    }
+}

clients/apple/Sources/PunktfunkKit/Video/ResizeIndicator.swift

@@ -0,0 +1,63 @@
+// Resize-in-progress indicator state (design/midstream-resolution-resize.md — client UX).
+//
+// A mid-stream resize takes the host 0.3–2 s to rebuild its virtual display + encoder, and the
+// first new-mode frame is an IDR that the decoder re-inits on. Rather than let the stream scale
+// (stretch/blur) to the changing window during that gap, the client EMBRACES the delay: it shows a
+// deliberate blur + spinner the instant a resize starts and clears it the instant the sharp
+// new-resolution frame is on screen — so the wait reads as intentional, not as lag.
+//
+// This is driven ENTIRELY by signals the client already has (no new protocol):
+//   * START — the Match-window follower reports the size it is steering toward (instant, on the
+//     first resize layout, before the debounced request even leaves).
+//   * END — the decode pipeline reports each new-mode IDR's dimensions; when they reach the target
+//     the new picture is here.
+//   * TIMEOUT — the safety net for a switch that never delivers the exact target: the host rejected
+//     it (gamescope), capped it to an advertised mode, or a corrective ack landed a different size.
+//
+// Pure + side-effect-free so the transition logic is unit-tested without a live session or UI
+// (`ResizeIndicatorTests`); `SessionModel` owns an instance and mirrors `active` into a @Published.
+
+import Foundation
+
+/// The pure state of the resize overlay. `now` is a monotonic time in seconds (the caller passes
+/// `ProcessInfo.processInfo.systemUptime` or a test clock).
+public struct ResizeIndicator {
+    /// Whether the blur + spinner should be shown.
+    public private(set) var active = false
+    /// The size the follower is steering toward — cleared once a decoded frame reaches it.
+    private var target: (width: UInt32, height: UInt32)?
+    /// When the current `active` span began — the timeout is measured from here.
+    private var since: TimeInterval?
+    /// How long to keep the overlay up if the target frame never arrives (rejected / capped switch).
+    public var timeout: TimeInterval
+
+    public init(timeout: TimeInterval = 2.5) { self.timeout = timeout }
+
+    /// The follower is steering toward `width`×`height` — a resize is under way. Show the overlay now
+    /// (instant feedback). Called only for a genuine change (the follower skips a target equal to the
+    /// live mode), possibly many times as a drag moves through sizes; the timeout re-arms whenever the
+    /// target actually changes so a slow drag never trips it mid-gesture.
+    public mutating func steering(width: UInt32, height: UInt32, now: TimeInterval) {
+        if !active || target?.width != width || target?.height != height {
+            since = now
+        }
+        target = (width, height)
+        active = true
+    }
+
+    /// A decoded frame arrived at `width`×`height` (a new-mode IDR). Clears the overlay once it
+    /// matches the steered target — the sharp new-resolution picture is on glass.
+    public mutating func decoded(width: UInt32, height: UInt32) {
+        guard active, let t = target, t.width == width, t.height == height else { return }
+        active = false
+        since = nil
+    }
+
+    /// Timeout safety net: stop showing the overlay once `timeout` has elapsed with no matching frame
+    /// (a rejected or host-capped switch never delivers the exact target).
+    public mutating func tick(now: TimeInterval) {
+        guard active, let s = since, now - s >= timeout else { return }
+        active = false
+        since = nil
+    }
+}

clients/apple/Sources/PunktfunkKit/Video/SessionPresenter.swift

@@ -85,7 +85,8 @@ final class SessionPresenter {
         displayMeter: LatencyMeter? = nil,
         makeDisplayLink: (AnyObject, Selector) -> CADisplayLink,
         onFrame: (@Sendable (AccessUnit) -> Void)?,
-        onSessionEnd: (@Sendable () -> Void)?
+        onSessionEnd: (@Sendable () -> Void)?,
+        onDecodedSize: (@Sendable (Int, Int) -> Void)? = nil
     ) {
         stop()
         self.connection = connection
@@ -128,12 +129,14 @@ final class SessionPresenter {
             link.add(to: .main, forMode: .common)
             stage2Link = link
             syncFrameRate(hz: connection.currentMode().refreshHz)
-            pipeline.start(connection: connection, onFrame: onFrame, onSessionEnd: onSessionEnd)
+            pipeline.start(
+                connection: connection, onFrame: onFrame, onSessionEnd: onSessionEnd,
+                onDecodedSize: onDecodedSize)
         } else {
             let pump = StreamPump()
             pump.start(
                 connection: connection, layer: baseLayer,
-                onFrame: onFrame, onSessionEnd: onSessionEnd)
+                onFrame: onFrame, onSessionEnd: onSessionEnd, onDecodedSize: onDecodedSize)
             self.pump = pump
         }
     }

