Merge origin/main; the presenter rebuild's four settings join the sidebar

`#20` landed while this branch was open and added four settings the
console screen groups under a new "Presentation" header: Prioritize,
Smoothness buffer, V-Sync and Follow variable refresh. A branch whose
whole claim is "everything the store holds is reachable" cannot merge
past those, so they get a Presentation page of their own, in the console
screen's position (after Video, before Audio) and with its wording.
Smoothness buffer is indented under Prioritize and disabled until the
intent is Smoothness — the same relationship the console's `enabled`
gate draws.

The docs conflict resolves to main's side plus this branch's correction:
the 4:4:4 advertisement claim main rewrote is the current one and stays,
while "Android, Decky and the console home don't offer it" was wrong
about two of the three before this branch and about all three after it.
The four new settings' paragraphs pick up the console home and Decky the
same way.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

clients/decky/README.md

@@ -28,8 +28,9 @@ the panel looks and feels native to Gaming Mode.
    own Settings: a left rail of categories (`SidebarNavigation`), one page each, so no page needs
    scrolling. The categories and their order are the console settings screen's — Stream (resolution
    / refresh / render scale / bitrate / compositor), Video (codec / decoder / GPU / HDR / 4:4:4),
-   Audio (channels / output + mic device / echo cancellation), Controllers, Touch & mouse,
-   Interface (stats overlay / auto-wake / library / fullscreen). The device pickers are populated
+   Presentation (prioritize / smoothness buffer / V-Sync / VRR), Audio (channels / output + mic
+   device / echo cancellation), Controllers, Touch & mouse, Interface (stats overlay / auto-wake /
+   library / fullscreen). The device pickers are populated
    from the session binary (`--list-adapters` / `--list-audio`); the GPU row appears only where
    there is more than one adapter.
 6. **About** — plugin version, an explicit "Check for updates" button, the setup-guide link, and
@@ -99,7 +100,7 @@ restart is required for an out-of-band install to appear.
 | --- | --- |
 | `src/index.tsx` | Plugin entry: the QAM panel + route registration. |
 | `src/page.tsx` | The `/punktfunk` fullscreen page — Hosts (with per-host details) / Settings / About tabs. |
-| `src/settings.tsx` · `src/pair.tsx` | The settings screen (a `SidebarNavigation` of six category pages over one shared settings object); the gamepad-navigable PIN-pairing modal. |
+| `src/settings.tsx` · `src/pair.tsx` | The settings screen (a `SidebarNavigation` of seven category pages over one shared settings object); the gamepad-navigable PIN-pairing modal. |
 | `src/library.tsx` | The per-host game picker (pin/unpin, "Open library on screen") + the pinned-game launch helper. |
 | `src/hostmgmt.tsx` | Add / edit host dialogs — mutate the shared known-hosts store (`client-known-hosts.json`) via the flatpak client's headless modes, so a host saved here shows up in the desktop client too. |
 | `src/ui.tsx` | Shared UI primitives for the fullscreen page + modals (right-aligned row actions, consistent Field layout). |

clients/decky/src/backend.ts

@@ -104,7 +104,7 @@ export interface RunnerInfo {
 // The flatpak client's settings JSON — the SAME `client-gtk-settings.json` the desktop client
 // and the console's settings screen own, so a value changed in any of them shows in the others.
 //
-// Every field the client's `Settings` struct persists is modelled here EXCEPT the four that
+// Every field the client's `Settings` struct persists is modelled here EXCEPT the ones that
 // cannot be answered from a plugin backend or aren't settings at all:
 //   • `forward_pad`   — which physical pad is player 1. Needs SDL's live device list, which only
 //                       the client process has; there is no CLI that enumerates pads.
@@ -136,6 +136,14 @@ export interface StreamSettings {
   enable_444?: boolean; // default off — ask for full chroma
   adapter?: string; // decode/present GPU by marketing name; "" = automatic
 
+  // ---- Presentation ----
+  // What the client optimises for when a decoded frame is ready: "latency" | "smooth". Shared
+  // with the Apple and Android clients under this name, so one profile reads the same everywhere.
+  present_priority?: string;
+  smooth_buffer?: number; // frames held back under "smooth"; 0 = Automatic (resolves to 2), else 1–3
+  vsync?: boolean; // default ON — tear-free; off asks for a tearing present mode (best-effort)
+  allow_vrr?: boolean; // default ON — let a VRR panel refresh in step with the stream
+
   // ---- Audio ----
   audio_channels?: number; // 2 (stereo) | 6 (5.1) | 8 (7.1)
   speaker_device?: string; // PipeWire node.name for playback; "" = system default

clients/decky/src/settings.tsx

@@ -40,6 +40,7 @@ import {
   FaGamepad,
   FaHandPointer,
   FaSlidersH,
+  FaTv,
   FaVideo,
   FaVolumeUp,
 } from "react-icons/fa";
@@ -112,6 +113,19 @@ const DECODERS: [string, string][] = [
   ["vaapi", "VAAPI"],
   ["software", "Software"],
 ];
+// Presentation intent — the `present_priority` key shared with the Apple and Android clients, so
+// one profile reads the same on every device.
+const PRESENT_PRIORITIES: [string, string][] = [
+  ["latency", "Lowest latency"],
+  ["smooth", "Smoothness"],
+];
+// Smoothness buffer depth in frames; 0 = Automatic (resolves to 2).
+const SMOOTH_BUFFERS: [number, string][] = [
+  [0, "Automatic"],
+  [1, "1 frame"],
+  [2, "2 frames"],
+  [3, "3 frames"],
+];
 const AUDIO_CHANNELS: [number, string][] = [
   [2, "Stereo"],
   [6, "5.1 surround"],
@@ -227,7 +241,7 @@ const DeviceRow: FC<{
 };
 
 // ----------------------------------------------------------------------------------------
-// The pages. One settings object, six views on it — every page takes the same context rather
+// The pages. One settings object, seven views on it — every page takes the same context rather
 // than fetching or holding state of its own, so a change on one page is visible on the others
 // the moment you switch.
 // ----------------------------------------------------------------------------------------
@@ -359,6 +373,43 @@ const VideoPage: FC<PageCtx> = ({ s, patch, devices }) => {
   );
 };
 
+const PresentationPage: FC<PageCtx> = ({ s, patch }) => {
+  const smooth = (s.present_priority ?? "latency") === "smooth";
+  return (
+    <div style={pageBody}>
+      <SelectRow
+        label="Prioritize"
+        description="What to optimise for when a decoded frame is ready. Lowest latency shows each frame the moment the display can take it — a network hiccup becomes an occasional repeated or skipped frame. Smoothness buffers a little to even those out."
+        options={PRESENT_PRIORITIES}
+        value={s.present_priority ?? "latency"}
+        onChange={(v) => patch({ present_priority: v })}
+      />
+      <SelectRow
+        label="Smoothness buffer"
+        description="Frames held back before showing. Each one absorbs about a refresh of network hiccup and adds a refresh of delay. Automatic holds two."
+        options={SMOOTH_BUFFERS}
+        value={s.smooth_buffer ?? 0}
+        formatUnknown={(v) => `${v} frames`}
+        onChange={(v) => patch({ smooth_buffer: v })}
+        disabled={!smooth}
+        indent
+      />
+      <ToggleField
+        label="V-Sync"
+        description="Tear-free. Off removes the wait for the screen's refresh — the lowest possible delay, at the cost of visible tearing. Best-effort: not every driver offers it, and the Detailed stats overlay names the mode actually in use."
+        checked={s.vsync ?? true}
+        onChange={(v) => patch({ vsync: v })}
+      />
+      <ToggleField
+        label="Follow variable refresh"
+        description="On a VRR screen, let the panel refresh in step with the stream instead of on a fixed cadence. Applies to fullscreen sessions — which a Gaming-Mode stream always is — and is harmless on a fixed-refresh screen."
+        checked={s.allow_vrr ?? true}
+        onChange={(v) => patch({ allow_vrr: v })}
+      />
+    </div>
+  );
+};
+
 const AudioPage: FC<PageCtx> = ({ s, patch, devices, reading, readDevices }) => {
   const micOn = s.mic_enabled;
   // What the pickers get: null while the enumeration is in flight (they show a loading state),
@@ -575,6 +626,12 @@ export const SettingsSection: FC = () => {
       pages={[
         { title: "Stream", identifier: "stream", icon: <FaDesktop />, content: <StreamPage {...ctx} /> },
         { title: "Video", identifier: "video", icon: <FaVideo />, content: <VideoPage {...ctx} /> },
+        {
+          title: "Presentation",
+          identifier: "presentation",
+          icon: <FaTv />,
+          content: <PresentationPage {...ctx} />,
+        },
         { title: "Audio", identifier: "audio", icon: <FaVolumeUp />, content: <AudioPage {...ctx} /> },
         {
           title: "Controllers",

clients/linux/src/ui_settings.rs

@@ -156,6 +156,20 @@ mod index {
     pub fn gamepad(s: &Settings) -> u32 {
         GAMEPADS.iter().position(|&g| g == s.gamepad).unwrap_or(0) as u32
     }
+
+    pub fn present_priority(s: &Settings) -> u32 {
+        // Unknown values (a newer client's intent) read as the default, exactly as
+        // `PresentPriority::resolve` treats them.
+        PRESENT_PRIORITIES
+            .iter()
+            .position(|&p| p == s.present_priority)
+            .unwrap_or(0) as u32
+    }
+
+    pub fn smooth_buffer(s: &Settings) -> u32 {
+        // The index IS the stored value: 0 = Automatic, 1..3 = frames.
+        u32::from(s.smooth_buffer).min(SMOOTH_BUFFER_LABELS.len() as u32 - 1)
+    }
 }
 
 /// The chip palette a profile can carry (`StreamProfile.accent`). Eight entries rather than a
@@ -634,6 +648,18 @@ fn commit_profile(active: &StreamProfile, touched: &Touched, values: &Settings)
     if touched.has("fullscreen_on_stream") {
         o.fullscreen_on_stream = Some(values.fullscreen_on_stream);
     }
+    if touched.has("present_priority") {
+        o.present_priority = Some(values.present_priority.clone());
+    }
+    if touched.has("smooth_buffer") {
+        o.smooth_buffer = Some(values.smooth_buffer);
+    }
+    if touched.has("vsync") {
+        o.vsync = Some(values.vsync);
+    }
+    if touched.has("allow_vrr") {
+        o.allow_vrr = Some(values.allow_vrr);
+    }
     // Resets are not handled here: they clear the field and re-seed their row the moment the
     // user asks, so by the time this runs the catalog already reflects them and the row is no
     // longer marked touched.
@@ -687,6 +713,20 @@ const TOUCH_MODE_CAPTIONS: &[&str] = &[
     "The cursor jumps to your finger — a tap clicks there",
     "Real multi-touch reaches the host — for touch-native apps",
 ];
+/// Presentation-intent values (persisted under the `present_priority` key the Apple and
+/// Android clients share) + labels + dynamic captions. Captions stay ONE line, like the
+/// touch/mouse rows.
+const PRESENT_PRIORITIES: &[&str] = &["latency", "smooth"];
+const PRESENT_PRIORITY_LABELS: &[&str] = &["Lowest latency", "Smoothness"];
+const PRESENT_PRIORITY_CAPTIONS: &[&str] = &[
+    "Each frame shows the moment the display can take it",
+    "Buffers a little to even out network hiccups",
+];
+/// Smoothness buffer depth, in frames — the index IS the stored `smooth_buffer` value
+/// (0 = Automatic, which resolves to 2). No millisecond hints: the cost is one refresh
+/// per frame, and the session's refresh isn't known here when the mode is Native.
+const SMOOTH_BUFFER_LABELS: &[&str] = &["Automatic", "1 frame", "2 frames", "3 frames"];
+
 /// Physical-mouse model values (persisted) + labels + dynamic captions — same idiom as
 /// the touch rows. Ctrl+Alt+Shift+M flips the model live in-stream.
 const MOUSE_MODES: &[&str] = &["capture", "desktop"];
@@ -1216,6 +1256,50 @@ pub fn show_scoped(
         row
     });
 
+    // ---- Display: Presentation ----
+    // The intent pair the Apple and Android clients already carry. The buffer row only
+    // means anything under Smoothness, so it hides itself the rest of the time rather
+    // than sitting there inert.
+    let present_row = ChoiceRow::new(
+        &dialog,
+        inline,
+        "Prioritize",
+        PRESENT_PRIORITY_CAPTIONS[0],
+        PRESENT_PRIORITY_LABELS,
+    );
+    let buffer_row = ChoiceRow::new(
+        &dialog,
+        inline,
+        "Smoothness buffer",
+        "Each frame held absorbs one refresh of hiccup and adds one of delay",
+        SMOOTH_BUFFER_LABELS,
+    );
+    {
+        let w = present_row.widget().clone();
+        let buffer = buffer_row.widget().clone();
+        present_row.connect_changed(move |i| {
+            let i = (i as usize).min(PRESENT_PRIORITY_CAPTIONS.len() - 1);
+            set_row_subtitle(&w, PRESENT_PRIORITY_CAPTIONS[i]);
+            buffer.set_visible(PRESENT_PRIORITIES[i] == "smooth");
+        });
+    }
+    let vsync_row = adw::SwitchRow::builder()
+        .title("V-Sync")
+        .subtitle(
+            "Tear-free. Turning it off removes the wait for the screen's refresh — the \
+             lowest possible delay, at the cost of visible tearing. Not every driver \
+             offers it; the stats overlay names the mode actually in use",
+        )
+        .build();
+    let vrr_row = adw::SwitchRow::builder()
+        .title("Follow variable refresh rate")
+        .subtitle(
+            "On a VRR/FreeSync/G-Sync screen, let the panel refresh in step with the \
+             stream instead of on a fixed cadence. Applies to fullscreen sessions; \
+             harmless on a fixed-refresh screen",
+        )
+        .build();
+
     // ---- Display: Host output ----
     let compositor_row = ChoiceRow::new(
         &dialog,
@@ -1506,6 +1590,19 @@ pub fn show_scoped(
         let codec_i = index::codec(s);
         codec_row.set_selected(codec_i);
         set_row_subtitle(codec_row.widget(), codec_caption(codec_i));
+        let present_i = index::present_priority(s);
+        present_row.set_selected(present_i);
+        set_row_subtitle(
+            present_row.widget(),
+            PRESENT_PRIORITY_CAPTIONS[present_i as usize],
+        );
+        buffer_row.set_selected(index::smooth_buffer(s));
+        // `set_selected` never fires the changed hook, so mirror its visibility rule here.
+        buffer_row
+            .widget()
+            .set_visible(PRESENT_PRIORITIES[present_i as usize] == "smooth");
+        vsync_row.set_active(s.vsync);
+        vrr_row.set_active(s.allow_vrr);
     }
 
     // ---- Override markers, per-row reset, and the touch that creates an override ----
@@ -1704,6 +1801,20 @@ pub fn show_scoped(
             o.gamepad_forwarding.is_some(),
             gamepad_forwarding
         );
+        choice!(
+            present_row,
+            "present_priority",
+            o.present_priority.is_some(),
+            index::present_priority
+        );
+        choice!(
+            buffer_row,
+            "smooth_buffer",
+            o.smooth_buffer.is_some(),
+            index::smooth_buffer
+        );
+        toggle!(vsync_row, "vsync", o.vsync.is_some(), vsync);
+        toggle!(vrr_row, "allow_vrr", o.allow_vrr.is_some(), allow_vrr);
         toggle!(hdr_row, "hdr_enabled", o.hdr_enabled.is_some(), hdr_enabled);
         toggle!(chroma_row, "enable_444", o.enable_444.is_some(), enable_444);
         toggle!(
@@ -1808,6 +1919,11 @@ pub fn show_scoped(
     if let (Some(r), false) = (&gpu_row, profile_mode) {
         quality_group.add(r.widget());
     }
+    let presentation_group = group("Presentation", "");
+    presentation_group.add(present_row.widget());
+    presentation_group.add(buffer_row.widget());
+    presentation_group.add(&vsync_row);
+    presentation_group.add(&vrr_row);
     // The one form-level note (deliberately not repeated on every row).
     let output_group = group(
         "Host output",
@@ -1816,6 +1932,7 @@ pub fn show_scoped(
     output_group.add(compositor_row.widget());
     display.add(&resolution_group);
     display.add(&quality_group);
+    display.add(&presentation_group);
     display.add(&output_group);
 
     let input = page("Input", "input-keyboard-symbolic");
@@ -1963,6 +2080,14 @@ pub fn show_scoped(
                 _ => 2,
             };
             s.codec = CODECS[(codec_row.selected() as usize).min(CODECS.len() - 1)].to_string();
+            s.present_priority = PRESENT_PRIORITIES
+                [(present_row.selected() as usize).min(PRESENT_PRIORITIES.len() - 1)]
+            .to_string();
+            // The index IS the value (0 = Automatic).
+            s.smooth_buffer =
+                (buffer_row.selected() as u8).min(SMOOTH_BUFFER_LABELS.len() as u8 - 1);
+            s.vsync = vsync_row.is_active();
+            s.allow_vrr = vrr_row.is_active();
             s.library_enabled = library_row.is_active();
         };
 

clients/session/src/console.rs

@@ -169,6 +169,11 @@ pub fn run(target: Option<&str>) -> u8 {
         mouse_mode: settings_at_start.mouse_mode(),
         invert_scroll: settings_at_start.invert_scroll,
         inhibit_shortcuts: settings_at_start.inhibit_shortcuts,
+        // Presentation-tier like the rows above: latched at console start, a per-host
+        // profile cannot move it in this mode (the documented P4 gap).
+        present_priority: settings_at_start.present_priority(),
+        vsync: settings_at_start.vsync,
+        allow_vrr: settings_at_start.allow_vrr,
         json_status,
         on_connected: Some(Box::new(move |fingerprint: [u8; 32]| {
             let fp_hex = trust::hex(&fingerprint);

clients/session/src/main.rs

@@ -623,6 +623,9 @@ mod session_main {
             mouse_mode: settings.mouse_mode(),
             invert_scroll: settings.invert_scroll,
             inhibit_shortcuts: settings.inhibit_shortcuts,
+            present_priority: settings.present_priority(),
+            vsync: settings.vsync,
+            allow_vrr: settings.allow_vrr,
             json_status: true,
             on_connected: Some(Box::new(|fingerprint: [u8; 32]| {
                 // This host's card carries the accent bar in the desktop client now.

clients/windows/src/app/hosts.rs

@@ -623,8 +623,14 @@ pub(crate) fn hosts_page(props: &HostsProps, cx: &mut RenderCx) -> Element {
                 actions.push(
                     icon_btn("Settings", Symbol::Setting)
                         .on_click({
-                            let ss = set_screen.clone();
-                            move || ss.call(Screen::Settings)
+                            let (c, ss) = (ctx.clone(), set_screen.clone());
+                            move || {
+                                // Re-base the settings snapshot on the file before the page
+                                // renders — this process is not its only writer (see
+                                // settings::refresh_snapshot).
+                                super::settings::refresh_snapshot(&c);
+                                ss.call(Screen::Settings)
+                            }
                         })
                         .into(),
                 );

clients/windows/src/app/licenses.rs

@@ -2,7 +2,8 @@
 //! Settings).
 
 use super::style::*;
-use super::Screen;
+use super::{AppCtx, Screen};
+use std::sync::Arc;
 use windows_reactor::*;
 
 /// punktfunk's own license (MIT OR Apache-2.0).
@@ -15,10 +16,15 @@ const APP_LICENSE: &str = concat!(
 /// scripts/gen-third-party-notices.sh; the MSIX also ships this under licenses/).
 const THIRD_PARTY_NOTICES: &str = include_str!("../../../../THIRD-PARTY-NOTICES.txt");
 
