The laptop shut off suddenly. Reported no signs of life. Did not take any charge current.
Initial visual inspection was not enough to diagnose the problem.
Short detection was successful at detecting a short on a 3v3 always-on power line. Injecting 1A from and external power supply caused a single capacitor to heat up visibly under a thermal camera.

Replacing the capacitor fixed the issue. A 10 cent part fixed a thousand dollar machine.