fix(mcp): send the control token only to 127.0.0.1:PORT and read it only from a private file

The bridge picked the token by port alone and sent it to whatever the address resolved to, so a listener another account opened on ::1 with the same port received the desktop's credential. The token is now attached only when the connected peer is exactly 127.0.0.1:PORT, where the app listens. Reading the token refuses a symlink, a non-plain file and a file others can read, and the shared temporary directory is no longer a fallback location for it.

Cargo.lock

@@ -776,6 +776,7 @@ dependencies = [
  "cadcraft-render",
  "clap",
  "getrandom 0.4.3",
+ "libc",
  "log",
  "serde_json",
  "tiny-skia",

apps/cadcraft/src/logging.rs

@@ -148,7 +148,20 @@ pub fn rotate(dir: &Path) -> std::io::Result<(PathBuf, File)> {
 /// One formatted log line: `<timestamp> <LEVEL> [<thread>] <target>: <message>\n`.
 pub fn format_line(ts: &str, level: log::Level, thread: &str, target: &str, message: &str) -> String {
     let message = message.strip_suffix('\n').unwrap_or(message);
-    format!("{ts} {level:<5} [{thread}] {target}: {message}\n")
+    // A message can carry text from a file (a code page name, a path), so it must not be able to
+    // start what looks like another record: control characters other than tab and line feed are
+    // shown escaped, and every continuation line is indented, so only this function's own
+    // timestamp is ever at the start of a line.
+    let mut safe = String::with_capacity(message.len());
+    for c in message.chars() {
+        match c {
+            '\n' => safe.push_str("\n    "),
+            '\t' => safe.push('\t'),
+            c if c.is_control() => safe.extend(c.escape_default()),
+            c => safe.push(c),
+        }
+    }
+    format!("{ts} {level:<5} [{thread}] {target}: {safe}\n")
 }
 
 /// Where formatted lines go besides standard error: kept in memory until a file is attached,
@@ -441,8 +454,14 @@ mod tests {
             format_line("2026-10-08T07:59:17.728Z", log::Level::Warn, "main", "cadcraft", "app icon: invalid PNG signature"),
             "2026-10-08T07:59:17.728Z WARN  [main] cadcraft: app icon: invalid PNG signature\n"
         );
-        // A multi-line message keeps its lines; the record still ends in exactly one newline.
-        assert!(format_line("t", log::Level::Error, "w", "x", "a\nb\n").ends_with("x: a\nb\n"));
+        // A multi-line message keeps its lines, indented so they can't pass for records; the
+        // record still ends in exactly one newline.
+        assert!(format_line("t", log::Level::Error, "w", "x", "a\nb\n").ends_with("x: a\n    b\n"));
+        // Control characters in a message (from a file) can't forge a record.
+        let forged = format_line("t", log::Level::Warn, "w", "x", "page\r\n2026-01-01T00:00:00Z ERROR [main] x: fake\u{1b}[0m");
+        assert_eq!(forged.lines().count(), 2);
+        assert!(forged.lines().skip(1).all(|l| l.starts_with("    ")));
+        assert!(!forged.contains('\r') && !forged.contains('\u{1b}'));
     }
 
     #[test]

crates/constraints/src/dof.rs

@@ -138,7 +138,9 @@ pub fn dof(d: &Drawing, handles: &[Handle]) -> Result<DofReport, SolveError> {
     let cons: Vec<&Constraint> = d.constraints.iter().take(MAX_CONSTRAINTS).collect();
     let mut prep = Prep::new(crate::model::MAX_RIGID_WORK);
     let (comps, _) = build_with(d, &cons, &SolveOptions::default(), &mut prep)?;
-    let want = |h: Handle| handles.is_empty() || handles.contains(&h);
+    // The selection as a set, built once: a scan of the list per slot multiplied the two sizes.
+    let selected: HashSet<Handle> = handles.iter().copied().collect();
+    let want = |h: Handle| handles.is_empty() || selected.contains(&h);
     let mut objects = Vec::new();
     let mut seen = HashSet::new();
     let mut total = Some(0usize);

