fix: resolve cyclic structure serialization crash in token counter

When the token count API call fails or is not available, the CLI fallback logic
serializes  using . However,
contains raw Zod schema objects (), which have circular references,
causing a  TypeError.

Changes:
- Added a  utility to strip circular references from objects.
- Sanitize the  inside  at creation time using
   so it is a plain, serializable object.
  This also prevents similar serialization failures when saving run state to disk.

Author: OmarAlaaeldein

packages/agent-runtime/src/run-agent-step.ts

@@ -57,6 +57,7 @@ import {
   countTokens,
   countTokensJson,
   countTokensMessages,
+  safeJsonStringify,
 } from './util/token-counter'
 
 import type { AgentTemplate } from '@codebuff/common/types/agent-template'
@@ -940,7 +941,7 @@ export async function loopAgentSteps(
   const toolDefinitions = mapValues(tools, (tool) => ({
     description:
       typeof tool.description === 'string' ? tool.description : undefined,
-    inputSchema: tool.inputSchema as {},
+    inputSchema: JSON.parse(safeJsonStringify(tool.inputSchema) ?? 'null'),
   }))
 
   const additionalToolDefinitionsWithCache = async () => {

packages/agent-runtime/src/util/__tests__/token-counter.test.ts

@@ -4,10 +4,33 @@ import {
   countTokens,
   countTokensJson,
   countTokensMessages,
+  safeJsonStringify,
 } from '../token-counter'
 
 import type { Message } from '@codebuff/common/types/messages/codebuff-message'
 
+describe('safeJsonStringify', () => {
+  test('handles circular references and drops function properties', () => {
+    const schema: { name: string; self?: unknown; transform?: () => void } = {
+      name: 'tool input',
+      transform: () => {},
+    }
+    schema.self = schema
+
+    expect(safeJsonStringify(schema)).toBe(
+      '{"name":"tool input","self":"[Circular]"}',
+    )
+    expect(() => countTokensJson(schema)).not.toThrow()
+    expect(countTokensJson(schema)).toBeGreaterThan(0)
+  })
+
+  test('preserves JSON string serialization when counting strings', () => {
+    expect(countTokensJson('tool input')).toBe(
+      countTokens(JSON.stringify('tool input')),
+    )
+  })
+})
+
 describe('countTokensMessages', () => {
   test('counts text content plus per-message overhead', () => {
     const messages = [

packages/agent-runtime/src/util/token-counter.ts

@@ -38,10 +38,27 @@ export function countTokens(text: string): number {
   }
 }
 
+/**
+ * Serialize arbitrary values for token counting and persisted tool metadata.
+ * Circular references are represented explicitly; functions follow
+ * JSON.stringify semantics and are omitted from object properties.
+ */
+export function safeJsonStringify(value: unknown): string | undefined {
+  const seen = new WeakSet<object>()
+  return JSON.stringify(value, (_key, nestedValue) => {
+    if (typeof nestedValue === 'function') return undefined
+    if (typeof nestedValue === 'object' && nestedValue !== null) {
+      if (seen.has(nestedValue)) return '[Circular]'
+      seen.add(nestedValue)
+    }
+    return nestedValue
+  })
+}
+
 export function countTokensJson(value: unknown): number {
   // JSON.stringify(undefined) returns undefined; fall back to '' so countTokens
   // always gets a string.
-  return countTokens(JSON.stringify(value) ?? '')
+  return countTokens(safeJsonStringify(value) ?? '')
 }
 
 /**
@@ -95,6 +112,7 @@ export function countTokensMessages(messages: Message[]): number {
   return total
 }
 
+
 export function countTokensForFiles(
   files: Record<string, string | null>,
 ): Record<string, number> {