docs: Add some comments warning about race conditions, rename some identifiers

src/geometry/with_rtree.rs

@@ -177,6 +177,8 @@ impl<
     }
 
     pub fn remove_dot(&mut self, dot: DI) {
+        // One of the possible causes: you have failed to delete navcord's final
+        // termseg.
         debug_assert!(self.geometry.joined_segs(dot).next().is_none());
         debug_assert!(self.geometry.joined_bends(dot).next().is_none());
 

src/math/bitangents.rs

@@ -70,7 +70,7 @@ fn bitangent_point_pairs(
     circle1: Circle,
     circle2: Circle,
 ) -> Result<Vec<(Point, Point)>, NoBitangents> {
-    let bitangents: Vec<(Point, Point)> = _bitangents(circle1, circle2)
+    let point_pairs: Vec<(Point, Point)> = _bitangents(circle1, circle2)
         .into_iter()
         .map(|tg| {
             (
@@ -80,11 +80,10 @@ fn bitangent_point_pairs(
         })
         .collect();
 
-    if bitangents.is_empty() {
+    if point_pairs.is_empty() {
         return Err(NoBitangents(circle1, circle2));
     }
-
-    Ok(bitangents)
+    Ok(point_pairs)
 }
 
 pub fn bitangents(

src/router/draw.rs

@@ -83,7 +83,7 @@ impl<R: AccessRules> Draw for Layout<R> {
         into: FixedDotIndex,
         width: f64,
     ) -> Result<BandTermsegIndex, DrawException> {
-        let tangent = self
+        let bitangent = self
             .drawing()
             .guide_for_head_into_dot(&head, into, width)
             .map_err(Into::<DrawException>::into)?;
@@ -96,7 +96,7 @@ impl<R: AccessRules> Draw for Layout<R> {
         self.extend_head(
             recorder,
             head,
-            tangent.start_point(),
+            bitangent.start_point(),
             |this, recorder| match head.face() {
                 DotIndex::Fixed(dot) => this
                     .add_lone_loose_seg(

src/router/navcorder.rs

@@ -94,6 +94,7 @@ impl<R: AccessRules> Navcorder for Layout<R> {
 
         let length = navcord.path.len();
         self.undo_path(navcord, length - prefix_length);
+        // XXX: If this fails now, there may be a race condition.
         self.path(navmesh, navcord, &path[prefix_length..])
     }