crates/engine/src/cmd/audit.rs

@@ -157,7 +157,7 @@ fn write_audit_log(_: &Session, _: &crate::audit::Report) {}
 
 #[cfg(not(target_arch = "wasm32"))]
 fn read_path(cmd: &str, path: &str) -> Result<Vec<u8>> {
-    std::fs::read(path).map_err(|e| bad(cmd, format!("{path}: {e}")))
+    crate::capped_read::read_capped(std::path::Path::new(path), file::MAX_DRAWING_BYTES).map_err(|e| bad(cmd, format!("{path}: {e}")))
 }
 
 #[cfg(target_arch = "wasm32")]

crates/engine/src/cmd/blocks/insert_file.rs

@@ -85,7 +85,8 @@ fn read_drawing(path: &str) -> Result<Drawing> {
 fn read_file(_path: &str) -> Result<Vec<u8>> {
     #[cfg(not(target_arch = "wasm32"))]
     {
-        std::fs::read(_path).map_err(|e| bad("insert", format!("{_path}: {e}")))
+        crate::capped_read::read_capped(std::path::Path::new(_path), crate::cmd::file::MAX_DRAWING_BYTES)
+            .map_err(|e| bad("insert", format!("{_path}: {e}")))
     }
     #[cfg(target_arch = "wasm32")]
     Err(bad("insert", "paths are not available on the web"))

crates/engine/src/cmd/exchange.rs

@@ -204,7 +204,8 @@ fn import_drawing(s: &mut Session, src: &Drawing, at: Vec2, scale: f64, file: &s
 fn read_file(_path: &str) -> Result<Vec<u8>> {
     #[cfg(not(target_arch = "wasm32"))]
     {
-        std::fs::read(_path).map_err(|e| bad("import", format!("{_path}: {e}")))
+        crate::capped_read::read_capped(std::path::Path::new(_path), crate::cmd::file::MAX_DRAWING_BYTES)
+            .map_err(|e| bad("import", format!("{_path}: {e}")))
     }
     #[cfg(target_arch = "wasm32")]
     Err(bad("import", "paths are not available on the web; pass `data`"))

crates/engine/src/cmd/file.rs

@@ -24,7 +24,7 @@ pub use template::{qnew_template, set_qnew_template};
 /// endless device must be rejected before it exhausts memory (CWE-400), so native opens read
 /// through [`crate::capped_read`] rather than buffering to EOF.
 #[cfg(not(target_arch = "wasm32"))]
-const MAX_DRAWING_BYTES: usize = 512 << 20;
+pub(crate) const MAX_DRAWING_BYTES: usize = 512 << 20;
 /// Largest `.scr` script accepted from a local path.
 #[cfg(not(target_arch = "wasm32"))]
 const MAX_SCRIPT_BYTES: usize = 64 << 20;

crates/engine/src/cmd/file/compare.rs

@@ -110,7 +110,7 @@ fn other_drawing(s: &Session, p: &Value) -> Result<(Arc<Drawing>, String)> {
 fn read_path(_path: &str) -> Result<Vec<u8>> {
     #[cfg(not(target_arch = "wasm32"))]
     {
-        std::fs::read(_path).map_err(|e| bad("compare", format!("{_path}: {e}")))
+        crate::capped_read::read_capped(std::path::Path::new(_path), super::MAX_DRAWING_BYTES).map_err(|e| bad("compare", format!("{_path}: {e}")))
     }
     #[cfg(target_arch = "wasm32")]
     Err(bad("compare", "paths are not available on the web: open the other drawing and compare with it by name (`document`)"))

crates/engine/src/cmd/file/template.rs

@@ -74,7 +74,7 @@ fn read_template(path: &str) -> Result<Drawing> {
 
 #[cfg(not(target_arch = "wasm32"))]
 fn read_bytes(path: &str) -> Result<Vec<u8>> {
-    std::fs::read(path).map_err(|e| bad("new", format!("template {path}: {e}")))
+    crate::capped_read::read_capped(std::path::Path::new(path), super::MAX_DRAWING_BYTES).map_err(|e| bad("new", format!("template {path}: {e}")))
 }
 
