diff --git a/crates/engine/src/cmd/fileio/mod.rs b/crates/engine/src/cmd/fileio/mod.rs
index c819b9ae6..8c224aa12 100644
--- a/crates/engine/src/cmd/fileio/mod.rs
+++ b/crates/engine/src/cmd/fileio/mod.rs
@@ -1366,15 +1366,17 @@ pub(crate) fn unique_file_names<'a>(names: impl IntoIterator<Item = (&'a str, St
 /// `names` with `-2`, `-3`… after a name already used (compared without case).
 fn distinct_names(names: impl IntoIterator<Item = String>) -> Vec<String> {
     let mut taken = std::collections::HashSet::new();
+    // The next number to try for each base: a name repeated many times doesn't search the numbers
+    // taken before it.
+    let mut next: std::collections::HashMap<String, usize> = std::collections::HashMap::new();
     names
         .into_iter()
         .map(|base| {
             let mut name = base.clone();
-            for i in 2.. {
-                if taken.insert(name.to_lowercase()) {
-                    break;
-                }
-                name = format!("{base}-{i}");
+            while !taken.insert(name.to_lowercase()) {
+                let n = next.entry(base.to_lowercase()).or_insert(1);
+                *n += 1;
+                name = format!("{base}-{n}");
             }
             name
         })
diff --git a/crates/engine/src/cmd/links.rs b/crates/engine/src/cmd/links.rs
index f74c344e7..e8f122e96 100644
--- a/crates/engine/src/cmd/links.rs
+++ b/crates/engine/src/cmd/links.rs
@@ -182,6 +182,8 @@ pub(crate) fn linked_groups(d: &Document) -> Vec<(String, Vec<u64>)> {
 fn groups(d: &Document, ids: Option<&[NodeId]>) -> Vec<Group> {
     let mut out: Vec<Group> = vec![];
     let mut index: BTreeMap<(String, String, bool), usize> = BTreeMap::new();
+    // Looked up for every linked node: a set, not the list (which may repeat an id many times).
+    let wanted: Option<std::collections::HashSet<NodeId>> = ids.map(|ids| ids.iter().copied().collect());
     let mut add = |link: &LinkInfo, key: &str, document: Option<Shown>, id: Option<NodeId>| {
         let i = *index.entry((link.path.clone(), key.to_string(), document.is_some())).or_insert_with(|| {
             out.push(Group { link: link.clone(), key: key.to_string(), ids: vec![], document });
@@ -193,7 +195,7 @@ fn groups(d: &Document, ids: Option<&[NodeId]>) -> Vec<Group> {
     };
     d.walk(|n| {
         if let Some((l, key, document)) = linked(n)
-            && ids.is_none_or(|ids| ids.contains(&n.id))
+            && wanted.as_ref().is_none_or(|ids| ids.contains(&n.id))
         {
             add(l, key, document, Some(n.id));
         }
diff --git a/crates/mcp/src/prompts.rs b/crates/mcp/src/prompts.rs
index 2dff4486e..0c0a43926 100644
--- a/crates/mcp/src/prompts.rs
+++ b/crates/mcp/src/prompts.rs
@@ -405,7 +405,10 @@ pub fn get(name: &str, args: &Value) -> Result<Value, String> {
         let ids: Vec<&str> = PROMPTS.iter().map(|p| p.name).collect();
         return Err(format!("unknown prompt `{name}` ({})", ids.join("|")));
     };
-    let mut text = flow(p.text);
+    let template = flow(p.text);
+    // (placeholder, value): filled in one pass over the template, so a value that looks like a
+    // placeholder stays as it is.
+    let mut values: Vec<(String, String)> = vec![];
     for a in p.arguments {
         let given = args.get(a.name).filter(|v| !v.is_null()).map(|v| match v {
             Value::String(s) => s.clone(),
@@ -416,7 +419,21 @@ pub fn get(name: &str, args: &Value) -> Result<Value, String> {
             _ if a.required => return Err(format!("prompt `{name}` needs the `{a_name}` argument", a_name = a.name)),
             _ => a.default.to_string(),
         };
-        text = text.replace(&format!("{{{}}}", a.name), &value);
+        values.push((format!("{{{}}}", a.name), value));
+    }
+    let mut text = String::with_capacity(template.len());
+    let mut rest = template.as_str();
+    while let Some(c) = rest.chars().next() {
+        match values.iter().find(|(placeholder, _)| rest.starts_with(placeholder.as_str())) {
+            Some((placeholder, value)) => {
+                text.push_str(value);
+                rest = rest.get(placeholder.len()..).unwrap_or_default();
+            }
+            None => {
+                text.push(c);
+                rest = rest.get(c.len_utf8()..).unwrap_or_default();
+            }
+        }
     }
     Ok(json!({
         "description": p.description,
diff --git a/crates/render/src/encode/quantize.rs b/crates/render/src/encode/quantize.rs
index 9c5061f1d..ec04c9f46 100644
--- a/crates/render/src/encode/quantize.rs
+++ b/crates/render/src/encode/quantize.rs
@@ -197,7 +197,9 @@ pub fn quantize_locked(rgba: &[u8], width: u32, height: u32, o: &PaletteOptions,
     }
     let weights = o.reduction.weights();
     let dither = if exact { Dither::None } else { o.dither };
-    let mut indices = map(&colors, width as usize, &palette, weights, dither, f32::from(o.dither_amount.min(100)) / 100.0, |i| clear(&px[i]));
+    // (A width past the pixels there are would size the error rows from a number nothing checked.)
+    let mut indices =
+        map(&colors, (width as usize).min(colors.len()), &palette, weights, dither, f32::from(o.dither_amount.min(100)) / 100.0, |i| clear(&px[i]));
     // Drop the entries no pixel uses (fixed palettes), keeping the order.
     let mut used = [false; 256];
     for (i, &ix) in indices.iter().enumerate() {
diff --git a/crates/render/src/encode/tga.rs b/crates/render/src/encode/tga.rs
index 884276eec..abac01dba 100644
--- a/crates/render/src/encode/tga.rs
+++ b/crates/render/src/encode/tga.rs
@@ -34,11 +34,11 @@ pub fn encode(rgba: &[u8], width: u32, height: u32, o: &TgaOptions) -> Result<Ve
         return Err(format!("{width} × {height} pixels is too large for Targa (at most 65535 pixels a side): lower the resolution"));
     };
     let (w, h) = (usize::from(w16), usize::from(h16));
-    if w == 0 || h == 0 || w * h * 4 != rgba.len() {
+    if w == 0 || h == 0 || (w * h).checked_mul(4) != Some(rgba.len()) {
         return Err("Targa encoding failed: the pixel buffer doesn't match the image size".into());
     }
     let px = rgba.as_chunks::<4>().0;
-    let mut out = Vec::with_capacity(18 + w * h * usize::from(o.depth / 8) + 26);
+    let mut out = Vec::with_capacity((w * h).saturating_mul(usize::from(o.depth / 8)).saturating_add(18 + 26));
     // No image id or colour map, uncompressed true colour, origin (0, 0).
     out.extend([0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0]);
     out.extend(w16.to_le_bytes());