diff --git a/src/app.rs b/src/app.rs
index 1064159..2391d59 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -943,6 +943,9 @@ impl App {
         for id in std::mem::take(&mut self.group_next) {
             if !self.streams.contains_key(&id) {
                 self.start_reply(ctx, id);
+            } else {
+                // Still busy: keep the turn queued instead of dropping it with the take().
+                self.group_next.push(id);
             }
         }
         for (id, texts) in std::mem::take(&mut self.pending_turns) {
@@ -951,7 +954,13 @@ impl App {
                     b.messages.push(Message::user(&t));
                 }
             }
-            self.start_reply(ctx, id);
+            if self.streams.contains_key(&id) {
+                // A turn just settled in the same tick we queued this one; starting now would
+                // replace the running Live and let two agent threads write one chat. Retry idle.
+                self.group_next.push(id);
+            } else {
+                self.start_reply(ctx, id);
+            }
         }
     }
 
@@ -1239,9 +1248,11 @@ impl App {
                 StreamEvent::Steered(m) => b.messages.push(m),
                 StreamEvent::NextStep(via) => b.messages.push(Message::assistant("", &via)),
                 StreamEvent::ToolResult(m) => b.messages.push(m),
-                StreamEvent::Compacted(n, summary) => {
-                    let n = n.min(b.messages.len());
-                    b.messages.splice(..n, [summary]);
+                StreamEvent::Compacted(n, summary, boundary) => {
+                    // The model's history can be shorter than the window's chat (group chats
+                    // filter); land the cut at the real first-kept message, not the raw index.
+                    let cut = b.messages.iter().position(|m| m.at == boundary && m.role == Role::User).unwrap_or(n.min(b.messages.len()));
+                    b.messages.splice(..cut, [summary]);
                 }
                 StreamEvent::ToolStatus(call_id, st) => {
                     if let Some(c) = b.messages.iter_mut().rev().flat_map(|m| m.tool_calls.iter_mut()).find(|c| c.id == call_id) {
@@ -2262,7 +2273,7 @@ impl App {
                         crate::icons::label(ui, crate::icons::Icon::Check, &t("輔助使用已打開"), 11.5, p.text3);
                     } else if ui.small_button(t("打開輔助使用")).on_hover_text(t("macOS 要你允許一次，AnyBot 才看得到你的瀏覽器視窗")).clicked() {
                         if !crate::axread::trusted(true) {
-                            let _ = std::process::Command::new("open").arg("x-apple.systempreferences:com.apple.preference.security?Privacy_Accessibility").spawn();
+                            let _ = crate::computer::spawn_reaped(&mut std::process::Command::new("open").arg("x-apple.systempreferences:com.apple.preference.security?Privacy_Accessibility"));
                         }
                     }
                     return;
@@ -3238,7 +3249,8 @@ impl App {
             std::thread::sleep(std::time::Duration::from_millis(100));
         }
         let secs = t0.elapsed().as_secs();
-        let msgs = app.state.bot(id).map(|b| b.messages[start..].to_vec()).unwrap_or_default();
+        // The chat can shrink (compaction) between the snapshot and now: slice safely.
+        let msgs = app.state.bot(id).and_then(|b| b.messages.get(start..)).map(|m| m.to_vec()).unwrap_or_default();
         let clip = |s: &str, n: usize| -> String {
             let one = s.replace('\n', " ⏎ ");
             if one.chars().count() > n { format!("{}…", one.chars().take(n).collect::<String>()) } else { one }
diff --git a/src/app/files_ui.rs b/src/app/files_ui.rs
index c2497d3..e980181 100644
--- a/src/app/files_ui.rs
+++ b/src/app/files_ui.rs
@@ -96,6 +96,18 @@ fn start_job(kind: &str, path: &str) -> Option<Arc<Mutex<PageJob>>> {
                 g.done = true;
             });
         }
+        "image" => {
+            // Decoding (a 6000×4000 photo, a big SVG) on the UI thread froze the window;
+            // the viewer shows a spinner until this thread is done.
+            std::thread::spawn(move || {
+                let img = preview::decode_image(&path);
+                let mut g = j.lock().unwrap();
+                if let Some(img) = img {
+                    g.ready.push(img);
+                }
+                g.done = true;
+            });
+        }
         "video" => {
             std::thread::spawn(move || {
                 let out = std::env::temp_dir().join(format!("anybot-poster-{}-{}.png", std::process::id(), crate::model::now_ms()));
@@ -258,8 +270,30 @@ impl App {
                         });
                     }
                     Preview::Image => {