 #[cfg(target_arch = "wasm32")]

crates/engine/src/cmd/layout/plotstyle.rs

@@ -303,11 +303,9 @@ fn run_stylesmanager(s: &mut Session, p: &Value) -> Result<Value> {
                 (None, Some(_path)) => {
                     #[cfg(not(target_arch = "wasm32"))]
                     {
-                        let meta = std::fs::metadata(_path).map_err(|e| bad(cmd, format!("{_path}: {e}")))?;
-                        if meta.len() > cadcraft_doc::MAX_TABLE_FILE as u64 {
-                            return Err(bad(cmd, format!("{_path}: the plot style table file is too large")));
-                        }
-                        std::fs::read_to_string(_path).map_err(|e| bad(cmd, format!("{_path}: {e}")))?
+                        let bytes = crate::capped_read::read_capped(std::path::Path::new(_path), cadcraft_doc::MAX_TABLE_FILE)
+                            .map_err(|e| bad(cmd, format!("{_path}: {e}")))?;
+                        String::from_utf8(bytes).map_err(|e| bad(cmd, format!("{_path}: {e}")))?
                     }
                     #[cfg(target_arch = "wasm32")]
                     return Err(bad(cmd, "files can't be read here: pass `text`"));

crates/engine/src/cmd/qselect.rs

@@ -175,8 +175,14 @@ pub fn compare(prop: &Value, op: Op, value: &Value) -> bool {
             if ptxt.eq_ignore_ascii_case(vtxt.trim()) {
                 return true;
             }
-            // Colours: `red` = `1` = `Red`; `bylayer` = `ByLayer`.
-            match (Color::parse(&ptxt), Color::parse(vtxt.trim())) {
+            // Colours: `red` = `1` = `Red`; `bylayer` = `ByLayer`. No colour spelling is long, so a
+            // long text (a layer name from a file) isn't parsed, copied and split per entity.
+            const MAX_COLOR_TEXT: usize = 64;
+            let (pc, vc) = (ptxt.trim(), vtxt.trim());
+            if pc.len() > MAX_COLOR_TEXT || vc.len() > MAX_COLOR_TEXT {
+                return false;
+            }
+            match (Color::parse(pc), Color::parse(vc)) {
                 (Some(a), Some(b)) => a == b,
                 _ => false,
             }
@@ -400,3 +406,26 @@ mod tests {
         assert!(!wildcard(&"*a".repeat(500), &"b".repeat(4000)));
     }
 }
+
+#[cfg(test)]
+mod long_text_tests {
+    use super::*;
+
+    /// A long string property is compared as text only, and a colour name still equals its index.
+    #[test]
+    fn long_values_skip_colour_parsing() {
+        let long = Value::String("x".repeat(100_000));
+        assert!(compare(&long, Op::Eq, &long));
+        assert!(!compare(&long, Op::Eq, &Value::String("red".into())));
+        assert!(compare(&Value::String("red".into()), Op::Eq, &Value::String("1".into())));
+    }
+
+    /// Padding is trimmed before the length limit, so a padded colour still matches.
+    #[test]
+    fn padded_colours_still_match() {
+        let padded = |c: &str| Value::String(format!("{}{c}{}", " ".repeat(100), " ".repeat(100)));
+        assert!(compare(&padded("red"), Op::Eq, &Value::String("1".into())));
+        assert!(compare(&Value::String("red".into()), Op::Eq, &padded("1")));
+        assert!(!compare(&padded("red"), Op::Ne, &padded("1")));
+    }
+}

crates/engine/src/cmd/table/breaks.rs

@@ -12,7 +12,7 @@ use crate::{Accept, Input, Interactive, Prompt, Result, Session, Step};
 