-pub(crate) fn licenses_page(set_screen: &AsyncSetState<Screen>) -> Element {
+pub(crate) fn licenses_page(ctx: &Arc<AppCtx>, set_screen: &AsyncSetState<Screen>) -> Element {
     let back_btn = button("Back").accent().icon(Symbol::Back).on_click({
-        let ss = set_screen.clone();
-        move || ss.call(Screen::Settings)
+        let (c, ss) = (ctx.clone(), set_screen.clone());
+        move || {
+            // Back RE-ENTERS the settings page — re-base its snapshot on the file, same
+            // as the hosts page's Settings button (see settings::refresh_snapshot).
+            super::settings::refresh_snapshot(&c);
+            ss.call(Screen::Settings)
+        }
     });
 
     let app_card = card(

clients/windows/src/app/mod.rs

@@ -172,6 +172,10 @@ pub(crate) struct Shared {
 
 pub struct AppCtx {
     pub(crate) identity: (String, String),
+    /// The settings snapshot the UI renders from. Loaded once at startup, and RE-BASED on
+    /// the file when the settings page is (re)entered (`settings::refresh_snapshot`) and
+    /// inside every `commit` — this process is not the file's only writer (session resize,
+    /// console UI, Decky), so a plain process-lifetime snapshot goes stale on screen.
     pub(crate) settings: Mutex<Settings>,
     pub(crate) gamepad: GamepadService,
     pub(crate) shared: Arc<Shared>,
@@ -688,7 +692,7 @@ fn root(cx: &mut RenderCx, ctx: &Arc<AppCtx>) -> Element {
             &set_settings_rev,
             nav_progress,
         ),
-        Screen::Licenses => licenses::licenses_page(&set_screen),
+        Screen::Licenses => licenses::licenses_page(ctx, &set_screen),
         Screen::Help => help::help_page(&set_screen),
         Screen::Pair => component(pair::pair_page, svc),
         Screen::SpeedTest => component(speed::speed_page, SpeedProps { svc, state: speed }),

clients/windows/src/app/settings.rs

@@ -101,6 +101,19 @@ const MOUSE_MODES: &[(&str, &str)] = &[
     ("capture", "Capture (games)"),
     ("desktop", "Desktop (absolute)"),
 ];
+/// Presentation intent: `(stored value, display label)` — the `present_priority` key the
+/// Apple and Android clients share, so one profile means the same thing everywhere.
+const PRESENT_PRIORITIES: &[(&str, &str)] =
+    &[("latency", "Lowest latency"), ("smooth", "Smoothness")];
+/// Smoothness buffer depth in frames: `(stored value, display label)`. `0` = Automatic,
+/// which resolves to 2 (`PresentPriority::resolve`). No millisecond hints — the cost is
+/// one refresh per frame, and the refresh isn't known here when the mode is Native.
+const SMOOTH_BUFFERS: &[(u8, &str)] = &[
+    (0, "Automatic"),
+    (1, "1 frame"),
+    (2, "2 frames"),
+    (3, "3 frames"),
+];
 /// Host compositor presets: `(stored value, display label)`. Advisory — the host falls back to
 /// auto-detect when the choice is unavailable. Only meaningful against a Linux host.
 const COMPOSITORS: &[(&str, &str)] = &[
@@ -411,7 +424,16 @@ fn commit(
         return;
     }
     let mut catalog = ProfilesFile::load();
-    let base = ctx.settings.lock().unwrap().clone();
+    // The same rebase as the global arm above: `base` is what `absorb`'s before/after
+    // effective settings derive from, and the snapshot is not the file — another process
+    // (session resize, console UI, Decky) may have moved a global under us. The historical
+    // rebase fix ("settings saves stop reverting each other") covered the whole-file
+    // writers but missed this arm.
+    let base = {
+        let mut s = ctx.settings.lock().unwrap();
+        *s = Settings::load();
+        s.clone()
+    };
     let Some(p) = catalog.profiles.iter_mut().find(|p| p.id == scope) else {
         return; // deleted from under us; the next render falls back to the defaults scope
     };
@@ -425,6 +447,17 @@ fn commit(
     rev.1.call(rev.0 + 1);
 }
 
+/// Re-base the process-lifetime settings snapshot on the file — called from the navigation
+/// handlers that (re)enter this page, NOT per render pass. `ctx.settings` is loaded once at
+/// process start and this process is not the file's only writer (a spawned session persists
+/// its match-window size, the console UI and Decky save too — profiles.rs documents the
+/// family), so without this the page opens showing values another process already replaced,
+/// which then visibly "jump" the moment a row is touched and `commit`'s rebase pulls the
+/// file in. The field report this fixes: a codec setting that "changed by itself".
+pub(crate) fn refresh_snapshot(ctx: &Arc<AppCtx>) {
+    *ctx.settings.lock().unwrap() = Settings::load();
+}
+
 /// Which tier-P rows the profile in scope overrides. Plain bools rather than a lookup so the
 /// call sites read as `over.codec` — the row and its flag stay visibly paired.
 #[derive(Default)]
@@ -448,6 +481,10 @@ struct OverrideFlags {
     gamepad_forwarding: bool,
     stats_verbosity: bool,
     fullscreen_on_stream: bool,
+    present_priority: bool,
+    smooth_buffer: bool,
+    vsync: bool,
+    allow_vrr: bool,
 }
 
 impl OverrideFlags {
@@ -477,6 +514,10 @@ impl OverrideFlags {
             gamepad_forwarding: o.gamepad_forwarding.is_some(),
             stats_verbosity: o.stats_verbosity.is_some(),
             fullscreen_on_stream: o.fullscreen_on_stream.is_some(),
+            present_priority: o.present_priority.is_some(),
+            smooth_buffer: o.smooth_buffer.is_some(),
+            vsync: o.vsync.is_some(),
+            allow_vrr: o.allow_vrr.is_some(),
         }
     }
 }
@@ -853,6 +894,32 @@ pub(crate) fn settings_page(
     let chroma_toggle = setting_toggle(ctx, scope, (rev, set_rev), s.enable_444, |s, on| {
         s.enable_444 = on
     });
+    // Presentation intent (design/desktop-presentation-rebuild.md). The buffer row is
+    // rendered only under Smoothness — `commit` bumps the revision, so flipping the
+    // intent re-renders the section and the row appears/disappears with it.
+    let (present_names, present_i) = presets(PRESENT_PRIORITIES, |v| *v == s.present_priority);
+    let present_combo = setting_combo(
+        ctx,
+        scope,
+        (rev, set_rev),
+        present_names,
+        present_i,
+        |s, i| s.present_priority = PRESENT_PRIORITIES[i].0.to_string(),
+    );
+    let smoothing = s.present_priority == "smooth";
+    let (buffer_names, buffer_i) = presets(SMOOTH_BUFFERS, |v| *v == s.smooth_buffer);
+    let buffer_combo = setting_combo(
+        ctx,
+        scope,
+        (rev, set_rev),
+        buffer_names,
+        buffer_i,
+        |s, i| s.smooth_buffer = SMOOTH_BUFFERS[i].0,
+    );
+    let vsync_toggle = setting_toggle(ctx, scope, (rev, set_rev), s.vsync, |s, on| s.vsync = on);
+    let vrr_toggle = setting_toggle(ctx, scope, (rev, set_rev), s.allow_vrr, |s, on| {
+        s.allow_vrr = on
+    });
 
     // --- Input -----------------------------------------------------------------------------
     // Controller forwarding: Automatic forwards EVERY real controller, each as its own pad;
@@ -978,6 +1045,16 @@ pub(crate) fn settings_page(
         let ss = set_screen.clone();
         button("Third-party licenses").on_click(move || ss.call(Screen::Licenses))
     };
+    // The client log's home (%LOCALAPPDATA%\punktfunk\logs) — the file every "check the
+    // client log" message means, which until this row had no way in from the UI at all.
+    // The folder rather than the file so the rotated `.old` generation is in reach too.
+    // Best-effort, like the log itself: a missing dir or a failed spawn stays silent.
+    let logs_button = button("Open log folder").on_click(|| {
+        if let Some(dir) = crate::logfile::log_dir() {
+            let _ = std::fs::create_dir_all(&dir);
+            let _ = std::process::Command::new("explorer.exe").arg(&dir).spawn();
+        }
+    });
     let library_toggle = setting_toggle(ctx, scope, (rev, set_rev), s.library_enabled, |s, on| {
         s.library_enabled = on
     });
@@ -1071,8 +1148,9 @@ pub(crate) fn settings_page(
                         "HDR10, when the host has HDR content and this display supports it. \
                          HEVC only; otherwise the stream stays SDR.",
                     ),
-                    // Wording shared with the GTK client (its chroma_row) — same setting,
-                    // same constraints.
+                    // First sentence shared with the GTK client (its chroma_row); the
+                    // constraint sentence names the real gate (host: PyroWave || NVENC) —
+                    // "where the host can encode it" cost field users the discovery time.
                     described_overridable(
                         (rev, set_rev),
                         scope,
@@ -1081,7 +1159,8 @@ pub(crate) fn settings_page(
                         over.enable_444,
                         chroma_toggle,
                         "Full-colour video: crisp small text and thin lines, at more \
-                         bandwidth. HEVC only, and only where the host can encode it.",
+                         bandwidth. Requires an NVIDIA host (NVENC) or the PyroWave \
+                         codec \u{2014} other encoders stream 4:2:0.",
                     ),
                 ],
                 None,
@@ -1111,6 +1190,60 @@ pub(crate) fn settings_page(
                 },
                 None,
             ));
+            out.extend(group(
+                Some("Presentation"),
+                {
+                    let mut fields = vec![described_overridable(
+                        (rev, set_rev),
+                        scope,
+                        "present_priority",
+                        "Prioritize",
+                        over.present_priority,
+                        present_combo,
+                        "Lowest latency shows each frame the moment the display can take \
+                         it \u{2014} a network hiccup becomes an occasional repeated or \
+                         skipped frame. Smoothness buffers a little to even those out.",
+                    )];
+                    if smoothing {
+                        fields.push(described_overridable(
+                            (rev, set_rev),
+                            scope,
+                            "smooth_buffer",
+                            "Smoothness buffer",
+                            over.smooth_buffer,
+                            buffer_combo,
+                            "Frames held back before showing. Each one absorbs about a \
+                             refresh of network hiccup and adds a refresh of delay. \
+                             Automatic holds two.",
+                        ));
+                    }
+                    fields.push(described_overridable(
+                        (rev, set_rev),
+                        scope,
+                        "vsync",
+                        "V-Sync",
+                        over.vsync,
+                        vsync_toggle,
+                        "Tear-free. Turning it off removes the wait for the screen\u{2019}s \
+                         refresh \u{2014} the lowest possible delay, at the cost of visible \
+                         tearing. Not every driver offers it; the stats overlay names the \
+                         mode actually in use.",
+                    ));
+                    fields.push(described_overridable(
+                        (rev, set_rev),
+                        scope,
+                        "allow_vrr",
+                        "Follow variable refresh rate",
+                        over.allow_vrr,
+                        vrr_toggle,
+                        "On a VRR/FreeSync/G-Sync screen, let the panel refresh in step with \
+                         the stream instead of on a fixed cadence. Applies to fullscreen \
+                         sessions; harmless on a fixed-refresh screen.",
+                    ));
+                    fields
+                },
+                None,
+            ));
             out.extend(group(
                 Some("Host output"),
                 vec![described_overridable(
@@ -1348,7 +1481,16 @@ pub(crate) fn settings_page(
             "About",
             group(
                 None,
-                vec![about_identity.into(), licenses_button.into()],
+                vec![
+                    about_identity.into(),
+                    described_labeled(
+                        "Diagnostics",
+                        logs_button,
+                        "The client log (client.log, plus the session\u{2019}s whole \
+                         receive/decode/present trail) \u{2014} attach it to a bug report.",
+                    ),
+                    licenses_button.into(),
+                ],
                 None,
             ),
         ),
@@ -1750,5 +1892,26 @@ mod tests {
         let f3 = OverrideFlags::of(Some(&p3));
         assert!(f3.echo_cancel);
         assert!(!f3.mic_enabled);
+
+        // The presentation pair, likewise independent: pinning the intent doesn't claim
+        // the buffer (a "Smoothness, whatever the global buffer is" profile is valid).
+        let mut p4 = StreamProfile::new("t4".to_string());
+        p4.overrides = SettingsOverlay {
+            present_priority: Some("smooth".into()),
+            ..Default::default()
+        };
+        let f4 = OverrideFlags::of(Some(&p4));
+        assert!(f4.present_priority);
+        assert!(!f4.smooth_buffer);
+
+        // V-Sync and VRR are independent of each other and of the intent pair.
+        let mut p5 = StreamProfile::new("t5".to_string());
+        p5.overrides = SettingsOverlay {
+            vsync: Some(false),
+            ..Default::default()
+        };
+        let f5 = OverrideFlags::of(Some(&p5));
+        assert!(f5.vsync);
+        assert!(!f5.allow_vrr && !f5.present_priority);
     }
 }

clients/windows/src/logfile.rs

@@ -21,11 +21,12 @@ const ROTATE_BYTES: u64 = 10 * 1024 * 1024;
 
 static SINK: OnceLock<Option<Arc<Mutex<File>>>> = OnceLock::new();
 
-fn log_dir() -> Option<PathBuf> {
+/// The log directory — Settings ▸ About's "Open log folder" opens it in Explorer.
+pub(crate) fn log_dir() -> Option<PathBuf> {
     Some(PathBuf::from(std::env::var_os("LOCALAPPDATA")?).join(r"punktfunk\logs"))
 }
 
-/// The log file's path, for the "logs land here" startup line (and any future UI affordance).
+/// The log file's path, for the "logs land here" startup line and the failed-spawn banner.
 pub(crate) fn path() -> Option<PathBuf> {
     Some(log_dir()?.join("client.log"))
 }

clients/windows/src/spawn.rs

@@ -105,7 +105,14 @@ fn parse_line(line: &str) -> Option<ChildLine> {
 /// connect that silently drops back to the host list.
 pub(crate) fn silent_exit_banner(code: i32) -> Option<String> {
     (code != 0 && code != -1).then(|| {
-        format!("The session didn't start (punktfunk-session exited with code {code}). Check the client log.")
+        // Name the log's actual location — "check the client log" without a path is a
+        // scavenger hunt (Settings ▸ About's "Open log folder" reaches it too).
+        let log = crate::logfile::path()
+            .map(|p| p.display().to_string())
+            .unwrap_or_else(|| "the client log".into());
+        format!(
+            "The session didn't start (punktfunk-session exited with code {code}). Check {log}."
+        )
     })
 }
 

crates/pf-client-core/src/orchestrate.rs

@@ -982,6 +982,10 @@ mod tests {
                 height: 1440,
                 bitrate_kbps: 55000,
                 codec: "av1".into(),
+                present_priority: "smooth".into(),
+                smooth_buffer: 2,
+                vsync: false,
+                allow_vrr: false,
                 ..Default::default()
             },
             clipboard: true,

crates/pf-client-core/src/profiles.rs

@@ -79,6 +79,18 @@ pub struct SettingsOverlay {
     pub stats_verbosity: Option<StatsVerbosity>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub fullscreen_on_stream: Option<bool>,
+    /// The presentation cluster — the keys the Apple client already writes into this
+    /// same catalog shape (`present_priority`/`smooth_buffer`/`vsync`/`allow_vrr`;
+    /// Android carries the first two). First-class here so a profile authored on any
+    /// client applies on all of them instead of riding `extra` unapplied.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub present_priority: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub smooth_buffer: Option<u8>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub vsync: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub allow_vrr: Option<bool>,
     /// Overlay keys a newer client wrote and this one doesn't model — carried through a
     /// load→save round-trip untouched.
     #[serde(flatten)]
@@ -155,6 +167,18 @@ impl SettingsOverlay {
         if let Some(v) = self.fullscreen_on_stream {
             s.fullscreen_on_stream = v;
         }
+        if let Some(v) = &self.present_priority {
+            s.present_priority = v.clone();
+        }
+        if let Some(v) = self.smooth_buffer {
+            s.smooth_buffer = v;
+        }
+        if let Some(v) = self.vsync {
+            s.vsync = v;
+        }
+        if let Some(v) = self.allow_vrr {
+            s.allow_vrr = v;
+        }
         s
     }
 
@@ -234,6 +258,18 @@ impl SettingsOverlay {
         if after.fullscreen_on_stream != before.fullscreen_on_stream {
             self.fullscreen_on_stream = Some(after.fullscreen_on_stream);
         }
+        if after.present_priority != before.present_priority {
+            self.present_priority = Some(after.present_priority.clone());
+        }
+        if after.smooth_buffer != before.smooth_buffer {
+            self.smooth_buffer = Some(after.smooth_buffer);
+        }
+        if after.vsync != before.vsync {
+            self.vsync = Some(after.vsync);
+        }
+        if after.allow_vrr != before.allow_vrr {
+            self.allow_vrr = Some(after.allow_vrr);
+        }
     }
 
     /// Drop one override by its overlay field name, putting the row back to inheriting. The
@@ -268,6 +304,10 @@ impl SettingsOverlay {
             "gamepad_forwarding" => self.gamepad_forwarding = None,
             "stats_verbosity" => self.stats_verbosity = None,
             "fullscreen_on_stream" => self.fullscreen_on_stream = None,
+            "present_priority" => self.present_priority = None,
+            "smooth_buffer" => self.smooth_buffer = None,
+            "vsync" => self.vsync = None,
+            "allow_vrr" => self.allow_vrr = None,
             _ => return false,
         }
         true
@@ -469,6 +509,10 @@ mod tests {
             match_window: Some(true),
             fullscreen_on_stream: Some(false),
             stats_verbosity: Some(StatsVerbosity::Detailed),
+            present_priority: Some("smooth".into()),
+            smooth_buffer: Some(3),
+            vsync: Some(false),
+            allow_vrr: Some(false),
             ..Default::default()
         };
         assert!(!overlay.is_empty());
@@ -491,6 +535,10 @@ mod tests {
         assert!(out.match_window);
         assert!(!out.fullscreen_on_stream);
         assert_eq!(out.stats_verbosity(), StatsVerbosity::Detailed);
+        assert_eq!(out.present_priority, "smooth");
+        assert_eq!(out.smooth_buffer, 3);
+        assert!(!out.vsync);
+        assert!(!out.allow_vrr);
         // The tier goes through the setter, so the legacy bool a pre-tier binary reads
         // stays coherent with it.
         assert!(out.show_stats);
@@ -588,6 +636,59 @@ mod tests {
         assert!(o.is_empty());
     }
 
+    /// The presentation cluster is first-class, not `extra` passengers: it applies,
+    /// absorbs, clears, and serialises under the exact keys the Apple client already
+    /// writes (`present_priority`/`smooth_buffer`/`vsync`/`allow_vrr`) — one catalog
+    /// has to round-trip through every platform, and a mismatched key would be carried
+    /// but never applied.
+    #[test]
+    fn presentation_cluster_is_first_class() {
+        let base = Settings::default();
+        let mut o = SettingsOverlay::default();
+        let before = o.apply(&base);
+        let mut after = before.clone();
+        after.present_priority = "smooth".into();
+        o.absorb(&before, &after);
+        let before = o.apply(&base);
+        let mut after = before.clone();
+        after.smooth_buffer = 1;
+        o.absorb(&before, &after);
+        assert_eq!(o.present_priority.as_deref(), Some("smooth"));
+        assert_eq!(o.smooth_buffer, Some(1));
+        assert!(
+            o.extra.is_empty(),
+            "modelled fields must never land in the passthrough"
+        );
+        let out = o.apply(&base);
+        assert_eq!(
+            out.present_priority(),
+            crate::trust::PresentPriority::Smooth { buffer: 1 }
+        );
+
+        // Serialised under the shared keys, and read back from a foreign client's file.
+        let text = serde_json::to_string(&o).unwrap();
+        assert!(text.contains("\"present_priority\":\"smooth\""), "{text}");
+        assert!(text.contains("\"smooth_buffer\":1"), "{text}");
+        let from_apple: SettingsOverlay = serde_json::from_str(
+            r#"{"present_priority":"latency","smooth_buffer":2,"vsync":true,"allow_vrr":false}"#,
+        )
+        .unwrap();
+        assert_eq!(from_apple.present_priority.as_deref(), Some("latency"));
+        assert_eq!(from_apple.smooth_buffer, Some(2));
+        assert_eq!(from_apple.vsync, Some(true));
+        assert_eq!(from_apple.allow_vrr, Some(false));
+        assert!(from_apple.extra.is_empty());
+
+        assert!(o.clear("present_priority"));
+        assert!(o.clear("smooth_buffer"));
+        assert_eq!(o.present_priority, None);
+        assert!(o.is_empty());
+        let mut vrr = from_apple;
+        assert!(vrr.clear("vsync"));
+        assert!(vrr.clear("allow_vrr"));
+        assert_eq!((vrr.vsync, vrr.allow_vrr), (None, None));
+    }
+
     /// `clear` is the explicit way back to inheriting, including the resolution tri-state.
     #[test]
     fn clear_drops_one_override() {

crates/pf-client-core/src/trust.rs

@@ -14,6 +14,7 @@ use anyhow::{anyhow, Context, Result};
 use punktfunk_core::client::NativeClient;
 use punktfunk_core::quic::endpoint;
 use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
 use std::path::{Path, PathBuf};
 
 pub fn config_dir() -> Result<PathBuf> {
@@ -787,6 +788,45 @@ impl MouseMode {
     }
 }
 