clients/apple/Sources/PunktfunkKit/Video/Stage2Pipeline.swift

@@ -329,7 +329,8 @@ public final class Stage2Pipeline {
     public func start(
         connection: PunktfunkConnection,
         onFrame: (@Sendable (AccessUnit) -> Void)?,
-        onSessionEnd: (@Sendable () -> Void)?
+        onSessionEnd: (@Sendable () -> Void)?,
+        onDecodedSize: (@Sendable (Int, Int) -> Void)? = nil
     ) {
         offsetNs = connection.clockOffsetNs
         recovery.bind(connection) // arm host-keyframe recovery for this session
@@ -350,6 +351,9 @@ public final class Stage2Pipeline {
         let thread = Thread {
             defer { pumpStopped.signal() } // let stop() join the pump (bounded) before decoder.reset()
             var format: CMVideoFormatDescription?
+            // Report coded dims to the resize overlay only on a CHANGE (new-mode IDR), not per
+            // loss-recovery IDR at the same size (see StreamPump).
+            var lastDecodedDims: CMVideoDimensions?
             var lastFramesDropped = connection.framesDropped()
             // Persistent recovery WANT, not a one-shot edge (see StreamPump for the full rationale):
             // keep asking until an IDR lands so a request swallowed by the throttle is re-sent.
@@ -387,6 +391,11 @@ public final class Stage2Pipeline {
                     onFrame?(au)
                     if let f = connection.videoCodec.formatDescription(fromKeyframe: au.data) {
                         format = f          // refreshed on every IDR (mode changes included)
+                        let dims = CMVideoFormatDescriptionGetDimensions(f)
+                        if lastDecodedDims?.width != dims.width || lastDecodedDims?.height != dims.height {
+                            lastDecodedDims = dims
+                            onDecodedSize?(Int(dims.width), Int(dims.height))
+                        }
                         awaitingIDR = false // a fresh IDR re-anchored decode — recovery complete
                     }
                     guard let f = format, !token.isStopped else { return true }

clients/apple/Sources/PunktfunkKit/Video/StreamPump.swift

@@ -21,7 +21,8 @@ final class StreamPump {
         connection: PunktfunkConnection,
         layer: AVSampleBufferDisplayLayer,
         onFrame: (@Sendable (AccessUnit) -> Void)?,
-        onSessionEnd: (@Sendable () -> Void)?
+        onSessionEnd: (@Sendable () -> Void)?,
+        onDecodedSize: (@Sendable (Int, Int) -> Void)? = nil
     ) {
         let token = token
         // Coalesced host keyframe requests (100 ms throttle — see KeyframeRecovery).
@@ -35,6 +36,9 @@ final class StreamPump {
 
         let thread = Thread {
             var format: CMVideoFormatDescription?
+            // Report the coded dims to the resize overlay only when they CHANGE (a new-mode IDR),
+            // not on every loss-recovery IDR at the same size — so it fires once per real switch.
+            var lastDecodedDims: CMVideoDimensions?
             var lastFramesDropped = connection.framesDropped()
             // Recovery is a persistent WANT, not a one-shot edge: set it on detected loss (or a
             // decoder reset), retry the throttled request EVERY iteration, and clear it only when a
@@ -79,6 +83,11 @@ final class StreamPump {
                     let idrFormat = connection.videoCodec.formatDescription(fromKeyframe: au.data)
                     if let f = idrFormat {
                         format = f          // refreshed on every IDR (mode changes included)
+                        let dims = CMVideoFormatDescriptionGetDimensions(f)
+                        if lastDecodedDims?.width != dims.width || lastDecodedDims?.height != dims.height {
+                            lastDecodedDims = dims
+                            onDecodedSize?(Int(dims.width), Int(dims.height))
+                        }
                         if awaitingIDR {
                             let ms = Int(Date().timeIntervalSince(awaitingSince) * 1000)
                             pumpLog.notice("video: recovery IDR received — resumed after \(ms, privacy: .public) ms")

