diff --git a/Cargo.lock b/Cargo.lock
index e8037a6f..0ad4ab84 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3352,6 +3352,7 @@ dependencies = [
  "lightcraft-engine",
  "lightcraft-faces",
  "lightcraft-geom",
+ "lightcraft-merge",
  "lightcraft-meta",
  "lightcraft-pipeline",
  "lightcraft-preview",
diff --git a/crates/ui-egui/Cargo.toml b/crates/ui-egui/Cargo.toml
index d67494b7..f7dbc65a 100644
--- a/crates/ui-egui/Cargo.toml
+++ b/crates/ui-egui/Cargo.toml
@@ -28,6 +28,7 @@ log = { workspace = true }
 lightcraft-denoise = { workspace = true, features = ["runtime"] }
 lightcraft-codecs = { workspace = true }
 lightcraft-faces = { workspace = true }
+lightcraft-merge = { workspace = true }
 
 [build-dependencies]
 serde_json = { workspace = true }
diff --git a/crates/ui-egui/locales/de-formats.json b/crates/ui-egui/locales/de-formats.json
index 3597ffdc..671da17d 100644
--- a/crates/ui-egui/locales/de-formats.json
+++ b/crates/ui-egui/locales/de-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct} %",
   "+{n} more": "+{n} weitere",
   "1 task is still running: {names}. Quitting stops it.": "1 Aufgabe läuft noch: {names}. Beenden bricht sie ab.",
-  "{n} tasks are still running: {names}. Quitting stops them.": "{n} Aufgaben laufen noch: {names}. Beenden bricht sie ab."
+  "{n} tasks are still running: {names}. Quitting stops them.": "{n} Aufgaben laufen noch: {names}. Beenden bricht sie ab.",
+  "{what} merge cancelled": "{what}-Zusammenfügung abgebrochen"
 }
diff --git a/crates/ui-egui/locales/de.json b/crates/ui-egui/locales/de.json
index 598ace82..1edf29ad 100644
--- a/crates/ui-egui/locales/de.json
+++ b/crates/ui-egui/locales/de.json
@@ -2026,5 +2026,6 @@
   "Building smart previews": "Smart-Vorschauen werden erstellt",
   "Discarding smart previews": "Smart-Vorschauen werden verworfen",
   "Importing Lightroom catalog": "Lightroom-Katalog wird importiert",
-  "Reading Lightroom catalog": "Lightroom-Katalog wird gelesen"
+  "Reading Lightroom catalog": "Lightroom-Katalog wird gelesen",
+  "Merging": "Zusammenfügen"
 }
diff --git a/crates/ui-egui/locales/es-formats.json b/crates/ui-egui/locales/es-formats.json
index ea502198..9ba1c8f1 100644
--- a/crates/ui-egui/locales/es-formats.json
+++ b/crates/ui-egui/locales/es-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct} %",
   "+{n} more": "+{n} más",
   "1 task is still running: {names}. Quitting stops it.": "1 tarea sigue en curso: {names}. Salir la detiene.",
-  "{n} tasks are still running: {names}. Quitting stops them.": "{n} tareas siguen en curso: {names}. Salir las detiene."
+  "{n} tasks are still running: {names}. Quitting stops them.": "{n} tareas siguen en curso: {names}. Salir las detiene.",
+  "{what} merge cancelled": "Combinación {what} cancelada"
 }
diff --git a/crates/ui-egui/locales/es.json b/crates/ui-egui/locales/es.json
index f0740bd5..701c91bd 100644
--- a/crates/ui-egui/locales/es.json
+++ b/crates/ui-egui/locales/es.json
@@ -1871,5 +1871,6 @@
   "Building smart previews": "Generando vistas previas inteligentes",
   "Discarding smart previews": "Descartando vistas previas inteligentes",
   "Importing Lightroom catalog": "Importando catálogo de Lightroom",
-  "Reading Lightroom catalog": "Leyendo catálogo de Lightroom"
+  "Reading Lightroom catalog": "Leyendo catálogo de Lightroom",
+  "Merging": "Combinando"
 }
diff --git a/crates/ui-egui/locales/fr-formats.json b/crates/ui-egui/locales/fr-formats.json
index f3907689..7ccaf5a3 100644
--- a/crates/ui-egui/locales/fr-formats.json
+++ b/crates/ui-egui/locales/fr-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct} %",
   "+{n} more": "+{n} autres",
   "1 task is still running: {names}. Quitting stops it.": "1 tâche est encore en cours : {names}. Quitter l'arrête.",
-  "{n} tasks are still running: {names}. Quitting stops them.": "{n} tâches sont encore en cours : {names}. Quitter les arrête."