+                        // The picture is decoded on a worker thread (start_job "image").
                         if fv.image.is_none() {
-                            fv.image = load_texture(ui.ctx(), &fv.path);
+                            if let Some(job) = fv.job.clone() {
+                                let (imgs, done) = {
+                                    let mut g = job.lock().unwrap();
+                                    (std::mem::take(&mut g.ready), g.done)
+                                };
+                                match imgs.into_iter().next() {
+                                    Some(img) => fv.image = Some(texture(ui.ctx(), "file-view", &img)),
+                                    None => {
+                                        ui.add_space(40.0);
+                                        ui.vertical_centered(|ui| {
+                                            if done {
+                                                ui.label(RichText::new(t("這張圖片打不開")).color(p.text3));
+                                            } else {
+                                                ui.spinner();
+                                                ui.ctx().request_repaint_after(std::time::Duration::from_millis(80));
+                                            }
+                                        });
+                                    }
+                                }
+                            } else {
+                                fv.image = load_texture(ui.ctx(), &fv.path);
+                            }
                         }
                         match &fv.image {
                             Some(tex) => {
diff --git a/src/app/markdown_ui.rs b/src/app/markdown_ui.rs
index b64b322..8422933 100644
--- a/src/app/markdown_ui.rs
+++ b/src/app/markdown_ui.rs
@@ -777,6 +777,12 @@ impl App {
         let dark = p.pane != LIGHT.pane;
         let key = key_of(src, dark);
         if !self.md.diagrams.contains_key(&key) {
+            // Keep a long chat from growing forever: every diagram is a GPU texture. Past a
+            // roomy cap, drop the whole cache — the diagrams shown again redraw on a worker
+            // thread (a brief spinner beats slowly eating hundreds of MBs).
+            if self.md.diagrams.len() >= 64 {
+                self.md.diagrams.clear();
+            }
             let slot = Arc::new(Mutex::new(None));
             let (s2, src2) = (slot.clone(), src.to_string());
             let ctx = ui.ctx().clone();
diff --git a/src/app/vault_ui.rs b/src/app/vault_ui.rs
index 5cc1c3f..ed13360 100644
--- a/src/app/vault_ui.rs
+++ b/src/app/vault_ui.rs
@@ -587,8 +587,11 @@ impl App {
             VaultDialog::Import(mut st) => {
                 if self.vault_import(ctx, &mut st) {
                     next = Some(VaultDialog::Import(st));
+                } else {
+                    // Only when it closed: marking saved every frame reloaded the whole
+                    // vault list on every repaint while the import dialog was open.
+                    saved = true;
                 }
-                saved = true;
             }
         }
         self.vault.dialog = next;
diff --git a/src/icons.rs b/src/icons.rs
index 4a5a2a9..153cddf 100644
--- a/src/icons.rs
+++ b/src/icons.rs
@@ -250,13 +250,19 @@ fn rasterize(icon: Icon, px: u32) -> Option<egui::ColorImage> {
 pub fn paint(p: &Painter, rect: Rect, icon: Icon, col: Color32) {
     let ppp = p.ctx().pixels_per_point();
     let side = rect.width().min(rect.height());
-    let px = (side * ppp).round().max(8.0) as u32;
+    // Quantised size (2 px steps, capped): a resized window used to create a new texture for
+    // every pixel width, so the cache grew without limit while the window was dragged.
+    let px = ((side * ppp).round().max(8.0) as u32 / 2 * 2).clamp(8, 512);
     let tex = {
         let mut c = cache().lock().unwrap();
         match c.get(&(icon, px)) {
             Some(t) => t.clone(),
             None => {
                 let Some(img) = rasterize(icon, px) else { return };
+                // Roomy hard cap: past it, start the cache fresh (textures reload on demand).
+                if c.len() >= 1500 {
+                    c.clear();
+                }
                 let t = p.ctx().load_texture(format!("icon-{icon:?}-{px}"), img, egui::TextureOptions::LINEAR);
                 c.insert((icon, px), t.clone());
                 t
diff --git a/src/notify.rs b/src/notify.rs
index a344f18..d3ba116 100644
--- a/src/notify.rs
+++ b/src/notify.rs
@@ -90,6 +90,7 @@ pub fn screensaver_active() -> bool {
         std::thread::sleep(std::time::Duration::from_millis(20));
     }
     let _ = c.kill();
+    let _ = c.wait();
     false
 }
 
