diff --git a/apps/sim/executor/execution/snapshot-serializer.test.ts b/apps/sim/executor/execution/snapshot-serializer.test.ts
index b2482ed1eff..3fb1451d70b 100644
--- a/apps/sim/executor/execution/snapshot-serializer.test.ts
+++ b/apps/sim/executor/execution/snapshot-serializer.test.ts
@@ -352,6 +352,20 @@ describe('buildCompletedExecutionState', () => {
       'a boxed number carrying a BigInt property',
       { value: Object.assign(Object(1), { big: BigInt(1) }) },
     ],
+    ['an object that only inherits from BigInt', { value: Object.create(BigInt.prototype) }],
+    [
+      'a proxy whose getPrototypeOf trap throws',
+      {
+        value: new Proxy(
+          { a: 1 },
+          {
+            getPrototypeOf: () => {
+              throw new Error('JSON.stringify never asks for the prototype')
+            },
+          }
+        ),
+      },
+    ],
   ])('serializes like the JSON-cloned pause state for %s', (_name, output) => {
     const context = contextWithOutput(output)
     expect(JSON.stringify(buildCompletedExecutionState(context))).toBe(
@@ -359,9 +373,25 @@ describe('buildCompletedExecutionState', () => {
     )
   })
 
+  const numberLookalike = Object.create(Number.prototype)
+  numberLookalike.self = numberLookalike
+
   it.each([
     ['a cycle', cyclic],
     ['a BigInt', { big: BigInt(1) }],
+    ['a cycle in an object that only inherits from Number', { value: numberLookalike }],
+    [
+      'a BigInt wrapper whose prototype was swapped',
+      { value: Object.setPrototypeOf(Object(BigInt(1)), {}) },
+    ],
+    [
+      'a BigInt wrapper whose prototype was reset to Object.prototype',
+      { value: Object.setPrototypeOf(Object(BigInt(1)), Object.prototype) },
+    ],
+    [
+      'a Number wrapper that converts to a BigInt',
+      { value: Object.assign(Object(1), { [Symbol.toPrimitive]: () => BigInt(1) }) },
+    ],
   ])('throws like the pause snapshot for %s', (_name, output) => {
     const context = contextWithOutput(output)
     expect(() => jsonClonedState(context)).toThrow(TypeError)
diff --git a/apps/sim/executor/execution/snapshot-serializer.ts b/apps/sim/executor/execution/snapshot-serializer.ts
index ec58b61adf5..f49c25c561e 100644
--- a/apps/sim/executor/execution/snapshot-serializer.ts
+++ b/apps/sim/executor/execution/snapshot-serializer.ts
@@ -1,3 +1,4 @@
+import { unboxJsonPrimitive } from '@/lib/core/utils/boxed-primitives'
 import { LARGE_VALUE_THRESHOLD_BYTES } from '@/lib/execution/payloads/large-value-ref'
 import type { DAG } from '@/executor/dag/builder'
 import type { EdgeManager } from '@/executor/execution/edge-manager'
@@ -353,14 +354,11 @@ function assertJsonSerializable(value: unknown): void {
       const toJSON = (current as { toJSON?: unknown }).toJSON
       if (typeof toJSON === 'function') current = toJSON.call(current, key)
     }
-    if (typeof current === 'bigint' || current instanceof BigInt) {
+    if (typeof current === 'object' && current !== null) current = unboxJsonPrimitive(current)
+    if (typeof current === 'bigint') {
       throw new TypeError('Do not know how to serialize a BigInt')
     }
     if (typeof current !== 'object' || current === null) return
-    // Serialized as their primitive value; their own properties are never read.
-    if (current instanceof Number || current instanceof String || current instanceof Boolean) {
-      return
-    }
     if (ancestors.has(current)) {
       throw new TypeError('Converting circular structure to JSON')
     }
diff --git a/apps/sim/lib/core/utils/boxed-primitives.ts b/apps/sim/lib/core/utils/boxed-primitives.ts
new file mode 100644
index 00000000000..f7088e59f9f
--- /dev/null
+++ b/apps/sim/lib/core/utils/boxed-primitives.ts
@@ -0,0 +1,22 @@