+/// Presentation intent — what the presenter optimizes for
+/// (design/desktop-presentation-rebuild.md; the Apple/Android clients' shared
+/// `present_priority`/`smooth_buffer` pair). Stored stringly in
+/// [`Settings::present_priority`] + [`Settings::smooth_buffer`]; resolved with
+/// [`PresentPriority::resolve`], whose rules match the Android reference
+/// (`decode/presenter.rs`): anything but an explicit `"smooth"` is latency, and a
+/// smooth buffer outside 1..=3 (including 0 = Automatic) becomes 2.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum PresentPriority {
+    /// Every frame presents the moment the display can take it; a network hiccup is an
+    /// occasional repeated or skipped frame. The default.
+    Latency,
+    /// A small frame buffer (1–3 frames) evens out network/decode jitter, at the
+    /// buffer's worth of added display latency.
+    Smooth { buffer: u8 },
+}
+
+impl PresentPriority {
+    /// The shared cross-client resolution rule — pure, so every embedder agrees on what
+    /// a foreign profile's values mean.
+    pub fn resolve(name: &str, buffer: u8) -> PresentPriority {
+        if name == "smooth" {
+            PresentPriority::Smooth {
+                buffer: if (1..=3).contains(&buffer) { buffer } else { 2 },
+            }
+        } else {
+            PresentPriority::Latency
+        }
+    }
+
+    /// Frames the smoothing store holds; `0` = newest-wins (the latency intent).
+    pub fn fifo_capacity(self) -> u8 {
+        match self {
+            PresentPriority::Latency => 0,
+            PresentPriority::Smooth { buffer } => buffer,
+        }
+    }
+}
+
 /// App settings, persisted as JSON. Stringly-typed gamepad/compositor prefs so the file
 /// stays readable; parsed with `*Pref::from_name` at connect time.
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
@@ -889,6 +929,32 @@ pub struct Settings {
     /// `default = true`: the Linux stores never carried this and always advertised.
     #[serde(default = "default_true")]
     pub hdr_enabled: bool,
+    /// Presentation intent: `"latency"` (default) or `"smooth"` — the Apple/Android
+    /// clients' shared `present_priority` profile key, resolved with
+    /// [`PresentPriority::resolve`] (via [`Settings::present_priority`]). Anything
+    /// unknown reads as latency, so a newer client's future value degrades safely.
+    #[serde(default = "default_present_priority")]
+    pub present_priority: String,
+    /// Smoothness buffer size in frames: `0` = Automatic (resolves to 2), else 1–3.
+    /// Only meaningful under `present_priority = "smooth"` (the shared `smooth_buffer`
+    /// key). Each buffered frame absorbs about one refresh of jitter and adds one
+    /// refresh of display latency.
+    #[serde(default)]
+    pub smooth_buffer: u8,
+    /// Tear-free presentation (default ON = today's behavior: MAILBOX, FIFO fallback).
+    /// Off asks for a tearing present mode (IMMEDIATE) for the lowest possible latch
+    /// latency — best-effort: platforms/drivers without tearing silently stay tear-free
+    /// and the active mode is visible in the detailed stats. The shared `vsync` profile
+    /// key; the desktop default differs from macOS's (`false` there) deliberately —
+    /// sync-off means something different on each platform, the key is the contract.
+    #[serde(default = "default_true")]
+    pub vsync: bool,
+    /// Let a variable-refresh display follow the stream cadence: prefers the present
+    /// mode that drives VRR panels directly when fullscreen. Inert on fixed-refresh
+    /// displays (detection is measured from on-glass timestamps, not queried). The
+    /// shared `allow_vrr` profile key. Default ON, like the Apple client.
+    #[serde(default = "default_true")]
+    pub allow_vrr: bool,
     /// Legacy on/off for the stats overlay — superseded by `stats_verbosity` but kept
     /// written in sync (`set_stats_verbosity`) so pre-tier binaries reading the same
     /// file keep working. `alias`: the pre-unification WinUI shell (≤ 0.8.4) persisted
@@ -940,6 +1006,14 @@ pub struct Settings {
     /// the user will be looking at. `0` = never stored → the 1280×720 default.
     pub last_window_w: u32,
     pub last_window_h: u32,
+    /// Settings keys this build doesn't model (a newer client's field), carried through a
+    /// load→save round-trip untouched — [`crate::profiles::SettingsOverlay`]'s `extra`
+    /// pattern extended to the globals. Without it, every whole-file writer of this store
+    /// (two shells, the console settings screen, the session's resize callback, Decky)
+    /// running as an OLDER binary silently drops what a newer one persisted. Empty on
+    /// every existing store, and an empty map serializes to nothing, so files don't churn.
+    #[serde(flatten)]
+    pub extra: BTreeMap<String, serde_json::Value>,
 }
 
 fn default_codec() -> String {
@@ -954,6 +1028,10 @@ fn default_mouse_mode() -> String {
     "capture".into()
 }
 
+fn default_present_priority() -> String {
+    "latency".into()
+}
+
 fn default_true() -> bool {
     true
 }
@@ -985,6 +1063,12 @@ impl Settings {
         MouseMode::from_name(&self.mouse_mode)
     }
 
+    /// The presentation intent for this session (the resolved
+    /// `present_priority` × `smooth_buffer` pair).
+    pub fn present_priority(&self) -> PresentPriority {
+        PresentPriority::resolve(&self.present_priority, self.smooth_buffer)
+    }
+
     /// The `codec` setting as a `quic::CODEC_*` preference bit (`0` = auto).
     pub fn preferred_codec(&self) -> u8 {
         match self.codec.as_str() {
@@ -1023,6 +1107,10 @@ impl Default for Settings {
             adapter: String::new(),
             enable_444: false,
             hdr_enabled: true,
+            present_priority: "latency".into(),
+            smooth_buffer: 0,
+            vsync: true,
+            allow_vrr: true,
             show_stats: true,
             stats_verbosity: None,
             fullscreen_on_stream: true,
@@ -1034,6 +1122,7 @@ impl Default for Settings {
             match_window: false,
             last_window_w: 0,
             last_window_h: 0,
+            extra: BTreeMap::new(),
         }
     }
 }
@@ -1160,6 +1249,43 @@ mod tests {
         }
     }
 
+    /// A settings file predating the presentation cluster loads with the shipped
+    /// defaults (latency intent, Automatic buffer, tear-free, VRR allowed), and the
+    /// resolution rules match the Apple/Android reference: anything but an explicit
+    /// `"smooth"` is latency, and a smooth buffer outside 1..=3 becomes 2.
+    #[test]
+    fn settings_presentation_defaults_and_resolution() {
+        let old = r#"{"width":1280,"height":720,"gamepad":"auto","compositor":"auto"}"#;
+        let s: Settings = serde_json::from_str(old).unwrap();
+        assert_eq!(s.present_priority, "latency");
+        assert_eq!(s.smooth_buffer, 0);
+        assert!(s.vsync);
+        assert!(s.allow_vrr);
+        assert_eq!(s.present_priority(), PresentPriority::Latency);
+
+        assert_eq!(
+            PresentPriority::resolve("smooth", 0),
+            PresentPriority::Smooth { buffer: 2 },
+            "Automatic resolves to 2"
+        );
+        assert_eq!(
+            PresentPriority::resolve("smooth", 3),
+            PresentPriority::Smooth { buffer: 3 }
+        );
+        assert_eq!(
+            PresentPriority::resolve("smooth", 9),
+            PresentPriority::Smooth { buffer: 2 },
+            "out-of-range pins to the Automatic resolution"
+        );
+        assert_eq!(
+            PresentPriority::resolve("balanced-from-the-future", 2),
+            PresentPriority::Latency,
+            "unknown intents degrade to latency"
+        );
+        assert_eq!(PresentPriority::Latency.fifo_capacity(), 0);
+        assert_eq!(PresentPriority::Smooth { buffer: 3 }.fifo_capacity(), 3);
+    }
+
     /// A pre-`forward_pad` settings file (≤ 0.5.0) loads with the pin on automatic.
     #[test]
     fn settings_forward_pad_defaults_empty() {
@@ -1208,6 +1334,28 @@ mod tests {
         assert!(s.echo_cancel);
     }
 
+    /// A key this build doesn't model (a newer client's setting) survives a load→save
+    /// round trip instead of being dropped by the next whole-file write — the same
+    /// contract `SettingsOverlay.extra` gives profiles. And when there are no unknown
+    /// keys, the flatten map adds nothing, so existing files don't churn.
+    #[test]
+    fn settings_unknown_keys_survive_round_trip() {
+        let newer = r#"{"width":1920,"height":1080,"frob_mode":"fancy","frob_level":3}"#;
+        let s: Settings = serde_json::from_str(newer).unwrap();
+        assert_eq!((s.width, s.height), (1920, 1080));
+        assert_eq!(
+            s.extra.get("frob_mode").and_then(|v| v.as_str()),
+            Some("fancy")
+        );
+        let out = serde_json::to_string(&s).unwrap();
+        assert!(out.contains(r#""frob_mode":"fancy""#), "{out}");
+        assert!(out.contains(r#""frob_level":3"#), "{out}");
+        // No unknown keys → no artifact of the passthrough field in the file.
+        let plain = serde_json::to_string(&Settings::default()).unwrap();
+        assert!(!plain.contains("extra"), "{plain}");
+        assert!(!plain.contains("frob"), "{plain}");
+    }
+
     /// Stats-tier resolution: a pre-tier store falls back to `show_stats` (off → Off,
     /// on/absent → Normal), an explicit tier wins, and setting a tier keeps the legacy
     /// bool in sync so pre-tier binaries reading the same file agree on off vs on.

crates/pf-console-ui/src/screens/settings.rs

@@ -26,6 +26,10 @@ enum RowId {
     Decoder,
     Hdr,
     Chroma444,
+    PresentPriority,
+    SmoothBuffer,
+    Vsync,
+    AllowVrr,
     Audio,
     Mic,
     EchoCancel,
@@ -47,7 +51,7 @@ enum RowId {
 // scroll/shortcut behavior, fullscreen-on-stream, auto-wake, the library toggle and echo
 // cancellation all were). Still deliberately smaller than the desktop dialogs — device
 // pickers (GPU/speaker/mic) and the profile catalog stay desktop-only.
-const ROWS: [RowId; 23] = [
+const ROWS: [RowId; 27] = [
     RowId::Resolution,
     RowId::Refresh,
     RowId::RenderScale,
@@ -57,6 +61,10 @@ const ROWS: [RowId; 23] = [
     RowId::Decoder,
     RowId::Hdr,
     RowId::Chroma444,
+    RowId::PresentPriority,
+    RowId::SmoothBuffer,
+    RowId::Vsync,
+    RowId::AllowVrr,
     RowId::Audio,
     RowId::Mic,
     RowId::EchoCancel,
@@ -119,6 +127,17 @@ const DECODERS: [(&str, &str); 4] = [
     ("software", "Software"),
 ];
 const AUDIO: [(u8, &str); 3] = [(2, "Stereo"), (6, "5.1"), (8, "7.1")];
+/// Presentation intent — the `present_priority` key shared with the Apple and Android
+/// clients, so one profile reads the same on every device.
+const PRESENT_PRIORITIES: [(&str, &str); 2] =
+    [("latency", "Lowest latency"), ("smooth", "Smoothness")];
+/// Smoothness buffer depth in frames; `0` = Automatic (resolves to 2).
+const SMOOTH_BUFFERS: [(u8, &str); 4] = [
+    (0, "Automatic"),
+    (1, "1 frame"),
+    (2, "2 frames"),
+    (3, "3 frames"),
+];
 const PAD_TYPES: [(&str, &str); 6] = [
     ("auto", "Automatic"),
     ("xbox360", "Xbox 360"),
@@ -224,12 +243,16 @@ impl SettingsScreen {
 
 fn row_spec(id: RowId, ctx: &Ctx) -> RowSpec {
     let s = &ctx.settings;
-    // Echo cancellation only means anything while the mic streams, and which controller to
-    // forward as which virtual pad only while any controller is forwarded at all — dimmed and
-    // inert otherwise, the same relationship the desktop shells draw with a greyed-out row.
+    // Several rows follow another: echo cancellation only means anything while the mic
+    // streams, the pad rows only while any controller is forwarded at all, and the
+    // smoothness buffer only while that intent is chosen. All go dim and inert otherwise
+    // — the same relationship the desktop shells draw by greying a row out (they hide the
+    // buffer row entirely; a fixed row list can't, and a row that vanished mid-list would
+    // move everything under the cursor).
     let enabled = match id {
         RowId::EchoCancel => s.mic_enabled,
         RowId::Pad | RowId::PadType => s.gamepad_forwarding,
+        RowId::SmoothBuffer => s.present_priority == "smooth",
         _ => true,
     };
     let (header, label, value): (Option<&'static str>, &str, String) = match id {
@@ -286,6 +309,22 @@ fn row_spec(id: RowId, ctx: &Ctx) -> RowSpec {
         RowId::Decoder => (None, "Decoder", label_for(&DECODERS, &s.decoder).into()),
         RowId::Hdr => (None, "10-bit HDR", on_off(s.hdr_enabled).into()),
         RowId::Chroma444 => (None, "Full chroma (4:4:4)", on_off(s.enable_444).into()),
+        RowId::PresentPriority => (
+            Some("Presentation"),
+            "Prioritize",
+            label_for(&PRESENT_PRIORITIES, &s.present_priority).into(),
+        ),
+        RowId::SmoothBuffer => (
+            None,
+            "Smoothness buffer",
+            SMOOTH_BUFFERS
+                .iter()
+                .find(|(v, _)| *v == s.smooth_buffer)
+                .map_or("Automatic", |(_, l)| l)
+                .into(),
+        ),
+        RowId::Vsync => (None, "V-Sync", on_off(s.vsync).into()),
+        RowId::AllowVrr => (None, "Follow variable refresh", on_off(s.allow_vrr).into()),
         RowId::Audio => (
             Some("Audio"),
             "Audio channels",
@@ -380,6 +419,24 @@ fn detail(id: RowId) -> &'static str {
              Needs an NVIDIA host (NVENC) or the PyroWave codec — other encoders \
              stream 4:2:0 and the session falls back silently."
         }
+        RowId::PresentPriority => {
+            "Lowest latency shows each frame the moment the display can take it — a \
+             network hiccup becomes an occasional repeated or skipped frame. Smoothness \
+             buffers a little to even those out."
+        }
+        RowId::SmoothBuffer => {
+            "Frames held back before showing. Each one absorbs about a refresh of network \
+             hiccup and adds a refresh of delay. Automatic holds two."
+        }
+        RowId::Vsync => {
+            "Tear-free. Off removes the wait for the screen's refresh — the lowest \
+             possible delay, at the cost of visible tearing. Not every driver offers it; \
+             the stats overlay names the mode actually in use."
+        }
+        RowId::AllowVrr => {
+            "On a VRR screen, let the panel refresh in step with the stream instead of on \
+             a fixed cadence. Applies to fullscreen sessions; harmless on a fixed screen."
+        }
         RowId::Audio => "The speaker layout requested from the host.",
         RowId::Mic => {
             "Send this device's microphone to the host's virtual mic. \
@@ -480,6 +537,27 @@ fn adjust(id: RowId, delta: i32, wrap: bool, ctx: &mut Ctx) -> bool {
         RowId::Decoder => step_str(&DECODERS, &mut s.decoder, delta, wrap),
         RowId::Hdr => toggle(&mut s.hdr_enabled, delta, wrap),
         RowId::Chroma444 => toggle(&mut s.enable_444, delta, wrap),
+        RowId::PresentPriority => {
+            let cur = PRESENT_PRIORITIES
+                .iter()
+                .position(|(v, _)| *v == s.present_priority);
+            step_option(cur, PRESENT_PRIORITIES.len(), delta, wrap)
+                .map(|i| s.present_priority = PRESENT_PRIORITIES[i].0.to_string())
+        }
+        // Inert unless smoothness is chosen — a boundary thud, matching the dimmed row.
+        RowId::SmoothBuffer => {
+            if s.present_priority == "smooth" {
+                let cur = SMOOTH_BUFFERS
+                    .iter()
+                    .position(|(v, _)| *v == s.smooth_buffer);
+                step_option(cur, SMOOTH_BUFFERS.len(), delta, wrap)
+                    .map(|i| s.smooth_buffer = SMOOTH_BUFFERS[i].0)
+            } else {
+                None
+            }
+        }
+        RowId::Vsync => toggle(&mut s.vsync, delta, wrap),
+        RowId::AllowVrr => toggle(&mut s.allow_vrr, delta, wrap),
         RowId::Audio => {
             let cur = AUDIO.iter().position(|(v, _)| *v == s.audio_channels);
             step_option(cur, AUDIO.len(), delta, wrap).map(|i| s.audio_channels = AUDIO[i].0)
@@ -674,6 +752,45 @@ mod tests {
         assert!(ctx.settings.echo_cancel);
     }
 
+    /// The smoothness buffer follows the presentation intent, exactly as echo cancellation
+    /// follows the mic: dimmed and inert under Lowest latency (where holding frames means
+    /// nothing), live under Smoothness. The desktop shells hide the row instead; a fixed
+    /// row list dims it, because a row vanishing mid-list would shift everything under the
+    /// cursor.
+    #[test]
+    fn smoothness_buffer_follows_the_intent() {
+        let (mut settings, pads) = ctx_parts();
+        assert_eq!(settings.present_priority, "latency", "the shipped default");
+        let library = crate::library::LibraryShared::default();
+        let mut ctx = Ctx {
+            hosts: &[],
+            library: &library,
+            settings: &mut settings,
+            pads: &pads,
+            deck: false,
+            device_name: "t",
+            t: 0.0,
+        };
+        assert!(!row_spec(RowId::SmoothBuffer, &ctx).enabled);
+        assert!(
+            !adjust(RowId::SmoothBuffer, 1, false, &mut ctx),
+            "latency intent = thud"
+        );
+        assert_eq!(ctx.settings.smooth_buffer, 0, "and nothing was written");
+
+        // Stepping the intent to Smoothness brings the buffer row to life.
+        assert!(adjust(RowId::PresentPriority, 1, false, &mut ctx));
+        assert_eq!(ctx.settings.present_priority, "smooth");
+        assert!(row_spec(RowId::SmoothBuffer, &ctx).enabled);
+        assert!(adjust(RowId::SmoothBuffer, 1, false, &mut ctx));
+        assert_eq!(ctx.settings.smooth_buffer, 1);
+
+        // The intent wraps back and the row goes inert again.
+        assert!(adjust(RowId::PresentPriority, -1, false, &mut ctx));
+        assert_eq!(ctx.settings.present_priority, "latency");
+        assert!(!row_spec(RowId::SmoothBuffer, &ctx).enabled);
+    }
+
     #[test]
     fn touch_mode_steps_and_wraps() {
         let (mut settings, pads) = ctx_parts();

crates/pf-presenter/src/lib.rs

@@ -52,6 +52,8 @@ pub mod keymap_sdl;
 #[cfg(any(target_os = "linux", windows))]
 pub mod overlay;
 #[cfg(any(target_os = "linux", windows))]
+mod present_pace;
+#[cfg(any(target_os = "linux", windows))]
 mod run;
 #[cfg(any(target_os = "linux", windows))]
 pub mod touch;

