Node.js CXone Social Webhook Merge/Split Idempotency Failure on Thread Reconstruct

app.post('/webhook/cxone/social', async (req, res) => {
 const { event, payload } = req.body;
 if (event === 'THREAD_MERGED') {
 await syncThread(payload.thread_id, payload.parent_ids);
 }
 res.status(200).send('OK');
});

Handler’s live. Merge events hit, CRM update returns 409. Token rotation’s fine. Signature validation passes. Delta encoding’s the problem. Latency’s spiking. 15s sync delay. CXone sends a partial payload for the child thread. Reconciler can’t map participant relationships.

{
 "error": "VALIDATION_ERROR",
 "details": "Field 'participants.0.role' violates constraint: must be one of [AGENT, CUSTOMER]",
 "trace": "reconciler.syncParticipants"
}

Queue’s growing. Schema validation’s breaking. Concurrency’s the issue. Webhook fires multiple events when agents bounce the thread. Locking assumes single writer.

const updateResult = await crmClient.updateRecord(threadId, {
 version: currentVersion,
 data: mergedData
});
// 409: Version mismatch

Unique thread identifier logic looks solid, but thread_id changes in CXone on split. CRM holds the old UUID. Mapping overwrites parent with child data. Breaks conversation reconstruction. Logs show gaps. Tracker’s unhappy. Delta payload drops the agent ID on the split child. Reconciler crashes on the null check.