The SPI OLEDs continue to misbehave, with this early morning glitch jamming the display into a complete lockup:
A normal, albeit blind, shutdown-and-reset brought it back to life.
Other OLEDs on other RPis have occasionally misbehaved since the most recent (attempted) tweak, so it hasn’t made any difference.
One obvious lesson: prefer OLEDs with I2C interfaces.
The Smell of Molten Projects in the Morning 