crates/pf-presenter/src/present_pace.rs

@@ -0,0 +1,751 @@
+//! The presentation intent engine (design/desktop-presentation-rebuild.md WP2): the
+//! store, clock, and gate the run loop composes into the two intents.
+//!
+//! * [`FrameStore`] — newest-wins slot (latency) or smoothing FIFO with preroll
+//!   (smoothness), ported from the Apple `FrameStore` / Android `presenter.rs` so all
+//!   three clients agree on what the intents mean.
+//! * [`LatchClock`] — the panel latch grid, learned from `VK_KHR_present_wait` on-glass
+//!   stamps (measured, never queried — the Android refresh-rate lie and VRR both punish
+//!   trusting a reported rate). Without present-wait it degrades to a grid rooted at the
+//!   last submit on the mode's refresh period.
+//! * [`PresentGate`] — the FIFO glass budget: one undisplayed present in flight, so the
+//!   swapchain's own queue can never become a standing queue (+1 refresh per slot,
+//!   forever — the law every bounded-FIFO pacing rediscovered on Apple). MAILBOX cannot
+//!   queue and never needs it.
+//!
+//! Everything here is pure state + arithmetic on `CLOCK_REALTIME` ns (the
+//! `pf_client_core::session::now_ns` domain the on-glass stamps live in); the run loop
+//! owns all clocks and Vulkan calls, which is what keeps this testable.
+
+use std::collections::VecDeque;
+
+/// Stale-present force-open: an undisplayed present older than this is presumed lost
+/// (occluded window, wedged compositor) and the gate opens anyway, counted as `forced`
+/// — reads 0 on healthy systems. The Apple/Android presenters use the same 100 ms.
+const STALE_REOPEN_NS: u64 = 100_000_000;
+
+/// The adaptive slot-pick margin's ceiling and step (Android's measured values: start
+/// at 0 — a fixed lead was pure display tax on the reference device — and widen only
+/// when measured misses demand it).
+pub(crate) const MARGIN_STEP_NS: u64 = 500_000;
+pub(crate) const MARGIN_MAX_NS: u64 = 2_500_000;
+
+/// The decoded-frame store between the wake channel and the present call.
+///
+/// `capacity == 0` = newest-wins (latency intent): `submit` replaces, `take` clears.
+/// `capacity 1..=3` = smoothing FIFO: preroll-to-capacity, drop-oldest on overflow,
+/// an underflow after preroll re-arms the preroll (the previous frame persists on
+/// glass — a repeat by omission) while headroom rebuilds.
+pub(crate) struct FrameStore<T> {
+    capacity: usize,
+    frames: VecDeque<T>,
+    prerolled: bool,
+    /// Newest-wins displacements (normal operation under latency, not a fault signal).
+    replaced: u32,
+    /// FIFO drop-oldest evictions — the Apple debug line's `qDrop`.
+    overflow_drops: u32,
+    /// FIFO dry-after-preroll events — `qDry`.
+    underflows: u32,
+}
+
+impl<T> FrameStore<T> {
+    pub(crate) fn new(capacity: usize) -> FrameStore<T> {
+        FrameStore {
+            capacity,
+            frames: VecDeque::with_capacity(capacity.max(1) + 1),
+            prerolled: false,
+            replaced: 0,
+            overflow_drops: 0,
+            underflows: 0,
+        }
+    }
+
+    pub(crate) fn is_smoothing(&self) -> bool {
+        self.capacity > 0
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.frames.is_empty()
+    }
+
+    pub(crate) fn submit(&mut self, f: T) {
+        if self.capacity == 0 {
+            if self.frames.pop_front().is_some() {
+                self.replaced += 1;
+            }
+            self.frames.push_back(f);
+        } else {
+            self.frames.push_back(f);
+            // Drop the OLDEST past capacity: bounded added latency, the newest keeps
+            // flowing. Also trims a transient capacity+1 a put_back left behind.
+            while self.frames.len() > self.capacity {
+                self.frames.pop_front();
+                self.overflow_drops += 1;
+            }
+        }
+    }
+
+    pub(crate) fn take(&mut self) -> Option<T> {
+        if self.capacity == 0 {
+            return self.frames.pop_front();
+        }
+        if !self.prerolled {
+            // Preroll gate: without it a steady stream drains every frame on arrival
+            // and jitter headroom never builds (the Apple store's lesson).
+            if self.frames.len() < self.capacity {
+                return None;
+            }
+            self.prerolled = true;
+        }
+        match self.frames.pop_front() {
+            Some(f) => Some(f),
+            None => {
+                self.underflows += 1;
+                self.prerolled = false;
+                None
+            }
+        }
+    }
+
+    /// A frame taken but not presented (gate closed, present failed before consuming
+    /// it). Newest-wins reinserts only into an empty slot — a fresher decode wins;
+    /// FIFO puts it back at the front (it is the oldest).
+    pub(crate) fn put_back(&mut self, f: T) {
+        if self.capacity == 0 {
+            if self.frames.is_empty() {
+                self.frames.push_back(f);
+            }
+        } else {
+            self.frames.push_front(f);
+        }
+    }
+
+    /// Collapse to newest-wins for the rest of the stream (PyroWave: its plane-ring
+    /// retirement accounting assumes the depth-2 newest-wins hand-off, and its all-intra
+    /// frames make buffering pointless anyway).
+    ///
+    /// Gated with its only caller: the power-user build (`--no-default-features`, which
+    /// the Windows ARM64 leg ships) has no PyroWave decode path, and an ungated helper
+    /// is dead code there.
+    #[cfg(feature = "pyrowave")]
+    pub(crate) fn force_latency(&mut self) {
+        if self.capacity == 0 {
+            return;
+        }
+        self.capacity = 0;
+        self.prerolled = false;
+        while self.frames.len() > 1 {
+            self.frames.pop_front();
+        }
+    }
+
+    /// Drain the window's counters: `(replaced, overflow_drops, underflows)`.
+    pub(crate) fn take_counters(&mut self) -> (u32, u32, u32) {
+        let c = (self.replaced, self.overflow_drops, self.underflows);
+        self.replaced = 0;
+        self.overflow_drops = 0;
+        self.underflows = 0;
+        c
+    }
+}
+
+/// The panel latch grid: a recent on-glass instant + the latch period, extrapolated
+/// forward for slot targeting.
+///
+/// The period learner is the SHARED [`punktfunk_core::phase::PanelGrid`], not a local
+/// rule. An earlier version of this clock capped the learned period at the display
+/// mode's refresh, on the reasoning that a stream running below panel rate spaces its
+/// presents at k×period and the cap stops a 30 fps stream claiming a 30 Hz panel. That
+/// cap is the same defect the Android presenter shipped in 0.23.0: the seed is only what
+/// the *mode* claims, and when the real panel is slower (a refused mode switch, a
+/// compositor running its own rate) a downward-only learner pins a grid that never
+/// arrives, for the whole session, with no way back. `PanelGrid` moves both ways —
+/// narrowing at once, widening only after eight consecutive agreeing observations and
+/// then to the narrowest of them.
+///
+/// What is fed to it is still the window's MIN spacing: within one window that resists
+/// the k×period inflation the old cap was aimed at, while the streak requirement means a
+/// genuinely slower panel is still discovered. Same grid the host-facing `LatchGrid`
+/// publish reads, so the phase-lock report and the local scheduler cannot disagree.
+pub(crate) struct LatchClock {
+    anchor_ns: u64,
+    /// The previous stamp, kept ACROSS calls. The run loop drains present-wait samples
+    /// every pass, so a "batch" is very often a single stamp — computing spacings only
+    /// within a batch (`windows(2)`) observed nothing at all on glass, and the learner
+    /// silently ran on its seed forever.
+    last_ns: u64,
+    /// Narrowest spacing seen since the last handoff to the grid, and how many have
+    /// accumulated. The grid is fed the MIN of a run rather than every spacing: our
+    /// observations are the spacing of OUR presents, which is k×period whenever the
+    /// stream runs below panel rate, and the min over a run is the best available
+    /// estimate of the true grid step.
+    pending_min_ns: u64,
+    pending_count: u32,
+    grid: punktfunk_core::phase::PanelGrid,
+    fallback_period_ns: u64,
+}
+
+/// Spacings per handoff to [`punktfunk_core::phase::PanelGrid`]. Small enough that a real
+/// mode change is picked up in well under a second at any sane frame rate.
+const GRID_OBSERVE_EVERY: u32 = 16;
+
+impl LatchClock {
+    pub(crate) fn new(refresh_hz: u32) -> LatchClock {
+        LatchClock {
+            anchor_ns: 0,
+            last_ns: 0,
+            pending_min_ns: 0,
+            pending_count: 0,
+            grid: punktfunk_core::phase::PanelGrid::seeded(refresh_hz as i32),
+            fallback_period_ns: 1_000_000_000 / u64::from(refresh_hz.max(1)),
+        }
+    }
+
+    /// Fold on-glass stamps (ascending). Spacings are measured against the previous
+    /// stamp whatever the batching, so the loop's one-sample-per-pass drain still feeds
+    /// the learner.
+    pub(crate) fn note_batch(&mut self, stamps: &[u64]) {
+        for &s in stamps {
+            if self.last_ns != 0 && s > self.last_ns {
+                let d = s - self.last_ns;
+                // < 1 ms apart = a queued pair, not a grid step.
+                if d > 1_000_000 {
+                    self.pending_min_ns = if self.pending_min_ns == 0 {
+                        d
+                    } else {
+                        self.pending_min_ns.min(d)
+                    };
+                    self.pending_count += 1;
+                    if self.pending_count >= GRID_OBSERVE_EVERY {
+                        self.grid.observe(self.pending_min_ns as i64);
+                        self.pending_min_ns = 0;
+                        self.pending_count = 0;
+                    }
+                }
+            }
+            self.last_ns = s;
+        }
+        if let Some(&last) = stamps.last() {
+            self.anchor_ns = last;
+        }
+    }
+
+    pub(crate) fn period_ns(&self) -> u64 {
+        let learned = self.grid.period_ns();
+        if learned > 0 {
+            learned as u64
+        } else {
+            self.fallback_period_ns
+        }
+    }
+
+    pub(crate) fn anchor_ns(&self) -> u64 {
+        self.anchor_ns
+    }
+
+    /// The first predicted latch strictly after `after_ns` (`anchor + k·period`). With
+    /// no anchor yet: one period out — callers get a usable, if unanchored, deadline.
+    pub(crate) fn next_slot_after(&self, after_ns: u64) -> u64 {
+        let p = self.period_ns();
+        if self.anchor_ns == 0 || after_ns < self.anchor_ns {
+            return after_ns.saturating_add(p);
+        }
+        let k = (after_ns - self.anchor_ns) / p + 1;
+        self.anchor_ns + k * p
+    }
+}
+
+/// Whether the panel is refreshing on a fixed grid or following our cadence.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
+pub(crate) enum Cadence {
+    /// Not enough evidence yet — say nothing rather than guess.
+    #[default]
+    Unknown,
+    /// On-glass instants land on multiples of the panel period: a fixed-refresh panel.
+    Fixed,
+    /// On-glass instants track our present spacing instead: variable refresh is live.
+    Variable,
+}
+
+impl Cadence {
+    pub(crate) fn label(self) -> &'static str {
+        match self {
+            Cadence::Unknown => "",
+            Cadence::Fixed => "no",
+            Cadence::Variable => "yes",
+        }
+    }
+}
+
+/// Is variable refresh actually live? **Measured, never queried** — no portable query
+/// exists (SDL exposes none, Wayland does not report adaptive-sync state, and Windows
+/// surfaces nothing through Vulkan), and the platforms that *do* answer have been caught
+/// lying before (Android reports a game-uid's down-rated refresh as the panel's).
+///
+/// The discriminator is quantization. On a fixed-refresh panel every on-glass instant
+/// lands on the vblank grid, so the spacing between consecutive presents is always
+/// ~k×period for whole k — even when the stream runs slower than the panel, where it just
+/// picks a larger k. Under real VRR the panel refreshes *when we present*, so the spacing
+/// follows our own cadence and sits wherever it likes relative to the grid.
+///
+/// So: fold each delta to its distance from the nearest multiple of the period. Tight
+/// against the grid ⇒ Fixed; consistently off it ⇒ Variable. A stream running exactly at
+/// panel rate is indistinguishable either way (both give delta ≈ period), which is
+/// harmless — at that rate VRR has nothing to do.
+pub(crate) struct CadenceProbe {
+    /// Off-grid distances as a fraction of the period, in thousandths.
+    off_grid_milli: Vec<u32>,
+    /// Previous stamp, kept across calls for the same reason [`LatchClock`] does: the
+    /// live drain hands over one sample at a time.
+    last_ns: u64,
+    /// The last round's raw reading and how many rounds have agreed — a verdict is only
+    /// published once [`CADENCE_STABLE_ROUNDS`] agree.
+    candidate: Cadence,
+    agree_rounds: u8,
+    verdict: Cadence,
+}
+
+/// Enough deltas to distinguish jitter from a real off-grid cadence.
+const CADENCE_MIN_SAMPLES: usize = 24;
+/// Consecutive agreeing rounds before a verdict is published.
+///
+/// ⭐ On glass (GNOME/Wayland, .21, 2026-08-02) the raw per-round verdict FLAPPED between
+/// runs with VRR provably disabled. The cause is structural, not a tuning miss: under a
+/// compositor our on-glass stamp is the compositor's release, so anything that perturbs
+/// delivery — an occluded or unfocused surface being throttled, a distressed pipeline
+/// missing vblanks — smears the spacings exactly the way real VRR does. This probe can
+/// therefore only ever say "presents are not landing on the grid", so it demands
+/// agreement across rounds and refuses evidence from a distressed window (see
+/// [`CadenceProbe::note`]'s `healthy` flag) before claiming anything.
+const CADENCE_STABLE_ROUNDS: u8 = 2;
+/// Median off-grid distance under this fraction of a period reads as grid-locked. Present
+/// stamps carry real measurement jitter (the wait returns, then we read the clock), so
+/// this is deliberately loose — the two regimes differ by far more than this in practice.
+const CADENCE_FIXED_MILLI: u32 = 150;
+
+impl CadenceProbe {
+    pub(crate) fn new() -> CadenceProbe {
+        CadenceProbe {
+            off_grid_milli: Vec::with_capacity(64),
+            last_ns: 0,
+            candidate: Cadence::Unknown,
+            agree_rounds: 0,
+            verdict: Cadence::Unknown,
+        }
+    }
+
+    /// Fold on-glass stamps against the learned panel period. Spacings are measured
+    /// against the previous stamp whatever the batching.
+    ///
+    /// `healthy` is the caller's statement that this window's presents were flowing
+    /// normally (no stale force-opens). A distressed pipeline smears spacings for reasons
+    /// that have nothing to do with the panel, so its evidence is dropped — the timeline
+    /// continuity is still advanced, it simply does not count as a sample.
+    pub(crate) fn note(&mut self, stamps: &[u64], period_ns: u64, healthy: bool) {
+        if period_ns == 0 || !healthy {
+            self.last_ns = stamps.last().copied().unwrap_or(self.last_ns);
+            return;
+        }
+        for &s in stamps {
+            let prev = std::mem::replace(&mut self.last_ns, s);
+            if prev == 0 || s <= prev {
+                continue;
+            }
+            let delta = s - prev;
+            let rem = delta % period_ns;
+            // Distance to the NEAREST multiple, so a delta just under k×period reads as
+            // close to the grid rather than a whole period away from k-1.
+            let off = rem.min(period_ns - rem);
+            self.off_grid_milli
+                .push((off.saturating_mul(1000) / period_ns) as u32);
+            // A round closes on the SAMPLE count, inside the loop — not once per call.
+            // Evaluating per call would make the verdict depend on how the caller happens
+            // to batch its stamps (one big batch = one round, forever short of the
+            // agreement requirement), and the live drain and the tests batch differently.
+            self.close_round_if_ready();
+        }
+    }
+
+    /// Publish a verdict once a round's worth of spacings agree with the previous round.
+    fn close_round_if_ready(&mut self) {
+        if self.off_grid_milli.len() >= CADENCE_MIN_SAMPLES {
+            self.off_grid_milli.sort_unstable();
+            let median = self.off_grid_milli[self.off_grid_milli.len() / 2];
+            let round = if median <= CADENCE_FIXED_MILLI {
+                Cadence::Fixed
+            } else {
+                Cadence::Variable
+            };
+            if round == self.candidate {
+                self.agree_rounds = self.agree_rounds.saturating_add(1);
+            } else {
+                self.candidate = round;
+                self.agree_rounds = 1;
+            }
+            if self.agree_rounds >= CADENCE_STABLE_ROUNDS {
+                self.verdict = round;
+            }
+            self.off_grid_milli.clear();
+        }
+    }
+
+    pub(crate) fn verdict(&self) -> Cadence {
+        self.verdict
+    }
+
+    /// A mode switch / display change invalidates the evidence.
+    pub(crate) fn reset(&mut self) {
+        self.off_grid_milli.clear();
+        self.last_ns = 0;
+        self.candidate = Cadence::Unknown;
+        self.agree_rounds = 0;
+        self.verdict = Cadence::Unknown;
+    }
+}
+
+/// The FIFO glass budget: at most one undisplayed present in flight, measured by the
+/// present-wait waiter's outstanding count. Never consulted under MAILBOX/IMMEDIATE
+/// (they cannot queue) or without present-wait (nothing to count with — behavior is
+/// then exactly the shipped arrival pacing).
+#[derive(Default)]
+pub(crate) struct PresentGate {
+    /// Submit stamp of the newest tracked present; 0 = none yet.
+    last_present_ns: u64,
+    gated: u32,
+    forced: u32,
+}
+
+impl PresentGate {
+    /// May a new present go out? Open when nothing undisplayed is in flight; a stale
+    /// in-flight present (occlusion, wedged compositor) force-opens after 100 ms so the
+    /// stream survives, counted as `forced`.
+    pub(crate) fn open(&mut self, outstanding: usize, now_ns: u64) -> bool {
+        if outstanding == 0 {
+            return true;
+        }
+        if self.last_present_ns != 0
+            && now_ns.saturating_sub(self.last_present_ns) > STALE_REOPEN_NS
+        {
+            self.forced += 1;
+            return true;
+        }
+        self.gated += 1;
+        false
+    }
+
+    pub(crate) fn note_present(&mut self, now_ns: u64) {
+        self.last_present_ns = now_ns;
+    }
+
+    /// Drain the window's counters: `(gated, forced)`.
+    pub(crate) fn take_counters(&mut self) -> (u32, u32) {
+        let c = (self.gated, self.forced);
+        self.gated = 0;
+        self.forced = 0;
+        c
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Newest-wins: submit replaces, take clears, put_back only fills an empty slot.
+    #[test]
+    fn newest_wins_replaces_and_putback_never_clobbers() {
+        let mut s: FrameStore<u32> = FrameStore::new(0);
+        assert!(!s.is_smoothing());
+        assert_eq!(s.take(), None);
+        s.submit(1);
+        s.submit(2);
+        s.submit(3);
+        assert_eq!(s.take(), Some(3), "only the newest survives");
+        assert_eq!(s.take(), None);
+        // A taken-but-unpresented frame returns — unless a fresher one arrived.
+        s.submit(4);
+        let f = s.take().unwrap();
+        s.put_back(f);
+        assert_eq!(s.take(), Some(4));
+        let f = s.take();
+        assert_eq!(f, None);
+        s.submit(5);
+        let f = s.take().unwrap();
+        s.submit(6);
+        s.put_back(f); // 6 arrived while 5 was out — 6 wins
+        assert_eq!(s.take(), Some(6));
+        assert_eq!(
+            s.take_counters(),
+            (2, 0, 0),
+            "two displacements, no fifo counters"
+        );
+    }
+
+    /// FIFO: preroll to capacity, drop-oldest overflow, underflow re-arms the preroll.
+    #[test]
+    fn fifo_prerolls_overflows_oldest_and_rearms_on_dry() {
+        let mut s: FrameStore<u32> = FrameStore::new(2);
+        assert!(s.is_smoothing());
+        s.submit(1);
+        assert_eq!(s.take(), None, "prerolling: below capacity, nothing vends");
+        s.submit(2);
+        assert_eq!(s.take(), Some(1), "preroll reached — FIFO order");
+        assert_eq!(
+            s.take(),
+            Some(2),
+            "once prerolled the buffer drains normally"
+        );
+        // Dry after preroll = one underflow, preroll re-arms.
+        assert_eq!(s.take(), None);
+        s.submit(3);
+        assert_eq!(s.take(), None, "re-armed preroll holds again");
+        s.submit(4);
+        assert_eq!(s.take(), Some(3));
+        // Overflow drops the OLDEST: [4] → [4,5] → 6 evicts 4 → 7 evicts 5.
+        s.submit(5);
+        s.submit(6);
+        s.submit(7);
+        assert_eq!(s.take(), Some(6));
+        assert_eq!(s.take(), Some(7));
+        let (replaced, drops, dry) = s.take_counters();
+        assert_eq!(replaced, 0);
+        assert_eq!(drops, 2, "6 evicted 4, 7 evicted 5");
+        assert_eq!(dry, 1);
+    }
+
+    /// put_back under FIFO goes to the FRONT (it is the oldest), and the transient
+    /// capacity+1 is trimmed by the next submit.
+    #[test]
+    fn fifo_putback_restores_order() {
+        let mut s: FrameStore<u32> = FrameStore::new(2);
+        s.submit(1);
+        s.submit(2);
+        let f = s.take().unwrap();
+        s.put_back(f);
+        assert_eq!(s.take(), Some(1), "the put-back frame is still first");
+    }
+
+    /// force_latency collapses a smoothing store to a newest-wins slot mid-stream.
+    #[cfg(feature = "pyrowave")]
+    #[test]
+    fn force_latency_collapses_to_one_slot() {
+        let mut s: FrameStore<u32> = FrameStore::new(3);
+        s.submit(1);
+        s.submit(2);
+        s.submit(3);
+        s.force_latency();
+        assert!(!s.is_smoothing());
+        assert_eq!(s.take(), Some(3), "only the newest survives the collapse");
+        s.submit(4);
+        s.submit(5);
+        assert_eq!(s.take(), Some(5));
+    }
+
+    /// The clock learns the min positive spacing (capped at the mode refresh), anchors
+    /// on the newest stamp, and extrapolates the next slot; sub-ms pairs (a queued
+    /// double-present) never become the period.
+    #[test]
+    fn latch_clock_learns_and_extrapolates() {
+        const P: u64 = 16_666_666; // 60 Hz
+        let mut c = LatchClock::new(60);
+        assert_eq!(c.period_ns(), P, "fallback = the mode refresh");
+        // No anchor: a usable deadline one period out.
+        assert_eq!(c.next_slot_after(1_000), 1_000 + P);
+
+        c.note_batch(&[1_000_000_000, 1_000_000_000 + P, 1_000_000_000 + 2 * P]);
+        assert_eq!(c.period_ns(), P);
+        assert_eq!(c.anchor_ns(), 1_000_000_000 + 2 * P);
+        let next = c.next_slot_after(c.anchor_ns());
+        assert_eq!(next, 1_000_000_000 + 3 * P);
+        // Mid-slot query lands on the same boundary; a later one steps whole periods.
+        assert_eq!(c.next_slot_after(next - 1), next);
+        assert_eq!(c.next_slot_after(next), next + P);
+
+        // A queued pair (< 1 ms apart) must not poison the period.
+        c.note_batch(&[2_000_000_000, 2_000_000_500]);
+        assert_eq!(c.period_ns(), P);
+        assert_eq!(c.anchor_ns(), 2_000_000_500, "the anchor still advances");
+
+        // A stream presenting every OTHER refresh spaces its glass stamps at 2×P. One
+        // such window must NOT move the grid — the shared learner needs a streak before
+        // it will widen, which is what keeps a briefly-slow stream from claiming a slow
+        // panel while still allowing a genuinely slower display to be discovered.
+        c.note_batch(&[3_000_000_000, 3_000_000_000 + 2 * P]);
+        assert_eq!(c.period_ns(), P, "one wide window is not a slower panel");
+
+        // A single stamp re-anchors without touching the period.
+        c.note_batch(&[5_000_000_000]);
+        assert_eq!(c.anchor_ns(), 5_000_000_000);
+        assert_eq!(c.period_ns(), P);
+
+        // A faster panel learns its own finer grid.
+        let mut fast = LatchClock::new(120);
+        fast.note_batch(&[1_000_000_000, 1_008_333_333]);
+        assert_eq!(fast.period_ns(), 8_333_333);
+    }
+
+    /// ⭐ The live loop drains present-wait samples EVERY pass, so stamps arrive one at a
+    /// time. Measuring spacings only within a batch meant the learner observed nothing on
+    /// glass and silently ran on its seed (found on .21, 2026-08-02: `period_us` read back
+    /// exactly the 60 Hz fallback while the panel really was 60 Hz — correct by luck, and
+    /// wrong the moment the mode lies).
+    #[test]
+    fn latch_clock_learns_from_one_sample_at_a_time() {
+        const REAL: u64 = 16_666_666;
+        let mut c = LatchClock::new(120); // seeded too fast, as a refused mode switch would
+        let mut t = 1_000_000_000u64;
+        for _ in 0..(GRID_OBSERVE_EVERY * 8 + 8) {
+            t += REAL;
+            c.note_batch(&[t]); // ONE stamp per call — the live shape
+        }
+        assert_eq!(
+            c.period_ns(),
+            REAL,
+            "single-stamp batches must still feed the grid learner"
+        );
+        assert_eq!(c.anchor_ns(), t);
+    }
+
+    /// The mode's refresh is a CLAIM, not a measurement — a refused mode switch or a
+    /// compositor running its own rate leaves the seed too fast. The old downward-only
+    /// cap pinned that wrong grid for the session (the Android 0.23.0 defect); the
+    /// shared learner climbs back out once the evidence is consistent.
+    #[test]
+    fn latch_clock_recovers_from_a_seed_faster_than_the_real_panel() {
+        const REAL: u64 = 16_666_666; // the panel is really 60 Hz…
+        let mut c = LatchClock::new(120); // …but the mode claimed 120
+        assert_eq!(c.period_ns(), 8_333_333, "seeded from the claim");
+
+        // Consistent 60 Hz evidence. The grid is fed the MIN of every
+        // GRID_OBSERVE_EVERY spacings, and PanelGrid widens only after 8 agreeing
+        // observations, so a real widen needs 8 × GRID_OBSERVE_EVERY spacings — the
+        // deliberate cost of not letting one slow patch redefine the panel.
+        let mut t = 1_000_000_000u64;
+        for _ in 0..(GRID_OBSERVE_EVERY * 8 + GRID_OBSERVE_EVERY) {
+            t += REAL;
+            c.note_batch(&[t]);
+        }
+        assert_eq!(
+            c.period_ns(),
+            REAL,
+            "a sustained slower grid is adopted instead of aimed past forever"
+        );
+    }
+
+    /// The VRR discriminator: presents landing on the vblank grid read Fixed, presents
+    /// landing wherever our own cadence puts them read Variable — including the case that
+    /// matters most, a stream SLOWER than the panel, where a fixed panel still quantizes
+    /// to a larger whole multiple.
+    #[test]
+    fn cadence_probe_separates_grid_locked_from_variable() {
+        const P: u64 = 8_333_333; // 120 Hz
+                                  // Enough spacings for CADENCE_STABLE_ROUNDS full rounds: a verdict is published
+                                  // only once consecutive rounds agree (on glass a single round FLAPPED).
+        const ROUNDS: u64 = (CADENCE_MIN_SAMPLES as u64) * (CADENCE_STABLE_ROUNDS as u64) + 4;
+
+        // Fixed panel, stream at panel rate: every delta is exactly one period.
+        let mut probe = CadenceProbe::new();
+        assert_eq!(probe.verdict(), Cadence::Unknown, "no evidence yet");
+        let stamps: Vec<u64> = (0..ROUNDS).map(|i| 1_000_000_000 + i * P).collect();
+        probe.note(&stamps, P, true);
+        assert_eq!(probe.verdict(), Cadence::Fixed);
+
+        // Fixed panel, stream at HALF panel rate: deltas are 2×P — still grid-locked.
+        let mut probe = CadenceProbe::new();
+        let stamps: Vec<u64> = (0..ROUNDS).map(|i| 1_000_000_000 + i * 2 * P).collect();
+        probe.note(&stamps, P, true);
+        assert_eq!(
+            probe.verdict(),
+            Cadence::Fixed,
+            "a slower stream on a fixed panel picks a larger k, it does not leave the grid"
+        );
+
+        // Fixed panel with realistic measurement jitter (±0.5 ms on an 8.3 ms period)
+        // must not read as variable.
+        let mut probe = CadenceProbe::new();
+        let jitter = [0i64, 300_000, -250_000, 120_000, -400_000, 80_000];
+        let stamps: Vec<u64> = (0..ROUNDS as usize)
+            .map(|i| (1_000_000_000 + i as i64 * P as i64 + jitter[i % jitter.len()]) as u64)
+            .collect();
+        probe.note(&stamps, P, true);
+        assert_eq!(probe.verdict(), Cadence::Fixed, "jitter is not VRR");
+
+        // VRR live: a 100 fps stream on a 120 Hz-max panel. 10 ms is not a multiple of
+        // 8.33 ms, so every present sits off the grid.
+        let mut probe = CadenceProbe::new();
+        let stamps: Vec<u64> = (0..ROUNDS)
+            .map(|i| 1_000_000_000 + i * 10_000_000)
+            .collect();
+        probe.note(&stamps, P, true);
+        assert_eq!(probe.verdict(), Cadence::Variable);
+
+        // A display change throws the evidence away rather than carrying a stale verdict.
+        probe.reset();
+        assert_eq!(probe.verdict(), Cadence::Unknown);
+
+        // Below the sample floor nothing is claimed.
+        let mut probe = CadenceProbe::new();
+        probe.note(&[1_000_000_000, 1_010_000_000, 1_020_000_000], P, true);
+        assert_eq!(probe.verdict(), Cadence::Unknown);
+
+        // ⭐ THE SHAPE THE LIVE LOOP ACTUALLY PRODUCES: the run loop drains present-wait
+        // samples every pass, so stamps arrive ONE AT A TIME. Measuring spacings only
+        // within a batch observed nothing at all on glass — `vrr` stayed Unknown and the
+        // latch clock ran on its seed forever. Found on .21, 2026-08-02.
+        let mut probe = CadenceProbe::new();
+        for i in 0..ROUNDS {
+            probe.note(&[1_000_000_000 + i * 10_000_000], P, true); // 100 fps, off a 120 Hz grid
+        }
+        assert_eq!(
+            probe.verdict(),
+            Cadence::Variable,
+            "one-sample batches must still yield spacings"
+        );
+
+        // A period we never learned can't discriminate anything.
+        let mut probe = CadenceProbe::new();
+        let stamps: Vec<u64> = (0..ROUNDS)
+            .map(|i| 1_000_000_000 + i * 10_000_000)
+            .collect();
+        probe.note(&stamps, 0, true);
+        assert_eq!(probe.verdict(), Cadence::Unknown);
+    }
+
+    /// ⭐ Batching must not change the verdict. The same spacings delivered as one big
+    /// batch, or one stamp at a time, must reach the same conclusion — the live loop
+    /// drains one at a time while tests hand over vectors, and an evaluation keyed to
+    /// call boundaries silently made the two disagree.
+    #[test]
+    fn cadence_verdict_is_independent_of_batching() {
+        const P: u64 = 8_333_333;
+        let n = (CADENCE_MIN_SAMPLES as u64) * (CADENCE_STABLE_ROUNDS as u64) + 4;
+
+        let stamps: Vec<u64> = (0..n).map(|i| 1_000_000_000 + i * P).collect();
+        let mut bulk = CadenceProbe::new();
+        bulk.note(&stamps, P, true);
+
+        let mut drip = CadenceProbe::new();
+        for s in &stamps {
+            drip.note(&[*s], P, true);
+        }
+
+        assert_eq!(bulk.verdict(), Cadence::Fixed);
+        assert_eq!(drip.verdict(), bulk.verdict(), "batching must not matter");
+    }
+
+    /// Gate: open at zero outstanding, closed at one, force-open past the stale bound.
+    #[test]
+    fn gate_budgets_one_undisplayed_present() {
+        let mut g = PresentGate::default();
+        let t0 = 1_000_000_000u64;
+        assert!(g.open(0, t0));
+        g.note_present(t0);
+        assert!(!g.open(1, t0 + 8_000_000), "one in flight — hold");
+        assert!(
+            g.open(1, t0 + STALE_REOPEN_NS + 1),
+            "stale in-flight present force-opens"
+        );
+        let (gated, forced) = g.take_counters();
+        assert_eq!((gated, forced), (1, 1));
+        assert_eq!(g.take_counters(), (0, 0), "counters drain");
+    }
+}