clients/apple/Sources/PunktfunkKit/Views/StreamView.swift

@@ -87,6 +87,8 @@ public struct StreamView: NSViewRepresentable {
     private let onDisconnectRequest: (() -> Void)?
     private let onFrame: (@Sendable (AccessUnit) -> Void)?
     private let onSessionEnd: (@Sendable () -> Void)?
+    private let onResizeTarget: ((UInt32, UInt32) -> Void)?
+    private let onDecodedSize: (@Sendable (Int, Int) -> Void)?
     private let endToEndMeter: LatencyMeter?
     private let decodeMeter: LatencyMeter?
     private let displayMeter: LatencyMeter?
@@ -108,6 +110,8 @@ public struct StreamView: NSViewRepresentable {
         onDisconnectRequest: (() -> Void)? = nil,
         onFrame: (@Sendable (AccessUnit) -> Void)? = nil,
         onSessionEnd: (@Sendable () -> Void)? = nil,
+        onResizeTarget: ((UInt32, UInt32) -> Void)? = nil,
+        onDecodedSize: (@Sendable (Int, Int) -> Void)? = nil,
         endToEndMeter: LatencyMeter? = nil,
         decodeMeter: LatencyMeter? = nil,
         displayMeter: LatencyMeter? = nil
@@ -118,6 +122,8 @@ public struct StreamView: NSViewRepresentable {
         self.onDisconnectRequest = onDisconnectRequest
         self.onFrame = onFrame
         self.onSessionEnd = onSessionEnd
+        self.onResizeTarget = onResizeTarget
+        self.onDecodedSize = onDecodedSize
         self.endToEndMeter = endToEndMeter
         self.decodeMeter = decodeMeter
         self.displayMeter = displayMeter
@@ -131,6 +137,8 @@ public struct StreamView: NSViewRepresentable {
         view.endToEndMeter = endToEndMeter
         view.decodeMeter = decodeMeter
         view.displayMeter = displayMeter
+        view.onResizeTarget = onResizeTarget
+        view.onDecodedSize = onDecodedSize
         view.start(connection: connection, onFrame: onFrame, onSessionEnd: onSessionEnd)
         return view
     }
@@ -142,6 +150,8 @@ public struct StreamView: NSViewRepresentable {
         view.endToEndMeter = endToEndMeter
         view.decodeMeter = decodeMeter
         view.displayMeter = displayMeter
+        view.onResizeTarget = onResizeTarget
+        view.onDecodedSize = onDecodedSize
         // SwiftUI reuses the NSView across state changes — repoint the pump only when the
         // connection identity actually changed.
         if view.connection !== connection {
@@ -165,6 +175,9 @@ public final class StreamLayerView: NSView {
     /// stage-1 StreamPump → displayLayer path as the Metal-unavailable / DEBUG fallback.
     private let presenter = SessionPresenter()
     public private(set) var connection: PunktfunkConnection?
+    /// Match-window resize follower (C3) — non-nil while a session is active AND the `matchWindow`
+    /// setting is on; fed the view's physical-pixel size on every relayout.
+    private var matchFollower: MatchWindowFollower?
     private let cursorCapture = CursorCapture()
     private var inputCapture: InputCapture?
     private var appObservers: [NSObjectProtocol] = []
@@ -201,6 +214,13 @@ public final class StreamLayerView: NSView {
     /// view can't do that itself (the connection's owner disconnects).
     public var onDisconnectRequest: (() -> Void)?
 
