From 75cb0bd80e029b962ebec37d8fde792b2786f9cc Mon Sep 17 00:00:00 2001
From: KazenDev <KazenDev@users.noreply.github.com>
Date: Thu, 6 Aug 2026 00:43:56 +0200
Subject: [PATCH] fix(sdk): handle cyclic run-state on session resume

---
 sdk/src/run-state.ts | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/sdk/src/run-state.ts b/sdk/src/run-state.ts
index ea226e94ac..b26aaa5070 100644
--- a/sdk/src/run-state.ts
+++ b/sdk/src/run-state.ts
@@ -790,10 +790,19 @@ export async function applyOverridesToSessionState(
     maxAgentSteps?: number
   },
 ): Promise<SessionState> {
-  // Deep clone to avoid mutating the original session state
-  const sessionState = JSON.parse(
-    JSON.stringify(baseSessionState),
-  ) as SessionState
+  // Deep clone to avoid mutating the original session state. A JSON
+  // round-trip is the fast path, but run state can carry cyclic values
+  // (e.g. recursive zod schemas inside tool blocks) that make
+  // JSON.stringify throw ("cannot serialize cyclic structures"); lodash
+  // cloneDeep handles cycles, so fall back to it. Mirrors cloneSessionState.
+  let sessionState: SessionState
+  try {
+    sessionState = JSON.parse(
+      JSON.stringify(baseSessionState),
+    ) as SessionState
+  } catch {
+    sessionState = cloneDeep(baseSessionState)
+  }
 
   // Apply maxAgentSteps override
   if (overrides.maxAgentSteps !== undefined) {