crates/pf-presenter/src/run.rs

@@ -18,12 +18,15 @@
 
 use crate::input::{Capture, FingerPhase};
 use crate::overlay::{FrameCtx, Overlay, OverlayAction, OverlayFrame, SessionPhase};
+use crate::present_pace::{
+    Cadence, CadenceProbe, FrameStore, LatchClock, PresentGate, MARGIN_MAX_NS, MARGIN_STEP_NS,
+};
 use crate::touch::Abs;
 use crate::vk::{FrameInput, Presenter};
 use anyhow::{Context as _, Result};
 use pf_client_core::gamepad::GamepadService;
 use pf_client_core::session::{self, SessionEvent, SessionHandle, SessionParams, Stats};
-use pf_client_core::trust::{MouseMode, StatsVerbosity, TouchMode};
+use pf_client_core::trust::{MouseMode, PresentPriority, StatsVerbosity, TouchMode};
 use pf_client_core::video::VulkanDecodeDevice;
 use pf_client_core::video::{DecodedFrame, DecodedImage};
 use punktfunk_core::client::NativeClient;
@@ -63,6 +66,20 @@ pub struct SessionOpts {
     /// work profile that streams on a second screen and still Alt-Tabs here. Never applies
     /// under the `desktop` mouse model, which is something you Alt-Tab *away* from.
     pub inhibit_shortcuts: bool,
+    /// Presentation intent ([`Settings::present_priority`] resolved): `Latency` keeps the
+    /// shipped arrival pacing (newest-wins, present the moment a frame can go out);
+    /// `Smooth { buffer }` runs the smoothing FIFO drained one frame per latch slot
+    /// (design/desktop-presentation-rebuild.md). `PUNKTFUNK_PRESENTER=arrival` overrides
+    /// the whole engine back to the legacy drain for field A/B without a rebuild.
+    pub present_priority: PresentPriority,
+    /// Tear-free presentation ([`Settings::vsync`], default on). Off asks for a tearing
+    /// present mode for the lowest possible latch — best-effort, and the mode that
+    /// actually took is named in the stats line.
+    pub vsync: bool,
+    /// Let a variable-refresh display follow the stream cadence ([`Settings::allow_vrr`],
+    /// default on) — prefers the present mode that drives VRR panels directly when the
+    /// session starts fullscreen.
+    pub allow_vrr: bool,
     /// Emit the `{"ready":true}` stdout line after the first presented frame.
     pub json_status: bool,
     /// Called once on `Connected` with the host's fingerprint (trust persistence is the
@@ -213,8 +230,47 @@ struct StreamState {
     // capture→displayed (host-clock corrected) p50+p95, display = decoded→displayed p50.
     win_e2e_us: Vec<u64>,
     win_disp_us: Vec<u64>,
+    /// The display stage's two halves (present-timing sessions only): decoded→submit and
+    /// submit→on-glass. See [`PresentedWindow::pace_ms`].
+    win_pace_us: Vec<u64>,
+    win_latch_us: Vec<u64>,
     win_start: Instant,
     presented: PresentedWindow,
+    /// The intent engine (design/desktop-presentation-rebuild.md WP2): the decoded-frame
+    /// store between the wake channel and the present call — a newest-wins slot under
+    /// the latency intent (behaviorally the shipped drain), the smoothing FIFO under
+    /// smoothness. NOTE: a smoothing store holds decoder-pool frames (Vulkan-Video
+    /// AVFrames) up to `buffer` deep on top of the depth-2 wake channels — within pool
+    /// headroom for 1..=3, but any deeper store must revisit pool sizing.
+    store: FrameStore<DecodedFrame>,
+    /// The panel latch grid (present-wait glass stamps; submit-anchored fallback) — the
+    /// smoothness slot clock, and the values published to the host-facing `latch_grid`.
+    clock: LatchClock,
+    /// The FIFO glass budget (one undisplayed present in flight) — inert off FIFO modes
+    /// or without present timing.
+    gate: PresentGate,
+    /// Is variable refresh actually live? Measured from the same on-glass stamps (no
+    /// portable query exists) — see [`CadenceProbe`].
+    cadence: CadenceProbe,
+    /// The DISPLAY MODE's refresh period — the vblank grid presents quantize to when
+    /// VRR is off, and so the cadence probe's reference. Deliberately not the learned
+    /// period (see the probe's call site).
+    mode_period_ns: u64,
+    /// The latch slot the last smoothness present served (one present per slot); 0 =
+    /// none yet.
+    last_target_ns: u64,
+    /// Smoothness slot-pick margin: starts 0 (a fixed lead is pure display tax —
+    /// measured on Android), widens +500 µs per >2-miss window toward 2.5 ms.
+    margin_ns: u64,
+    /// This window's latch misses (a present that reached glass > 1.5 latch periods
+    /// after submit) — the adaptive margin's error signal.
+    win_misses: u32,
+    /// This window's peak undisplayed-presents-in-flight (present timing only).
+    win_out_max: usize,
+    /// One-shot log latch: smoothness was requested but a PyroWave stream collapsed the
+    /// store to latency (its plane-ring retirement assumes the newest-wins hand-off).
+    #[cfg(all(any(target_os = "linux", windows), feature = "pyrowave"))]
+    pyro_latency_forced: bool,
     // Hardware-path health: a failure streak (or a device with no import support at
     // all) demotes the decoder to software via the shared flag — once per session.
     dmabuf_demoted: bool,
@@ -279,6 +335,8 @@ impl StreamState {
         params: SessionParams,
         force_software: Arc<AtomicBool>,
         wake: sdl3::event::EventSender,
+        priority: PresentPriority,
+        native_refresh_hz: u32,
     ) -> StreamState {
         let profile = params.profile.clone();
         // The presenter's half of phase-locked capture: it writes the latch grid the
@@ -316,8 +374,21 @@ impl StreamState {
             hdr_untonemapped: false,
             win_e2e_us: Vec::with_capacity(256),
             win_disp_us: Vec::with_capacity(256),
+            win_pace_us: Vec::with_capacity(256),
+            win_latch_us: Vec::with_capacity(256),
             win_start: Instant::now(),
             presented: PresentedWindow::default(),
+            store: FrameStore::new(usize::from(priority.fifo_capacity())),
+            clock: LatchClock::new(native_refresh_hz),
+            gate: PresentGate::default(),
+            cadence: CadenceProbe::new(),
+            mode_period_ns: 1_000_000_000 / u64::from(native_refresh_hz.max(1)),
+            last_target_ns: 0,
+            margin_ns: 0,
+            win_misses: 0,
+            win_out_max: 0,
+            #[cfg(all(any(target_os = "linux", windows), feature = "pyrowave"))]
+            pyro_latency_forced: false,
             dmabuf_demoted: false,
             #[cfg(all(any(target_os = "linux", windows), feature = "pyrowave"))]
             pyro_present_warned: false,
@@ -356,6 +427,25 @@ impl StreamState {
         }
         self.handle.stop.store(true, Ordering::SeqCst);
     }
+
+    /// The event-loop wait bound: a smoothness stream with buffered frames sleeps only
+    /// to its next latch-slot deadline; everything else keeps the 15 ms housekeeping
+    /// tick (frames, input, and present completions all wake the loop early anyway).
+    fn wake_timeout(&self) -> Duration {
+        const TICK: Duration = Duration::from_millis(15);
+        if !self.store.is_smoothing() || self.store.is_empty() {
+            return TICK;
+        }
+        let now = session::now_ns();
+        let mut target = self
+            .clock
+            .next_slot_after(now.saturating_add(self.margin_ns));
+        if target == self.last_target_ns {
+            // This slot is already served — the next boundary is the deadline.
+            target += self.clock.period_ns();
+        }
+        Duration::from_nanos(target.saturating_sub(now)).clamp(Duration::from_millis(1), TICK)
+    }
 }
 