+  "{n} tasks are still running: {names}. Quitting stops them.": "{n} tâches sont encore en cours : {names}. Quitter les arrête.",
+  "{what} merge cancelled": "Fusion {what} annulée"
 }
diff --git a/crates/ui-egui/locales/fr.json b/crates/ui-egui/locales/fr.json
index 51dab1b2..59631e84 100644
--- a/crates/ui-egui/locales/fr.json
+++ b/crates/ui-egui/locales/fr.json
@@ -1871,5 +1871,6 @@
   "Building smart previews": "Génération des aperçus dynamiques",
   "Discarding smart previews": "Suppression des aperçus dynamiques",
   "Importing Lightroom catalog": "Importation du catalogue Lightroom",
-  "Reading Lightroom catalog": "Lecture du catalogue Lightroom"
+  "Reading Lightroom catalog": "Lecture du catalogue Lightroom",
+  "Merging": "Fusion en cours"
 }
diff --git a/crates/ui-egui/locales/ja-formats.json b/crates/ui-egui/locales/ja-formats.json
index f42118d5..f1c06351 100644
--- a/crates/ui-egui/locales/ja-formats.json
+++ b/crates/ui-egui/locales/ja-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct}%",
   "+{n} more": "ほか{n}件",
   "1 task is still running: {names}. Quitting stops it.": "1件のタスクが実行中です：{names}。終了すると停止します。",
-  "{n} tasks are still running: {names}. Quitting stops them.": "{n}件のタスクが実行中です：{names}。終了すると停止します。"
+  "{n} tasks are still running: {names}. Quitting stops them.": "{n}件のタスクが実行中です：{names}。終了すると停止します。",
+  "{what} merge cancelled": "{what}合成をキャンセルしました"
 }
diff --git a/crates/ui-egui/locales/ja.json b/crates/ui-egui/locales/ja.json
index a10a08e1..520452a8 100644
--- a/crates/ui-egui/locales/ja.json
+++ b/crates/ui-egui/locales/ja.json
@@ -1873,5 +1873,6 @@
   "Building smart previews": "スマートプレビューを作成中",
   "Discarding smart previews": "スマートプレビューを破棄中",
   "Importing Lightroom catalog": "Lightroom カタログを読み込み中",
-  "Reading Lightroom catalog": "Lightroom カタログを読み取り中"
+  "Reading Lightroom catalog": "Lightroom カタログを読み取り中",
+  "Merging": "合成中"
 }
diff --git a/crates/ui-egui/locales/pt-br-formats.json b/crates/ui-egui/locales/pt-br-formats.json
index 8bd5bcae..4a9d1168 100644
--- a/crates/ui-egui/locales/pt-br-formats.json
+++ b/crates/ui-egui/locales/pt-br-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct}%",
   "+{n} more": "+{n} mais",
   "1 task is still running: {names}. Quitting stops it.": "1 tarefa ainda está em andamento: {names}. Sair a interrompe.",
-  "{n} tasks are still running: {names}. Quitting stops them.": "{n} tarefas ainda estão em andamento: {names}. Sair as interrompe."