+    /// Resize overlay signals (design/midstream-resolution-resize.md client UX): `onResizeTarget`
+    /// (main thread, via the follower) fires the instant the window starts steering toward a new
+    /// size; `onDecodedSize` (PUMP thread) fires when a new-mode IDR's dims land. The owner drives
+    /// the blur+spinner from these — set before `start()`.
+    public var onResizeTarget: ((UInt32, UInt32) -> Void)?
+    public var onDecodedSize: (@Sendable (Int, Int) -> Void)?
+
     /// Main-thread only. False = input capture disabled outright (UI layered over the
     /// stream); flipping to true auto-engages once.
     public var captureEnabled = true {
@@ -626,15 +646,32 @@ public final class StreamLayerView: NSView {
             displayMeter: displayMeter,
             makeDisplayLink: { displayLink(target: $0, selector: $1) },
             onFrame: onFrame,
-            onSessionEnd: onSessionEnd)
+            onSessionEnd: onSessionEnd,
+            onDecodedSize: onDecodedSize) // resize overlay END signal (new-mode IDR dims)
+        // Match-window (C3): follow the window's pixel size when the setting is on. Latched at
+        // session start (mirrors the other clients); the first real `layout()` feeds the initial
+        // size, so the stream converges to the window even if the connect used the explicit mode.
+        let follower = MatchWindowFollower(
+            connection: connection,
+            enabled: UserDefaults.standard.bool(forKey: DefaultsKey.matchWindow))
+        follower.onResizeTarget = onResizeTarget // resize overlay START signal (instant, on the follower)
+        matchFollower = follower
         layoutPresenter()
         requestAutoCapture() // entering a session is the deliberate "capture me" moment
     }
 
     /// Aspect-fit the stage-2 metal sublayer to the view; refresh contentsScale on a
-    /// retina↔non-retina move (see SessionPresenter.layout).
+    /// retina↔non-retina move (see SessionPresenter.layout). Also feeds the Match-window follower
+    /// the view's physical-pixel size (bounds → backing), so a window resize / retina move follows.
     private func layoutPresenter() {
         presenter.layout(in: bounds, contentsScale: window?.backingScaleFactor ?? 1)
+        // Feed the follower only once in a window (backing scale is real then) and with real
+        // bounds — a pre-window layout would report point-sized dimensions.
+        if window != nil, bounds.width > 0, bounds.height > 0 {
+            let px = convertToBacking(bounds).size
+            matchFollower?.noteSize(
+                widthPx: Int(px.width.rounded()), heightPx: Int(px.height.rounded()))
+        }
     }
 
     public override func viewDidChangeBackingProperties() {
@@ -650,6 +687,7 @@ public final class StreamLayerView: NSView {
         inputCapture?.stop()
         inputCapture = nil
         presenter.stop()
+        matchFollower = nil
         connection = nil
     }
 

clients/apple/Sources/PunktfunkKit/Views/StreamViewIOS.swift

@@ -53,6 +53,8 @@ public struct StreamView: UIViewControllerRepresentable {
     private let onCaptureChange: ((Bool) -> Void)?
     private let onFrame: (@Sendable (AccessUnit) -> Void)?
     private let onSessionEnd: (@Sendable () -> Void)?
+    private let onResizeTarget: ((UInt32, UInt32) -> Void)?
+    private let onDecodedSize: (@Sendable (Int, Int) -> Void)?
     private let endToEndMeter: LatencyMeter?
     private let decodeMeter: LatencyMeter?
     private let displayMeter: LatencyMeter?
@@ -68,6 +70,8 @@ public struct StreamView: UIViewControllerRepresentable {
         onDisconnectRequest: (() -> Void)? = nil,
         onFrame: (@Sendable (AccessUnit) -> Void)? = nil,
         onSessionEnd: (@Sendable () -> Void)? = nil,
+        onResizeTarget: ((UInt32, UInt32) -> Void)? = nil,
+        onDecodedSize: (@Sendable (Int, Int) -> Void)? = nil,
         endToEndMeter: LatencyMeter? = nil,
         decodeMeter: LatencyMeter? = nil,
         displayMeter: LatencyMeter? = nil
@@ -77,6 +81,8 @@ public struct StreamView: UIViewControllerRepresentable {
         self.onCaptureChange = onCaptureChange
         self.onFrame = onFrame
         self.onSessionEnd = onSessionEnd
+        self.onResizeTarget = onResizeTarget
+        self.onDecodedSize = onDecodedSize
         self.endToEndMeter = endToEndMeter
         self.decodeMeter = decodeMeter
         self.displayMeter = displayMeter
@@ -89,6 +95,8 @@ public struct StreamView: UIViewControllerRepresentable {
         controller.endToEndMeter = endToEndMeter
         controller.decodeMeter = decodeMeter
         controller.displayMeter = displayMeter
+        controller.onResizeTarget = onResizeTarget
+        controller.onDecodedSize = onDecodedSize
         controller.start(connection: connection, onFrame: onFrame, onSessionEnd: onSessionEnd)
         return controller
     }
@@ -99,6 +107,8 @@ public struct StreamView: UIViewControllerRepresentable {
         controller.endToEndMeter = endToEndMeter
         controller.decodeMeter = decodeMeter
         controller.displayMeter = displayMeter
+        controller.onResizeTarget = onResizeTarget
+        controller.onDecodedSize = onDecodedSize
         if controller.connection !== connection {
             controller.start(connection: connection, onFrame: onFrame, onSessionEnd: onSessionEnd)
         }
@@ -147,6 +157,11 @@ public final class StreamViewController: StreamViewControllerBase {
     /// Capture state at the last resign, restored on the next foreground — otherwise the
     /// mouse/keyboard stay released after navigating out and nothing re-grabs them.
     private var wasCapturedOnResign = false
+    /// Match-window resize follower (C3) — non-nil while a session is active AND the `matchWindow`
+    /// setting is on; fed the view's physical-pixel size from `viewDidLayoutSubviews` so an iPad
+    /// Stage Manager / Split View scene resize renegotiates the host mode. iOS only (iPhone
+    /// naturally no-ops fullscreen; tvOS drives display modes via AVDisplayManager instead).
+    private var matchFollower: MatchWindowFollower?
     #endif
 