 /// Whether a present error is `VK_ERROR_DEVICE_LOST` anywhere in its chain. A lost
@@ -438,9 +528,43 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
     let instance_exts = window
         .vulkan_instance_extensions()
         .map_err(|e| anyhow::anyhow!("vulkan instance extensions: {e}"))?;
-    let mut presenter = Presenter::new(&window, &instance_exts).context("vulkan presenter")?;
+    let mut presenter = Presenter::new(
+        &window,
+        &instance_exts,
+        crate::vk::PresentPref {
+            vsync: opts.vsync,
+            allow_vrr: opts.allow_vrr,
+            fullscreen: opts.fullscreen,
+            // `vrr_fifo_opt_in` (env) and `fifo_latest_ready` (device capability) are
+            // both resolved inside `Presenter::new` — the swapchain owns those, so every
+            // caller gets the same answer. `..Default` keeps this site from breaking each
+            // time the struct learns another one.
+            ..Default::default()
+        },
+    )
+    .context("vulkan presenter")?;
     // A valid black frame immediately — the window is honest while the connect runs.
     presenter.present(&window, FrameInput::Redraw, None)?;
+
+    // `PUNKTFUNK_PRESENTER=arrival` — the legacy drain, the intent engine's field-A/B
+    // kill switch (the Android sysprop pattern: no rebuild to bisect a pacing suspicion).
+    let arrival_override = std::env::var("PUNKTFUNK_PRESENTER").ok().as_deref() == Some("arrival");
+    let present_priority = if arrival_override {
+        tracing::info!("PUNKTFUNK_PRESENTER=arrival — presentation pacing disabled");
+        PresentPriority::Latency
+    } else {
+        opts.present_priority
+    };
+    let pacing_active = !arrival_override;
+    let present_debug = std::env::var_os("PUNKTFUNK_PRESENT_DEBUG").is_some();
+    // Present completions wake the loop exactly like decoded frames: a glass-gate
+    // reopen or a smoothness slot must not wait out the event timeout.
+    {
+        let sender = events.event_sender();
+        presenter.set_present_wake(Box::new(move || {
+            let _ = sender.push_custom_event(FrameWake);
+        }));
+    }
     // Browse mode is "ready" the moment the library window presents — there may never be
     // a stream. (Single mode announces on the first VIDEO frame instead, further down, so
     // a shell only yields to a window that actually shows the stream.)
@@ -517,6 +641,8 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                 params,
                 force_software,
                 events.event_sender(),
+                present_priority,
+                native.refresh_hz,
             ))
         }
         ModeCtl::Browse(_) => None,
@@ -544,8 +670,11 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
         // forwarder's FrameWake) all land in this one queue, so the loop wakes exactly
         // when there is work — a short-timeout poll here burned a full core (measured;
         // the timeout only bounds stop-flag/pump-tick latency now). In browse-idle the
-        // per-iteration FIFO present vsync-throttles the loop anyway.
-        let timeout = Duration::from_millis(15);
+        // per-iteration FIFO present vsync-throttles the loop anyway. A smoothness
+        // stream tightens the bound to its next latch-slot deadline.
+        let timeout = stream
+            .as_ref()
+            .map_or(Duration::from_millis(15), |st| st.wake_timeout());
         let first = event_pump.wait_event_timeout(timeout);
         let mut queued: Vec<Event> = Vec::new();
         if let Some(e) = first {
@@ -608,6 +737,29 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                             }
                         }
                     }
+                    // Dragged to another monitor (or the mode changed under us): the
+                    // latch grid and the VRR verdict both belong to the OLD panel. The
+                    // refresh rate used to be read once at startup and never revisited,
+                    // so a 60 Hz-seeded clock would keep pacing a 144 Hz panel.
+                    WindowEvent::DisplayChanged(..) => {
+                        let hz = window
+                            .get_display()
+                            .and_then(|d| d.get_mode())
+                            .map(|m| m.refresh_rate.round().max(0.0) as u32)
+                            .unwrap_or(0);
+                        if let Some(st) = stream.as_mut() {
+                            if hz > 0 {
+                                st.clock = LatchClock::new(hz);
+                                st.mode_period_ns = 1_000_000_000 / u64::from(hz);
+                            }
+                            st.cadence.reset();
+                            st.last_target_ns = 0;
+                            tracing::info!(
+                                refresh_hz = hz,
+                                "display changed — relearning the latch grid"
+                            );
+                        }
+                    }
                     WindowEvent::Exposed => {
                         presenter.present(&window, FrameInput::Redraw, overlay_frame.as_ref())?;
                     }
@@ -1032,6 +1184,8 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                                     *params,
                                     force_software,
                                     events.event_sender(),
+                                    present_priority,
+                                    native.refresh_hz,
                                 ));
                                 if let Some(o) = overlay.as_mut() {
                                     o.session_phase(SessionPhase::Connecting);
@@ -1279,11 +1433,148 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                     presenter.set_hdr_metadata(m);
                 }
             }
-            let mut newest: Option<DecodedFrame> = None;
-            while let Ok(f) = st.frames.try_recv() {
-                newest = Some(f);
+            // Present-wait completions drive the latch clock, the glass gate, and the
+            // host-facing grid — drained every pass (a 1 Hz batch would starve all
+            // three; the waiter's SDL wake pairs with this so completions never wait
+            // out the event timeout).
+            if presenter.present_timing_active() {
+                let samples = presenter.take_presented_samples();
+                if !samples.is_empty() {
+                    let clock_offset_ns = st
+                        .clock_offset
+                        .as_ref()
+                        .map_or(0, |o| o.load(Ordering::Relaxed));
+                    let period = st.clock.period_ns();
+                    let mut stamps = Vec::with_capacity(samples.len());
+                    for s in &samples {
+                        let e2e = (s.displayed_ns as i128 + clock_offset_ns as i128
+                            - s.pts_ns as i128)
+                            .max(0) as u64;
+                        if e2e > 0 && e2e < 10_000_000_000 {
+                            st.win_e2e_us.push(e2e / 1000);
+                        }
+                        st.win_disp_us
+                            .push(s.displayed_ns.saturating_sub(s.decoded_ns) / 1000);
+                        // The display split (WP4): our pipeline vs the vsync latch. Only
+                        // meaningful with true glass stamps, which is exactly when this
+                        // branch runs.
+                        st.win_pace_us
+                            .push(s.submitted_ns.saturating_sub(s.decoded_ns) / 1000);
+                        st.win_latch_us
+                            .push(s.displayed_ns.saturating_sub(s.submitted_ns) / 1000);
+                        // Latch miss (the adaptive margin's error signal): glass later
+                        // than one panel period past submit, PLUS the lead we already
+                        // applied — i.e. the slot we aimed at was missed. Measuring the
+                        // real latch rather than the store's own evictions is the
+                        // Android 0.23.0 correction: policy drops happen whenever the
+                        // stream out-runs the panel and say nothing about the latch, and
+                        // widening on them walked the margin to its ceiling on healthy
+                        // devices, re-imposing the very display latency it had removed.
+                        if st.store.is_smoothing()
+                            && s.displayed_ns.saturating_sub(s.submitted_ns) > period + st.margin_ns
+                        {
+                            st.win_misses += 1;
+                        }
+                        stamps.push(s.displayed_ns);
+                    }
+                    st.clock.note_batch(&stamps);
+                    // Same stamps answer "is VRR live" — the panel either quantizes them
+                    // to its grid or follows our cadence. Evidence only counts from a
+                    // window whose presents were flowing normally: a distressed pipeline
+                    // (stale force-opens) smears spacings for reasons that have nothing
+                    // to do with the panel, and on glass that flapped the verdict.
+                    //
+                    // ⚠ The reference is the DISPLAY MODE's period, NOT the learned one.
+                    // The learned grid comes from our own present spacings, and a stream
+                    // running below panel rate only ever produces multiples ≥ its frame
+                    // interval — so the learner adopts our cadence as "the grid" and every
+                    // delta then looks on-grid by construction. Measured on .21
+                    // (2026-08-02): a 40-50 fps stream on a 60 Hz panel learned 18-22 ms
+                    // and the probe reported VRR on a display with VRR provably disabled.
+                    // The vblank grid is the mode's refresh; that is what presents
+                    // quantize to when VRR is off.
+                    //
+                    // ⚠⚠ And it is only asked under a FIFO-family mode. The whole test
+                    // rests on "with VRR off, a present waits for vblank" — MAILBOX and
+                    // IMMEDIATE deliberately break that, so their stamps are never
+                    // grid-quantized and the probe would call every mailbox session VRR.
+                    // Measured on .21: same panel, same second — fifo read `no`
+                    // (correct, period 16.56 ms), mailbox read `yes` (wrong). Outside
+                    // FIFO the honest answer is "cannot tell", i.e. Unknown.
+                    let healthy = st.presented.forced == 0;
+                    if presenter.vblank_locked() {
+                        st.cadence.note(&stamps, st.mode_period_ns, healthy);
+                    }
+                    // Phase-locked capture, the presenter's half: publish the grid the
+                    // local clock just learned — a recent TRUE on-glass instant plus
+                    // the latch period — for the pump's ~1 Hz PhaseReport. One learner
+                    // feeds both, so the report and the scheduler cannot disagree.
+                    if let Some(grid) = &st.latch_grid {
+                        grid.period_ns
+                            .store(st.clock.period_ns(), Ordering::Relaxed);
+                        grid.anchor_ns
+                            .store(st.clock.anchor_ns(), Ordering::Relaxed);
+                    }
+                }
             }
-            if let Some(f) = newest {
+
+            // Intake into the intent store: a newest-wins slot under latency (the
+            // shipped drain, now with displacement counters), the smoothing FIFO under
+            // smoothness. PyroWave collapses smoothness to latency for the stream: its
+            // plane-ring retirement accounting assumes the newest-wins hand-off
+            // (`video_pyrowave::RETIRE_HANDOVERS`), and all-intra frames make
+            // buffering moot anyway.
+            while let Ok(f) = st.frames.try_recv() {
+                #[cfg(all(any(target_os = "linux", windows), feature = "pyrowave"))]
+                if st.store.is_smoothing() && matches!(f.image, DecodedImage::PyroWave(_)) {
+                    st.store.force_latency();
+                    if !st.pyro_latency_forced {
+                        st.pyro_latency_forced = true;
+                        tracing::info!(
+                            "PyroWave stream — smoothness buffering does not apply \
+                             (latency pacing)"
+                        );
+                    }
+                }
+                st.store.submit(f);
+            }
+
+            // One frame out, by intent: latency takes the newest whenever the glass
+            // gate allows; smoothness serves at most one frame per latch slot (the
+            // preroll/underflow behavior lives in the store).
+            let now_ns = session::now_ns();
+            let mut slot_target = 0u64;
+            let mut to_present = if st.store.is_smoothing() {
+                let target = st
+                    .clock
+                    .next_slot_after(now_ns.saturating_add(st.margin_ns));
+                if target != st.last_target_ns {
+                    slot_target = target;
+                    st.store.take()
+                } else {
+                    None
+                }
+            } else {
+                st.store.take()
+            };
+            // The FIFO glass budget: one undisplayed present in flight, so the
+            // swapchain's own FIFO can never become a standing queue (a measured
+            // 11-13 ms at 60 Hz on MAILBOX-less drivers). Only FIFO modes queue and
+            // only present timing can count, so everywhere else this stays inert and
+            // behavior is the shipped arrival pacing.
+            if pacing_active && presenter.needs_glass_gate() && presenter.present_timing_active() {
+                if let Some(f) = to_present.take() {
+                    if st.gate.open(presenter.presents_outstanding(), now_ns) {
+                        to_present = Some(f);
+                    } else {
+                        // Parked: a newest-wins store replaces it if a fresher frame
+                        // lands; the waiter's wake (or the 100 ms stale force-open)
+                        // retries.
+                        st.store.put_back(f);
+                    }
+                }
+            }
+            if let Some(f) = to_present {
                 // Resize END: a frame at the steered target size means the sharp new-mode
                 // picture is here — lift the scrim. A no-op unless a switch is in flight.
                 let (fw, fh) = f.image.dimensions();
@@ -1472,6 +1763,12 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                 };
                 if did_present {
                     presented_video = true;
+                    // Smoothness: this latch slot is served — one present per slot.
+                    // (Set only on success: a gated or failed present leaves the slot
+                    // open for the retry.)
+                    if slot_target != 0 {
+                        st.last_target_ns = slot_target;
+                    }
                     if opts.json_status && !st.ready_announced {
                         st.ready_announced = true;
                         println!("{{\"ready\":true}}");
@@ -1481,6 +1778,8 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                         // e2e/display samples arrive via `take_presented_samples` with a
                         // TRUE on-glass stamp instead of the submit-time one below.
                         presenter.note_presented(pts_ns, decoded_ns);
+                        st.gate.note_present(now_ns);
+                        st.win_out_max = st.win_out_max.max(presenter.presents_outstanding());
                     } else {
                         let displayed_ns = session::now_ns();
                         // The `displayed` stamp (same clamp rules as the pump's windows).
@@ -1495,59 +1794,81 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                         }
                         st.win_disp_us
                             .push(displayed_ns.saturating_sub(decoded_ns) / 1000);
+                        // No glass stamps on this stack: the submit instant anchors an
+                        // approximate grid on the mode's refresh period, so smoothness
+                        // still drains one frame per (approximate) slot.
+                        st.clock.note_batch(&[displayed_ns]);
                     }
                 }
             }
 
             // Fold the presenter window into the shared stats line once per second.
+            // (The on-glass samples themselves are drained every pass above — they
+            // drive the latch clock and glass gate, not just this fold.)
             if st.win_start.elapsed() >= Duration::from_secs(1) {
-                // On-glass samples the present-wait waiter completed this window (empty
-                // when timing is inactive — the legacy submit-time pushes fill in then).
-                let clock_offset_ns = st
-                    .clock_offset
-                    .as_ref()
-                    .map_or(0, |o| o.load(Ordering::Relaxed));
-                let samples = presenter.take_presented_samples();
-                // Phase-locked capture, the presenter's half: publish this window's latch
-                // grid — a recent TRUE on-glass instant plus the panel period — for the
-                // pump's ~1 Hz PhaseReport. The period is the min positive spacing of
-                // consecutive on-glass stamps (Apple's method: honest under VRR), capped
-                // by the display mode's refresh — under arrival-paced MAILBOX a stream
-                // running below the panel rate spaces its presents at k×period, and the
-                // cap keeps a 30 fps stream from claiming a 30 Hz panel grid.
-                if let Some(grid) = &st.latch_grid {
-                    if let Some(last) = samples.last() {
-                        let refresh_period = 1_000_000_000u64 / u64::from(native.refresh_hz.max(1));
-                        let min_delta = samples
-                            .windows(2)
-                            .map(|w| w[1].displayed_ns.saturating_sub(w[0].displayed_ns))
-                            .filter(|&d| d > 1_000_000) // < 1 ms apart = queued pair, not a grid step
-                            .min()
-                            .unwrap_or(refresh_period);
-                        grid.period_ns
-                            .store(min_delta.min(refresh_period), Ordering::Relaxed);
-                        grid.anchor_ns.store(last.displayed_ns, Ordering::Relaxed);
-                    }
-                }
-                for s in samples {
-                    let e2e = (s.displayed_ns as i128 + clock_offset_ns as i128 - s.pts_ns as i128)
-                        .max(0) as u64;
-                    if e2e > 0 && e2e < 10_000_000_000 {
-                        st.win_e2e_us.push(e2e / 1000);
-                    }
-                    st.win_disp_us
-                        .push(s.displayed_ns.saturating_sub(s.decoded_ns) / 1000);
-                }
                 let (e2e_p50, e2e_p95) = session::window_percentiles(&mut st.win_e2e_us);
                 let (disp_p50, _) = session::window_percentiles(&mut st.win_disp_us);
+                let (pace_p50, _) = session::window_percentiles(&mut st.win_pace_us);
+                let (latch_p50, _) = session::window_percentiles(&mut st.win_latch_us);
+                // Drained ONCE per window and shared by the HUD and the log line below —
+                // a second `take_counters` would read zeros.
+                let (replaced, q_drop, q_dry) = st.store.take_counters();
+                let (gated, forced) = st.gate.take_counters();
                 st.presented = PresentedWindow {
                     e2e_p50_ms: e2e_p50 as f32 / 1000.0,
                     e2e_p95_ms: e2e_p95 as f32 / 1000.0,
                     display_ms: disp_p50 as f32 / 1000.0,
+                    pace_ms: pace_p50 as f32 / 1000.0,
+                    latch_ms: latch_p50 as f32 / 1000.0,
+                    mode: presenter.present_mode_name(),
+                    vrr: st.cadence.verdict(),
+                    smoothing: st.store.is_smoothing(),
+                    q_drop,
+                    q_dry,
+                    gated,
+                    forced,
                 };
                 st.win_e2e_us.clear();
                 st.win_disp_us.clear();
+                st.win_pace_us.clear();
+                st.win_latch_us.clear();
                 st.win_start = Instant::now();
+                // Adaptive slot margin (the Android presenter's measured recipe):
+                // start at 0 — a fixed lead is pure display tax — and widen one step
+                // per window whose measured latch misses demand it. One-way per
+                // stream; the next stream restarts at 0.
+                if st.store.is_smoothing() && st.win_misses > 2 && st.margin_ns < MARGIN_MAX_NS {
+                    st.margin_ns = (st.margin_ns + MARGIN_STEP_NS).min(MARGIN_MAX_NS);
+                    tracing::info!(
+                        margin_us = st.margin_ns / 1000,
+                        misses = st.win_misses,
+                        "smoothness slot margin widened (measured latch misses)"
+                    );
+                }
+                // The 1 Hz presenter line (the Apple `pf-present` analogue): emitted
+                // when anything moved, or always under PUNKTFUNK_PRESENT_DEBUG=1 —
+                // the field-triage instrument for the intent engine.
+                if pacing_active && (present_debug || q_drop + q_dry + gated + forced > 0) {
+                    tracing::info!(
+                        smoothing = st.presented.smoothing,
+                        mode = st.presented.mode,
+                        vrr = st.presented.vrr.label(),
+                        replaced,
+                        q_drop,
+                        q_dry,
+                        gated,
+                        forced,
+                        misses = st.win_misses,
+                        out_max = st.win_out_max,
+                        pace_ms = st.presented.pace_ms,
+                        latch_ms = st.presented.latch_ms,
+                        period_us = st.clock.period_ns() / 1000,
+                        margin_us = st.margin_ns / 1000,
+                        "presenter window"
+                    );
+                }
+                st.win_misses = 0;
+                st.win_out_max = 0;
             }
         }
 
@@ -2007,6 +2328,32 @@ struct PresentedWindow {
     e2e_p50_ms: f32,
     e2e_p95_ms: f32,
     display_ms: f32,
+    /// The display stage split (design/desktop-presentation-rebuild.md WP4):
+    /// `pace` = decoded → present-submit (our own pipeline), `latch` = submit → on-glass
+    /// (the presentation engine's queue + the vblank wait). Both `0` without
+    /// `VK_KHR_present_wait`, where the two are not separable — the HUD then shows the
+    /// unsplit figure rather than inventing a zero latch.
+    ///
+    /// This split is what makes a high `display` self-diagnosing: latch dominating means
+    /// the vsync/queue floor (or a standing queue), pace dominating means us.
+    /// `pace` is also the honest cross-platform twin of the Apple client's shaved
+    /// number — Apple subtracts its measured OS present floor, and the latch IS our
+    /// floor, so `pace` is what remains on both sides of that comparison.
+    pace_ms: f32,
+    latch_ms: f32,
+    /// The live swapchain present mode (`mailbox`/`fifo`/…). Shown because a mode is
+    /// chosen from what the surface offers, so "why is my latch a refresh long" is
+    /// usually answered by a MAILBOX request having landed on FIFO.
+    mode: &'static str,
+    /// Whether variable refresh is measurably live (never claimed without evidence).
+    vrr: Cadence,
+    /// Presenter-engine counters for the window: the smoothing FIFO's overflow drops and
+    /// post-preroll underflows, and the FIFO glass gate's holds/stale force-opens.
+    smoothing: bool,
+    q_drop: u32,
+    q_dry: u32,
+    gated: u32,
+    forced: u32,
 }
 
 /// The capture hints (`ui_stream` parity — the words the user reads while released).
@@ -2112,6 +2459,15 @@ fn stats_text(
             " · decode {:.1} · display {:.1} ms",
             s.decode_ms, p.display_ms
         ));
+        // The display split (WP4). Only with true on-glass stamps — without them the
+        // two halves are not separable and the unsplit figure stands alone rather than
+        // implying a zero latch.
+        if p.latch_ms > 0.0 || p.pace_ms > 0.0 {
+            text.push_str(&format!(
+                " (pace {:.1} + latch {:.1})",
+                p.pace_ms, p.latch_ms
+            ));
+        }
         // Extended 0xCF host-stage split (T0.1): its own line so the per-stage attribution
         // (queue → encode → seal/xfer → pace) reads as the host pipeline in order.
         if s.staged {
@@ -2120,6 +2476,32 @@ fn stats_text(
                 s.host_queue_ms, s.host_encode_ms, s.host_xfer_ms, s.host_pace_ms
             ));
         }
+        // The presenter line: the swapchain mode that is actually live, the chosen
+        // intent, and the engine's own counters. Present-mode alone answers most
+        // "why is my latch a whole refresh" questions; the counters only render when
+        // they are non-zero, so a healthy latency session shows just the mode.
+        if !p.mode.is_empty() {
+            text.push_str(&format!("\npresent: {}", p.mode));
+            // Only once measured — an unproven "vrr no" would be a claim, not a reading.
+            if p.vrr != Cadence::Unknown {
+                text.push_str(&format!(" · vrr {}", p.vrr.label()));
+            }
+            if p.smoothing {
+                text.push_str(" · smoothing");
+            }
+            if p.q_drop > 0 {
+                text.push_str(&format!(" · qdrop {}", p.q_drop));
+            }
+            if p.q_dry > 0 {
+                text.push_str(&format!(" · qdry {}", p.q_dry));
+            }
+            if p.gated > 0 {
+                text.push_str(&format!(" · gated {}", p.gated));
+            }
+            if p.forced > 0 {
+                text.push_str(&format!(" · forced {}", p.forced));
+            }
+        }
     }
     if s.lost > 0 {
         text.push_str(&format!("\nlost {} ({:.1}%)", s.lost, s.lost_pct));
@@ -2393,6 +2775,7 @@ mod tests {
                 e2e_p50_ms: 6.4,
                 e2e_p95_ms: 9.1,
                 display_ms: 1.1,
+                ..Default::default()
             },
         )
     }
@@ -2430,6 +2813,70 @@ mod tests {
             !normal.contains("queue"),
             "host-stage split is Detailed-only"
         );
+        assert!(
+            !detailed.contains("pace 1.1"),
+            "no glass stamps in this sample — the display stage stays unsplit"
+        );
+    }
+
+    /// WP4: with true on-glass stamps the display stage reads as its two halves, the
+    /// live present mode is named, and the engine counters render only when non-zero —
+    /// so a healthy latency session shows the mode and nothing else. Without glass
+    /// stamps (no `VK_KHR_present_wait`) the split is absent rather than a zero latch.
+    #[test]
+    fn detailed_splits_display_into_pace_and_latch() {
+        let (s, mut p) = sample();
+        p.display_ms = 12.4;
+        p.pace_ms = 1.1;
+        p.latch_ms = 11.3;
+        p.mode = "fifo";
+        let split = stats_text(
+            StatsVerbosity::Detailed,
+            "m",
+            &s,
+            &p,
+            false,
+            false,
+            false,
+            None,
+        );
+        assert!(split.contains("display 12.4 ms (pace 1.1 + latch 11.3)"));
+        assert!(split.contains("\npresent: fifo"));
+        assert!(
+            !split.contains("qdrop") && !split.contains("gated") && !split.contains("smoothing"),
+            "quiet counters stay off the HUD: {split}"
+        );
+
+        // The smoothing FIFO and the glass gate surface once they actually do something.
+        p.smoothing = true;
+        p.q_drop = 2;
+        p.q_dry = 1;
+        p.gated = 7;
+        p.forced = 1;
+        let busy = stats_text(
+            StatsVerbosity::Detailed,
+            "m",
+            &s,
+            &p,
+            false,
+            false,
+            false,
+            None,
+        );
+        assert!(busy.contains("present: fifo · smoothing · qdrop 2 · qdry 1 · gated 7 · forced 1"));
+
+        // A tier below Detailed never carries any of it.
+        let normal = stats_text(
+            StatsVerbosity::Normal,
+            "m",
+            &s,
+            &p,
+            false,
+            false,
+            false,
+            None,
+        );
+        assert!(!normal.contains("present:") && !normal.contains("pace"));
     }
 
