diff --git a/crates/ui-egui/src/headless.rs b/crates/ui-egui/src/headless.rs
index db87ab07..819617a9 100644
--- a/crates/ui-egui/src/headless.rs
+++ b/crates/ui-egui/src/headless.rs
@@ -553,6 +553,41 @@ mod tests {
 
     /// The Export dialog hands its batch to a worker thread: the UI keeps drawing frames, shows
     /// progress, and reports the result when the files are written.
+    #[test]
+    fn export_dialog_keeps_its_width() {
+        // A dialog row sized as "available width − a guessed button width" made the auto-sized
+        // window grow a little every frame when the real button was wider (issue #8, Linux).
+        let mut h = demo([1400.0, 900.0]);
+        let t = Duration::from_secs(10);
+        h.app.services.pick_folder = Some(Box::new(|| None));
+        h.app.services.pick_files = Some(Box::new(Vec::new));
+        h.request("engine.execute", json!({"command": "dialog.export", "params": {}}), t);
+        // the widest variant: watermark graphic and every optional row
+        if let Some(crate::state::Dialog::Export { opts, .. }) = &mut h.app.ui.dialog {
+            let mut wm = lightcraft_engine::export::Watermark { image: "logo.png".into(), ..Default::default() };
+            wm.text.clear();
+            opts.watermark = Some(wm);
+        }
+        let width = |h: &mut Headless| {
+            let r = h.request("ui.widgets", json!({}), t);
+            r["result"]
+                .as_array()
+                .and_then(|a| a.iter().find(|w| w["id"] == "dialog:window"))
+                .map(|w| w["rect"][2].as_f64().unwrap())
+                .expect("dialog on screen")
+        };
+        for _ in 0..5 {
+            h.step();
+        }
+        let w0 = width(&mut h);
+        for _ in 0..60 {
+            h.step();
+        }
+        let w1 = width(&mut h);
+        assert!((w1 - w0).abs() < 0.5, "the export dialog grew from {w0} to {w1}");
+        assert!(w1 < 700.0, "{w1}");
+    }
+
     #[test]
     fn export_dialog_runs_in_the_background() {
         let mut h = demo([1200.0, 900.0]);
diff --git a/crates/ui-egui/src/panels/dialogs.rs b/crates/ui-egui/src/panels/dialogs.rs
index 2a784382..07dd0720 100644
--- a/crates/ui-egui/src/panels/dialogs.rs
+++ b/crates/ui-egui/src/panels/dialogs.rs
@@ -528,15 +528,15 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         }
                         if graphic {
                             field(ui, "Graphic", |ui| {
-                                let can_pick = app.services.pick_files.is_some();
-                                let w = ui.available_width() - if can_pick { 76.0 } else { 0.0 };
-                                ui.add(egui::TextEdit::singleline(&mut wm.image).hint_text("logo.png").desired_width(w));
-                                if can_pick
-                                    && crate::widgets::text_button(ui, "exportWmChoose", "Choose…", false).clicked()
-                                    && let Some(f) = app.services.pick_files.as_mut().and_then(|pick| pick().into_iter().next())
-                                {
-                                    wm.image = f;
-                                }
+                                trailing_button_row(ui, |ui| {
+                                    if app.services.pick_files.is_some()
+                                        && crate::widgets::text_button(ui, "exportWmChoose", "Choose…", false).clicked()
+                                        && let Some(f) = app.services.pick_files.as_mut().and_then(|pick| pick().into_iter().next())
+                                    {
+                                        wm.image = f;
+                                    }
+                                    ui.add(egui::TextEdit::singleline(&mut wm.image).hint_text("logo.png").desired_width(ui.available_width()));
+                                });
                             });
                             let mut width = wm.image_width as f64 * 100.0;
                             if num(ui, &WM_IMAGE_WIDTH, &mut width) {
@@ -586,16 +586,16 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                         }
                     }
                     field(ui, "Folder", |ui| {
-                        let can_pick = app.services.pick_folder.is_some();
-                        let w = ui.available_width() - if can_pick { 76.0 } else { 0.0 };
-                        ui.add(egui::TextEdit::singleline(dir).desired_width(w));
-                        if can_pick
-                            && crate::widgets::text_button(ui, "exportChooseFolder", "Choose…", false).clicked()
