Decoded a T-Deck coredump (Task WDT, loopTask stuck in spiffs_gc_clean under
DataStore::saveContacts): a contact save on a churned SPIFFS can trigger a
multi-second garbage-collection pass that starves core 0 and trips the task
watchdog, giving a reboot loop.
- Route contacts/channels to SD when a card is present, even on upgraded
devices whose data is still on SPIFFS (main.cpp mounts SD every boot; if not
fully adopting SD, store.setSecondaryFS(&SD)). DataStore::begin() migrates the
existing /contacts3 + /channels2 to the card once; identity/prefs stay put.
- Move the ref-counted WdtHeavyGuard into a shared header so the core
DataStore::saveContacts shares one count with the UI history/backup saves, and
wrap saveContacts with it (guaranteed fix for card-less devices).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