 /// Largest linked file read (bytes).
 #[cfg(not(target_arch = "wasm32"))]
-const MAX_LINK_BYTES: u64 = 8 << 20;
+const MAX_LINK_BYTES: usize = 8 << 20;
 
 pub fn specs() -> Vec<CommandSpec> {
     vec![
@@ -238,11 +238,9 @@ fn read_link(id: &str, file: &std::path::Path) -> Result<String> {
     let path = file.display();
     #[cfg(not(target_arch = "wasm32"))]
     {
-        let meta = std::fs::metadata(file).map_err(|e| bad(id, format!("{path}: {e}")))?;
-        if meta.len() > MAX_LINK_BYTES {
-            return Err(bad(id, format!("{path}: larger than {} MB", MAX_LINK_BYTES >> 20)));
-        }
-        let bytes = std::fs::read(file).map_err(|e| bad(id, format!("{path}: {e}")))?;
+        // The limit is enforced on the bytes read, not on reported metadata, so a device or FIFO
+        // that misreports its length can't be buffered to EOF.
+        let bytes = crate::capped_read::read_capped(file, MAX_LINK_BYTES).map_err(|e| bad(id, format!("{path}: {e}")))?;
         let text = String::from_utf8_lossy(&bytes);
         Ok(text.strip_prefix('\u{feff}').unwrap_or(&text).to_owned())
     }
@@ -370,6 +368,16 @@ fn run_update(s: &mut Session, p: &Value) -> Result<Value> {
 mod tests {
     use super::*;
 
+    /// A linked path naming an endless device is refused instead of buffered to EOF.
+    #[cfg(all(unix, not(target_arch = "wasm32")))]
+    #[test]
+    fn link_to_endless_device_is_rejected() {
+        let dev = std::path::Path::new("/dev/zero");
+        if dev.exists() {
+            assert!(read_link("datalink", dev).is_err());
+        }
+    }
+
     #[test]
     fn csv_parsing() {
         assert_eq!(parse_csv("a,b\r\n\"c,d\",\"e\"\"f\"\n", ','), vec![vec!["a", "b"], vec!["c,d", "e\"f"]]);

crates/engine/src/lisp.rs

@@ -415,9 +415,12 @@ impl Session {
 
     /// Move printed text to the command history: complete lines, and with `all` the rest too.
     fn lisp_flush(&mut self, env: &mut Env, all: bool) {
-        while let Some(i) = env.out.find('\n') {
-            let line: String = env.out.drain(..=i).collect();
-            let line = line.trim_end_matches(['\n', '\r']).to_string();
+        // One pass over the buffer, dropping the printed lines once at the end: draining each line
+        // from the front shifted the rest every time, quadratic in newline-dense output.
+        let mut done = 0;
+        while let Some(i) = env.out.get(done..).and_then(|rest| rest.find('\n')) {
+            let line = env.out.get(done..done + i).unwrap_or_default().trim_end_matches('\r').to_string();
+            done += i + 1;
             // `(princ "\nText")` after a prompt or a command's echo ends that line instead of
             // leaving an empty one; after LISP's own line it does print an empty line.
             if line.is_empty() && env.printed_at != Some(self.log.len()) {
@@ -427,6 +430,7 @@ impl Session {
             self.echo(line);
             env.printed_at = Some(self.log.len());
         }
+        env.out.drain(..done);
         if all && !env.out.is_empty() {
             let line = std::mem::take(&mut env.out);
             self.echo(line);

crates/engine/src/lisp/tests.rs

@@ -307,6 +307,16 @@ fn printing() {
     assert_eq!(ok(&mut s, "(rtos 12.5 2 2)"), "\"12.50\"");
 }
 
