diff --git a/apps/photocraft/src/gpu_startup.rs b/apps/photocraft/src/gpu_startup.rs
index 66acb9a42f..e79b4bafac 100644
--- a/apps/photocraft/src/gpu_startup.rs
+++ b/apps/photocraft/src/gpu_startup.rs
@@ -443,6 +443,14 @@ pub fn read_display_server(path: Option<&Path>) -> photocraft_engine::prefs::Lin
         .unwrap_or_default()
 }
 
+/// Preferences › Performance › Low-Latency Drawing (`performance.lowLatencyDrawing`, off unless
+/// turned on), read before the window opens: it picks the surface's present mode.
+pub fn read_low_latency(path: Option<&Path>) -> bool {
+    let v: Value = path.and_then(|p| std::fs::read_to_string(p).ok()).and_then(|t| serde_json::from_str(&t).ok()).unwrap_or(Value::Null);
+    let default = photocraft_engine::prefs::Preferences::default().performance.low_latency_drawing;
+    v.get("performance").and_then(|p| p.get("lowLatencyDrawing")).and_then(Value::as_bool).unwrap_or(default)
+}
+
 /// Read the policy leniently at startup, including old settings without renderingMode.
 pub fn read_rendering_prefs(path: Option<&Path>) -> (GpuBackend, RenderingMode) {
     let v: Value = path.and_then(|p| std::fs::read_to_string(p).ok()).and_then(|t| serde_json::from_str(&t).ok()).unwrap_or(Value::Null);
@@ -463,6 +471,23 @@ mod tests {
         Marker { backend: backend.into(), adapter: "Intel(R) UHD Graphics".into(), adapter_backend: adapter_backend.into(), ..Default::default() }
     }
 