+  "{n} tasks are still running: {names}. Quitting stops them.": "{n} tarefas ainda estão em andamento: {names}. Sair as interrompe.",
+  "{what} merge cancelled": "{what} mesclagem cancelada"
 }
diff --git a/crates/ui-egui/locales/pt-br.json b/crates/ui-egui/locales/pt-br.json
index d9d07b5f..ad269f96 100644
--- a/crates/ui-egui/locales/pt-br.json
+++ b/crates/ui-egui/locales/pt-br.json
@@ -1871,5 +1871,6 @@
   "Building smart previews": "Gerando prévias inteligentes",
   "Discarding smart previews": "Descartando prévias inteligentes",
   "Importing Lightroom catalog": "Importando catálogo do Lightroom",
-  "Reading Lightroom catalog": "Lendo catálogo do Lightroom"
+  "Reading Lightroom catalog": "Lendo catálogo do Lightroom",
+  "Merging": "Mesclando"
 }
diff --git a/crates/ui-egui/locales/ru-formats.json b/crates/ui-egui/locales/ru-formats.json
index 53a54f6c..ba3560ad 100644
--- a/crates/ui-egui/locales/ru-formats.json
+++ b/crates/ui-egui/locales/ru-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct} %",
   "+{n} more": "ещё {n}",
   "1 task is still running: {names}. Quitting stops it.": "Ещё выполняется задача: {names}. Выход прервёт её.",
-  "{n} tasks are still running: {names}. Quitting stops them.": "Ещё выполняется задач: {n} — {names}. Выход прервёт их."
+  "{n} tasks are still running: {names}. Quitting stops them.": "Ещё выполняется задач: {n} — {names}. Выход прервёт их.",
+  "{what} merge cancelled": "{what}: слияние отменено"
 }
diff --git a/crates/ui-egui/locales/ru.json b/crates/ui-egui/locales/ru.json
index 3a442515..6a4e4d52 100644
--- a/crates/ui-egui/locales/ru.json
+++ b/crates/ui-egui/locales/ru.json
@@ -1584,5 +1584,6 @@
   "Building smart previews": "Создание смарт-просмотров",
   "Discarding smart previews": "Удаление смарт-просмотров",
   "Importing Lightroom catalog": "Импорт каталога Lightroom",
-  "Reading Lightroom catalog": "Чтение каталога Lightroom"
+  "Reading Lightroom catalog": "Чтение каталога Lightroom",
+  "Merging": "Слияние"
 }
diff --git a/crates/ui-egui/locales/uk-formats.json b/crates/ui-egui/locales/uk-formats.json
index 9562c8f9..c33dd0cb 100644
--- a/crates/ui-egui/locales/uk-formats.json
+++ b/crates/ui-egui/locales/uk-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct} %",
   "+{n} more": "+{n} ще",
   "1 task is still running: {names}. Quitting stops it.": "1 завдання ще виконується: {names}. Вихід зупинить його.",
-  "{n} tasks are still running: {names}. Quitting stops them.": "Ще виконуються завдання ({n}): {names}. Вихід зупинить їх."
+  "{n} tasks are still running: {names}. Quitting stops them.": "Ще виконуються завдання ({n}): {names}. Вихід зупинить їх.",
+  "{what} merge cancelled": "Об’єднання {what} скасовано"
 }
diff --git a/crates/ui-egui/locales/uk.json b/crates/ui-egui/locales/uk.json
index a18094f4..3c765a1b 100644
--- a/crates/ui-egui/locales/uk.json
+++ b/crates/ui-egui/locales/uk.json
@@ -2065,5 +2065,6 @@
   "Building smart previews": "Створення смарт-переглядів",
   "Discarding smart previews": "Видалення смарт-переглядів",
   "Importing Lightroom catalog": "Імпорт каталогу Lightroom",
-  "Reading Lightroom catalog": "Читання каталогу Lightroom"
+  "Reading Lightroom catalog": "Читання каталогу Lightroom",
+  "Merging": "Об’єднання"
 }
diff --git a/crates/ui-egui/locales/zh-hans-formats.json b/crates/ui-egui/locales/zh-hans-formats.json
index cf28c11a..eb429af4 100644
--- a/crates/ui-egui/locales/zh-hans-formats.json
