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b4b1ece8f1
The Arduino loop task runs Meshtastic's entire cooperative OSThread scheduler on the Adafruit core's stock 4 KB (1024-word) stack. The 2.8 first-sync path - AdminModule::handleSetConfig -> saveChanges -> configChanged -> RadioInterface::reloadConfig -> LR11x0 reconfigure -> SPI Lock::lock, with vsnprintf/USB-CDC logging frames stacked on top - overflows it. SWD fault capture on a T1000-E (pyocd vector_catch=h) proved it: the loop task's SP was driven 40 bytes BELOW its own pxStack base, the stack paint was consumed to the floor, and the crash was a BusFault in xQueueSemaphoreTake dereferencing a semaphore handle that adjacent-heap corruption had overwritten with log text (0x3f3f207c = "| ??"). The core's HardFault handler is a bare NVIC_SystemReset, so in the field this presents as a silent reboot ~seconds after a phone pairs (or a 30 s zombie hang -> supervision timeout 0x8 when the corruption lands on task TCBs instead). Also explains the set_time_only -> immediate-NodeInfo crash variant reported on empty-DB nodes: same task, different deep chain. 2.7.26 is unaffected because the deep frames (XEdDSA, satellite map conversion, replay engine) did not exist. Fix: set -DLOOP_STACK_SZ=2048 (words = 8 KB) for all nrf52840 targets. Requires the #ifndef guard from meshtastic/Adafruit_nRF52_Arduino#7; until that merges the flag is a harmless redefinition warning. Validated on hardware: pairing + full sync completes, stack paint shows healthy margin under load. Also fix the boot-time reset-reason log: the core's init() caches RESETREAS and W1C-clears the register before setup() runs, so the raw read here has always printed 0. Use readResetReason() instead. (preFSBegin's RESETREAS==0 gate is intentionally left as-is - its degenerate GPREGRET-only behavior is what makes lfs recovery work.)