     /// The honest HDR badges: a PQ stream on the software-decode lane is shown WITHOUT

crates/pf-presenter/src/vk/mod.rs

@@ -33,7 +33,7 @@ mod reconfig;
 mod resources;
 mod setup;
 
-pub use setup::list_adapters;
+pub use setup::{list_adapters, PresentPref};
 
 /// One presenter iteration's video input.
 pub enum FrameInput<'a> {
@@ -247,10 +247,75 @@ impl Presenter {
     /// (the presenter itself never sees them). No-op when timing is inactive.
     pub(crate) fn note_presented(&mut self, pts_ns: u64, decoded_ns: u64) {
         if let (Some(t), Some((sc, id))) = (&self.present_timer, self.last_presented.take()) {
-            t.enqueue(sc, id, pts_ns, decoded_ns);
+            // The submit stamp: `present()` already returned, so "now" is within the
+            // present-call tail — the pace/latch split point.
+            t.enqueue(
+                sc,
+                id,
+                pts_ns,
+                decoded_ns,
+                pf_client_core::session::now_ns(),
+            );
         }
     }
 
+    /// Undisplayed id-carrying presents in flight (0 when timing is inactive) — the
+    /// FIFO glass gate's budget count.
+    pub(crate) fn presents_outstanding(&self) -> usize {
+        self.present_timer.as_ref().map_or(0, |t| t.outstanding())
+    }
+
+    /// Install the run loop's wake for present completions (an SDL event push). No-op
+    /// without present timing — there is nothing to wake on then.
+    pub(crate) fn set_present_wake(&self, cb: Box<dyn Fn() + Send>) {
+        if let Some(t) = &self.present_timer {
+            t.set_wake(cb);
+        }
+    }
+
+    /// The live swapchain present mode, for the stats overlay: a mode is picked from
+    /// what the surface actually offers, so the requested one and this can differ (a
+    /// MAILBOX request lands on FIFO wherever the driver has no mailbox — AMD's Windows
+    /// driver, notably). Showing it is what makes that visible instead of puzzling.
+    pub(crate) fn present_mode_name(&self) -> &'static str {
+        match self.present_mode {
+            vk::PresentModeKHR::MAILBOX => "mailbox",
+            vk::PresentModeKHR::FIFO => "fifo",
+            vk::PresentModeKHR::FIFO_RELAXED => "fifo-relaxed",
+            vk::PresentModeKHR::IMMEDIATE => "immediate",
+            setup::fifo_latest_ready::MODE => "fifo-latest-ready",
+            _ => "other",
+        }
+    }
+
+    /// The active present mode QUEUES presents — the only modes where the swapchain
+    /// itself can become a standing queue, and so the only ones the glass gate governs.
+    ///
+    /// MAILBOX and IMMEDIATE replace/flip and never queue. Nor does
+    /// `FIFO_LATEST_READY`, which retires stale images in the driver: gating on top of it
+    /// would hold frames back to emulate something the presentation engine is already
+    /// doing, paying the serialisation twice.
+    pub(crate) fn needs_glass_gate(&self) -> bool {
+        matches!(
+            self.present_mode,
+            vk::PresentModeKHR::FIFO | vk::PresentModeKHR::FIFO_RELAXED
+        )
+    }
+
+    /// The active present mode shows images ON THE VBLANK GRID — the premise the VRR
+    /// cadence probe rests on ("with VRR off, a present waits for vblank"). The whole
+    /// FIFO family qualifies, `FIFO_LATEST_READY` included: it drops stale images but
+    /// still presents on the refresh boundary. MAILBOX/IMMEDIATE do not, and under them
+    /// the probe reports Unknown rather than calling every session VRR.
+    pub(crate) fn vblank_locked(&self) -> bool {
+        matches!(
+            self.present_mode,
+            vk::PresentModeKHR::FIFO
+                | vk::PresentModeKHR::FIFO_RELAXED
+                | setup::fifo_latest_ready::MODE
+        )
+    }
+
     /// Take the window's completed on-glass samples (empty when timing is inactive).
     pub(crate) fn take_presented_samples(&self) -> Vec<present_timing::PresentedSample> {
         self.present_timer

crates/pf-presenter/src/vk/present_timing.rs

@@ -26,6 +26,9 @@ pub(crate) struct PresentedSample {
     pub pts_ns: u64,
     /// Decode-complete stamp (client clock) — the display-stage anchor.
     pub decoded_ns: u64,
+    /// `vkQueuePresentKHR`-return stamp (client clock) — the pace/latch split point:
+    /// `submitted − decoded` is our pipeline, `displayed − submitted` the vsync latch.
+    pub submitted_ns: u64,
     /// `vkWaitForPresentKHR` completion = the image is visible (client clock).
     pub displayed_ns: u64,
 }
@@ -35,15 +38,24 @@ struct Job {
     present_id: u64,
     pts_ns: u64,
     decoded_ns: u64,
+    submitted_ns: u64,
 }
 
+/// The run loop's wake callback (an SDL event push), shared with the waiter thread.
+type WakeSlot = Arc<Mutex<Option<Box<dyn Fn() + Send>>>>;
+
 /// The waiter: a channel-fed thread turning (swapchain, present-id) pairs into
 /// [`PresentedSample`]s. One frame in flight upstream keeps the queue depth ~1.
 pub(crate) struct PresentTimer {
     tx: Option<mpsc::Sender<Job>>,
-    /// Jobs enqueued but not yet finished — the drain barrier for swapchain teardown.
+    /// Jobs enqueued but not yet finished — the drain barrier for swapchain teardown,
+    /// and the glass gate's "undisplayed presents in flight" count.
     pending: Arc<AtomicUsize>,
     results: Arc<Mutex<Vec<PresentedSample>>>,
+    /// Called by the waiter after each completed wait (sample or not) — the run loop
+    /// installs an SDL wake here so a gate reopen / smoothness slot never waits out the
+    /// event-loop timeout.
+    wake: WakeSlot,
     join: Option<std::thread::JoinHandle<()>>,
 }
 
@@ -52,7 +64,8 @@ impl PresentTimer {
         let (tx, rx) = mpsc::channel::<Job>();
         let pending = Arc::new(AtomicUsize::new(0));
         let results = Arc::new(Mutex::new(Vec::with_capacity(256)));
-        let (pending_t, results_t) = (pending.clone(), results.clone());
+        let wake: WakeSlot = Arc::new(Mutex::new(None));
+        let (pending_t, results_t, wake_t) = (pending.clone(), results.clone(), wake.clone());
         let join = std::thread::Builder::new()
             .name("pf-present-wait".into())
             .spawn(move || {
@@ -69,12 +82,20 @@ impl PresentTimer {
                         results_t.lock().unwrap().push(PresentedSample {
                             pts_ns: job.pts_ns,
                             decoded_ns: job.decoded_ns,
+                            submitted_ns: job.submitted_ns,
                             displayed_ns,
                         });
                     }
                     // SUBOPTIMAL/TIMEOUT/DEVICE_LOST: no sample; the frame still showed
                     // (or the loop is about to find out) — never poison the window.
                     pending_t.fetch_sub(1, Ordering::AcqRel);
+                    // Wake the run loop AFTER the count dropped: what it observes on
+                    // wake is the post-completion state (the gate may now be open).
+                    // Called under the slot lock — the callback is a bare SDL event
+                    // push and never reenters this type.
+                    if let Some(cb) = wake_t.lock().unwrap().as_ref() {
+                        cb();
+                    }
                 }
             })
             .expect("spawn pf-present-wait");
@@ -82,10 +103,23 @@ impl PresentTimer {
             tx: Some(tx),
             pending,
             results,
+            wake,
             join: Some(join),
         }
     }
 
+    /// Install the run loop's wake callback (an SDL event push — thread-safe by design).
+    pub(crate) fn set_wake(&self, cb: Box<dyn Fn() + Send>) {
+        *self.wake.lock().unwrap() = Some(cb);
+    }
+
+    /// Presents handed to the waiter and not yet resolved to glass — the glass gate's
+    /// budget count. (Also counts a wait that will end SUBOPTIMAL/TIMEOUT; those resolve
+    /// within the 250 ms cap, far past the gate's own 100 ms stale force-open.)
+    pub(crate) fn outstanding(&self) -> usize {
+        self.pending.load(Ordering::Acquire)
+    }
+
     /// Hand a successfully submitted present to the waiter.
     pub(crate) fn enqueue(
         &self,
@@ -93,6 +127,7 @@ impl PresentTimer {
         present_id: u64,
         pts_ns: u64,
         decoded_ns: u64,
+        submitted_ns: u64,
     ) {
         if let Some(tx) = &self.tx {
             self.pending.fetch_add(1, Ordering::AcqRel);
@@ -102,6 +137,7 @@ impl PresentTimer {
                     present_id,
                     pts_ns,
                     decoded_ns,
+                    submitted_ns,
                 })
                 .is_err()
             {

crates/pf-presenter/src/vk/setup.rs

@@ -13,10 +13,55 @@ use ash::vk;
 use ash::vk::Handle as _;
 use std::ffi::{c_char, CString};
 
+/// `VK_EXT_present_mode_fifo_latest_ready`, hand-declared: it postdates the Vulkan headers
+/// ash 0.38 is generated from (1.3.281), so there is no binding for it — which is also why
+/// an unenabled driver reports the mode back as the bare number `1000361000`.
+///
+/// The mode is FIFO's tear-free vblank pacing that presents the **latest ready** image at
+/// each refresh and retires the older ones, instead of draining a queue. That is precisely
+/// what [`super::super::present_pace::PresentGate`] emulates in software, done by the
+/// driver — and it matters most exactly where the gate does: on a surface that offers no
+/// MAILBOX, this restores newest-wins behaviour without the app holding frames back.
+pub(crate) mod fifo_latest_ready {
+    use ash::vk;
+
+    /// `VK_EXT_present_mode_fifo_latest_ready` (extension 361).
+    pub(super) const NAME: &std::ffi::CStr = c"VK_EXT_present_mode_fifo_latest_ready";
+    /// `VK_PRESENT_MODE_FIFO_LATEST_READY_EXT`.
+    pub(crate) const MODE: vk::PresentModeKHR = vk::PresentModeKHR::from_raw(1000361000);
+    /// `VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_PRESENT_MODE_FIFO_LATEST_READY_FEATURES_EXT`.
+    const S_TYPE: vk::StructureType = vk::StructureType::from_raw(1000361000);
+
+    /// `VkPhysicalDevicePresentModeFifoLatestReadyFeaturesEXT`. The mode is usable only
+    /// when this feature is enabled at device creation, so the surface advertising the
+    /// mode is NOT on its own permission to request it.
+    #[repr(C)]
+    #[derive(Clone, Copy)]
+    pub(super) struct Features {
+        pub s_type: vk::StructureType,
+        pub p_next: *mut std::ffi::c_void,
+        pub present_mode_fifo_latest_ready: vk::Bool32,
+    }
+
+    impl Default for Features {
+        fn default() -> Features {
+            Features {
+                s_type: S_TYPE,
+                p_next: std::ptr::null_mut(),
+                present_mode_fifo_latest_ready: vk::FALSE,
+            }
+        }
+    }
+}
+
 impl Presenter {
     /// Bring up instance → surface → device → swapchain over an SDL window.
     /// `instance_extensions` comes from `VideoSubsystem::vulkan_instance_extensions()`.
-    pub fn new(window: &sdl3::video::Window, instance_extensions: &[String]) -> Result<Presenter> {
+    pub fn new(
+        window: &sdl3::video::Window,
+        instance_extensions: &[String],
+        pref: PresentPref,
+    ) -> Result<Presenter> {
         // SAFETY: per the Vulkan contract above - a create/allocate call on the live device, over
         // builder structs that are locals outliving the call; the handle it returns is owned by
         // the value being built here.
@@ -176,6 +221,21 @@ impl Presenter {
         // structs through its pNext chain, so any later use of it would pin those borrows —
         // every read of a chained struct below must come after this, have_f2's last use.
         let have_shader_int16 = have_f2.features.shader_int16;
+        // FIFO_LATEST_READY: the surface may list the mode even with the extension
+        // disabled, so the device feature is the real gate on using it.
+        let flr_ok = if has(fifo_latest_ready::NAME) {
+            let mut feat = fifo_latest_ready::Features::default();
+            let mut probe = vk::PhysicalDeviceFeatures2 {
+                p_next: (&mut feat) as *mut _ as *mut std::ffi::c_void,
+                ..Default::default()
+            };
+            // SAFETY: per the Vulkan contract above - a read-only query on the live
+            // instance/device, filling locals returned by value; `feat` outlives the call.
+            unsafe { instance.get_physical_device_features2(pdev, &mut probe) };
+            feat.present_mode_fifo_latest_ready == vk::TRUE
+        } else {
+            false
+        };
         let present_wait_ok = present_wait_exts
             && have_pid.present_id == vk::TRUE
             && have_pwait.present_wait == vk::TRUE;
@@ -273,6 +333,13 @@ impl Presenter {
             dev_exts.push(ash::khr::present_id::NAME.as_ptr());
             dev_exts.push(ash::khr::present_wait::NAME.as_ptr());
         }
+        if flr_ok {
+            dev_exts.push(fifo_latest_ready::NAME.as_ptr());
+        }
+        let mut en_flr = fifo_latest_ready::Features {
+            present_mode_fifo_latest_ready: vk::TRUE,
+            ..Default::default()
+        };
         let mut en_pid = vk::PhysicalDevicePresentIdFeaturesKHR::default().present_id(true);
         let mut en_pwait = vk::PhysicalDevicePresentWaitFeaturesKHR::default().present_wait(true);
 
@@ -295,6 +362,11 @@ impl Presenter {
         if present_wait_ok {
             en_f2 = en_f2.push_next(&mut en_pid).push_next(&mut en_pwait);
         }
+        if flr_ok {
+            // Hand-rolled struct, so chain it by hand: splice into the pNext list head.
+            en_flr.p_next = en_f2.p_next;
+            en_f2.p_next = (&mut en_flr) as *mut _ as *mut std::ffi::c_void;
+        }
         en_f2.features.shader_int16 = if pyrowave_ok { vk::TRUE } else { vk::FALSE };
 
         let priorities = [1.0f32];
@@ -450,11 +522,17 @@ impl Presenter {
         if let Some(v) = video_export.as_mut() {
             v.d3d11_hdr10 = win_capable && import_rgb10 && hdr10_format.is_some();
         }
-        let present_mode = pick_present_mode(&surface_i, pdev, surface)?;
+        let mut pref = pref;
+        pref.vrr_fifo_opt_in = vrr_fifo_opt_in();
+        pref.fifo_latest_ready = flr_ok;
+        let present_mode = pick_present_mode(&surface_i, pdev, surface, pref)?;
         tracing::info!(
             ?format,
             ?hdr10_format,
             ?present_mode,
+            vsync = pref.vsync,
+            allow_vrr = pref.allow_vrr,
+            fifo_latest_ready = flr_ok,
             hdr_metadata = has_hdr_metadata,
             "swapchain config"
         );
@@ -730,42 +808,275 @@ pub(super) fn pick_formats(
     Ok((sdr, hdr10))
 }
 
