fix(extension): await init in onMessage to fix lost click after SW sleeps (MV3 cold-start race)

[thiagomendonca-eu]

What

Fixes the MV3 service-worker cold-start race that drops Option+Click selections after the worker goes idle.

Closes #19

Problem

ElementSenderService disconnects its WebSocket after 10s of inactivity, removing the last thing keeping the service worker alive, so Chrome terminates the SW. The next Option+Click wakes it via runtime.sendMessage, but the onMessage handler used elementSender / currentConfig directly while the top-level initialize() was still awaiting the async config load:

async function initialize() {
  currentConfig = await ConfigStorageService.load(); // async
  elementSender = new ElementSenderService();
}

chrome.runtime.onMessage.addListener((request, _sender, sendResponse) => {
  if (request.type === 'DOM_ELEMENT_POINTED' && request.data) {
    elementSender.sendElement(...); // elementSender is undefined on a cold start
  }
});

initialize();

On a cold start the message arrives before initialize() resolves, so elementSender is undefined → TypeError → the click is silently lost. This matches the diagnosis already in #19 ("initialize() hasn't completed when the message handler fires"). In practice, users had to keep the SW console open (which keeps the worker alive) for pointing to work.

Fix

Make initialization idempotent (ensureInitialized() returns a cached promise) and await it inside the listener before using elementSender / currentConfig. Following MV3 messaging guidance, the listener stays synchronous, the async work runs in an inner IIFE, and it returns true to keep the channel open for sendResponse.

Testing

• Windows 11, Chrome 145, extension 0.6.0, Claude Code.
• Before: once the SW went inactive, the first Option+Click was lost and get-pointed-element returned stale/empty data — unless the SW console was kept open.
• After: let the SW go inactive, closed all devtools, then Option+Click → element was sent and get-pointed-element returned it immediately. No console needed.

Single-file change; the listener contract (synchronous + return true) is preserved.