+    #[test]
+    fn low_latency_drawing_is_read_before_the_window_opens_and_defaults_off() {
+        let dir = std::env::temp_dir().join(format!("photocraft-low-latency-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let file = dir.join("preferences.json");
+        let read = |json: &str| {
+            std::fs::write(&file, json).unwrap();
+            read_low_latency(Some(&file))
+        };
+        assert!(read(r#"{"performance":{"lowLatencyDrawing":true}}"#));
+        assert!(!read(r#"{"performance":{"lowLatencyDrawing":false}}"#));
+        assert!(!read(r#"{"performance":{"lowLatencyDrawing":"nope"}}"#), "garbage keeps the default (off)");
+        assert!(!read("not json"));
+        assert!(!read_low_latency(None), "no settings file: the default (off)");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     #[test]
     fn display_server_preference_is_read_before_the_window_opens() {
         use photocraft_engine::prefs::LinuxDisplayServer;
diff --git a/apps/photocraft/src/main.rs b/apps/photocraft/src/main.rs
index de1155edbd..0b82237a39 100644
--- a/apps/photocraft/src/main.rs
+++ b/apps/photocraft/src/main.rs
@@ -2,7 +2,13 @@
 //!
 //! Usage: `photocraft [--control <port>] [--control-token <64-hex> |
 //! --control-token-file <path>] [--automation-read-root <dir>]
-//! [--automation-write-root <dir>] [--safe-gpu] [--in-window-menus] [files…]`
+//! [--automation-write-root <dir>] [--safe-gpu] [--in-window-menus] [--present-mode <mode>]
+//! [--frame-latency <n>] [--stroke-trace <stderr|file.csv>] [files…]`
+//!
+//! `--present-mode` (`fifo`, `autovsync`, `novsync`) and `--frame-latency` (1–3) override how
+//! frames reach the display for this launch (`PHOTOCRAFT_PRESENT_MODE` / `…_FRAME_LATENCY`;
+//! `presentation`); `--stroke-trace` times each brush stroke's frames (`PHOTOCRAFT_STROKE_TRACE`;
+//! `photocraft_ui_egui::stroke_trace`).
 //!
 //! `--safe-gpu` starts with the CPU renderer (no GPU canvas; a software adapter for the window
 //! where the platform has one) for this launch, e.g. after a graphics driver crash. A start that
@@ -44,6 +50,7 @@ mod linux_libs;
 mod logging;
 mod monitor_profile;
 mod photoshop_settings;
+mod presentation;
 mod screen_color;
 mod services;
 // Windows gets pen pressure from winit (WM_POINTER); the web runner has its own listener.
@@ -191,6 +198,7 @@ fn main() -> eframe::Result {
     // reported in a notice once the app is up; a control token is a usage error like a bad port.
     let mut unreadable_paths: Vec<String> = Vec::new();
     let mut safe_gpu = false;
+    let (mut present_mode_arg, mut frame_latency_arg, mut stroke_trace_arg): (Option<String>, Option<String>, Option<String>) = (None, None, None);
     let mut in_window_menus = std::env::var_os("PHOTOCRAFT_IN_WINDOW_MENUS").is_some_and(|v| !v.is_empty() && v != "0");
     let mut args = std::env::args_os().skip(1);
     while let Some(a) = args.next() {
@@ -211,6 +219,18 @@ fn main() -> eframe::Result {
             Some("--automation-read-root") => automation_read_root = args.next().map(std::path::PathBuf::from),
             Some("--automation-write-root") => automation_write_root = args.next().map(std::path::PathBuf::from),
             Some("--safe-gpu") => safe_gpu = true,
+            Some(flag @ ("--present-mode" | "--frame-latency" | "--stroke-trace")) => {
+                let flag = flag.to_string();
+                match args.next().map(std::ffi::OsString::into_string) {
+                    Some(Ok(v)) => match flag.as_str() {
+                        "--present-mode" => present_mode_arg = Some(v),
+                        "--frame-latency" => frame_latency_arg = Some(v),
+                        _ => stroke_trace_arg = Some(v),
+                    },
+                    // A bad value is reported and ignored; it never fails the launch.
+                    _ => eprintln!("photocraft: {flag}: missing or unreadable value; ignored"),
+                }
+            }
             Some("--in-window-menus") => in_window_menus = true,
             Some("--version") => {
                 println!("photocraft {}", photocraft_engine::build_info::long_version());
@@ -364,6 +384,21 @@ fn main() -> eframe::Result {
     let gpu_note: std::sync::Arc<std::sync::Mutex<Option<String>>> = Default::default();
     // The adapter's real texture limits (egui asks for 8192 px), so big documents stay on the GPU.
     gpu_startup::configure(&mut options.wgpu_options.wgpu_setup, &plan, os, sentinel.clone(), gpu_note.clone());
+    // Preferences › Performance › Low-Latency Drawing (#1343): without vsync a stroke shows about
+    // 50 ms sooner; wgpu picks Immediate, else Mailbox, else Fifo by what the driver offers.
+    if gpu_startup::read_low_latency(services::prefs_file().as_deref()) {
+        options.wgpu_options.surface.present_mode = eframe::wgpu::PresentMode::AutoNoVsync;
+    }
+    // Testers' present mode and frame latency overrides (#1343), after the preference.
+    let present = presentation::Overrides::from_args_or_env(present_mode_arg.as_deref(), frame_latency_arg.as_deref());
+    options.wgpu_options.surface = present.apply(options.wgpu_options.surface);
+    let present_desc = presentation::describe(&options.wgpu_options.surface, &present);
+    // Without vsync, frames are capped at 240 fps (#4472) so repaint loops don't spin flat out.
+    let uncapped = !matches!(
+        options.wgpu_options.surface.present_mode,
+        eframe::wgpu::PresentMode::Fifo | eframe::wgpu::PresentMode::FifoRelaxed | eframe::wgpu::PresentMode::AutoVsync
+    );
+    log::info!("presentation: {present_desc}");
     let sentinel_ms = t_sentinel.elapsed().as_secs_f64() * 1000.0;
     log::info!("GPU startup: {:?} ({sentinel_ms:.2} ms)", plan);
     let retry_cpu = !safe_gpu && plan.backend != photocraft_engine::prefs::GpuBackend::Cpu;
@@ -392,6 +427,7 @@ fn main() -> eframe::Result {
                 }
             }
             let mut app = PhotocraftApp::new(Session::new(), services);
+            app.min_frame_ms = uncapped.then_some(1000.0 / 240.0);
             app.integrated_titlebar = cfg!(target_os = "macos");
             app.custom_titlebar = custom_titlebar;
             // Only the title bar's free gap drags the window, never the menus (mac_window.rs).
@@ -423,6 +459,10 @@ fn main() -> eframe::Result {
             // composites on the CPU).
             let info = &mut app.perf.gpu_info;
             info.preference = pref.name().to_string();
+            info.present = present_desc.clone();
+            if let Some(v) = &stroke_trace_arg {
+                app.stroke_trace.set(v);
+            }
             info.selected = if plan.env.is_some() { "env".into() } else { plan.backend.name().to_string() };
             info.fallback = match (plan.reason.clone(), gpu_note.lock().unwrap_or_else(std::sync::PoisonError::into_inner).clone()) {
                 (Some(reason), Some(note)) => Some(format!("{reason}. {note}")),
diff --git a/apps/photocraft/src/presentation.rs b/apps/photocraft/src/presentation.rs
new file mode 100644
index 0000000000..c6f7e4196a
--- /dev/null
+++ b/apps/photocraft/src/presentation.rs
@@ -0,0 +1,121 @@
+//! Launch overrides for how frames reach the display, so testers can compare input-to-pixel
+//! latency without a rebuild (#1343): `PHOTOCRAFT_PRESENT_MODE` (`fifo`, `autovsync`, or `novsync`,
+//! also spelled `immediate`, `mailbox` or `autonovsync`: no vsync, wgpu's Immediate → Mailbox → Fifo
+//! by what the driver offers) and `PHOTOCRAFT_FRAME_LATENCY` (`1` to `3`, frames the swap chain may
+//! queue). Unset, the platform default applies. A value that isn't one of these is ignored with a
+//! warning in the log, never a failed start; a mode the driver may not offer is never requested.
+//! The result is logged at start and shown in the stroke trace.
+
+use eframe::egui_wgpu::SurfaceConfig;
+use eframe::wgpu::PresentMode;
+
+/// The present mode and frame latency this launch asked for (`None`: the default).
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct Overrides {
+    pub mode: Option<PresentMode>,
+    pub latency: Option<u32>,
+}
+
+/// Parse the two variables' values. Returns the overrides and a warning per rejected value.
+pub fn parse(mode: Option<&str>, latency: Option<&str>) -> (Overrides, Vec<String>) {
+    let mut warnings = Vec::new();
+    let mode = mode.map(str::trim).filter(|v| !v.is_empty()).and_then(|v| {
+        let m = match v.to_ascii_lowercase().as_str() {
+            // Only modes every surface takes: wgpu crashes on an explicit Immediate, Mailbox or
+            // FifoRelaxed the driver doesn't offer (X11/NVIDIA has no Mailbox, #1343). Without
