fix(js): deepFreeze recurses below already-frozen parents

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

js/solutions/util.js

@@ -18,12 +18,13 @@ export const compose = (...fns) => (x) => fns.reduceRight((acc, f) => f(acc), x)
 /**
  * Freeze `obj` and everything reachable from it, then return it.
  * Freezing is the one deliberate "mutation" here: it makes later accidental mutation throw.
+ * We recurse even into children that are already frozen (a frozen parent can still hold
+ * unfrozen children). `ancestors` is the path from the root to `obj`; passing it down
+ * (instead of keeping a shared "seen" set) stops cyclic structures without any mutable state.
  */
-export const deepFreeze = (obj) => {
+export const deepFreeze = (obj, ancestors = []) => {
+  if (obj === null || typeof obj !== 'object' || ancestors.includes(obj)) return obj
   Object.freeze(obj)
-  // Freezing before recursing means cyclic structures stop at the already-frozen node.
-  Object.values(obj).forEach((v) => {
-    if (v !== null && typeof v === 'object' && !Object.isFrozen(v)) deepFreeze(v)
-  })
+  Object.values(obj).forEach((v) => deepFreeze(v, [...ancestors, obj]))
   return obj
 }