Fix handling of frozen objects in proxy

.changeset/fix-proxy-frozen-values.md

@@ -0,0 +1,7 @@
+---
+"@tanstack/db": patch
+---
+
+Fix proxy to handle frozen objects correctly. Previously, creating a proxy for a frozen object (such as data from state management libraries that freeze their state) would throw a TypeError when attempting to modify properties via the proxy. The proxy now uses an unfrozen internal copy as the Proxy target, allowing modifications to be tracked correctly while preserving the immutability of the original object.
+
+Also adds support for `Object.seal()` and `Object.preventExtensions()` on proxies, allowing these operations to work correctly on change-tracking proxies.

packages/db/src/proxy.ts

@@ -994,21 +994,31 @@ export function createChangeProxy<
         return true
       },
 
-      defineProperty(_ptarget, prop, descriptor) {
-        // const result = Reflect.defineProperty(
-        //   changeTracker.copy_,
-        //   prop,
-        //   descriptor
-        // )
-        // if (result) {
-        if (`value` in descriptor) {
+      defineProperty(ptarget, prop, descriptor) {
+        // Forward the defineProperty to the target to maintain Proxy invariants
+        // This allows Object.seal() and Object.freeze() to work on the proxy
+        const result = Reflect.defineProperty(ptarget, prop, descriptor)
+        if (result && `value` in descriptor) {
           changeTracker.copy_[prop as keyof T] = deepClone(descriptor.value)
           changeTracker.assigned_[prop.toString()] = true
           markChanged(changeTracker)
         }
-        // }
-        // return result
-        return true
+        return result
+      },
+
+      getOwnPropertyDescriptor(ptarget, prop) {
+        // Forward to target to maintain Proxy invariants for seal/freeze
+        return Reflect.getOwnPropertyDescriptor(ptarget, prop)
+      },
+
+      preventExtensions(ptarget) {
+        // Forward to target to allow Object.seal() and Object.preventExtensions()
+        return Reflect.preventExtensions(ptarget)
+      },
+
+      isExtensible(ptarget) {
+        // Forward to target to maintain consistency
+        return Reflect.isExtensible(ptarget)
       },
 
       deleteProperty(dobj, prop) {
@@ -1020,33 +1030,36 @@ export function createChangeProxy<
           const hadPropertyInOriginal =
             stringProp in changeTracker.originalObject
 
-          // Delete the property from the copy
-          // Use type assertion to tell TypeScript this is allowed
-          delete (changeTracker.copy_ as Record<string | symbol, unknown>)[prop]
+          // Forward the delete to the target using Reflect
+          // This respects Object.seal/preventExtensions constraints
+          const result = Reflect.deleteProperty(dobj, prop)
 
-          // If the property didn't exist in the original object, removing it
-          // should revert to the original state
-          if (!hadPropertyInOriginal) {
-            delete changeTracker.copy_[stringProp]
-            delete changeTracker.assigned_[stringProp]
+          if (result) {
+            // If the property didn't exist in the original object, removing it
+            // should revert to the original state
+            if (!hadPropertyInOriginal) {
+              delete changeTracker.assigned_[stringProp]
 
-            // If this is the last change and we're not a nested object,
-            // mark the object as unmodified
-            if (
-              Object.keys(changeTracker.assigned_).length === 0 &&
-              Object.getOwnPropertySymbols(changeTracker.assigned_).length === 0
-            ) {
-              changeTracker.modified = false
+              // If this is the last change and we're not a nested object,
+              // mark the object as unmodified
+              if (
+                Object.keys(changeTracker.assigned_).length === 0 &&
+                Object.getOwnPropertySymbols(changeTracker.assigned_).length ===
+                  0
+              ) {
+                changeTracker.modified = false
+              } else {
+                // We still have changes, keep as modified
+                changeTracker.modified = true
+              }
             } else {
-              // We still have changes, keep as modified
-              changeTracker.modified = true
+              // Mark this property as deleted
+              changeTracker.assigned_[stringProp] = false
+              markChanged(changeTracker)
             }
-          } else {
-            // Mark this property as deleted
-            changeTracker.assigned_[stringProp] = false
-            changeTracker.copy_[stringProp as keyof T] = undefined as T[keyof T]
-            markChanged(changeTracker)
           }
+
+          return result
         }
 
         return true
@@ -1060,7 +1073,9 @@ export function createChangeProxy<
   }
 
   // Create a proxy for the target object
-  const proxy = createObjectProxy(target)
+  // Use the unfrozen copy_ as the proxy target to avoid Proxy invariant violations
+  // when the original target is frozen (e.g., from Immer)
+  const proxy = createObjectProxy(changeTracker.copy_ as unknown as T)
 
   // Return the proxy and a function to get the changes
   return {