+            // vsync, wgpu picks Immediate, else Mailbox, else Fifo.
+            "fifo" | "vsync" => PresentMode::Fifo,
+            "autovsync" => PresentMode::AutoVsync,
+            "novsync" | "immediate" | "mailbox" | "autonovsync" => PresentMode::AutoNoVsync,
+            _ => {
+                warnings.push(format!("PHOTOCRAFT_PRESENT_MODE={v:?} isn't fifo, autovsync or novsync (immediate, mailbox); ignored"));
+                return None;
+            }
+        };
+        Some(m)
+    });
+    let latency = latency.map(str::trim).filter(|v| !v.is_empty()).and_then(|v| match v.parse::<u32>() {
+        Ok(n @ 1..=3) => Some(n),
+        _ => {
+            warnings.push(format!("PHOTOCRAFT_FRAME_LATENCY={v:?} isn't 1, 2 or 3; ignored"));
+            None
+        }
+    });
+    (Overrides { mode, latency }, warnings)
+}
+
+impl Overrides {
+    /// `--present-mode` / `--frame-latency` when given, else `PHOTOCRAFT_PRESENT_MODE` /
+    /// `PHOTOCRAFT_FRAME_LATENCY`; rejected values are logged.
+    pub fn from_args_or_env(mode: Option<&str>, latency: Option<&str>) -> Self {
+        let env_mode = std::env::var("PHOTOCRAFT_PRESENT_MODE").ok();
+        let env_latency = std::env::var("PHOTOCRAFT_FRAME_LATENCY").ok();
+        let (o, warnings) = parse(mode.or(env_mode.as_deref()), latency.or(env_latency.as_deref()));
+        for w in warnings {
+            log::warn!("{w}");
+        }
+        o
+    }
+
+    /// `surface` with the overrides applied.
+    pub fn apply(&self, surface: SurfaceConfig) -> SurfaceConfig {
+        SurfaceConfig {
+            present_mode: self.mode.unwrap_or(surface.present_mode),
+            desired_maximum_frame_latency: self.latency.or(surface.desired_maximum_frame_latency),
+        }
+    }
+}
+
+/// How `surface` presents, for the stroke trace and System Info: "fifo, latency 2", with
+/// "(override)" after a value an environment variable set. wgpu's GL backend ignores the latency.
+pub fn describe(surface: &SurfaceConfig, overrides: &Overrides) -> String {
+    let mode = match surface.present_mode {
+        PresentMode::AutoVsync => "autovsync",
+        PresentMode::AutoNoVsync => "autonovsync",
+        PresentMode::Fifo => "fifo",
+        PresentMode::FifoRelaxed => "fiforelaxed",
+        PresentMode::Immediate => "immediate",
+        PresentMode::Mailbox => "mailbox",
+    };
+    let latency = surface.desired_maximum_frame_latency.map_or("default".to_string(), |n| n.to_string());
+    let tag = |set: bool| if set { " (override)" } else { "" };
+    format!("{mode}{}, latency {latency}{}", tag(overrides.mode.is_some()), tag(overrides.latency.is_some()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn values_parse_and_bad_ones_are_ignored_with_a_warning() {
+        assert_eq!(parse(None, None), (Overrides::default(), vec![]));
+        assert_eq!(parse(Some(""), Some(" ")), (Overrides::default(), vec![]));
+        let (o, w) = parse(Some(" Mailbox "), Some("1"));
+        assert_eq!((o.mode, o.latency, w.len()), (Some(PresentMode::AutoNoVsync), Some(1), 0));
+        assert_eq!(parse(Some("vsync"), None).0.mode, Some(PresentMode::Fifo));
+        // Never a mode a driver may lack (wgpu crashes on it): no vsync falls back by support.
+        for v in ["IMMEDIATE", "mailbox", "novsync", "autonovsync"] {
+            assert_eq!(parse(Some(v), None).0.mode, Some(PresentMode::AutoNoVsync), "{v}");
+        }
+        for (mode, latency) in
+            [(Some("fast"), None), (None, Some("0")), (None, Some("4")), (None, Some("-1")), (None, Some("one")), (None, Some("99999999999"))]
+        {
+            let (o, w) = parse(mode, latency);
+            assert_eq!((o, w.len()), (Overrides::default(), 1), "{mode:?} {latency:?}");
+        }
+    }
+
+    #[test]
+    fn overrides_replace_only_what_they_set_and_are_described() {
+        let default = SurfaceConfig::HIGH_THROUGHPUT;
+        assert_eq!(Overrides::default().apply(default), default);
+        let latency_only = Overrides { mode: None, latency: Some(1) };
+        let s = latency_only.apply(default);
+        assert_eq!((s.present_mode, s.desired_maximum_frame_latency), (PresentMode::AutoVsync, Some(1)));
+        assert_eq!(describe(&s, &latency_only), "autovsync, latency 1 (override)");
+        let novsync = Overrides { mode: Some(PresentMode::AutoNoVsync), latency: None };
+        assert_eq!(describe(&novsync.apply(default), &novsync), "autonovsync (override), latency 2");
+        let none = SurfaceConfig { present_mode: PresentMode::Fifo, desired_maximum_frame_latency: None };
+        assert_eq!(describe(&none, &Overrides::default()), "fifo, latency default");
+    }
+}
diff --git a/crates/engine/src/prefs.rs b/crates/engine/src/prefs.rs
index c732daeefd..838e6fe25e 100644
--- a/crates/engine/src/prefs.rs
+++ b/crates/engine/src/prefs.rs
@@ -529,6 +529,13 @@ pub struct Performance {
     /// sliders while they drag) render on a reduced copy: fast, but blocky when zoomed in. Off:
     /// they render at full resolution.
     pub low_resolution_previews: bool,
+    /// Low-latency drawing (applies at next launch): frames reach the screen without waiting for
+    /// vsync, so a stroke follows the pen about 50 ms sooner (the swap chain's wait, #1343). wgpu
+    /// picks Immediate where the driver has it (most Vulkan and DX12 drivers on Windows and X11),
+    /// so the canvas usually tears while it changes; Mailbox (no tearing) only where Immediate is
+    /// missing. Frames are capped at 240 fps. Off (the default): vsync, smooth but late. Desktop
+    /// only.
+    pub low_latency_drawing: bool,
     /// Linux display server (applies at next launch; see [`LinuxDisplayServer`]).
     pub linux_display_server: LinuxDisplayServer,
     /// Memory budget of the layer-effect cache, in MB.
@@ -560,6 +567,7 @@ impl Default for Performance {
             rendering_mode: None,
             gpu_backend: GpuBackend::Auto,
             low_resolution_previews: true,
+            low_latency_drawing: false,
             linux_display_server: LinuxDisplayServer::Auto,
             effect_cache_mb: 768,
             legacy_compositing: false,
diff --git a/crates/ui-egui/src/control.rs b/crates/ui-egui/src/control.rs
index ff786be197..8cddc60b23 100644
--- a/crates/ui-egui/src/control.rs
+++ b/crates/ui-egui/src/control.rs
@@ -131,8 +131,9 @@ pub enum Outcome {
 /// field's value is validated before the first one is applied, so a typo, an unknown field, a
 /// bad value or a bad nested key can't reply with success while nothing — or only half of it —
 /// changed (#412).
-pub const UI_SET_FIELDS: [&str; 37] = [
+pub const UI_SET_FIELDS: [&str; 38] = [
     "tool",
+    "strokeTrace",
     "panels",
     "dock",
     "dockTabs",
@@ -492,6 +493,19 @@ fn dispatch(app: &mut PhotocraftApp, ctx: &egui::Context, req: &ControlRequest)
                     None => None,
                 };
                 let gradient_classic = bool_field(p, "gradientClassic")?;
+                // The stroke latency trace (`stroke_trace`), at runtime: on (stderr) or off. A CSV
+                // file is only for the user's own launch (`--stroke-trace <path>`): a path over the
+                // control channel would write outside the automation write root.
+                let stroke_trace = match p.get("strokeTrace") {
+                    None | Some(Value::Null) => None,
+                    Some(Value::Bool(b)) => Some(if *b { "stderr" } else { "off" }),
+                    Some(Value::String(v)) => match v.trim() {
+                        "stderr" | "on" | "true" => Some("stderr"),
+                        "off" | "false" => Some("off"),
+                        _ => return Err("strokeTrace must be true, false, \"stderr\" or \"off\"; a CSV file is set at launch (--stroke-trace <path>)".into()),
+                    },
+                    Some(_) => return Err("strokeTrace must be true, false, \"stderr\" or \"off\"".into()),
+                };
                 // The Eyedropper's options bar (#1649): Sample Size, Sample, Show Sampling Ring.
                 let eyedropper_size = match p.get("eyedropperSampleSize") {
                     Some(v) => Some(
@@ -663,6 +677,9 @@ fn dispatch(app: &mut PhotocraftApp, ctx: &egui::Context, req: &ControlRequest)
                 if let Some(mode) = gradient_blend {
                     app.ui.tool_options.gradient_blend_mode = mode;
                 }
+                if let Some(v) = &stroke_trace {
+                    app.stroke_trace.set(v);
+                }
                 if let Some(classic) = gradient_classic {
                     app.ui.tool_options.gradient_classic = classic;
                 }
@@ -1385,6 +1402,26 @@ mod tests {
         }
     }
 
