optimize sync & add accept popup

src/preload.js

@@ -23,6 +23,13 @@ let lanSyncProgressCb = null
 ipcRenderer.on('lansync:progress', (e, data) => {
   if (lanSyncProgressCb) lanSyncProgressCb(data)
 })
+
+// Incoming sync consent: the receiver's Accept/Decline popup. Single slot for
+// the same reason - one pending request at a time (the server enforces it).
+let lanSyncIncomingCb = null
+ipcRenderer.on('lansync:incoming', (e, data) => {
+  if (lanSyncIncomingCb) lanSyncIncomingCb(data)
+})
 const fs = require('fs')
 const path = require('path')
 
@@ -91,10 +98,14 @@ contextBridge.exposeInMainWorld('plwl', {
   lansyncRerollSyncCode: () => ipcRenderer.invoke('lansync:rerollSyncCode'),
   lansyncForget: id => ipcRenderer.invoke('lansync:forget', id),
   lansyncSync: payload => ipcRenderer.invoke('lansync:sync', payload),
+  lansyncRespondIncoming: (requestId, accept) => ipcRenderer.invoke('lansync:respondIncoming', requestId, accept),
   onLanSyncDevices: cb => ipcRenderer.on('lansync:devices', (e, data) => cb(data)),
   onLanSyncProgress: cb => {
     lanSyncProgressCb = cb
   },
+  onLanSyncIncoming: cb => {
+    lanSyncIncomingCb = cb
+  },
   onLanSyncApplied: cb => ipcRenderer.on('lansync:applied', (e, data) => cb(data)),
   onLanSyncReceiving: cb => ipcRenderer.on('lansync:receiving', (e, data) => cb(data))
 })