diff --git a/packages/junior/src/chat/sandbox/session.ts b/packages/junior/src/chat/sandbox/session.ts
index fd73a5a0b5..10c9999014 100644
--- a/packages/junior/src/chat/sandbox/session.ts
+++ b/packages/junior/src/chat/sandbox/session.ts
@@ -628,8 +628,9 @@ export function createSandboxRuntime(
         return null;
       }
       if (isSandboxUnavailableError(error)) {
+        sandboxRef = undefined;
         invalidateSession();
-        throw error;
+        return null;
       }
       throw new Error("sandbox restore failed", { cause: error });
     }
@@ -641,9 +642,10 @@ export function createSandboxRuntime(
       await persistSandboxRef({ ...ref, id: hintedSandbox.sandboxId });
       return rememberSandbox(hintedSandbox, networkPolicyKey);
     } catch (error) {
-      // Keep the durable VM alive so a later reacquire can reuse it.
       if (isSandboxUnavailableError(error)) {
-        throw error;
+        sandboxRef = undefined;
+        invalidateSession();
+        return null;
       }
       return failSetup(error);
     }
diff --git a/packages/junior/tests/component/task-execution/conversation-work.test.ts b/packages/junior/tests/component/task-execution/conversation-work.test.ts
index 9f2a55fa32..323d891f0d 100644
--- a/packages/junior/tests/component/task-execution/conversation-work.test.ts
+++ b/packages/junior/tests/component/task-execution/conversation-work.test.ts
@@ -1808,8 +1808,8 @@ describe("conversation work execution", () => {
             return target.acquireLock(key, ttlMs);
           };
         }
-        const value = Reflect.get(target, prop, receiver);
-        return typeof value === "function" ? value.bind(target) : value;
+        const value = (target as Record<string | symbol, unknown>)[prop];
+        return typeof value === "function" ? (value as (...args: unknown[]) => unknown).bind(target) : value;
       },
     }) as StateAdapter;