+    #[test]
+    fn ui_set_turns_the_stroke_trace_on_and_off_at_runtime() {
+        let mut app = PhotocraftApp::new(photocraft_engine::Session::new(), crate::Services::default());
+        let ctx = egui::Context::default();
+        assert!(!app.stroke_trace.enabled());
+        assert_eq!(call(&mut app, &ctx, "ui.set", json!({"strokeTrace": true}))["ok"], true);
+        assert!(app.stroke_trace.enabled());
+        assert_eq!(call(&mut app, &ctx, "ui.set", json!({"strokeTrace": "off"}))["ok"], true);
+        assert!(!app.stroke_trace.enabled());
+        let bad = call(&mut app, &ctx, "ui.set", json!({"strokeTrace": 3, "tool": "Pencil"}));
+        assert_eq!(bad["ok"], false);
+        // A file path isn't accepted over the channel (it would write outside the automation
+        // write root); nothing is created.
+        let path = std::env::temp_dir().join(format!("photocraft-trace-{}.csv", std::process::id()));
+        let bad = call(&mut app, &ctx, "ui.set", json!({"strokeTrace": path.to_str().unwrap(), "tool": "Pencil"}));
+        assert_eq!(bad["ok"], false);
+        assert!(!path.exists());
+        assert!(!app.stroke_trace.enabled() && app.ui.tool != crate::state::Tool::Pencil, "a rejected call applies nothing");
+    }
+
     #[test]
     fn camera_raw_control_updates_and_commits_or_cancels_an_open_raw() {
         use photocraft_raw::testgen::{DngSpec, mosaic, scene};
diff --git a/crates/ui-egui/src/gpu_canvas.rs b/crates/ui-egui/src/gpu_canvas.rs
index 2e583e8e5b..391b0b64a3 100644
--- a/crates/ui-egui/src/gpu_canvas.rs
+++ b/crates/ui-egui/src/gpu_canvas.rs
@@ -945,6 +945,9 @@ pub struct GpuInfo {
     pub canvas: String,
     /// Why the GPU canvas was dropped during this session (device lost or a GPU error).
     pub lost: Option<String>,
+    /// Present mode and frame latency ("fifo, latency 2"; launch overrides marked, see the
+    /// app's `presentation`). Empty in hosts that don't set it.
+    pub present: String,
 }
 