-                            && let Some(pick) = app.services.pick_folder.as_mut()
-                            && let Some(d) = pick()
-                        {
-                            *dir = d;
-                        }
+                        trailing_button_row(ui, |ui| {
+                            if app.services.pick_folder.is_some()
+                                && crate::widgets::text_button(ui, "exportChooseFolder", "Choose…", false).clicked()
+                                && let Some(pick) = app.services.pick_folder.as_mut()
+                                && let Some(d) = pick()
+                            {
+                                *dir = d;
+                            }
+                            ui.add(egui::TextEdit::singleline(dir).desired_width(ui.available_width()));
+                        });
                     });
                     field(ui, "Subfolder", |ui| {
                         ui.add(egui::TextEdit::singleline(&mut opts.subfolder).hint_text("none").desired_width(f32::INFINITY))
@@ -610,19 +610,20 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
                     );
                     ui.add_space(4.0);
                     field(ui, "Save preset", |ui| {
-                        let w = ui.available_width() - 60.0;
-                        ui.add(egui::TextEdit::singleline(preset_name).hint_text("Preset name").desired_width(w));
-                        let named = !preset_name.trim().is_empty();
-                        if crate::widgets::text_button(ui, "exportSavePreset", "Save", false).clicked() && named {
-                            let params = export_dialog_params(opts, *full_size, resize, *limit_kb);
-                            match app.run("export.savePreset", json!({"name": preset_name.trim(), "params": params})) {
-                                Ok(_) => {
-                                    app.toast(ui.ctx(), format!("Saved export preset “{}”", preset_name.trim()));
-                                    preset_name.clear();
+                        trailing_button_row(ui, |ui| {
+                            let named = !preset_name.trim().is_empty();
+                            if crate::widgets::text_button(ui, "exportSavePreset", "Save", false).clicked() && named {
+                                let params = export_dialog_params(opts, *full_size, resize, *limit_kb);
+                                match app.run("export.savePreset", json!({"name": preset_name.trim(), "params": params})) {
+                                    Ok(_) => {
+                                        app.toast(ui.ctx(), format!("Saved export preset “{}”", preset_name.trim()));
+                                        preset_name.clear();
+                                    }
+                                    Err(e) => app.toast(ui.ctx(), e),
                                 }
-                                Err(e) => app.toast(ui.ctx(), e),
                             }
-                        }
+                            ui.add(egui::TextEdit::singleline(preset_name).hint_text("Preset name").desired_width(ui.available_width()));
+                        });
                     });
                 }
                 Dialog::Merge { opts } => crate::merge::body(app, ui, opts),
@@ -722,6 +723,7 @@ pub fn show(app: &mut LightcraftApp, ctx: &egui::Context) {
         });
     if let Some(w) = shown {
         ctx.move_to_top(w.response.layer_id);
+        crate::widgets::register(ctx, "dialog:window", w.response.rect);
     }
     if ctx.input(|i| i.key_pressed(egui::Key::Escape)) {
         close = true;
@@ -983,6 +985,14 @@ fn field<R>(ui: &mut egui::Ui, label: &str, add: impl FnOnce(&mut egui::Ui) -> R
     .inner
 }
 
+/// The rest of a [`field`] row, laid out right to left: `add` places its trailing button(s) first,
+/// then a text field taking exactly the width that's left. (Subtracting a guessed button width
+/// instead made the auto-sized dialog grow every frame when the real button was wider, #8.)
+fn trailing_button_row(ui: &mut egui::Ui, add: impl FnOnce(&mut egui::Ui)) {
+    let h = ui.spacing().interact_size.y.max(24.0);
+    ui.allocate_ui_with_layout(egui::vec2(ui.available_width(), h), egui::Layout::right_to_left(egui::Align::Center), add);
+}
+
 /// A labelled row of mutually exclusive choice buttons (ids `button:{id}-{index}`).
 fn choices<V: PartialEq + Copy>(ui: &mut egui::Ui, label: &str, id: &str, options: &[(V, &str)], value: &mut V) {
     field(ui, label, |ui| {