Thank you everyone! Each of those posts was super helpful.
I need 50mA at 3.3V, so my plan at the moment is to pick up an 'industrialised' voltage regulator, having its input protected by a resistor&TVS, and all this being fed an LC low-pass filter. I'll need to do some efficiency calcs to work out if I should do a 3.3V regulator or a 12V regulator (followed by a cheap 3.3V switcher).
duak, when you say a 1uF to circuit common what do you mean? I.e. if I put a 15 uF from 14V (unregulated) to ground, where exactly would I put this 1uF?
DBecker, I do not need the module to work during cranking transients, but I do need the module to not blow-up

I assume that the above-mentioned plans should be sufficient for that, but do tell me if I'm missing something. Incidentally, thanks for sharing the guidelines re 28V/35V. Super helpful.
A few other FYIs:
- The 1117 regulator came with the cheap-as-chips aliexpress ESP32, so it is likely very suspect here. Lesson learned.
- I want to avoid messing with the car's original electronics (e.g. by adding capacitors). The distributor contains a condenser between the coil and ground, but afaik there's nothing on the other side of the coil, and I'm not sure that the Lucas RF95 regulator has any capacitors in it.
- You're correct in noting that it isn't just the ignition system, but also generator, regulators, and fuel pump. I confirmed that my multimeter still glitches when the generator is disconnected, but that doesn't mean it wasn't a problem in its own right.