From d04ccb3f1f10f3dcc788af010be7394bc67b2c8c Mon Sep 17 00:00:00 2001
From: Gideon Wald <gideon.wald@gmail.com>
Date: Tue, 4 Nov 2025 14:05:05 -0800
Subject: [PATCH 1/3] small script showcasing typechecking issue with
 CELL_BRAND mechanism in case of OpaqueRef<Cell<T>>

---
 cell-brand-bug-reproduction.ts | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 cell-brand-bug-reproduction.ts

diff --git a/cell-brand-bug-reproduction.ts b/cell-brand-bug-reproduction.ts
new file mode 100644
index 000000000..28d82c278
--- /dev/null
+++ b/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.
+}

From 3771aa9a1e95a6d69fa156eebd141c790b0594fd Mon Sep 17 00:00:00 2001
From: Gideon Wald <gideon.wald@gmail.com>
Date: Tue, 4 Nov 2025 14:24:10 -0800
Subject: [PATCH 2/3] attempt to fix CELL_BRAND issue

---
 packages/api/index.ts | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/packages/api/index.ts b/packages/api/index.ts
index 8d7c7331b..51f90c183 100644
--- a/packages/api/index.ts
+++ b/packages/api/index.ts
@@ -352,11 +352,18 @@ 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. Already-branded cells are preserved as-is rather than
+ * being wrapped again to prevent cell-of-cell situations.
  */
 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]:
+          T[K] extends BrandedCell<any, any> ? T[K] : OpaqueRef<T[K]>
+      }
     : T);
 
 // ============================================================================

From dd12a0de68110ced6e6a96fb201da7f80587a5f4 Mon Sep 17 00:00:00 2001
From: Gideon Wald <gideon.wald@gmail.com>
Date: Tue, 4 Nov 2025 14:34:30 -0800
Subject: [PATCH 3/3] next attempt

---
 cell-brand-bug-reproduction.ts | 2 +-
 packages/api/index.ts          | 8 ++------
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/cell-brand-bug-reproduction.ts b/cell-brand-bug-reproduction.ts
index 28d82c278..13a90ff03 100644
--- a/cell-brand-bug-reproduction.ts
+++ b/cell-brand-bug-reproduction.ts
@@ -15,7 +15,7 @@ interface State {
 }
 
 // Accessing properties on OpaqueRef<Cell<T>> fails type-checking
-function reproducesBug(state: OpaqueRef<State>) {
+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'
diff --git a/packages/api/index.ts b/packages/api/index.ts
index 51f90c183..668cf0c99 100644
--- a/packages/api/index.ts
+++ b/packages/api/index.ts
@@ -354,16 +354,12 @@ export interface WriteonlyCell<T>
  * This is temporary until AST transformation handles .key() automatically.
  *
  * Note: Symbol keys (like CELL_BRAND) are excluded from mapping to avoid
- * brand conflicts. Already-branded cells are preserved as-is rather than
- * being wrapped again to prevent cell-of-cell situations.
+ * 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 as K extends symbol ? never : K]:
-          T[K] extends BrandedCell<any, any> ? T[K] : OpaqueRef<T[K]>
-      }
+    : T extends object ? { [K in keyof T as K extends symbol ? never : K]: OpaqueRef<T[K]> }
     : T);
 
 // ============================================================================