Smoother WhatsApp connection and pairing

A round of work entirely focused on making WhatsApp connections feel boring.

What's new

• QR pairing is more reliable — codes refresh correctly and the first scan succeeds more often.
• Corrupted sessions are now detected and recovered automatically instead of getting stuck.
• A heartbeat watches each connection in the background and intervenes early when one starts to drift.
• Cleaner internal logs mean we resolve incidents faster when something does go wrong.