@@ -116,10 +117,10 @@ pub fn banner(title: &str, body: &str) {
     if !cfg!(target_os = "macos") {
         // The desktop's notification service (GNOME, KDE, XFCE…) through notify-send.
         let body: String = body.chars().take(180).collect();
-        let _ = Command::new("notify-send").args(["-a", "AnyBot", title, &body]).stdin(Stdio::null()).stdout(Stdio::null()).stderr(Stdio::null()).spawn();
+        let _ = crate::computer::spawn_reaped(&mut Command::new("notify-send").args(["-a", "AnyBot", title, &body]).stdin(Stdio::null()).stdout(Stdio::null()).stderr(Stdio::null()));
         return;
     }
-    let _ = Command::new("osascript").arg("-e").arg(banner_script(title, body)).stdin(Stdio::null()).stdout(Stdio::null()).stderr(Stdio::null()).spawn();
+    let _ = crate::computer::spawn_reaped(&mut Command::new("osascript").arg("-e").arg(banner_script(title, body)).stdin(Stdio::null()).stdout(Stdio::null()).stderr(Stdio::null()));
 }
 
 #[cfg(test)]
diff --git a/src/preview.rs b/src/preview.rs
index 0402a2d..632cf3e 100644
--- a/src/preview.rs
+++ b/src/preview.rs
@@ -114,7 +114,8 @@ pub fn system_open(target: impl AsRef<std::ffi::OsStr>) -> std::process::Command
 }
 
 pub fn open_with_system(target: &str) {
-    if let Err(e) = system_open(target).spawn() {
+    let mut c = system_open(target);
+    if let Err(e) = crate::computer::spawn_reaped(&mut c) {
         eprintln!("anybot: couldn't open {target}: {e}");
     }
 }
@@ -138,7 +139,13 @@ fn clip(t: String) -> String {
 }
 
 fn read_text(path: &Path) -> Result<String, String> {
-    let bytes = std::fs::read(path).map_err(|e| format!("讀不到檔案：{e}"))?;
+    use std::io::Read;
+    // Read only the head of the file: a preview never shows more than clip() keeps (200 K
+    // chars), and reading a multi-GB log whole on the UI thread froze the whole window.
+    const HEAD: u64 = 4 << 20;
+    let mut f = std::fs::File::open(path).map_err(|e| format!("讀不到檔案：{e}"))?;
+    let mut bytes = Vec::new();
+    f.by_ref().take(HEAD).read_to_end(&mut bytes).map_err(|e| format!("讀不到檔案：{e}"))?;
     if bytes.iter().take(8000).any(|b| *b == 0) {
         return Err("這是二進位檔案，沒辦法當文字顯示。".into());
     }
@@ -456,15 +463,36 @@ fn md_table(rows: &[Vec<String>]) -> String {
     s
 }
 