     /// Reads whether the scene's pointer is actually locked right now; nil = state
@@ -161,6 +176,13 @@ public final class StreamViewController: StreamViewControllerBase {
     }
 
     var onCaptureChange: ((Bool) -> Void)?
+    /// Resize-overlay START: forwarded to the Match-window follower so a scene resize drives the
+    /// blur+spinner the instant the window differs from the live mode (iOS only — tvOS has no
+    /// follower). See `MatchWindowFollower.onResizeTarget`.
+    var onResizeTarget: ((UInt32, UInt32) -> Void)?
+    /// Resize-overlay END: the presenter reports the coded dims of each new-mode IDR here, so the
+    /// overlay clears when a frame at the requested size actually decodes.
+    var onDecodedSize: (@Sendable (Int, Int) -> Void)?
 
     var captureEnabled = true {
         didSet {
@@ -327,6 +349,14 @@ public final class StreamViewController: StreamViewControllerBase {
         }
         capture.start()
         inputCapture = capture
+        // Match-window (C3): follow the scene's pixel size when the setting is on. Latched at
+        // session start (mirrors the other clients); `viewDidLayoutSubviews` feeds it — covers
+        // Stage Manager / Split View resizes and rotation. iPhone fullscreen naturally no-ops.
+        let follower = MatchWindowFollower(
+            connection: connection,
+            enabled: UserDefaults.standard.bool(forKey: DefaultsKey.matchWindow))
+        follower.onResizeTarget = onResizeTarget
+        matchFollower = follower
         #endif
 
         // Presenter choice + lifecycle live in SessionPresenter (shared with macOS): stage-2
@@ -340,7 +370,8 @@ public final class StreamViewController: StreamViewControllerBase {
             displayMeter: displayMeter,
             makeDisplayLink: { CADisplayLink(target: $0, selector: $1) },
             onFrame: onFrame,
-            onSessionEnd: onSessionEnd)
+            onSessionEnd: onSessionEnd,
+            onDecodedSize: onDecodedSize)
         layoutMetalLayer()
 
         #if os(iOS)
@@ -411,6 +442,7 @@ public final class StreamViewController: StreamViewControllerBase {
         streamView.onPointerButton = nil
         streamView.onScroll = nil
         streamView.currentHostMode = nil
+        matchFollower = nil
         #endif
         #if os(tvOS)
         // Return the TV to the user's preferred mode — the home screen must not stay in the
@@ -425,6 +457,16 @@ public final class StreamViewController: StreamViewControllerBase {
     public override func viewDidLayoutSubviews() {
         super.viewDidLayoutSubviews()
         layoutMetalLayer()
+        #if os(iOS)
+        // Match-window (C3): feed the follower the view's physical-pixel size (points × scale).
+        let b = streamView.bounds
+        if b.width > 0, b.height > 0 {
+            let scale = renderScale
+            matchFollower?.noteSize(
+                widthPx: Int((b.width * scale).rounded()),
+                heightPx: Int((b.height * scale).rounded()))
+        }
+        #endif
         #if os(tvOS)
         applyDisplayCriteriaIfNeeded()
         #endif