+/// Output with many lines moves to the history in one pass, not one buffer shift per line.
+#[test]
+fn printing_many_lines_is_linear() {
+    let mut s = session();
+    let started = std::time::Instant::now();
+    ok(&mut s, "(setq x \"a\\r\\n\") (repeat 17 (setq x (strcat x x))) (princ x) (princ)");
+    assert!(started.elapsed() < std::time::Duration::from_secs(10), "took {:?}", started.elapsed());
+    assert_eq!(s.log.last().map(String::as_str), Some("a"));
+}
+
 #[test]
 fn command_draws_and_one_routine_is_one_undo_step() {
     let mut s = session();

crates/geom/src/curve.rs

@@ -484,6 +484,9 @@ pub struct Polyline {
     pub closed: bool,
 }
 
+/// Sampled points one [`Polyline::tessellate`] call produces before arcs become chords.
+pub const MAX_TESSELLATED_POINTS: usize = 4_000_000;
+
 impl Polyline {
     pub fn from_points(pts: &[Vec2], closed: bool) -> Self {
         Polyline { vertices: pts.iter().map(|p| PolyVertex::new(*p)).collect(), closed }
@@ -516,10 +519,24 @@ impl Polyline {
         b
     }
     pub fn tessellate(&self, tol: f64) -> Vec<Vec2> {
+        let mut budget = MAX_TESSELLATED_POINTS;
+        self.tessellate_within(tol, &mut budget)
+    }
+    /// [`Polyline::tessellate`] spending about `budget` sampled points (shared by the caller
+    /// across many polylines). The budget is checked before each segment, so the last segment
+    /// started may overshoot it by that one segment's samples. Once it is spent, the remaining arcs are drawn as chords, so the
+    /// output stays proportional to the input vertices. Each arc can sample thousands of points,
+    /// so a compact polyline could otherwise expand into gigabytes (CWE-400).
+    pub fn tessellate_within(&self, tol: f64, budget: &mut usize) -> Vec<Vec2> {
         let mut out: Vec<Vec2> = Vec::new();
         for s in self.segments() {
             let mut pts = Vec::new();
-            s.tessellate(tol, &mut pts);
+            if *budget > 0 {
+                s.tessellate(tol, &mut pts);
+                *budget = budget.saturating_sub(pts.len());
+            } else {
+                pts.extend([s.start(), s.end()]);
+            }
             let skip = usize::from(out.last().is_some_and(|l| pts.first().is_some_and(|f| l.near(*f, 1e-9))));
             out.extend(pts.into_iter().skip(skip));
         }

crates/geom/src/lib.rs

@@ -20,7 +20,8 @@ mod vec;
 
 pub use bounds::Bounds2;
 pub use curve::{
-    Arc, Circle, Ellipse, Line, PolyVertex, Polyline, Segment, arc_to_bulge, bulge_to_arc, point_in_polygon, polygon_centroid, shoelace,
+    Arc, Circle, Ellipse, Line, MAX_TESSELLATED_POINTS, PolyVertex, Polyline, Segment, arc_to_bulge, bulge_to_arc, point_in_polygon,
+    polygon_centroid, shoelace,
 };
 pub use fillet::{CornerFit, TanCurve, tangent_circles};
 pub use intersect::{circle_circle, intersect_ext, intersect_segments, line_circle, line_line, line_line_infinite};

crates/geom/src/tests.rs

@@ -221,6 +221,18 @@ fn segment_offset() {
     assert!(s.offset(6.0).is_none());
 }
 
