Java 21 patterns — records, sealed types, virtual threads

Prerequisites: a Java 21 project the agent can read and refactor (JDK 21, Maven or Gradle) — the skill is a pattern guide, not software to install Install "Java 21 patterns — records, sealed types, virtual threads" for me. It gives my agent @gentleman-programming's Java 21 patterns: records with compact-constructor validation for immutable DTOs and value objects, sealed interfaces plus pattern-matching switch for exhaustive closed hierarchies, virtual threads via newVirtualThreadPerTaskExecutor for blocking I/O without giant thread pools — each with good/bad code examples, anti-patterns (mutable DTOs, raw platform threads per request), a quick-reference table, and links to the Java 21 release notes and JEP index. MIT-licensed. Repository: https://github.com/gentleman-programming/gentleman-skills/blob/main/community/java-21/SKILL.md 1. Fetch the SKILL.md file (and any helper files) from the repository path into a temporary folder and summarize what it does in one or two sentences. 2. Safety check: review the SKILL.md for anything suspicious (unexpected network calls, shell commands, credential harvesting). This repo should contain zero secrets in code. Verify that holds here; STOP on any red flag and tell me. 3. Install it as a skill: copy SKILL.md and its helper files into the agent's skills directory, in a folder named "java-21". 4. Verify with no network calls: frontmatter valid, files in place. 5. Report what was installed, where, and what I still need to do myself (e.g. point the agent at my Java 21 project or file; nothing else — it's a pattern guide). GitHub is optional: if I have a GitHub account or the gh CLI, you may use it; otherwise public access is fine. Never require it unless it's in the prerequisites above. Rules: don't touch anything outside the temp folder and the install target. If anything looks off, stop and ask me.