 impl GpuInfo {
diff --git a/crates/ui-egui/src/i18n/cs.tsv b/crates/ui-egui/src/i18n/cs.tsv
index 376757e866..1329378dc2 100644
--- a/crates/ui-egui/src/i18n/cs.tsv
+++ b/crates/ui-egui/src/i18n/cs.tsv
@@ -3804,3 +3804,4 @@ navigator	Zoom	Zvětšení
 	Take the shortcut from the other command and select it	Odebrat zkratku druhému příkazu a vybrat ho
 	Undo Changes	Vrátit změny
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} je vyhrazena systémem a nelze ji přiřadit.
+	Low-Latency Drawing (vsync off, applies at next launch)	Kreslení s nízkou latencí (bez vertikální synchronizace, platí po dalším spuštění)
diff --git a/crates/ui-egui/src/i18n/de.tsv b/crates/ui-egui/src/i18n/de.tsv
index 59a9d470cd..5f56421233 100644
--- a/crates/ui-egui/src/i18n/de.tsv
+++ b/crates/ui-egui/src/i18n/de.tsv
@@ -3198,3 +3198,4 @@ curves	Smooth	Glätten
 	Take the shortcut from the other command and select it	Den Kurzbefehl dem anderen Befehl entziehen und diesen auswählen
 	Undo Changes	Änderungen rückgängig machen
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} ist vom System reserviert und kann nicht zugewiesen werden.
+	Low-Latency Drawing (vsync off, applies at next launch)	Zeichnen mit geringer Latenz (ohne VSync, gilt ab dem nächsten Start)
diff --git a/crates/ui-egui/src/i18n/el.tsv b/crates/ui-egui/src/i18n/el.tsv
index 0a2e6ddc7c..715e41cb1f 100644
--- a/crates/ui-egui/src/i18n/el.tsv
+++ b/crates/ui-egui/src/i18n/el.tsv
@@ -3896,3 +3896,4 @@ curves	Smooth	Εξομάλυνση
 	Take the shortcut from the other command and select it	Αφαίρεση της συντόμευσης από την άλλη εντολή και επιλογή της
 	Undo Changes	Αναίρεση αλλαγών
 	{shortcut} is reserved by the system and can't be assigned.	Η συντόμευση {shortcut} δεσμεύεται από το σύστημα και δεν μπορεί να εκχωρηθεί.
+	Low-Latency Drawing (vsync off, applies at next launch)	Σχεδίαση χαμηλής καθυστέρησης (χωρίς vsync, ισχύει στην επόμενη εκκίνηση)
diff --git a/crates/ui-egui/src/i18n/es.tsv b/crates/ui-egui/src/i18n/es.tsv
index 2069b068e5..4a0f1c8556 100644
--- a/crates/ui-egui/src/i18n/es.tsv
+++ b/crates/ui-egui/src/i18n/es.tsv
@@ -4158,3 +4158,4 @@ navigator	Zoom	Zoom
 	Take the shortcut from the other command and select it	Quitar el método abreviado al otro comando y seleccionarlo
 	Undo Changes	Deshacer cambios
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} está reservado por el sistema y no se puede asignar.
+	Low-Latency Drawing (vsync off, applies at next launch)	Dibujo de baja latencia (sin sincronización vertical, se aplica al volver a iniciar)
diff --git a/crates/ui-egui/src/i18n/fr.tsv b/crates/ui-egui/src/i18n/fr.tsv
index d528f1e7ce..2402aec160 100644
--- a/crates/ui-egui/src/i18n/fr.tsv
+++ b/crates/ui-egui/src/i18n/fr.tsv
@@ -3201,3 +3201,4 @@ curves	Smooth	Lisser
 	Take the shortcut from the other command and select it	Retirer le raccourci de l’autre commande et la sélectionner
 	Undo Changes	Annuler les modifications
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} est réservé par le système et ne peut pas être attribué.
+	Low-Latency Drawing (vsync off, applies at next launch)	Dessin à faible latence (sans synchronisation verticale, au prochain lancement)
diff --git a/crates/ui-egui/src/i18n/hu.tsv b/crates/ui-egui/src/i18n/hu.tsv
index e9f3d33907..343dcadc0c 100644
--- a/crates/ui-egui/src/i18n/hu.tsv
+++ b/crates/ui-egui/src/i18n/hu.tsv
@@ -4115,3 +4115,4 @@ cameraRaw	Yellow	Sárga
 	Take the shortcut from the other command and select it	A billentyűparancs elvétele a másik parancstól, és annak kijelölése
 	Undo Changes	Változások visszavonása
 	{shortcut} is reserved by the system and can't be assigned.	A(z) {shortcut} a rendszer számára fenntartott, nem rendelhető hozzá.
+	Low-Latency Drawing (vsync off, applies at next launch)	Kis késleltetésű rajzolás (vsync nélkül, a következő indításkor lép életbe)
diff --git a/crates/ui-egui/src/i18n/id.tsv b/crates/ui-egui/src/i18n/id.tsv
index 141f956c8e..e4ba61e1a1 100644
--- a/crates/ui-egui/src/i18n/id.tsv
+++ b/crates/ui-egui/src/i18n/id.tsv
@@ -3188,3 +3188,4 @@ curves	Smooth	Haluskan
 	Take the shortcut from the other command and select it	Ambil pintasan dari perintah lain dan pilih perintah itu
 	Undo Changes	Batalkan Perubahan
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} dicadangkan oleh sistem dan tidak dapat ditetapkan.
+	Low-Latency Drawing (vsync off, applies at next launch)	Menggambar latensi rendah (tanpa vsync, berlaku saat peluncuran berikutnya)
diff --git a/crates/ui-egui/src/i18n/it.tsv b/crates/ui-egui/src/i18n/it.tsv
index 714932312e..6b933287c6 100644
--- a/crates/ui-egui/src/i18n/it.tsv
+++ b/crates/ui-egui/src/i18n/it.tsv
@@ -4317,3 +4317,4 @@ shape	Appearance	Aspetto
 	Take the shortcut from the other command and select it	Togli la scorciatoia all'altro comando e selezionalo
 	Undo Changes	Annulla modifiche
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} è riservata dal sistema e non può essere assegnata.
+	Low-Latency Drawing (vsync off, applies at next launch)	Disegno a bassa latenza (senza vsync, si applica al prossimo avvio)
diff --git a/crates/ui-egui/src/i18n/ja.tsv b/crates/ui-egui/src/i18n/ja.tsv
index a78fe8e7ca..2f6b7d7f5e 100644
--- a/crates/ui-egui/src/i18n/ja.tsv
+++ b/crates/ui-egui/src/i18n/ja.tsv
@@ -3872,3 +3872,4 @@ curves	Smooth	スムーズ
 	Take the shortcut from the other command and select it	もう一方のコマンドからショートカットを外して選択
 	Undo Changes	変更を取り消し
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} はシステムで予約されているため割り当てられません。
+	Low-Latency Drawing (vsync off, applies at next launch)	低遅延描画（垂直同期オフ、次回起動時に適用）
diff --git a/crates/ui-egui/src/i18n/ko.tsv b/crates/ui-egui/src/i18n/ko.tsv
index 2e12c33799..3c056c627b 100644
--- a/crates/ui-egui/src/i18n/ko.tsv
+++ b/crates/ui-egui/src/i18n/ko.tsv
@@ -3374,3 +3374,4 @@ curves	Smooth	매끄럽게
 	Take the shortcut from the other command and select it	다른 명령에서 단축키를 빼고 그 명령 선택
 	Undo Changes	변경 사항 취소
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut}은(는) 시스템에서 예약되어 할당할 수 없습니다.
+	Low-Latency Drawing (vsync off, applies at next launch)	저지연 그리기(수직 동기화 끔, 다음 실행 시 적용)
diff --git a/crates/ui-egui/src/i18n/nl.tsv b/crates/ui-egui/src/i18n/nl.tsv
index 32df1e20a2..c80f86bf81 100644
--- a/crates/ui-egui/src/i18n/nl.tsv
+++ b/crates/ui-egui/src/i18n/nl.tsv
@@ -3956,3 +3956,4 @@ curves	Smooth	Vloeiend maken
 	Take the shortcut from the other command and select it	De sneltoets van de andere opdracht afnemen en die selecteren
 	Undo Changes	Wijzigingen ongedaan maken
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} is door het systeem gereserveerd en kan niet worden toegewezen.
+	Low-Latency Drawing (vsync off, applies at next launch)	Tekenen met lage latentie (zonder vsync, na de volgende start)
diff --git a/crates/ui-egui/src/i18n/pl.tsv b/crates/ui-egui/src/i18n/pl.tsv
index 8b571ff7d6..85df6b8157 100644
--- a/crates/ui-egui/src/i18n/pl.tsv
+++ b/crates/ui-egui/src/i18n/pl.tsv
@@ -3794,3 +3794,4 @@ curves	Smooth	Wygładź
 	Take the shortcut from the other command and select it	Odbierz skrót drugiemu poleceniu i zaznacz je
 	Undo Changes	Cofnij zmiany
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} jest zarezerwowany przez system i nie można go przypisać.
+	Low-Latency Drawing (vsync off, applies at next launch)	Rysowanie z małym opóźnieniem (bez synchronizacji pionowej, od następnego uruchomienia)
diff --git a/crates/ui-egui/src/i18n/pt-br.tsv b/crates/ui-egui/src/i18n/pt-br.tsv
index 8e6dcc4993..211442ba20 100644
--- a/crates/ui-egui/src/i18n/pt-br.tsv
+++ b/crates/ui-egui/src/i18n/pt-br.tsv
@@ -3986,3 +3986,4 @@ layerLabel	No Color	Sem cor
 	Take the shortcut from the other command and select it	Tirar o atalho do outro comando e selecioná-lo
 	Undo Changes	Desfazer alterações
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} é reservado pelo sistema e não pode ser atribuído.
+	Low-Latency Drawing (vsync off, applies at next launch)	Desenho de baixa latência (sem sincronização vertical, aplicado na próxima inicialização)
diff --git a/crates/ui-egui/src/i18n/ru.tsv b/crates/ui-egui/src/i18n/ru.tsv
index 6c80c470cf..9dfcc85093 100644
--- a/crates/ui-egui/src/i18n/ru.tsv
+++ b/crates/ui-egui/src/i18n/ru.tsv
@@ -3166,3 +3166,4 @@ curves	Smooth	Сгладить
 	Take the shortcut from the other command and select it	Снять комбинацию с другой команды и выбрать её
 	Undo Changes	Отменить изменения
 	{shortcut} is reserved by the system and can't be assigned.	Комбинация {shortcut} зарезервирована системой и не может быть назначена.
+	Low-Latency Drawing (vsync off, applies at next launch)	Рисование с малой задержкой (без вертикальной синхронизации, после перезапуска)
diff --git a/crates/ui-egui/src/i18n/sr.tsv b/crates/ui-egui/src/i18n/sr.tsv
index 9b30313e22..bbc0ef528d 100644
--- a/crates/ui-egui/src/i18n/sr.tsv
+++ b/crates/ui-egui/src/i18n/sr.tsv
@@ -4269,3 +4269,4 @@ shape	Appearance	Izgled
 	Take the shortcut from the other command and select it	Uzmi prečicu drugoj komandi i izaberi je
 	Undo Changes	Poništi izmene
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} je rezervisana od strane sistema i ne može se dodeliti.
+	Low-Latency Drawing (vsync off, applies at next launch)	Crtanje sa malim kašnjenjem (bez vsync-a, primenjuje se pri sledećem pokretanju)
diff --git a/crates/ui-egui/src/i18n/tr.tsv b/crates/ui-egui/src/i18n/tr.tsv
index 8e20ad53dc..b63bdd7349 100644
--- a/crates/ui-egui/src/i18n/tr.tsv
+++ b/crates/ui-egui/src/i18n/tr.tsv
@@ -3926,3 +3926,4 @@ cameraData	Lens	Lens
 	Take the shortcut from the other command and select it	Kısayolu diğer komuttan al ve o komutu seç
 	Undo Changes	Değişiklikleri Geri Al
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} sistem tarafından ayrılmıştır ve atanamaz.
+	Low-Latency Drawing (vsync off, applies at next launch)	Düşük gecikmeli çizim (dikey eşitleme kapalı, sonraki açılışta geçerli)
diff --git a/crates/ui-egui/src/i18n/uk.tsv b/crates/ui-egui/src/i18n/uk.tsv
index 9fcf5e85bc..923ec694af 100644
--- a/crates/ui-egui/src/i18n/uk.tsv
+++ b/crates/ui-egui/src/i18n/uk.tsv
@@ -3895,3 +3895,4 @@ curves	Smooth	Згладити
 	Take the shortcut from the other command and select it	Забрати скорочення в іншої команди й вибрати її
 	Undo Changes	Скасувати зміни
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} зарезервовано системою, його не можна призначити.
+	Low-Latency Drawing (vsync off, applies at next launch)	Малювання з малою затримкою (без вертикальної синхронізації, після перезапуску)
diff --git a/crates/ui-egui/src/i18n/vi.tsv b/crates/ui-egui/src/i18n/vi.tsv
index 515966c515..be40230ca3 100644
--- a/crates/ui-egui/src/i18n/vi.tsv
+++ b/crates/ui-egui/src/i18n/vi.tsv
@@ -3682,3 +3682,4 @@ curves	Smooth	Làm mượt
 	Take the shortcut from the other command and select it	Lấy phím tắt khỏi lệnh kia và chọn lệnh đó
 	Undo Changes	Hoàn tác thay đổi
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} được hệ thống dành riêng và không thể gán.
+	Low-Latency Drawing (vsync off, applies at next launch)	Vẽ độ trễ thấp (tắt vsync, áp dụng ở lần khởi động sau)
diff --git a/crates/ui-egui/src/i18n/zh-hans.tsv b/crates/ui-egui/src/i18n/zh-hans.tsv
index cbf3c9d08f..7c563780db 100644
--- a/crates/ui-egui/src/i18n/zh-hans.tsv
+++ b/crates/ui-egui/src/i18n/zh-hans.tsv
@@ -2812,3 +2812,4 @@ curves	Smooth	平滑
 	Take the shortcut from the other command and select it	从另一个命令移除该快捷键并选中它
 	Undo Changes	撤消更改
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} 由系统保留，无法指定。
+	Low-Latency Drawing (vsync off, applies at next launch)	低延迟绘画（关闭垂直同步，下次启动时生效）
diff --git a/crates/ui-egui/src/i18n/zh-hant.tsv b/crates/ui-egui/src/i18n/zh-hant.tsv
index 30aa3f5a94..9376cb05bb 100644
--- a/crates/ui-egui/src/i18n/zh-hant.tsv
+++ b/crates/ui-egui/src/i18n/zh-hant.tsv
@@ -2797,3 +2797,4 @@ curves	Smooth	平滑
 	Take the shortcut from the other command and select it	從另一個指令移除該快速鍵並選取它
 	Undo Changes	還原變更
 	{shortcut} is reserved by the system and can't be assigned.	{shortcut} 由系統保留，無法指定。
+	Low-Latency Drawing (vsync off, applies at next launch)	低延遲繪圖（關閉垂直同步，下次啟動時生效）
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 3a981c41f3..34b346af00 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -800,6 +800,12 @@ pub struct PhotocraftApp {
     /// `jobs_ui`). The desktop app turns it on; off (the default), everything runs inline as
     /// before, which tests and scripts rely on.
     pub background_jobs: bool,
+    /// Shortest time between frames (ms), or `None` for no cap. A present mode that doesn't wait
+    /// for the display (Low-Latency Drawing) would otherwise redraw as fast as it can while
+    /// anything keeps requesting repaints (a drag hovering, autoscroll, Liquify held still).
+    /// After #4472 (astigmata).
+    pub min_frame_ms: Option<f64>,
+    last_frame_start_ms: f64,
     /// Background job bookkeeping: opening tabs, control replies waiting on a job.
     pub jobs: jobs_ui::JobsUi,
     #[cfg(all(debug_assertions, not(target_arch = "wasm32")))]
@@ -935,6 +941,8 @@ impl PhotocraftApp {
             allow_close: false,
             stylus: Default::default(),
             background_jobs: false,
+            min_frame_ms: None,
+            last_frame_start_ms: 0.0,
             jobs: Default::default(),
             #[cfg(all(debug_assertions, not(target_arch = "wasm32")))]
             live_tokens: theme::live::LiveTokens::from_env(),
@@ -1759,6 +1767,20 @@ impl PhotocraftApp {
     }
 }
 
