internal: clarify intent of Scalar.denormalize falsy guard

Made-with: Cursor

Author: ntucker

packages/endpoint/src/schemas/Scalar.ts

@@ -156,6 +156,18 @@ export default class Scalar implements Mergeable {
   }
 
   denormalize(input: any, delegate: IDenormalizeDelegate): any {
+    // Deliberately broad falsy guard — not just `null`/`undefined`. In normal
+    // flow `input` is a wrapper tuple (array), a cpk string, a cell object, or
+    // a symbol (INVALID propagation). A primitive non-string like `0`/`false`
+    // can only appear from a malformed store or a direct unit-test call; if
+    // one reached the Values branch below it would infinite-recurse via
+    // `delegate.unvisit(this, 0) → unvisit → schema.denormalize(0, …)` since
+    // `isEntity(this)` is false and the string-input fast path doesn't match.
+    // Returning it verbatim is the safe terminal case. Memoization stays
+    // coherent because `input` comes from the stored entity row, so any shape
+    // change implies a new entity reference and a full re-traversal — the
+    // cached `argsKey`-bearing chain is never replayed against a frame that
+    // skipped the guard.
     if (!input || typeof input === 'symbol') return input;
 
     // Entity-field wrapper: `[entityPk, fieldName, entityKey]` (see normalize).