+++ b/crates/ui-egui/locales/zh-hans-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct}%",
   "+{n} more": "还有 {n} 项",
   "1 task is still running: {names}. Quitting stops it.": "仍有 1 个任务在运行：{names}。退出将停止它。",
-  "{n} tasks are still running: {names}. Quitting stops them.": "仍有 {n} 个任务在运行：{names}。退出将停止它们。"
+  "{n} tasks are still running: {names}. Quitting stops them.": "仍有 {n} 个任务在运行：{names}。退出将停止它们。",
+  "{what} merge cancelled": "已取消 {what} 合并"
 }
diff --git a/crates/ui-egui/locales/zh-hans.json b/crates/ui-egui/locales/zh-hans.json
index c2c29b47..24a47421 100644
--- a/crates/ui-egui/locales/zh-hans.json
+++ b/crates/ui-egui/locales/zh-hans.json
@@ -1871,5 +1871,6 @@
   "Building smart previews": "正在构建智能预览",
   "Discarding smart previews": "正在丢弃智能预览",
   "Importing Lightroom catalog": "正在导入 Lightroom 目录",
-  "Reading Lightroom catalog": "正在读取 Lightroom 目录"
+  "Reading Lightroom catalog": "正在读取 Lightroom 目录",
+  "Merging": "正在合并"
 }
diff --git a/crates/ui-egui/locales/zh-hant-formats.json b/crates/ui-egui/locales/zh-hant-formats.json
index 61e7cef8..0b2ec765 100644
--- a/crates/ui-egui/locales/zh-hant-formats.json
+++ b/crates/ui-egui/locales/zh-hant-formats.json
@@ -227,5 +227,6 @@
   "{pct} %": "{pct}%",
   "+{n} more": "還有 {n} 項",
   "1 task is still running: {names}. Quitting stops it.": "仍有 1 個工作在執行：{names}。結束將停止它。",
-  "{n} tasks are still running: {names}. Quitting stops them.": "仍有 {n} 個工作在執行：{names}。結束將停止它們。"
+  "{n} tasks are still running: {names}. Quitting stops them.": "仍有 {n} 個工作在執行：{names}。結束將停止它們。",
+  "{what} merge cancelled": "已取消{what}合併"
 }
diff --git a/crates/ui-egui/locales/zh-hant.json b/crates/ui-egui/locales/zh-hant.json
index e808c312..caf5f9bc 100644
--- a/crates/ui-egui/locales/zh-hant.json
+++ b/crates/ui-egui/locales/zh-hant.json
@@ -1871,5 +1871,6 @@
   "Building smart previews": "正在建立智慧型預覽",
   "Discarding smart previews": "正在捨棄智慧型預覽",
   "Importing Lightroom catalog": "正在匯入 Lightroom 目錄",
-  "Reading Lightroom catalog": "正在讀取 Lightroom 目錄"
+  "Reading Lightroom catalog": "正在讀取 Lightroom 目錄",
+  "Merging": "正在合併"
 }
diff --git a/crates/ui-egui/src/lightroom_import.rs b/crates/ui-egui/src/lightroom_import.rs
index b05b381c..28101ed2 100644
--- a/crates/ui-egui/src/lightroom_import.rs
+++ b/crates/ui-egui/src/lightroom_import.rs
@@ -468,7 +468,8 @@ mod tests {
     fn demo() -> crate::headless::Headless {
         let app = crate::LightcraftApp::new(lightcraft_engine::Session::with_demo(), crate::Services { png: None, ..Default::default() });
         let mut h = crate::headless::Headless::new(app, [1200.0, 800.0], 1.0);
-        h.step();
+        // no render left running at exit (see tests_activity::demo)
+        h.settle(std::time::Duration::from_secs(20));
         h
     }
 
diff --git a/crates/ui-egui/src/merge.rs b/crates/ui-egui/src/merge.rs
index 3849a191..b1d066a7 100644
--- a/crates/ui-egui/src/merge.rs
+++ b/crates/ui-egui/src/merge.rs
@@ -4,7 +4,7 @@
 //! Previews and the final merge run [`lightcraft_engine::merge::MergeJob`]s on worker threads with
 //! progress and cancellation; the window stays responsive. Changing an option cancels the running
 //! preview and starts a new one. The final merge keeps running after the dialog closes (progress
-//! in a toast); when it finishes, the result is written, imported and selected
+//! in the activity stack); when it finishes, the result is written, imported and selected
 //! ([`lightcraft_engine::Session::finish_merge`]).