clients/apple/Tests/PunktfunkKitTests/MatchWindowTests.swift

@@ -0,0 +1,43 @@
+// The Match-window trigger discipline (design/midstream-resolution-resize.md D2), as pure
+// functions — the same rules the session binary's `resize_decision` unit-tests: physical pixels
+// even-floored and clamped ≥ 320×200, skip a size equal to the live mode, and request each
+// distinct size at most once (so a rejected size / a host rollback can't loop).
+
+import XCTest
+
+@testable import PunktfunkKit
+
+final class MatchWindowTests: XCTestCase {
+    func testNormalizeEvenFloorsAndClamps() {
+        // Odd pixels floor to even (the host rejects odd dimensions).
+        let a = MatchWindow.normalize(widthPx: 1001, heightPx: 601)
+        XCTAssertEqual(a.width, 1000)
+        XCTAssertEqual(a.height, 600)
+        // Already-even sizes pass through.
+        let b = MatchWindow.normalize(widthPx: 2560, heightPx: 1440)
+        XCTAssertEqual(b.width, 2560)
+        XCTAssertEqual(b.height, 1440)
+        // Tiny / zero clamp to the host floor.
+        let c = MatchWindow.normalize(widthPx: 100, heightPx: 80)
+        XCTAssertEqual(c.width, 320)
+        XCTAssertEqual(c.height, 200)
+        let z = MatchWindow.normalize(widthPx: 0, heightPx: -4)
+        XCTAssertEqual(z.width, 320)
+        XCTAssertEqual(z.height, 200)
+    }
+
+    func testRequestSkipsEqualAndAlreadyRequested() {
+        // A new size (different from the live mode, not yet requested) → request it.
+        let r = MatchWindow.request(
+            target: (1000, 600), current: (1280, 720), lastRequested: (800, 500))
+        XCTAssertEqual(r?.width, 1000)
+        XCTAssertEqual(r?.height, 600)
+        // Equal to the live mode → nothing to do.
+        XCTAssertNil(MatchWindow.request(
+            target: (1280, 720), current: (1280, 720), lastRequested: nil))
+        // Already requested once → don't re-ask (covers a rejected size AND a host rollback:
+        // accepted → rebuild failed → corrective ack restored the old mode must not loop).
+        XCTAssertNil(MatchWindow.request(
+            target: (1000, 600), current: (1280, 720), lastRequested: (1000, 600)))
+    }
+}

clients/apple/Tests/PunktfunkKitTests/ResizeIndicatorTests.swift

@@ -0,0 +1,52 @@
+import XCTest
+
+@testable import PunktfunkKit
+
+final class ResizeIndicatorTests: XCTestCase {
+    func testInactiveUntilSteered() {
+        var r = ResizeIndicator()
+        XCTAssertFalse(r.active)
+        // A decoded frame with nothing pending is a no-op (session start / steady state).
+        r.decoded(width: 1920, height: 1080)
+        XCTAssertFalse(r.active)
+    }
+
+    func testSteeringActivatesAndDecodedTargetClears() {
+        var r = ResizeIndicator()
+        r.steering(width: 2560, height: 1440, now: 0)
+        XCTAssertTrue(r.active)
+        // A frame at a DIFFERENT size (the old mode still draining) doesn't clear it.
+        r.decoded(width: 1920, height: 1080)
+        XCTAssertTrue(r.active)
+        // The target frame lands → clear.
+        r.decoded(width: 2560, height: 1440)
+        XCTAssertFalse(r.active)
+    }
+
+    func testTimeoutClearsWhenTargetNeverArrives() {
+        var r = ResizeIndicator(timeout: 2.5)
+        r.steering(width: 2560, height: 1440, now: 10)
+        r.tick(now: 12) // 2 s < timeout — still up
+        XCTAssertTrue(r.active)
+        r.tick(now: 12.6) // 2.6 s ≥ timeout — a rejected/capped switch clears
+        XCTAssertFalse(r.active)
+    }
+
+    func testDragReArmsTimeoutOnEachNewTarget() {
+        var r = ResizeIndicator(timeout: 2.5)
+        r.steering(width: 2000, height: 1200, now: 0)
+        r.steering(width: 2200, height: 1200, now: 2) // target changed → since re-armed to 2
+        r.tick(now: 4) // only 2 s since the last change — still up (drag isn't a timeout)
+        XCTAssertTrue(r.active)
+        r.tick(now: 4.6) // 2.6 s since the last change → clears
+        XCTAssertFalse(r.active)
+    }
+
+    func testSteadyDragDoesNotResetTimeout() {
+        var r = ResizeIndicator(timeout: 2.5)
+        r.steering(width: 2560, height: 1440, now: 0)
+        r.steering(width: 2560, height: 1440, now: 1) // SAME target → since stays 0
+        r.tick(now: 2.6) // 2.6 s since the ORIGINAL steer → clears (not reset by the repeat)
+        XCTAssertFalse(r.active)
+    }
+}

