400 ad accounts 3 subrequests = silent data loss in Cloudflare Workers (and how I fixed it)

Adding a single KV cache write broke my Worker — and it didn't throw a single error to the caller. I run a Korean D2C ad-ops pipeline where one Worker fans out performance checks across ~400 ad accounts per request. The math looked fine: 400 accounts × 2 API calls = 800 subrequests, safely under Clo