+impl PhotocraftApp {
+    /// Wait out the rest of [`Self::min_frame_ms`] since the last frame started.
+    fn cap_frame_rate(&mut self) {
+        #[cfg(not(target_arch = "wasm32"))]
+        if let Some(min) = self.min_frame_ms.filter(|m| m.is_finite() && *m > 0.0) {
+            let wait = min.min(100.0) - (gpu_canvas::now_ms() - self.last_frame_start_ms);
+            if wait > 0.0 {
+                std::thread::sleep(std::time::Duration::from_secs_f64(wait / 1000.0));
+            }
+        }
+        self.last_frame_start_ms = gpu_canvas::now_ms();
+    }
+}
+
 impl eframe::App for PhotocraftApp {
     fn on_exit(&mut self) {
         if let Err(err) = tool_memory::save_on_exit(self) {
@@ -1767,6 +1789,7 @@ impl eframe::App for PhotocraftApp {
     }
 
     fn logic(&mut self, ctx: &egui::Context, frame: &mut eframe::Frame) {
+        self.cap_frame_rate();
         i18n::set_current(i18n::Lang::from_pref(&self.session.prefs().interface.language));
         // Caps Lock state read from the OS once per frame (see `Services::caps_lock`): the canvas
         // cursor block needs it before the frame renders. `None` (Wayland/web) keeps `false`.
@@ -2004,7 +2027,10 @@ impl eframe::App for PhotocraftApp {
         if self.stroke_trace.enabled() {
             self.stroke_trace.canvas(self.perf.frame_refresh_ms);
             let info = &self.perf.gpu_info;
-            self.stroke_trace.end_frame(ui_ms, self.live_stroke.is_some(), || format!("{} {}", info.backend, info.adapter).trim().to_string());
+            self.stroke_trace.end_frame(ui_ms, self.live_stroke.is_some(), || {
+                let gpu = format!("{} {}", info.backend, info.adapter).trim().to_string();
+                if info.present.is_empty() { gpu } else { format!("{gpu}, {}", info.present) }
+            });
         }
         // Synthetic input is injected one press/release step per frame: keep frames coming until
         // the queue is empty, then release control replies waiting on it.
diff --git a/crates/ui-egui/src/prefs_ui.rs b/crates/ui-egui/src/prefs_ui.rs
index 99750ae7f1..795ea84cea 100644
--- a/crates/ui-egui/src/prefs_ui.rs
+++ b/crates/ui-egui/src/prefs_ui.rs
@@ -1120,6 +1120,11 @@ fn humanize(key: &str) -> String {
     if key == "nudgeBundlePauseMs" {
         return "Nudge Bundle Pause (ms)".into();
     }
+    // Performance: presentation without vsync (#1343); like the other graphics settings, it
+    // takes effect when the window next opens.
+    if key == "lowLatencyDrawing" {
+        return "Low-Latency Drawing (vsync off, applies at next launch)".into();
+    }
     let mut s = String::new();
     for (i, ch) in key.chars().enumerate() {
         if i == 0 {
@@ -1556,6 +1561,8 @@ fn field_visible(section: &str, obj: &Map<String, Value>, k: &str, query: &str)
         // View › Rulers (⌘R) sets it, as in Photoshop.
         || path == "unitsAndRulers.showRulers"
         || (section == "performance" && matches!(k, "useGpu" | "gpuBackend" | "renderingMode"))
+        // The browser presents frames itself: Low-Latency Drawing does nothing there.
+        || (cfg!(target_arch = "wasm32") && path == "performance.lowLatencyDrawing")
         || (section == "export" && !export_field_visible(obj, k))
         || (section == "tools" && !tools_field_visible(obj, k));
     (query.is_empty() || preference_matches(section, k, query))
diff --git a/crates/ui-egui/src/stroke_trace.rs b/crates/ui-egui/src/stroke_trace.rs
index 206cc7e81a..809414ed49 100644
--- a/crates/ui-egui/src/stroke_trace.rs
+++ b/crates/ui-egui/src/stroke_trace.rs
@@ -113,13 +113,32 @@ impl StrokeTrace {
     /// Reads `PHOTOCRAFT_STROKE_TRACE` (off on the web, where there is no clock).
     pub fn from_env() -> Self {
         #[cfg(not(target_arch = "wasm32"))]
-        if let Some(v) = std::env::var_os("PHOTOCRAFT_STROKE_TRACE").filter(|v| !v.is_empty()) {
-            let output = if v == "1" || v == "stderr" { Output::Stderr } else { Output::Csv(v.into()) };
-            return Self { output, ..Default::default() };
+        if let Some(v) = std::env::var_os("PHOTOCRAFT_STROKE_TRACE") {
+            return Self::from_value(&v.to_string_lossy());
         }
         Self::default()
     }
 
