Why my CI got 4 minutes faster

Caches solve a problem and create three new ones: invalidation, observability, and the slow drift between what the cache thinks is true and what the source thinks is true.

If a config file has more than a dozen options, half of them aren't being used. The other half are being used in ways the original author didn't predict.

The fastest debugging trick I've learned is to write out, in one sentence, what the system is supposed to be doing. Half the time I notice the bug while writing the sentence.

I used to add a layer of abstraction the first time I saw a pattern repeat. Now I wait for the third. The waiting is uncomfortable, but the abstractions that survive that wait tend to last.

Most retry logic I've removed turned out to be hiding a real bug. The retries made the failure invisible, and the bug compounded for months in the background.