+/// A polyline of many fine arcs samples at most the point budget, then draws chords.
+#[test]
+fn polyline_tessellation_is_bounded() {
+    let vertices: Vec<PolyVertex> = (0..3000).map(|i| PolyVertex { bulge: 1.0, ..PolyVertex::new(Vec2::new(f64::from(i) * 1e6, 0.0)) }).collect();
+    let pl = Polyline { vertices, closed: false };
+    let pts = pl.tessellate(1e-9);
+    assert!(pts.len() <= MAX_TESSELLATED_POINTS + 2 * 3000 + 4096, "{}", pts.len());
+    assert!(pts.len() > 3000);
+    let mut budget = 10;
+    assert!(pl.tessellate_within(1e-9, &mut budget).len() <= 4096 + 2 * 3000);
+}
+
 #[test]
 fn arc_segments_bounded() {
     assert_eq!(arc_segments(0.0, 1.0, 0.1), 1);

crates/mcp/Cargo.toml

@@ -21,3 +21,6 @@ getrandom = "0.4"
 [dev-dependencies]
 # Reads the pixels of rendered PNGs in the tests.
 tiny-skia = { workspace = true }
+[target.'cfg(unix)'.dependencies]
+# O_NOFOLLOW when reading the token file (MIT OR Apache-2.0).
+libc = "0.2"

crates/mcp/src/backend.rs

@@ -1,7 +1,7 @@
 //! Where MCP tool calls end up: a control-channel method call.
 
 use std::io::{BufRead, BufReader, Read, Write};
-use std::net::{TcpStream, ToSocketAddrs};
+use std::net::{Ipv4Addr, SocketAddr, TcpStream, ToSocketAddrs};
 use std::time::Duration;
 
 use cadcraft_engine::Session;
@@ -76,9 +76,17 @@ impl Remote {
     /// The per-session token for this port, read (and cached) from the owner-only token file. A
     /// missing file is not fatal here: the request is sent without a token and the server replies
     /// with an authentication error the user can act on.
+    ///
+    /// The desktop app listens only on `127.0.0.1:PORT`, so the token goes only to that exact
+    /// peer: a name that also resolves elsewhere (`localhost` → `::1`, where another local account
+    /// may listen on the same port) must not be handed the desktop's credential (CWE-522).
     fn token(&mut self) -> Option<&str> {
+        let port = port_of(&self.addr)?;
+        let peer = self.conn.as_ref().and_then(|(_, s)| s.peer_addr().ok());
+        if peer != Some(SocketAddr::from((Ipv4Addr::LOCALHOST, port))) {
+            return None;
+        }
         if self.token.is_none()
-            && let Some(port) = port_of(&self.addr)
             && let Ok(t) = crate::control_token::read(port)
         {
             self.token = Some(t);
@@ -207,6 +215,14 @@ fn is_read_only(method: &str) -> bool {
 
 impl Remote {
     /// Put the current token (if any) on `req`, replacing the one it carries.
+    /// Connect if needed, put the token for the peer actually connected to on `req`, and send it.
+    fn sign_and_send(&mut self, req: &mut Value) -> Result<String, (std::io::Error, bool)> {
+        if self.conn.is_none() {
+            self.reach().map_err(|e| (e, false))?;
+        }
+        self.set_token(req);
+        self.roundtrip(&req.to_string())
+    }
     fn set_token(&mut self, req: &mut Value) {
         let token = self.token().map(str::to_string);
         if let Some(obj) = req.as_object_mut() {
@@ -219,7 +235,7 @@ impl Remote {
     /// Send `req` and parse the reply, refreshing the token before a safe retry after a transport
     /// error. A mutation that may have reached the server is never resent automatically.
     fn exchange(&mut self, method: &str, req: &mut Value) -> Result<Value, String> {
-        let reply = match self.roundtrip(&req.to_string()) {
+        let reply = match self.sign_and_send(req) {
             Ok(r) => r,
             Err((e, sent)) => {
                 self.token = None;
@@ -232,8 +248,7 @@ impl Remote {
                     ));
                 }
                 // A restarted server may have rotated its token before dropping the old socket.
-                self.set_token(req);
-                self.roundtrip(&req.to_string()).map_err(|(e, _)| {
+                self.sign_and_send(req).map_err(|(e, _)| {
                     self.token = None;
                     self.conn = None;
                     format!("CADCraft at {}: {e}", self.addr)
@@ -256,14 +271,12 @@ impl Backend for Remote {
         let id = self.next_id;
         self.next_id += 1;
         let mut req = json!({"id": id, "method": method, "params": params});
-        self.set_token(&mut req);
         let mut v = self.exchange(method, &mut req)?;
         // The token is read before `--launch` opens the app, which then writes a new one (#2087); the
         // file can also be left over from an earlier session. Once, so a wrong token can't loop.
         if unauthorized(&v) && v.get("state").and_then(Value::as_str) == Some("not-run") {
             self.token = None;
             self.conn = None;
-            self.set_token(&mut req);
             v = self.exchange(method, &mut req)?;
         }
         if v.get("ok").and_then(Value::as_bool) == Some(true) {
@@ -595,6 +608,24 @@ mod tests {
         })
     }
 