+    /// A trace set by value: `""`, `"0"` or `"off"` is off, `"1"` or `"stderr"` prints
+    /// summaries, anything else is a CSV path (`--stroke-trace`, `PHOTOCRAFT_STROKE_TRACE`; the
+    /// control channel's `ui.set {"strokeTrace"}` passes only on or off, never a path).
+    pub fn from_value(v: &str) -> Self {
+        let v = v.trim();
+        let output = match v {
+            _ if cfg!(target_arch = "wasm32") => Output::Off,
+            "" | "0" | "off" | "false" => Output::Off,
+            "1" | "stderr" | "true" => Output::Stderr,
+            path => Output::Csv(path.into()),
+        };
+        Self { output, ..Default::default() }
+    }
+
+    /// Switch the output, keeping the last summary.
+    pub fn set(&mut self, v: &str) {
+        let last = self.last.take();
+        *self = Self { last, ..Self::from_value(v) };
+    }
+
     pub fn enabled(&self) -> bool {
         self.output != Output::Off
     }
@@ -265,6 +284,19 @@ mod tests {
         assert!(off.last.is_none() && off.rows.is_empty());
     }
 
+    #[test]
+    fn a_trace_is_set_by_value() {
+        assert_eq!(StrokeTrace::from_value("off").output, Output::Off);
+        assert_eq!(StrokeTrace::from_value(" 0 ").output, Output::Off);
+        assert_eq!(StrokeTrace::from_value("stderr").output, Output::Stderr);
+        assert_eq!(StrokeTrace::from_value("true").output, Output::Stderr);
+        assert_eq!(StrokeTrace::from_value("t.csv").output, Output::Csv("t.csv".into()));
+        let mut t = on();
+        t.last = Some(Summary::default());
+        t.set("off");
+        assert!(!t.enabled() && t.last.is_some(), "turning it off keeps the last summary");
+    }
+
     #[test]
     fn csv_rows_and_odd_numbers() {
         let rows = [Row { t: 1.0, interval: 16.5, moves: 2, stroke: 0.25, canvas: 1.0, ui: 3.0, cpu_prev: None }];
diff --git a/docs/control-protocol.md b/docs/control-protocol.md
index 8536507104..2bbcab2469 100644
--- a/docs/control-protocol.md
+++ b/docs/control-protocol.md
@@ -53,6 +53,7 @@ The transport is `apps/photocraft/src/control_server.rs`, and the handlers are i
 - `ui.set` also accepts `gradientBlendMode` (a layer blend mode name, such as `Difference`) and `gradientClassic` (boolean) for the Gradient tool options bar.
 - `ui.set` also accepts `camTransformOnDrop` (boolean), the Content-Aware Move tool's Transform On Drop checkbox: a drop then puts a scale/rotate box on the patch (`ui.inspect` › `camTransform`: its document/revision, drag `offset` and `frame`), driven with `ui.pointer` (handles as Free Transform's; outside the box rotates), committed with `ui.key Enter` (one `paint.contentAwareMove` with `scaleX`, `scaleY`, `rotate`) or dropped with `Escape`.
 - `ui.set` also accepts `tileGrid` (boolean), a developer overlay of the active layer's storage tiles: the tile grid over the document, every stored tile filled and labelled `tx,ty`, tiles with identical pixels in a shared colour and unique ones in blue. It has no menu item and View › Extras doesn't hide it. `ui.inspect` reports it as `view.tile_grid`.
+- `ui.set` also accepts `strokeTrace` (`true`, `false`, `"stderr"` or `"off"`): turn the stroke latency trace on or off at runtime; each stroke's summary is in `ui.inspect` `perf.strokeTrace`. A CSV file of every frame is set only at launch (`PHOTOCRAFT_STROKE_TRACE=<file.csv>` / `--stroke-trace <file.csv>`): the control channel doesn't write files outside the automation write root
 - `ui.set` also accepts `layerFilter` (#5048), the Layers panel filter row: `{by?, kinds?, name?, mode?}`, any subset. `by` is `kind`, `name` or `mode` (the filter-type dropdown); `kinds` lists the Kind toggles that are on (`pixel`, `adjustment`, `type`, `shape`, `smart`); `name` matches part of a layer name, ignoring case; `mode` is a blend mode name (`Multiply`, `Pass Through`). Kind and Name filter only once a kind is on or text is typed; Mode always filters, by Normal at first, as in Photoshop. Fields left out keep their value; a bad one is an error and changes nothing.
 - Each painting tool keeps its own brush, as in Photoshop: `tools.setBrush` and `ui.set {brushSize}` change the active tool's brush, and switching tools swaps in that tool's own (size, hardness, mode, opacity, flow, dynamics, smoothing). A tool used for the first time starts from the brush in hand. The colours, the erase flag and the stroke seed stay shared. So `ui.set {tool: "eraser", brushSize: 12}` sets the Eraser's size, and `ui.set {tool: "brush"}` afterwards brings the Brush's own size back.
 - `ui.set` also accepts the Eyedropper options bar (#1649): `eyedropperSampleSize` (`"point"` or 1, 3, 5, 11, 31, 51, 101: the side of the averaged square, shared by the Eyedropper, a painting tool's Alt-click eyedropper, the Curves/Color Picker eyedroppers and the Info panel), `eyedropperSample` (`current`, `currentAndBelow`, `all`, `allNoAdjustments`, `currentAndBelowNoAdjustments`) and `eyedropperRing` (boolean, Show Sampling Ring). `ui.inspect` reports them under `toolOptions` (`eyedropper_size`, `eyedropper_sample`, `eyedropper_ring`). The engine command `document.sampleColor {x, y, size, sampleLayer}` returns the colour such a sample picks.
diff --git a/docs/development.md b/docs/development.md
index 3e7f5fb66e..76b4a2e31c 100644
--- a/docs/development.md
+++ b/docs/development.md
@@ -119,7 +119,9 @@ By default PhotoCraft's own crates log at `info` and everything else at `warn`.
 | `PHOTOCRAFT_CPU_COMPOSE=1` | Keep the wgpu canvas but composite on the CPU (compare GPU vs CPU renders, e.g. with the snapshot example) |
 | `PHOTOCRAFT_LOCALE` | Override Auto's native UI language for this launch; unsupported tags use English. See [system language detection](localization.md#first-launch-and-system-language). |
 | `PHOTOCRAFT_FX_TRACE=1` | Print the CPU time spent on GPU effect shapes and distance fields per rebuild |
-| `PHOTOCRAFT_STROKE_TRACE=1` (or `=<file.csv>`) | Time every frame of each brush stroke; print a summary per stroke, and with a path also append each frame to that CSV (see [Stroke latency trace](#stroke-latency-trace)) |
+| `PHOTOCRAFT_STROKE_TRACE=1` (or `=<file.csv>`; also `--stroke-trace <stderr|file.csv>`, or `ui.set {"strokeTrace": true|false}` at runtime, without a file) | Time every frame of each brush stroke; print a summary per stroke, and with a path also append each frame to that CSV (see [Stroke latency trace](#stroke-latency-trace)) |
+| `PHOTOCRAFT_PRESENT_MODE=novsync` (or `--present-mode`) | Present mode for this launch: `fifo`, `autovsync`, or `novsync` (also `immediate`, `mailbox`: no vsync, the first of Immediate, Mailbox, Fifo the driver offers). Default: vsync, or no vsync when Preferences › Performance › Low-Latency Drawing is on (it ships off). For latency comparisons; shown in the stroke trace |
+| `PHOTOCRAFT_FRAME_LATENCY=1` (or `--frame-latency`) | Frames the swap chain may queue, 1 to 3 (wgpu's GL backend ignores it). For latency comparisons; shown in the stroke trace |
 | `PHOTOCRAFT_THEME_FILE=tokens.json` | **Debug builds only:** live design-token overrides, re-read on change |
 
