I still think that's goal-oriented, or at the very least a hybrid approach. I wonder if the better term might be "objectives," e.g. each day, I have an objective to fix at least X bugs and make Y commits. But then that seems to increase the relative danger of encouraging yourself to do more make-work just to reach some slated goal at the end of the day.

That does give me some insight. To translate this to a habit-oriented system, you could improve or streamline your commit process, reorganize things to deal more readily with possible distractions (or deal with distractions in a single chunk of the day, such as the morning, to leave more time available for coding in the afternoon), and work on honing your habits. By doing so, getting certain goals done each day--and increasing the number of goals reached--would be a side effect of improved habits.

I guess I've been stumped because I'm looking at it from the wrong perspective (and I'm not especially prone to insight). Dumping goals entirely and focusing on the tools and techniques to get there seems more pertinent than establishing some baseline to work toward for a tangible reward. In some ways, it's like the football team example: If the team focuses on improving their fitness and practice habits (making progression itself a habit, such as the mile run by 5 seconds every few days), their competitiveness will improve as a consequence and become more predictable.