feat: lookup at downgrade time

works, but leaks memory

src/ty/internal/string.rs

@@ -1,16 +1,15 @@
 // TODO: Contextful String
 
 use ecow::EcoString;
-use rpds::List;
 
 pub struct StringContext {
-    context: List<()>,
+    context: Vec<()>,
 }
 
 impl StringContext {
     pub fn new() -> StringContext {
         StringContext {
-            context: List::new(),
+            context: Vec::new(),
         }
     }
 }