Concurrent + Cached External Fetching

Sequential, uncached external calls are the single most common avoidable performance sink in agent-written code. Ten lookups that each take 300 ms run in 3 seconds when serialized; fanned out they finish in ~300 ms. And on the next run — a re-analysis, a follow-up question, a re-run after an unrelated bug fix — uncached code pays that cost all over again, plus hammers a public endpoint that may rate-limit or ban you.

This skill exists to make two properties the default for any code that touches the network in bulk:

1. Concurrency — independent calls run in parallel, at least ~10 in flight at once.
2. Disk caching — every response is persisted, keyed by request content, so an identical call is served from disk and never re-issued unless explicitly refreshed.

These are code patterns you write into the product, not something you do by hand. The goal is that the code stays fast and cache-warm every time it runs, including in follow-up work.