fix: report the missing message instead of failing a delivered send

[DenysSamoiliuk]

The problem

POST /client/sendMessage can answer {"success": true} with no message at all. Callers keep the returned id to correlate the message later, so a success with nothing in it leaves them dereferencing undefined.

Why this is not a 500

My first version of this PR answered 500. That was wrong, and worth spelling out.

window.WWebJS.sendMessage hands the message to the chat and awaits it, and only then looks it up — src/util/Injected/Utils.js:

const [msgPromise, sendMsgResultPromise] = window
  .require('WAWebSendMsgChatAction')
  .addAndSendMsgToChat(chat, message);
await msgPromise;                                  // the message is already on its way

return window.require('WAWebCollections')
  .Msg.get(newMsgKey._serialized);                 // and only now do we look for it

So a lookup that misses says nothing about whether the contact received the message. On WhatsApp Web 2.3000.x, which no longer exposes _serialized on MsgKey, it misses on every send — and a caller that retries on 500 delivers a second copy of something the contact already has.

What it does now

Answer 200 with an explicit message: null and a warning:

{
  "success": true,
  "message": null,
  "warning": "whatsapp-web.js did not return the sent message; it may still have been delivered"
}

The caller still learns it has no id to correlate on — which is what the silent {"success": true} failed to tell it — but nothing invites a retry. Same treatment in channelController.

logMissingMessage stays. It reports what the page looked like at that moment — whether a fresh MsgKey exposes _serialized, and how the keys of the messages already in the chat are shaped. That is what identified the cause in the first place.

Related

#150 removes the common cause: the _serialized getter it installs is what makes that Msg.get hit, and it now survives page reloads. With that in, this path should be rare — but the response shape should still not lie either way.

Testing

npm test  → 43 passed
npx eslint src tests