 
 use std::sync::atomic::{AtomicBool, Ordering};
@@ -12,6 +12,7 @@ use std::sync::mpsc::{Receiver, channel};
 use std::sync::{Arc, Mutex};
 
 use lightcraft_catalog::PhotoId;
+use lightcraft_engine::activity::{Cancel, TaskGuard, Unit};
 use lightcraft_engine::merge::{MergeJob, MergeOutput};
 use serde::{Deserialize, Serialize};
 use serde_json::{Value, json};
@@ -88,6 +89,8 @@ pub struct MergeTask {
     pub progress: Arc<Mutex<(f32, String)>>,
     pub cancel: Arc<AtomicBool>,
     rx: Receiver<Result<MergeOutput, String>>,
+    /// The final merge's row in the activity stack (previews have none).
+    guard: Option<TaskGuard>,
 }
 
 /// Merge state of the app.
@@ -140,7 +143,7 @@ fn spawn(app: &LightcraftApp, options: &MergeDialog, ids: &[PhotoId], preview: b
     std::thread::Builder::new().name("photo-merge".into()).spawn(work).map_err(|e| e.to_string())?;
     #[cfg(target_arch = "wasm32")]
     work();
-    Ok(MergeTask { preview, job, options: options.clone(), progress, cancel, rx })
+    Ok(MergeTask { preview, job, options: options.clone(), progress, cancel, rx, guard: None })
 }
 
 /// Open the merge dialog for the selection.
@@ -169,7 +172,11 @@ pub fn start_final(app: &mut LightcraftApp, opts: &MergeDialog) -> Result<Value,
         t.cancel.store(true, Ordering::Relaxed);
     }
     let ids = app.merge.ids.clone();
-    let task = spawn(app, opts, &ids, false)?;
+    let mut task = spawn(app, opts, &ids, false)?;
+    let guard = app.session.activity.start("merge", "Merging", Cancel::Flag(task.cancel.clone()));
+    guard.set_unit(Unit::Percent);
+    guard.progress(0, 1000);
+    task.guard = Some(guard);
     app.merge.final_task = Some(task);
     app.merge.last.insert(opts.command.clone(), opts.clone());
     Ok(json!({"started": true, "photos": ids.len()}))
@@ -265,6 +272,7 @@ pub fn poll(app: &mut LightcraftApp, ctx: &egui::Context) {
                         app.merge.last_result = Some(v);
                         app.toast(ctx, crate::i18n::tr_format!("{what} merge added", what = what));
                     }
+                    Err(_) if t.cancel.load(Ordering::Relaxed) => app.toast(ctx, crate::i18n::tr_format!("{what} merge cancelled", what = what)),
                     Err(e) => {
                         app.ui.status = e.to_string();
                         app.toast(ctx, crate::i18n::tr_format!("{what} merge failed: {e}", e = e, what = what));
@@ -273,8 +281,11 @@ pub fn poll(app: &mut LightcraftApp, ctx: &egui::Context) {
             }
             Err(_) => {
                 let (f, stage) = t.progress.lock().map(|g| g.clone()).unwrap_or_default();
-                let now = ctx.input(|i| i.time);
-                app.ui.toast = Some((crate::i18n::tr_format!("Merging… {stage} {:.0}%", f * 100.0, stage = stage), now + 0.5, None));
+                if let Some(guard) = &t.guard {
+                    let f = if f.is_finite() { f.clamp(0.0, 1.0) } else { 0.0 };
+                    guard.progress((f * 1000.0) as u64, 1000);
+                    guard.detail(crate::i18n::tr(&stage));
+                }
                 ctx.request_repaint_after(std::time::Duration::from_millis(100));
             }
         }
diff --git a/crates/ui-egui/src/tests_activity.rs b/crates/ui-egui/src/tests_activity.rs
index 5e8e967d..db4b5829 100644
--- a/crates/ui-egui/src/tests_activity.rs
+++ b/crates/ui-egui/src/tests_activity.rs
@@ -14,7 +14,9 @@ const T: Duration = Duration::from_secs(20);
 fn demo() -> Headless {
     let app = LightcraftApp::new(lightcraft_engine::Session::with_demo(), Services { png: None, ..Default::default() });
