diff --git a/extensions/whatsapp/src/monitor-inbox.test-harness.ts b/extensions/whatsapp/src/monitor-inbox.test-harness.ts
index 11733a5b54f1..5af334a8ed66 100644
--- a/extensions/whatsapp/src/monitor-inbox.test-harness.ts
+++ b/extensions/whatsapp/src/monitor-inbox.test-harness.ts
@@ -257,25 +257,6 @@ export type InboxMonitorOptions = Parameters<MonitorWebInbox>[0];
 let monitorWebInbox: MonitorWebInbox;
 let resetWebInboundDedupe: ResetWebInboundDedupe;
 
-function expectInboxPairingReplyText(
-  text: string,
-  params: {
-    channel: string;
-    idLine: string;
-    code?: string;
-  },
-): string {
-  const code = text.match(/Pairing code:\s*```[\r\n]+([A-Z2-9]{6,})/)?.[1];
-  expect(code).toBeDefined();
-  const resolvedCode = params.code ?? code ?? "";
-  expect(text).toContain("OpenClaw: access not configured.");
-  expect(text).toContain(params.idLine);
-  expect(text).toContain("Pairing code:");
-  expect(text).toContain(`\n\`\`\`\n${resolvedCode}\n\`\`\`\n`);
-  expect(text).toContain(`pairing approve ${params.channel} ${resolvedCode}`);
-  return resolvedCode;
-}
-
 // Yields two macrotask ticks so already-scheduled inbound continuations run.
 // This deliberately does NOT wait for pending inbound work to finish — tests
 // observing intermediate states (held handlers, parked debounce batches) rely
@@ -291,23 +272,7 @@ export async function settleInboundWork() {
 
 type InboundWorkTracker = { pending: number };
 const inboundWorkTrackers = new Set<InboundWorkTracker>();
-let inboundDrainWaiters: Array<() => void> = [];
-
-function releaseInboundDrainWaitersIfIdle() {
-  if (inboundDrainWaiters.length === 0) {
-    return;
-  }
-  for (const tracker of inboundWorkTrackers) {
-    if (tracker.pending > 0) {
-      return;
-    }
-  }
-  const waiters = inboundDrainWaiters;
-  inboundDrainWaiters = [];
-  for (const release of waiters) {
-    release();
-  }
-}
+let inboundIdle: { promise: Promise<void>; release: () => void } | undefined;
 
 function hasPendingInboundWork(): boolean {
   for (const tracker of inboundWorkTrackers) {
@@ -318,6 +283,14 @@ function hasPendingInboundWork(): boolean {
   return false;
 }
 
+function publishInboundPendingWork(tracker: InboundWorkTracker, pending: number) {
+  tracker.pending = pending;
+  if (inboundIdle && !hasPendingInboundWork()) {
+    inboundIdle.release();
+    inboundIdle = undefined;
+  }
+}
+
 // Event-driven drain: resolves when every harness-started listener reports zero
 // pending inbound work. Unlike a vi.waitFor deadline, this cannot fail spuriously
 // when a saturated no-isolate worker stalls mid-flow (sync module fetches against
@@ -329,9 +302,14 @@ export async function waitForInboundWorkDrained() {
     throw new Error("waitForInboundWorkDrained requires a listener started via startInboxMonitor");
   }
   if (hasPendingInboundWork()) {
-    await new Promise<void>((resolve) => {
-      inboundDrainWaiters.push(resolve);
-    });
+    if (!inboundIdle) {
+      let release!: () => void;
+      const promise = new Promise<void>((resolve) => {
+        release = resolve;
+      });
+      inboundIdle = { promise, release };
+    }
+    await inboundIdle.promise;
   }
   // One extra tick lets drained-callback continuations (delivery bookkeeping) run.
   await new Promise((resolve) => {
@@ -377,8 +355,7 @@ export async function startInboxMonitor(
   const listener = await monitorWebInbox({
     ...merged,
     onPendingWorkChanged: (pendingWorkCount: number, at?: number) => {
-      tracker.pending = pendingWorkCount;
-      releaseInboundDrainWaitersIfIdle();
+      publishInboundPendingWork(tracker, pendingWorkCount);
       callerOnPendingWorkChanged?.(pendingWorkCount, at);
     },
   });
@@ -411,15 +388,18 @@ export function buildNotifyMessageUpsert(params: {
   };
 }
 
+// The mocked pairing upsert always issues PAIRCODE, so the reply text can be
+// asserted directly instead of re-extracting the code from the message.
 function expectPairingPromptSent(sock: MockSock, jid: string, senderE164: string) {
   expect(sock.sendMessage).toHaveBeenCalledTimes(1);
   const sendCall = sock.sendMessage.mock.calls.at(0);
   expect(sendCall?.[0]).toBe(jid);
-  expectInboxPairingReplyText((sendCall?.[1] as { text?: string } | undefined)?.text ?? "", {
-    channel: "whatsapp",
-    idLine: `Your WhatsApp phone number: ${senderE164}`,
-    code: "PAIRCODE",
-  });
+  const text = (sendCall?.[1] as { text?: string } | undefined)?.text ?? "";
+  expect(text).toContain("OpenClaw: access not configured.");
+  expect(text).toContain(`Your WhatsApp phone number: ${senderE164}`);
+  expect(text).toContain("Pairing code:");
+  expect(text).toContain("\n```\nPAIRCODE\n```\n");
+  expect(text).toContain("pairing approve whatsapp PAIRCODE");
 }
 
 // The pairing reply is sent before the inbound handler completes, so a full
@@ -446,7 +426,7 @@ export function installWebMonitorInboxUnitTestHooks(opts?: { authDir?: boolean }
     vi.useRealTimers();
     vi.clearAllMocks();
     inboundWorkTrackers.clear();
-    inboundDrainWaiters = [];
+    inboundIdle = undefined;
     channelActivityMocks.recordChannelActivity.mockClear();
     pluginRuntimeMocks.reset();
     setWhatsAppRuntime({