diff --git a/src/tasks/task-registry.store.test.ts b/src/tasks/task-registry.store.test.ts
index 2751884924b..7bcdb9bfbc9 100644
--- a/src/tasks/task-registry.store.test.ts
+++ b/src/tasks/task-registry.store.test.ts
@@ -25,10 +25,14 @@ function requireFirstUpsertParams(upsertTaskWithDeliveryState: ReturnType<typeof
   task?: { taskId?: string };
   deliveryState?: { lastNotifiedEventAt?: number };
 } {
-  const params = upsertTaskWithDeliveryState.mock.calls[0]?.[0];
-  if (!params) {
+  const [call] = upsertTaskWithDeliveryState.mock.calls;
+  if (!call) {
     throw new Error("expected task upsert params");
   }
+  const [params] = call;
+  if (typeof params !== "object" || params === null || Array.isArray(params)) {
+    throw new Error("expected task upsert params to be an object");
+  }
   return params;
 }
 
diff --git a/src/tasks/task-registry.test.ts b/src/tasks/task-registry.test.ts
index a88217b83a7..861a0ff11a1 100644
--- a/src/tasks/task-registry.test.ts
+++ b/src/tasks/task-registry.test.ts
@@ -287,6 +287,17 @@ function sentMessageCall(callIndex = 0): Record<string, unknown> {
   return call[0] as Record<string, unknown>;
 }
 
+function firstMockArg(
+  mock: { mock: { calls: readonly unknown[][] } },
+  label: string,
+): Record<string, unknown> {
+  const [call] = mock.mock.calls;
+  if (!call) {
+    throw new Error(`Expected ${label} call`);
+  }
+  return expectRecordFields(call[0], {});
+}
+
 function createInMemoryTaskRegistryStore() {
   const tasks = new Map<string, TaskRecord>();
   const deliveryStates = new Map<string, TaskDeliveryState>();
@@ -2897,7 +2908,7 @@ describe("task-registry", () => {
         taskId: task.taskId,
       });
 
-      const cancelArgs = hoisted.cancelSessionMock.mock.calls[0]?.[0];
+      const cancelArgs = firstMockArg(hoisted.cancelSessionMock, "cancelSession");
       expectRecordFields(cancelArgs, {
         cfg: {},
         sessionKey: "agent:codex:acp:child",
@@ -2950,7 +2961,7 @@ describe("task-registry", () => {
         taskId: task.taskId,
       });
 
-      const killArgs = hoisted.killSubagentRunAdminMock.mock.calls[0]?.[0];
+      const killArgs = firstMockArg(hoisted.killSubagentRunAdminMock, "killSubagentRunAdmin");
       expectRecordFields(killArgs, {
         cfg: {},
         sessionKey: "agent:worker:subagent:child",