+import { types } from 'node:util'
+
+/**
+ * Unwraps a primitive wrapper the way `JSON.stringify` does: by its internal
+ * slot, not its prototype, so an object that merely inherits from
+ * `Number.prototype` stays an object and a wrapper with a replaced prototype is
+ * still unwrapped. Number and String wrappers convert through ToNumber and
+ * ToString (unary `+` and a template literal, which run any user
+ * `valueOf`/`toString` and throw where JSON would, e.g. on a BigInt or Symbol
+ * result); Boolean and BigInt wrappers read their stored value. The slot check
+ * runs no Proxy traps. Anything else is returned unchanged.
+ */
+export function unboxJsonPrimitive(value: unknown): unknown {
+  if (typeof value !== 'object' || value === null || !types.isBoxedPrimitive(value)) {
+    return value
+  }
+  if (types.isNumberObject(value)) return +value
+  if (types.isStringObject(value)) return `${value}`
+  if (types.isBooleanObject(value)) return Boolean.prototype.valueOf.call(value)
+  if (types.isBigIntObject(value)) return BigInt.prototype.valueOf.call(value)
+  return value
+}
diff --git a/apps/sim/lib/logs/execution/json-byte-size.test.ts b/apps/sim/lib/logs/execution/json-byte-size.test.ts
index b696328ae94..c9f00da1749 100644
--- a/apps/sim/lib/logs/execution/json-byte-size.test.ts
+++ b/apps/sim/lib/logs/execution/json-byte-size.test.ts
@@ -40,6 +40,31 @@ describe('getJsonByteSize', () => {
       },
     ],
     ['a function with toJSON', { fn: Object.assign(() => 1, { toJSON: () => 'serialized' }) }],
+    [
+      'objects that only inherit from wrapper prototypes',
+      {
+        n: Object.assign(Object.create(Number.prototype), { a: 1 }),
+        s: Object.assign(Object.create(String.prototype), { b: 'x' }),
+      },
+    ],
+    ['a Number wrapper whose prototype was swapped', { n: Object.setPrototypeOf(Object(42), {}) }],
+    [
+      'a Number wrapper whose prototype was reset to Object.prototype',
+      { n: Object.setPrototypeOf(Object(7), Object.prototype) },
+    ],
+    [
+      'a proxy whose getPrototypeOf trap throws',
+      {
+        p: new Proxy(
+          { a: 1 },
+          {
+            getPrototypeOf: () => {
+              throw new Error('JSON.stringify never asks for the prototype')
+            },
+          }
+        ),
+      },
+    ],
     ['escapes, multi-byte text, and lone surrogates', { 'k"\\': 'a\n\u0001é漢😀\ud800' }],
   ])('matches JSON.stringify for %s', (_name, payload) => {
     expect(getJsonByteSize(payload, LIMIT)).toBe(jsonBytes(payload))
diff --git a/apps/sim/lib/logs/execution/json-byte-size.ts b/apps/sim/lib/logs/execution/json-byte-size.ts
index f7d3f866fc0..b602db1820f 100644
--- a/apps/sim/lib/logs/execution/json-byte-size.ts
+++ b/apps/sim/lib/logs/execution/json-byte-size.ts
@@ -1,5 +1,6 @@
 import { getErrorMessage } from '@sim/utils/errors'
 import { quotedStringBytes } from '@/lib/core/utils/bounded-json'
+import { unboxJsonPrimitive } from '@/lib/core/utils/boxed-primitives'
 
 /**
  * Byte length of `JSON.stringify(value)`, measured without building the string.
@@ -35,11 +36,7 @@ export function getJsonByteSize(value: unknown, maxBytes: number): number | unde
         ? (raw as { toJSON?: unknown }).toJSON
         : undefined
     const value = typeof toJSON === 'function' ? toJSON.call(raw, key) : raw
-    if (value instanceof Number) return Number(value)
-    if (value instanceof String) return String(value)
-    if (value instanceof Boolean) return Boolean.prototype.valueOf.call(value)
-    if (value instanceof BigInt) return BigInt.prototype.valueOf.call(value)
-    return value
+    return typeof value === 'object' && value !== null ? unboxJsonPrimitive(value) : value
   }
 
   const isOmitted = (item: unknown): boolean =>