+    /// A listener on another loopback address with the desktop's port (here `::1`) never receives
+    /// the desktop's token.
+    #[test]
+    fn token_is_not_sent_to_another_loopback_listener() {
+        let Ok(listener) = TcpListener::bind("[::1]:0") else { return };
+        let addr = listener.local_addr().unwrap();
+        crate::control_token::issue(addr.port()).unwrap();
+        let server = fake_app(listener, move |req, _| {
+            assert!(req.get("token").is_none(), "token leaked to {addr}");
+            json!({"ok": true, "result": "x"})
+        });
+        let mut remote = Remote::lazy(&addr.to_string(), false);
+        let got = remote.call("ping", json!({}));
+        crate::control_token::revoke(addr.port());
+        assert_eq!(got, Ok(json!("x")));
+        assert_eq!(server.join().unwrap(), 1);
+    }
+
     /// `--launch` reads the token before it opens the app, so the first request carries the token
     /// of an earlier session (or none); the app refuses it without running it, and the call is
     /// resent once with the token the app has just written (#2087).

crates/mcp/src/control_token.rs

@@ -32,7 +32,9 @@ fn private_dir() -> io::Result<PathBuf> {
     if let Some(h) = std::env::var_os("HOME").filter(|v| !v.is_empty()) {
         return Ok(PathBuf::from(h).join(".cache"));
     }
-    Ok(std::env::temp_dir())
+    // The shared temporary directory would put the credential at a path any local account can
+    // predict and plant a link at: refuse instead.
+    Err(io::Error::new(io::ErrorKind::NotFound, "XDG_RUNTIME_DIR or HOME is required for a private control token"))
 }
 
 /// Require the Windows per-user local app-data directory for session token storage.
@@ -75,7 +77,31 @@ fn issue_at(path: &std::path::Path, bytes: &[u8]) -> io::Result<()> {
 
 /// Read the token for `port`, trimming trailing whitespace. Used by clients (the MCP bridge).
 pub fn read(port: u16) -> io::Result<String> {
-    let raw = std::fs::read_to_string(token_path(port)?)?;
+    read_at(&token_path(port)?)
+}
+
+/// Read a token file the issuer wrote: not through a link, a plain file, and (Unix) readable by
+/// its owner only, so a file another account planted or left open is not taken as the credential.
+fn read_at(path: &std::path::Path) -> io::Result<String> {
+    use std::io::Read;
+    let mut options = std::fs::OpenOptions::new();
+    options.read(true);
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::OpenOptionsExt;
+        options.custom_flags(libc::O_NOFOLLOW | libc::O_NONBLOCK);
+    }
+    let file = options.open(path)?;
+    let meta = file.metadata()?;
+    if !meta.is_file() {
+        return Err(io::Error::new(io::ErrorKind::InvalidData, "the control token is not a plain file"));
+    }
+    #[cfg(unix)]
+    if std::os::unix::fs::PermissionsExt::mode(&meta.permissions()) & 0o077 != 0 {
+        return Err(io::Error::new(io::ErrorKind::PermissionDenied, "the control token file is readable by other users"));
+    }
+    let mut raw = String::new();
+    file.take(1024).read_to_string(&mut raw)?;
     let token = raw.trim().to_string();
     if token.is_empty() {
         return Err(io::Error::new(io::ErrorKind::InvalidData, "empty control token"));
@@ -181,6 +207,24 @@ mod tests {
         assert_eq!(windows_private_dir(Some("private-app-data".into())).unwrap(), PathBuf::from("private-app-data"));
     }
 
