Engine shuts off unexpectedly and then won't restart on passage

During a night passage toward Tahiti, Lauren Landers Sailing experienced a sudden engine shutdown that was especially confusing because the two symptoms did not match a single obvious cause. The engine shut off in a way that sounded like it was being turned off while in gear, yet the propeller shaft was not spinning at the time. When she tried to restart it immediately after, it fired up fine, but then it refused to start again and was not even turning over. As she noted, if the problem were purely fuel starvation, the engine should still have turned over. The mismatch between how it shut off and how it failed to restart made diagnosis difficult and the situation genuinely scary.