-/// MAILBOX when the surface offers it, FIFO otherwise (`PUNKTFUNK_PRESENT_MODE=
-/// fifo|mailbox|immediate|fifo_relaxed` overrides). Both defaults are tear-free, but an
-/// arrival-paced presenter must not block in FIFO's present queue: when the compositor
-/// holds images for a vblank pass (gamescope's composite path) or arrival cadence drifts
-/// against refresh, `acquire_next_image` stalls most of a refresh — a standing 11-13 ms
-/// added to every frame at 60 Hz. MAILBOX never queues more than the newest frame, so the
-/// pipeline stays at decode latency and a late frame is replaced, not waited for.
+/// What the user asked the presentation to be, resolved into a swapchain present mode by
+/// [`present_mode_chain`] (design/desktop-presentation-rebuild.md WP3).
+#[derive(Clone, Copy, Debug, Default)]
+pub struct PresentPref {
+    /// Tear-free presentation (the `vsync` setting, default on).
+    pub vsync: bool,
+    /// Let a variable-refresh display follow the stream cadence (`allow_vrr`, default on).
+    pub allow_vrr: bool,
+    /// Opt-in for the VRR FIFO-first ladder (`PUNKTFUNK_VRR_FIFO=1`). Off by default on
+    /// measured evidence — see [`present_mode_chain`].
+    pub vrr_fifo_opt_in: bool,
+    /// `VK_EXT_present_mode_fifo_latest_ready` is enabled on the device, so the mode may
+    /// be requested. Resolved during device creation; never set by callers.
+    pub fifo_latest_ready: bool,
+    /// The session STARTED fullscreen. The mode is chosen once, at swapchain creation, so
+    /// this is the starting state and an F11 mid-session does not re-pick — consistent
+    /// with the shells' "Display changes apply from the next session" footer, and why
+    /// live present-mode switching is an explicit non-goal.
+    pub fullscreen: bool,
+}
+
+/// The preference ladder, most to least wanted. The caller takes the first entry the
+/// surface actually offers; FIFO ends every chain because the spec guarantees it.
+///
+/// * **V-Sync off** — IMMEDIATE (tears, no wait at all), then FIFO_RELAXED (tears only on
+///   a late frame), then the tear-free modes. Asking for tearing and silently getting
+///   vsync is a lie the stats line now exposes, but the ladder still degrades safely.
+/// * **V-Sync on + VRR allowed + fullscreen + `PUNKTFUNK_VRR_FIFO=1`** — FIFO first. On a
+///   variable-refresh panel with direct scanout the FIFO present IS the flip, so the panel
+///   follows the stream's cadence; MAILBOX would decouple presents from scanout and
+///   re-quantize to the compositor's clock.
+///
+///   **Automatic where a queue-free vblank mode exists, opt-in otherwise.** The history is
+///   worth keeping: this was default-on, then measured on glass (.21, GNOME/Wayland,
+///   NVIDIA, *non*-VRR 60 Hz panel, 2026-08-02) to cost ~27 ms of display stage against
+///   MAILBOX — `28.4 ms (pace 11.8 + latch 16.6)` versus `1.4 ms (0.2 + 1.2)` — because a
+///   plain-FIFO present's on-glass confirmation lands a whole refresh later and the
+///   presenter serialises behind it. It became opt-in on that evidence.
+///
+///   `FIFO_LATEST_READY` removes the cause rather than working around it: the driver
+///   retires stale images, so the vblank-locked path measured **2.6 ms** on the same box —
+///   0.6 ms over MAILBOX instead of 27. So where the device offers it, following the panel
+///   is cheap enough to be the default again; where it does not, the ladder would fall
+///   back to plain FIFO and the regression returns, so it stays behind
+///   `PUNKTFUNK_VRR_FIFO=1` there. The win on a genuine VRR panel is still UNMEASURED —
+///   no VRR display was available — but the cost of trying is now small and bounded.
+/// * **Otherwise** — MAILBOX, then FIFO: the shipped default. MAILBOX never queues more
+///   than the newest frame, so an arrival-paced presenter doesn't block in the present
+///   queue (a measured 11-13 ms standing wait at 60 Hz when the compositor holds images
+///   for a vblank pass, or when arrival cadence drifts against refresh).
 ///
 /// AMD's Windows driver offers no MAILBOX (NVIDIA does), so those clients land on FIFO —
-/// expected, not a client misconfiguration. FIFO_RELAXED is opt-in only: it tears exactly
-/// when a stream frame misses the vblank it was pacing for, which on a drifting arrival
-/// cadence is often — a trade the user must choose, never a silent fallback.
+/// expected, not a misconfiguration, and now visible in the `present:` stats line.
+fn present_mode_chain(pref: PresentPref) -> Vec<vk::PresentModeKHR> {
+    use vk::PresentModeKHR as M;
+    let flr = pref.fifo_latest_ready.then_some(fifo_latest_ready::MODE);
+    let mut chain: Vec<M> = if !pref.vsync {
+        vec![M::IMMEDIATE, M::FIFO_RELAXED, M::MAILBOX]
+    } else if pref.allow_vrr && pref.fullscreen && (pref.fifo_latest_ready || pref.vrr_fifo_opt_in)
+    {
+        // The VRR ladder wants the vblank-locked family; LATEST_READY is that with the
+        // queue removed, so it outranks plain FIFO here too.
+        vec![]
+            .into_iter()
+            .chain(flr)
+            .chain([M::FIFO, M::MAILBOX, M::FIFO_RELAXED, M::IMMEDIATE])
+            .collect()
+    } else {
+        // MAILBOX first (measured good), then LATEST_READY — which is what gives a
+        // MAILBOX-less surface the same newest-wins behaviour, in the driver instead of
+        // in our glass gate.
+        vec![M::MAILBOX]
+            .into_iter()
+            .chain(flr)
+            .chain([M::FIFO_RELAXED, M::IMMEDIATE])
+            .collect()
+    };
+    if !pref.vsync {
+        chain.extend(flr);
+    }
+    // FIFO ends every chain: the spec guarantees it exists, so there is always a landing.
+    chain.push(M::FIFO);
+    chain
+}
+
+/// `PUNKTFUNK_VRR_FIFO=1` — opt into the FIFO-first ladder for variable-refresh panels.
+/// See [`present_mode_chain`] for the measurement that made this opt-in rather than
+/// default.
+fn vrr_fifo_opt_in() -> bool {
+    std::env::var("PUNKTFUNK_VRR_FIFO").is_ok_and(|v| v != "0")
+}
+
+/// Resolve the present mode: `PUNKTFUNK_PRESENT_MODE` pins one outright (the debug lever,
+/// unchanged), otherwise the first entry of [`present_mode_chain`] the surface offers.
 fn pick_present_mode(
     surface_i: &ash::khr::surface::Instance,
     pdev: vk::PhysicalDevice,
     surface: vk::SurfaceKHR,
+    pref: PresentPref,
 ) -> Result<vk::PresentModeKHR> {
     // SAFETY: per the Vulkan contract above - a read-only query on the live instance/device,
     // filling locals returned by value.
     let modes = unsafe { surface_i.get_physical_device_surface_present_modes(pdev, surface) }?;
-    let want = match std::env::var("PUNKTFUNK_PRESENT_MODE").ok().as_deref() {
-        Some("fifo") => vk::PresentModeKHR::FIFO,
-        Some("immediate") => vk::PresentModeKHR::IMMEDIATE,
-        Some("fifo_relaxed") => vk::PresentModeKHR::FIFO_RELAXED,
-        Some("mailbox") | None => vk::PresentModeKHR::MAILBOX,
+    let pinned = match std::env::var("PUNKTFUNK_PRESENT_MODE").ok().as_deref() {
+        Some("fifo") => Some(vk::PresentModeKHR::FIFO),
+        Some("immediate") => Some(vk::PresentModeKHR::IMMEDIATE),
+        Some("fifo_relaxed") => Some(vk::PresentModeKHR::FIFO_RELAXED),
+        Some("mailbox") => Some(vk::PresentModeKHR::MAILBOX),
+        None => None,
         Some(other) => {
             tracing::warn!(
                 value = other,
-                "unknown PUNKTFUNK_PRESENT_MODE (expected fifo|mailbox|immediate|fifo_relaxed) — using mailbox"
+                "unknown PUNKTFUNK_PRESENT_MODE (expected fifo|mailbox|immediate|fifo_relaxed) — following the settings"
             );
-            vk::PresentModeKHR::MAILBOX
+            None
         }
     };
-    Ok(if modes.contains(&want) {
-        want
-    } else {
-        vk::PresentModeKHR::FIFO // always available per spec
-    })
+    if let Some(want) = pinned {
+        if modes.contains(&want) {
+            return Ok(want);
+        }
+        tracing::warn!(
+            ?want,
+            "PUNKTFUNK_PRESENT_MODE not offered by this surface — falling back"
+        );
+    }
+    // What the surface ACTUALLY offers, logged unconditionally. "AMD's Windows driver
+    // has no MAILBOX" is the premise the FIFO glass gate is built on, and it has been
+    // carried in comments rather than measured — present modes are a property of the
+    // (surface, device) pair, so they vary by platform surface, driver version and
+    // fullscreen state, and the only way to settle it is to read it back from real
+    // machines. One line here makes every field log answer the question.
+    tracing::info!(
+        available = ?modes,
+        "surface present modes"
+    );
+    let chain = present_mode_chain(pref);
+    let chosen = chain
+        .iter()
+        .copied()
+        .find(|m| modes.contains(m))
+        .unwrap_or(vk::PresentModeKHR::FIFO); // always available per spec
+                                              // The one line that answers "did V-Sync off actually take?" — a request the surface
+                                              // can't serve is a fact about the driver, and it must not look like our choice.
+    if chosen != chain[0] {
+        tracing::info!(
+            requested = ?chain[0],
+            active = ?chosen,
+            vsync = pref.vsync,
+            allow_vrr = pref.allow_vrr,
+            "the surface does not offer the preferred present mode"
+        );
+    }
+    Ok(chosen)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use vk::PresentModeKHR as M;
+
+    /// The preference ladders (WP3). Every chain must end at FIFO, which the spec
+    /// guarantees exists — a chain whose entries a surface all refuses would otherwise
+    /// have no landing.
+    #[test]
+    fn present_mode_chains_rank_by_intent() {
+        let pref = |vsync, allow_vrr, fullscreen| PresentPref {
+            vsync,
+            allow_vrr,
+            fullscreen,
+            vrr_fifo_opt_in: true, // the ladder under test; the DEFAULT is off (see below)
+            fifo_latest_ready: false,
+        };
+        let flr = fifo_latest_ready::MODE;
+
+        // V-Sync off asks to tear, hardest first, and outranks the VRR rule (tearing
+        // already gives a VRR-like latch, so the two never fight).
+        assert_eq!(present_mode_chain(pref(false, true, true))[0], M::IMMEDIATE);
+        assert_eq!(
+            present_mode_chain(pref(false, false, false))[0],
+            M::IMMEDIATE
+        );
+        assert_eq!(
+            present_mode_chain(pref(false, true, true))[1],
+            M::FIFO_RELAXED,
+            "tears only on a late frame — the gentler tearing rung"
+        );
+
+        // Tear-free + VRR allowed + fullscreen prefers the vblank-locked family — but
+        // ONLY when opted in.
+        assert_eq!(present_mode_chain(pref(true, true, true))[0], M::FIFO);
+        // Without the opt-in the shipped MAILBOX-first default stands: measured on glass
+        // to be ~27 ms of display stage better on a non-VRR panel.
+        assert_eq!(
+            present_mode_chain(PresentPref {
+                vsync: true,
+                allow_vrr: true,
+                fullscreen: true,
+                vrr_fifo_opt_in: false,
+                fifo_latest_ready: false,
+            })[0],
+            M::MAILBOX,
+            "without a queue-free vblank mode the VRR ladder would lead with plain FIFO, \
+             which measured ~27 ms worse — so it stays opt-in there"
+        );
+        assert_eq!(
+            present_mode_chain(PresentPref {
+                vsync: true,
+                allow_vrr: true,
+                fullscreen: true,
+                vrr_fifo_opt_in: false,
+                fifo_latest_ready: true,
+            })[0],
+            fifo_latest_ready::MODE,
+            "with LATEST_READY available, following the panel costs 0.6 ms over MAILBOX \
+             instead of 27 — cheap enough to be automatic"
+        );
+
+        // FIFO_LATEST_READY only appears where the device enabled it, and it outranks
+        // plain FIFO everywhere: it is FIFO's vblank pacing WITHOUT the queue, which is
+        // what a MAILBOX-less surface otherwise needs the software glass gate for.
+        let with_flr = |vsync, allow_vrr, fullscreen| PresentPref {
+            vsync,
+            allow_vrr,
+            fullscreen,
+            vrr_fifo_opt_in: true,
+            fifo_latest_ready: true,
+        };
+        for p in [
+            pref(true, false, false),
+            pref(true, true, true),
+            pref(false, true, true),
+        ] {
+            assert!(
+                !present_mode_chain(p).contains(&flr),
+                "never requested unless the device enabled the extension"
+            );
+        }
+        let default_flr = present_mode_chain(with_flr(true, false, false));
+        assert_eq!(
+            default_flr[0],
+            M::MAILBOX,
+            "MAILBOX still leads by measurement"
+        );
+        assert_eq!(default_flr[1], flr, "then the driver-native newest-wins");
+        assert!(
+            default_flr.iter().position(|m| *m == flr)
+                < default_flr.iter().position(|m| *m == M::FIFO),
+            "LATEST_READY must outrank plain FIFO — it is FIFO minus the standing queue"
+        );
+        assert_eq!(
+            present_mode_chain(with_flr(true, true, true))[0],
+            flr,
+            "the VRR ladder takes the queue-free vblank mode first"
+        );
+
+        // Every ladder can land: FIFO appears in all of them.
+        for p in [
+            pref(true, true, true),
+            pref(true, true, false),
+            pref(true, false, true),
+            pref(false, true, true),
+            pref(false, false, false),
+            with_flr(true, false, false),
+        ] {
+            assert!(
+                present_mode_chain(p).contains(&M::FIFO),
+                "FIFO is the guaranteed landing"
+            );
+        }
+    }
 }

docs-site/content/docs/client-settings.md

@@ -85,10 +85,38 @@ Full detail: [HDR](/docs/hdr).
 **Full chroma (4:4:4)** — *default: off.* Crisp small text and thin lines, at more bandwidth. It
 needs HEVC or PyroWave, the host's own 4:4:4 policy left on, a capture path that delivers full
 chroma, and a GPU that can encode it; if any gate fails the host says 4:2:0 before your decoder is
-built. **Today only the Apple app actually advertises 4:4:4**, and only when its hardware decode
-probe passes — the Linux and Windows apps store the toggle but their session doesn't advertise the
-capability yet, so it has no effect there. The console home and Decky offer the toggle; Android
-doesn't.
+built. The Apple, Linux and Windows apps all advertise it (Apple additionally requires its hardware
+decode probe to pass). The console home and Decky offer the toggle; Android doesn't.
+
+**Prioritize** — *default: Lowest latency.* What the client optimizes for when a decoded frame is
+ready. **Lowest latency** shows every frame the moment the display can take it, so a network hiccup
+becomes an occasional repeated or skipped frame. **Smoothness** holds a small buffer that evens
+those hiccups out, at that buffer's worth of added delay. Linux and Windows apps, the console home
+and Decky; the Apple and Android apps have carried the same setting for a while, and it is stored
+under the same name, so a [profile](/docs/profiles-and-links) means the same thing on every device.
+
+**Smoothness buffer** — *default: Automatic (two frames).* Only shown under **Smoothness**. How
+many frames are held back before showing. Each frame absorbs roughly one screen refresh of network
+hiccup and costs one refresh of delay — so on a 120 Hz screen, two frames is about 17 ms of extra
+delay bought against 17 ms of jitter. If you never see stutter, you don't need this. Wherever
+**Prioritize** is offered, and greyed out until you pick Smoothness.
+
+**V-Sync** — *default: on.* Tear-free presentation. Turning it off asks the GPU to show each frame
+the instant it's ready instead of waiting for the screen's next refresh: the lowest delay a display
+can give you, at the cost of visible tearing on fast motion. It is **best-effort** — not every
+driver or compositor offers a tearing mode, and where none is available the stream stays tear-free.
+The Detailed [stats overlay](/docs/stats) names the mode actually in use, so you can tell "off"
+from "off but unavailable". Linux and Windows apps, the console home and Decky.
+
+**Follow variable refresh rate** — *default: on.* On a VRR / FreeSync / G-Sync screen, let the panel
+refresh in step with the stream rather than on a fixed cadence — which removes the wait between a
+frame being ready and the screen being willing to show it. Applies to **fullscreen** sessions (a
+windowed one is at the compositor's mercy) and is harmless on a fixed-refresh screen. It needs a
+graphics driver that offers the modern queue-free display mode; on an older driver it does nothing
+unless you also set `PUNKTFUNK_VRR_FIFO=1` (see [configuration](/docs/configuration)), because the
+older way of following a panel costs noticeable latency on a fixed-refresh screen. The stats overlay
+reports `vrr yes` once it has *measured* that the panel really is following. Linux and Windows apps,
+the console home and Decky.
 
 **Host compositor** — *default: Automatic.* Which backend a **Linux** host uses to drive the virtual
 output. Advisory: a host without that backend quietly auto-detects instead.

docs-site/content/docs/configuration.md

@@ -242,6 +242,9 @@ A few knobs are read by the native **clients**, not the host:
 | `PUNKTFUNK_OSD_SCALE` | multiplier, e.g. `1.5` *(default `1`)* | Size of the in-stream overlay — the stats OSD, the capture hint and the start banner. They already follow your display's scaling setting (200 % display → twice the pixels), so set this only to nudge that: bigger for a TV across the room, smaller if your compositor reports an aggressive scale. Clamped to 0.5×–4×, and a line that would run off the screen is shrunk to fit. |
 | `PUNKTFUNK_NO_AEC` | `1` | Turn the microphone's echo cancellation off for this run, whatever **Echo cancellation** says in [client settings](/docs/client-settings#audio). One-way: it can only switch the processing off, never back on, and the setting is the normal way to control it. Linux and Windows clients. |
 | `PUNKTFUNK_PRESENT_MODE` | `mailbox` *(default)* · `fifo` · `immediate` · `fifo_relaxed` | How decoded frames meet the display (the Vulkan present mode). The default prefers MAILBOX — tear-free without queueing behind the vertical refresh — and falls back to FIFO (classic vsync) where the driver doesn't offer it. **AMD's Windows driver offers no MAILBOX**, so those clients run FIFO, which adds a standing frame-pacing wait (up to one refresh interval). `immediate` removes that wait but can tear; `fifo_relaxed` only tears when a frame is late. If your latency floor matters more than tearing, try `immediate` and judge by eye. |
+| `PUNKTFUNK_PRESENTER` | `arrival` | Turn the frame-pacing engine off for this run: frames present the instant they decode, exactly as they did before the **Prioritize** setting existed. A diagnostic — if a pacing change is suspected of causing judder or added delay, this switches it off without reinstalling anything. Linux and Windows clients. |
+| `PUNKTFUNK_VRR_FIFO` | `1` | Force the display mode used to follow a **variable-refresh (VRR / FreeSync / G-Sync)** screen, on graphics drivers too old to offer the modern one. You almost certainly don't need this: where the driver supports the modern mode — which is what **Follow variable refresh rate** in [client settings](/docs/client-settings#video) uses — following the panel is already automatic and costs almost nothing. On an older driver the only way to follow the panel is a mode that measured roughly 27 ms *worse* on a fixed-refresh screen, so it stays off unless you ask for it, and it's only worth asking if you genuinely have a VRR screen and play fullscreen. Check the Detailed [stats overlay](/docs/stats): `vrr yes` means the panel really is following the stream. Linux and Windows clients. |
+| `PUNKTFUNK_PRESENT_DEBUG` | `1` | Log the presenter's own 1-second summary (display mode, buffer drops, pacing counters) every second, even when nothing is going wrong. Without it the line appears only when there is something to report. |
 | `PUNKTFUNK_ABR_PROBE_KBPS` | kbps, e.g. `900000` | The startup link-capacity probe's burst target (default 2 Gbps — deliberately above any plausible link so the burst measures the link, not itself). Lower it on links the burst shouldn't slam, or when the measured ceiling comes out wrong for your setup. |
 | `PUNKTFUNK_ABR_PROBE` | `0` | Skip the startup link-capacity probe entirely. The adaptive-bitrate climb ceiling then stays at the negotiated starting rate — a blunt instrument; prefer `PUNKTFUNK_ABR_MAX_MBPS`. |
 | `PUNKTFUNK_ABR_MAX_MBPS` | Mbps, e.g. `300` | Hard cap on the adaptive bitrate's climb ceiling, whatever the startup probe measured. The escape hatch when adaptive sessions keep climbing past what your client's **decoder** can sustain (periodic hitch + "receive backlog stopped draining" in the client log). An explicit bitrate setting still bypasses ABR entirely. |

docs-site/content/docs/stats.md

@@ -62,8 +62,9 @@ differently. Linux · Windows · Steam Deck:
 
 ```
 1920×1080@120 · 120 fps · 24.3 Mb/s · target 30 Mb/s (auto) · vulkan · HDR
-e2e 14.2/19.8 ms (p50/p95) · host 3.1 · net 6.7 · decode 2.1 · display 2.3 ms
+e2e 14.2/19.8 ms (p50/p95) · host 3.1 · net 6.7 · decode 2.1 · display 2.3 ms (pace 0.6 + latch 1.7)
 host: queue 0.6 · encode 1.8 · xfer 0.2 · pace 0.5 ms
+present: mailbox
 lost 3 (2.4%)
 ```
 
@@ -109,10 +110,11 @@ lost 3 (2.4%)
   which otherwise reads as inexplicable judder plus a refresh of extra latency.
 - **Line 2 — the headline.** `end-to-end` (`e2e` on Linux/Windows) is the *directly
   measured* time from host capture to the endpoint named at the end of the line —
-  `capture→on-glass` or `capture→displayed`. Linux/Windows don't spell the endpoint out,
-  because their presenter always measures to the present instant. `p50` = the typical
-  frame (median), `p95` = the slow outliers. This is the one number that summarizes your
-  stream.
+  `capture→on-glass` or `capture→displayed`. On Linux/Windows the endpoint is the moment
+  the frame is genuinely **visible** wherever the GPU driver can report it (most can);
+  where it can't, the measurement stops at the instant the frame is handed to the display
+  and so reads slightly optimistic. `p50` = the typical frame (median), `p95` = the slow
+  outliers. This is the one number that summarizes your stream.
 - **Line 3 — where the time goes.** The first four stages **tile the end-to-end interval** —
   each starts where the previous one ends, so they add up to the headline. The two extra
   terms under them are not extra time: one is excluded from the total, the other sits inside a
@@ -123,7 +125,12 @@ lost 3 (2.4%)
     reassembly on your device.
   - `decode` — received → decoded, on your device.
   - `display` — decoded → displayed: waiting for the right screen refresh, rendering,
-    and vsync.
+    and vsync. On Linux/Windows it splits into `(pace + latch)` when your driver reports
+    true on-glass timing: **pace** is Punktfunk's own work — getting the decoded frame
+    submitted — and **latch** is the wait for the display to take it. A large `latch` is
+    the screen's refresh cycle, not the stream; a large `pace` is us. (`pace` is also the
+    fair number to compare against an iPhone or iPad, whose figure already has its
+    equivalent of `latch` removed.)
   - `os present` *(iOS and tvOS)* — the fixed depth of the OS present pipeline, which is
     excluded from both the headline and `display` and printed here so you can add it
     back.
@@ -143,6 +150,15 @@ lost 3 (2.4%)
   encode … · xfer … · pace …` — splitting the host's own share into its stages, when the
   host reports them.
 
+  Linux/Windows Detailed also carries a **`present:`** line naming how frames are reaching
+  your screen: the display mode in use (`mailbox`, `fifo`, `fifo-latest-ready`, …), `vrr yes`/`vrr no` once the
+  client has *measured* whether your screen is following the stream's cadence (it is
+  reported only when measured — no guess from what the display claims), and, when the
+  [presentation setting](/docs/client-settings#video) is *Smoothness*, the word
+  `smoothing`. Counters join it only when they're doing something — `qdrop`/`qdry` mean
+  the smoothing buffer overflowed or ran dry (a jittery link), and `gated`/`forced`
+  belong to the pacing that keeps frames from stacking up behind the display.
+
   (Stage values are per-stage medians, so they sum only *approximately* to the
   headline median — percentiles aren't perfectly additive. The headline is measured
   directly, never computed as a sum.)