clients/linux/src/ui_settings.rs

@@ -264,21 +264,23 @@ pub fn show(
     let page = adw::PreferencesPage::new();
 
     let stream = adw::PreferencesGroup::builder().title("Stream").build();
-    let res_names: Vec<String> = RESOLUTIONS
-        .iter()
-        .map(|&(w, h)| {
-            if w == 0 {
-                "Native display".to_string()
-            } else {
-                format!("{w} × {h}")
-            }
-        })
+    // The D1 tri-state: Native, Match window (a virtual index 1, stored as the
+    // `match_window` flag), then the explicit sizes.
+    let res_names: Vec<String> = std::iter::once("Native display".to_string())
+        .chain(std::iter::once("Match window".to_string()))
+        .chain(
+            RESOLUTIONS
+                .iter()
+                .skip(1)
+                .map(|&(w, h)| format!("{w} × {h}")),
+        )
         .collect();
     let res_row = ChoiceRow::new(
         &dialog,
         inline,
         "Resolution",
-        "The host creates a virtual output at exactly this size",
+        "The host creates a virtual output at exactly this size — Match window follows \
+         the stream window, including mid-stream resizes",
         &res_names.iter().map(String::as_str).collect::<Vec<_>>(),
     );
     let hz_names: Vec<String> = REFRESH
@@ -470,10 +472,15 @@ pub fn show(
     // Seed from the current settings.
     {
         let s = settings.borrow();
-        let res_i = RESOLUTIONS
-            .iter()
-            .position(|&(w, h)| w == s.width && h == s.height)
-            .unwrap_or(0);
+        let res_i = if s.match_window {
+            1
+        } else {
+            RESOLUTIONS
+                .iter()
+                .position(|&(w, h)| w == s.width && h == s.height)
+                .map(|i| if i == 0 { 0 } else { i + 1 })
+                .unwrap_or(0)
+        };
         res_row.set_selected(res_i as u32);
         let hz_i = REFRESH.iter().position(|&r| r == s.refresh_hz).unwrap_or(0);
         hz_row.set_selected(hz_i as u32);
@@ -508,8 +515,14 @@ pub fn show(
     dialog.add(&page);
     dialog.connect_closed(move |_| {
         let mut s = settings.borrow_mut();
-        let (w, h) = RESOLUTIONS[(res_row.selected() as usize).min(RESOLUTIONS.len() - 1)];
-        (s.width, s.height) = (w, h);
+        // Index 1 is the virtual "Match window" option; 0 = Native, 2.. = explicit.
+        let res_i = (res_row.selected() as usize).min(RESOLUTIONS.len());
+        s.match_window = res_i == 1;
+        (s.width, s.height) = if res_i <= 1 {
+            (0, 0)
+        } else {
+            RESOLUTIONS[res_i - 1]
+        };
         s.refresh_hz = REFRESH[(hz_row.selected() as usize).min(REFRESH.len() - 1)];
         s.bitrate_kbps = (bitrate_row.value() * 1000.0) as u32;
         s.gamepad = GAMEPADS[(pad_row.selected() as usize).min(GAMEPADS.len() - 1)].to_string();

clients/session/src/console.rs

@@ -145,6 +145,10 @@ pub fn run(target: Option<&str>) -> u8 {
             trust::touch_last_used(&trust::hex(&fingerprint));
         })),
         overlay: Some(Box::new(overlay)),
+        window_size: crate::session_main::window_size(&settings_at_start),
+        // Latched at console start (like the stats tier above): toggling Match window in
+        // the console's settings screen applies from the next console launch.
+        match_window: crate::session_main::match_window(&settings_at_start),
     };
 
