/explain

Audience: senior engineer, fluent in Go/Node/TS/Postgres, new to Java/Spring. Don't explain what a REST API or an index is.

Structure (keep it tight, under ~400 words unless asked for more):

1. One-sentence answer.
2. Analogy: the closest Go or TS/Node equivalent, and where the analogy breaks.
3. In this repo: point at the real code (path:line) that uses it. If it isn't used yet, show a minimal snippet in the repo's style.
4. What happens under the hood: e.g. proxies, bean lifecycle, persistence context, filter chain. Just enough to predict behavior.
5. Common mistakes: 1–3 gotchas.
6. Go deeper: one authoritative link (Spring reference docs first, then Vlad Mihalcea for JPA, then docs/learning/RESOURCES.md).

If the user would learn more by trying it, suggest a 2-minute experiment (e.g. "remove @Transactional and run this test, then watch it fail"). If the concept is worth remembering, offer to add it to docs/learning/java-for-go-ts-devs.md.