+/// Find `<tag` followed by `>` or a space, ASCII case-insensitive, on the original string.
+/// (Lowercasing the whole page first shifts byte offsets — "İ" becomes 3 bytes when lowered —
+/// and cutting the original at those offsets panics.)
+fn find_open_tag(s: &str, tag: &str) -> Option<usize> {
+    let (b, t) = (s.as_bytes(), tag.as_bytes());
+    (0..b.len()).find(|&i| {
+        b[i] == b'<'
+            && b.len() >= i + 1 + t.len()
+            && b[i + 1..].iter().zip(t).all(|(a, c)| a.eq_ignore_ascii_case(c))
+            && matches!(b.get(i + 1 + t.len()), Some(c) if *c == b'>' || c.is_ascii_whitespace())
+    })
+}
+
+/// `needle` (ASCII) in `hay`, ASCII case-insensitive, as a byte offset.
+fn find_ci(hay: &str, needle: &str) -> Option<usize> {
+    let (h, n) = (hay.as_bytes(), needle.as_bytes());
+    if n.is_empty() || h.len() < n.len() {
+        return None;
+    }
+    (0..=h.len() - n.len()).find(|&i| h[i..i + n.len()].iter().zip(n).all(|(a, c)| a.eq_ignore_ascii_case(c)))
+}
+
 /// A web page as Markdown: headings, paragraphs, lists, tables, bold, links ("text (url)").
 /// Scripts, styles and the <head> are dropped.
 pub fn html_markdown(html: &str) -> String {
     let mut s = html.to_string();
     for tag in ["head", "script", "style", "noscript", "svg", "template"] {
         loop {
-            let low = s.to_lowercase();
-            let Some(a) = low.find(&format!("<{tag}")).filter(|a| low[a + tag.len() + 1..].starts_with(|c: char| c == '>' || c.is_whitespace())) else { break };
-            let end = low[a..].find(&format!("</{tag}>")).map(|e| a + e + tag.len() + 3).unwrap_or(s.len());
+            let Some(a) = find_open_tag(&s, tag) else { break };
+            let end = find_ci(&s[a..], &format!("</{tag}>")).map(|e| a + e + tag.len() + 3).unwrap_or(s.len());
             s.replace_range(a..end, "");
         }
     }
@@ -586,7 +614,12 @@ pub fn html_markdown(html: &str) -> String {
 }
 
 fn load_sheet(path: &Path, name: &str) -> Result<Preview, String> {
+    // calamine parses the whole workbook on the UI thread: a huge .xlsx froze the window.
+    // (CSV/TSV are fine: read_text reads only the head.)
     let ext = name.rsplit('.').next().unwrap_or("").to_lowercase();
+    if matches!(ext.as_str(), "xlsx" | "xls" | "ods") && std::fs::metadata(path).map(|m| m.len() > 50 << 20).unwrap_or(false) {
+        return Err("這個試算表太大（超過 50 MB），在 AnyBot 裡預覽會卡住；請用其他 App 打開。".into());
+    }
     if ext == "csv" || ext == "tsv" {
         let text = read_text(path)?;
         let sep = if ext == "tsv" { '\t' } else { ',' };
@@ -623,6 +656,11 @@ fn load_sheet(path: &Path, name: &str) -> Result<Preview, String> {
 
 /// An Excel date number (days since 1899-12-30) as "2026-10-31" or "2026-10-29 20:13".
 pub fn excel_date(v: f64) -> String {
+    // A cell formatted as a date can hold any number (Excel cells go to 1e308); beyond any
+    // real date, show the number — the date maths would overflow chrono and panic.
+    if !v.is_finite() || v.abs() > 3_000_000.0 {
+        return if v.fract().abs() < 0.000001 { format!("{}", v as i64) } else { format!("{v}") };
+    }
     let base = chrono::NaiveDate::from_ymd_opt(1899, 12, 30).unwrap().and_hms_opt(0, 0, 0).unwrap();
     let t = base + chrono::Duration::milliseconds((v * 86_400_000.0).round() as i64);
     if v.fract().abs() < 1e-9 {