     let result =

clients/session/src/main.rs

@@ -164,6 +164,34 @@ mod session_main {
         }
     }
 
+    /// The window's starting size under Match-window: the persisted last size, so the
+    /// first connect's mode already matches the glass; `None` (policy off / never
+    /// stored) = the 1280×720 default.
+    pub(crate) fn window_size(settings: &trust::Settings) -> Option<(u32, u32)> {
+        (settings.match_window && settings.last_window_w > 0 && settings.last_window_h > 0)
+            .then_some((settings.last_window_w, settings.last_window_h))
+    }
+
+    /// The Match-window policy hook for the presenter loop
+    /// (design/midstream-resolution-resize.md D1/D2): `Some(persist)` turns the
+    /// debounced resize→`Reconfigure` machinery on; the callback stores each resize-end's
+    /// logical window size (load-modify-save, like the console settings screen) so the
+    /// next launch opens at it.
+    pub(crate) fn match_window(
+        settings: &trust::Settings,
+    ) -> Option<Box<dyn FnMut(u32, u32)>> {
+        settings.match_window.then(|| {
+            Box::new(|w: u32, h: u32| {
+                let mut s = trust::Settings::load();
+                if (s.last_window_w, s.last_window_h) != (w, h) {
+                    s.last_window_w = w;
+                    s.last_window_h = h;
+                    s.save();
+                }
+            }) as Box<dyn FnMut(u32, u32)>
+        })
+    }
+
     /// One JSON status line on stdout (the shell parses these; strings hand-escaped via
     /// the minimal rules a reason string can need). `pub(crate)`: browse mode emits its
     /// failure through the same contract when spawned with `--json-status`.
@@ -343,6 +371,8 @@ mod session_main {
             overlay: Some(Box::new(pf_console_ui::SkiaOverlay::new())),
             #[cfg(not(feature = "ui"))]
             overlay: None,
+            window_size: window_size(&settings),
+            match_window: match_window(&settings),
         };
 
         let outcome =

clients/windows/src/app/settings.rs

@@ -136,29 +136,37 @@ pub(crate) fn settings_page(
     let s = ctx.settings.lock().unwrap().clone();
 
     // --- Display ---------------------------------------------------------------------------
+    // The D1 tri-state: Native, Match window (a virtual index 1, stored as the
+    // `match_window` flag), then the explicit sizes.
     let (res_names, res_i) = {
-        let names: Vec<String> = RESOLUTIONS
-            .iter()
-            .map(|&(w, h)| {
-                if w == 0 {
-                    "Native display".into()
-                } else {
-                    format!("{w} \u{00D7} {h}")
-                }
-            })
+        let names: Vec<String> = std::iter::once("Native display".to_string())
+            .chain(std::iter::once("Match window".to_string()))
+            .chain(
+                RESOLUTIONS
+                    .iter()
+                    .skip(1)
+                    .map(|&(w, h)| format!("{w} \u{00D7} {h}")),
+            )
             .collect();
-        let i = RESOLUTIONS
-            .iter()
-            .position(|&(w, h)| w == s.width && h == s.height)
-            .unwrap_or(0);
+        let i = if s.match_window {
+            1
+        } else {
+            RESOLUTIONS
+                .iter()
+                .position(|&(w, h)| w == s.width && h == s.height)
+                .map(|i| if i == 0 { 0 } else { i + 1 })
+                .unwrap_or(0)
+        };
         (names, i)
     };
     let res_combo = setting_combo(ctx, "Resolution", res_names, res_i, |s, i| {
-        (s.width, s.height) = RESOLUTIONS[i];
+        s.match_window = i == 1;
+        (s.width, s.height) = if i <= 1 { (0, 0) } else { RESOLUTIONS[i - 1] };
     })
     .tooltip(
         "The host creates a virtual display at exactly this size. \u{201C}Native display\u{201D} \
-         resolves to the monitor this window is on at connect.",
+         resolves to the monitor this window is on at connect; \u{201C}Match window\u{201D} \
+         follows the stream window, including mid-stream resizes.",
     );
     let (hz_names, hz_i) = {
         let names: Vec<String> = REFRESH