Assertion failed when pairing

[agaeb]

When trying to pair a device, I got
assertion "false" failed: file ".../pico/pico-sdk/src/rp2_common/pico_flash/flash.c", line 183, function: default_enter_ss
and the pico halted.
This seems to be related to the Bluetooth stack trying to write to flash from the second core, without having been given the guarantee that it is safe to do so, see https://www.raspberrypi.com/documentation/pico-sdk/high_level.html#pico_flash.
To give this guarantee (assuming the first core isn't actually writing to flash),
flash_safe_execute_core_init();
must be called somewhere early in the main function, which is declared in
#include "pico/flash.h".
With this addition, I was able to pair the device alright.
Another possibility would be to set PICO_FLASH_ASSUME_CORE0_SAFE=1, but I did not try that.