     let mut h = Headless::new(app, [1200.0, 800.0], 1.0);
-    h.step();
+    // let the first renders finish: a render still running when the test binary exits can crash in the
+    // GPU driver's teardown (the preview pool doesn't join its workers)
+    h.settle(T);
     h
 }
 
@@ -53,7 +55,10 @@ fn rows_appear_after_half_a_second_and_cancel_by_click() {
     let g = h.app.session.activity.start("export", "Exporting", Cancel::Yes);
     g.progress(2, 5);
     h.step();
-    assert!(!has(&h, &format!("activity:row:{}", g.id())), "not before 0.5 s");
+    // a frame on a loaded machine can outlast the half second: only judge a task still young after it
+    if h.app.session.activity.list()[0].age_ms < crate::panels::activity::SHOW_AFTER_MS {
+        assert!(!has(&h, &format!("activity:row:{}", g.id())), "not before 0.5 s");
+    }
     wait_visible(&mut h);
     assert!(has(&h, &format!("activity:row:{}", g.id())));
     click(&mut h, &format!("activity:cancel:{}", g.id()));
@@ -242,7 +247,7 @@ fn slow_import(tag: &str, n: usize) -> (Headless, std::path::PathBuf) {
         })
     }));
     let mut h = Headless::new(LightcraftApp::new(s, Services { png: None, ..Default::default() }), [1200.0, 800.0], 1.0);
-    h.step();
+    h.settle(T);
     (h, dir)
 }
 
@@ -282,3 +287,45 @@ fn scan_shows_a_row_and_cancel_closes_it() {
     assert!(h.app.ui.dialog.is_none(), "no review opened");
     let _ = std::fs::remove_dir_all(&dir);
 }
+
+/// A library of three bracketed DNGs (−2, 0, +2 EV) on disk, all selected.
+fn bracket(tag: &str) -> (Headless, std::path::PathBuf) {
+    let dir = std::env::temp_dir().join(format!("lc-activity-{tag}-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let mut paths = Vec::new();
+    for (i, bytes) in lightcraft_merge::synth::bracket_dngs(1600, 1200, &[-2.0, 0.0, 2.0]).unwrap().into_iter().enumerate() {
+        let p = dir.join(format!("IMG_{i}.dng"));
+        std::fs::write(&p, bytes).unwrap();
+        paths.push(p.to_string_lossy().to_string());
+    }
+    let mut session = lightcraft_engine::Session::new().with_fs();
+    let r = session.execute("library.import", &json!({"paths": paths})).unwrap();
+    let ids: Vec<u64> = r["imported"].as_array().unwrap().iter().map(|v| v.as_u64().unwrap()).collect();
+    session.execute("library.select", &json!({"ids": ids})).unwrap();
+    let app = LightcraftApp::new(session, Services { png: None, ..Default::default() });
+    let mut h = Headless::new(app, [1200.0, 800.0], 1.0);
+    h.settle(T);
+    (h, dir)
+}
+
+#[test]
+fn final_merge_shows_a_row_and_cancels() {
+    let (mut h, dir) = bracket("merge");
+    let before = h.app.session.catalog.len();
+    crate::merge::start_last(&mut h.app, "merge.hdr").unwrap();
+    h.step();
+    let rows = h.app.session.activity.list();
+    assert_eq!(rows.len(), 1);
+    assert_eq!((rows[0].kind, rows[0].label.as_str(), rows[0].unit), ("merge", "Merging", Unit::Percent));
+    assert!(rows[0].cancellable);
+    assert_eq!(rows[0].total, 1000);
+    h.app.session.activity.cancel(rows[0].id).unwrap();
+    assert!(h.step_until(T, |h| h.app.merge.final_task.is_none()));
+    assert!(h.app.merge.last_result.is_none(), "nothing merged");
+    assert_eq!(h.app.session.catalog.len(), before, "no photo added");
+    assert!(h.app.session.activity.list().is_empty());
+    let toast = h.app.ui.toast.as_ref().map(|t| t.0.clone()).unwrap_or_default();
+    assert_eq!(toast, "HDR merge cancelled");
+    let _ = std::fs::remove_dir_all(dir);
+}