Bug/cell brand

cell-brand-bug-reproduction.ts

@@ -0,0 +1,24 @@
+/**
+ * Minimal test case for OpaqueRef<Cell<T>> CELL_BRAND conflict
+ *
+ * PROBLEM: OpaqueRef<T> recursively wraps ALL properties of T (including [CELL_BRAND]).
+ * When T is Cell<number>, this creates conflicting types for [CELL_BRAND]:
+ *   - OpaqueCell<Cell<number>> has [CELL_BRAND]: "opaque"
+ *   - { counter: OpaqueRef<Cell<number>> } creates [CELL_BRAND]: OpaqueRef<"cell">
+ * The intersection reduces to 'never'.
+ */
+
+import { type Cell, type OpaqueRef } from "./packages/api/index.ts";
+
+interface State {
+  counter: Cell<number>;
+}
+
+// Accessing properties on OpaqueRef<Cell<T>> fails type-checking
+function _reproducesBug(state: OpaqueRef<State>) {
+  state.counter.set(state.counter.get() + 1);
+  //            ^^^ Property 'set' does not exist on type 'never'
+  //                                  ^^^ Property 'get' does not exist on type 'never'
+  // ERROR: The intersection 'OpaqueRef<Cell<number>>' was reduced to 'never'
+  // because property '[CELL_BRAND]' has conflicting types in some constituents.
+}

packages/api/index.ts

@@ -352,11 +352,14 @@ export interface WriteonlyCell<T>
  * OpaqueRef is a variant of OpaqueCell with recursive proxy behavior.
  * Each key access returns another OpaqueRef, allowing chained property access.
  * This is temporary until AST transformation handles .key() automatically.
+ *
+ * Note: Symbol keys (like CELL_BRAND) are excluded from mapping to avoid
+ * brand conflicts when wrapping branded cells.
  */
 export type OpaqueRef<T> =
   & OpaqueCell<T>
   & (T extends Array<infer U> ? Array<OpaqueRef<U>>
-    : T extends object ? { [K in keyof T]: OpaqueRef<T[K]> }
+    : T extends object ? { [K in keyof T as K extends symbol ? never : K]: OpaqueRef<T[K]> }
     : T);
 
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