+    /// A link, or a file other users can read, is not accepted as the token.
+    #[cfg(unix)]
+    #[test]
+    fn read_refuses_links_and_shared_files() {
+        use std::os::unix::fs::PermissionsExt;
+        let dir = std::env::temp_dir().join(format!("cadcraft-token-read-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let secret = dir.join("secret");
+        issue_at(&secret, b"abc").unwrap();
+        assert_eq!(read_at(&secret).unwrap(), "abc");
+        let link = dir.join("link");
+        std::os::unix::fs::symlink(&secret, &link).unwrap();
+        assert!(read_at(&link).is_err());
+        std::fs::set_permissions(&secret, std::fs::Permissions::from_mode(0o644)).unwrap();
+        assert!(read_at(&secret).is_err());
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
     /// Token issuance creates its missing directory hierarchy before writing the credential.
     #[test]
     fn issuance_creates_missing_parent() {

crates/render/src/hatch.rs

@@ -128,7 +128,10 @@ const MAX_DEDUP_COMPARISONS: u64 = 50_000_000;
 /// within islands alternate), 1 outer keeps the outermost loops and their first islands, 2
 /// ignore keeps only the outermost loops. Nesting depth = how many other loops enclose a loop.
 pub fn fill_loops(h: &Hatch, tol: f64) -> Vec<Vec<Vec2>> {
-    let mut loops: Vec<Vec<Vec2>> = h.loops.iter().map(|l| Polyline { vertices: l.vertices.clone(), closed: true }.tessellate(tol)).collect();
+    // One point budget for all the loops: many short arcs across loops must not add up unbounded.
+    let mut budget = cadcraft_geom::MAX_TESSELLATED_POINTS;
+    let mut loops: Vec<Vec<Vec2>> =
+        h.loops.iter().map(|l| Polyline { vertices: l.vertices.clone(), closed: true }.tessellate_within(tol, &mut budget)).collect();
     dedup_polygons(&mut loops);
     let max_depth = match h.style {
         1 => 1,

crates/ui-egui/src/xrefs.rs

@@ -77,10 +77,16 @@ fn rows(app: &CadApp, ui: &egui::Ui) -> Vec<Row> {
     let xrefs: Vec<_> = d.blocks.values().filter(|b| b.xref_path.is_some() && !b.name.contains('|')).collect();
     let mut counts = vec![0usize; xrefs.len()];
     if !xrefs.is_empty() {
+        // Xref name (ASCII-upper-cased) → its row, the first of names that differ only in case, so
+        // each INSERT is one lookup instead of a scan of the xref list.
+        let mut index: std::collections::HashMap<String, usize> = std::collections::HashMap::new();
+        for (k, b) in xrefs.iter().enumerate() {
+            index.entry(b.name.to_ascii_uppercase()).or_insert(k);
+        }
         let mut count = |store: &cadcraft_engine::doc::EntityStore| {
             for e in store.iter() {
                 if let cadcraft_engine::doc::EntityKind::Insert(i) = &e.kind
-                    && let Some(k) = xrefs.iter().position(|b| b.name.eq_ignore_ascii_case(&i.block))
+                    && let Some(&k) = index.get(&i.block.to_ascii_uppercase())
                     && let Some(c) = counts.get_mut(k)
                 {
                     *c += 1;