 ### Live design tokens
@@ -148,7 +150,7 @@ stroke trace: 62 frames on vulkan NVIDIA GeForce RTX 5090 (p50/p95 ms): interval
 | `cpu` | eframe's CPU time per frame: UI, tessellation and GPU submission, without the vsync wait |
 | `wait` | `interval − cpu`: waiting on vsync or the swap chain, or idle |
 
-What the app can't time is the rest of input-to-photon: the OS input queue before a frame starts (up to one `interval`), frames queued for the display (the surface keeps up to two; the GL backend ignores that setting), and the compositor. So the first line names the backend. The last summary is also in the control channel's `perf.strokeTrace` (`ui.inspect`). The code is `crates/ui-egui/src/stroke_trace.rs`.
+What the app can't time is the rest of input-to-photon: the OS input queue before a frame starts (up to one `interval`), frames queued for the display (the surface keeps up to two; the GL backend ignores that setting), and the compositor. So the first line names the backend and how frames are presented. To compare presentation settings without rebuilding, launch with `PHOTOCRAFT_PRESENT_MODE` and `PHOTOCRAFT_FRAME_LATENCY` (see [Environment variables](#environment-variables)): with `novsync` the app no longer waits on vsync (`wait` near 0): each refresh shows the newest frame, and where the driver only offers Immediate, the screen may tear. The last summary is also in the control channel's `perf.strokeTrace` (`ui.inspect`). The code is `crates/ui-egui/src/stroke_trace.rs`.
 
 ## Driving the app programmatically
 
diff --git a/docs/scorecard.md b/docs/scorecard.md
index 1e0576ba02..8dbbea612e 100644
--- a/docs/scorecard.md
+++ b/docs/scorecard.md
@@ -9,7 +9,7 @@ Generated by `cargo xtask scorecard` from `perf/budgets.toml`, `perf/baseline.js
 | [Performance](#performance) | 3 | 22 | 22 | 56 scenarios: 3 within budget, 22 over budget or failing, 9 tracked only, 17 not run, 5 not measurable yet (baseline 2026-10-05) |
 | [File compatibility](#file-compatibility) | 7 | 14 | 6 | io corpus: oracle ≥ 148/170, round trip ≥ 169/170; psd-tools corpus: oracle ≥ 249/309, round trip ≥ 308/309; photoshop oracles: oracle ≥ 188/256, round trip ≥ 258/256 |
 | [Tools](#tools) | 33 | 11 | 0 |  |
-| [Workspace and UI](#workspace-and-ui) | 13 | 6 | 4 | settings that do nothing: 26 of 166 (target 0) |
+| [Workspace and UI](#workspace-and-ui) | 13 | 6 | 4 | settings that do nothing: 26 of 167 (target 0) |
 | [Type](#type) | 4 | 3 | 2 |  |
 | [Automation](#automation) | 5 | 2 | 4 | 631 of 631 menu items live (100.0%) |
 | [Reliability](#reliability) | 5 | 2 | 0 | never-crash lints on 29 of 29 crates; panic_hunt present |
@@ -177,7 +177,7 @@ Corpus floors (`crates/io/tests/corpus.rs`): the enforced minimums; the corpus t
 
 ## Workspace and UI
 
-**Settings that do nothing: 26 of 166** (target 0, #204). Counted by the prefs audit (`xtask/src/scorecard.rs`): a `Preferences` field counts as read when code outside the prefs model (`prefs.rs` except its `impl Session` blocks; tests excluded; the schema-driven dialog never names a field) accesses `section.field`, or `.section` and `.field` in the same file, or calls a section method that reads `self.field`. It is a heuristic lower bound: a generic name can look read when it isn't.
+**Settings that do nothing: 26 of 167** (target 0, #204). Counted by the prefs audit (`xtask/src/scorecard.rs`): a `Preferences` field counts as read when code outside the prefs model (`prefs.rs` except its `impl Session` blocks; tests excluded; the schema-driven dialog never names a field) accesses `section.field`, or `.section` and `.field` in the same file, or calls a section method that reads `self.field`. It is a heuristic lower bound: a generic name can look read when it isn't.
 
 Unread: `general.color_picker`, `general.animated_zoom`, `general.zoom_resizes_windows`, `workspace.auto_show_hidden_panels`, `workspace.enable_floating_document_window_docking`, `file_handling.save_in_background`, `performance.cache_levels`, `performance.legacy_compositing`, `scratch_disks.disks`, `units_and_rulers.column_width`, `units_and_rulers.gutter`, `plug_ins.show_extension_panels`, `plug_ins.allow_scripts_to_connect`, `plug_ins.generator_enabled`, `type_.text_engine`, `type_.recent_fonts`, `enhanced_controls.scrubby_slider_acceleration`, `enhanced_controls.touch_gestures`, `raw_defaults.color_space`, `raw_defaults.bit_depth`, `raw_defaults.resolution`, `raw_defaults.sharpen_for`, `raw_defaults.open_as_smart_object`, `raw_defaults.apply_auto_tone`, `integrations.allow_agent_control`, `integrations.control_port`.