Designing a Community Skill for AWS Transform Custom: AWS Glue 5.0 Upgrade Readiness

TL;DR I designed a proposed AWS Transform Custom community skill that prepares Glue 2.0, 3.0, and 4.0 repositories for Glue 5.0. It separates safe mechanical transformations from changes that require human evidence, generates a migration report, and preserves already-compatible files unchanged. Because I didn't have live atx access, the benchmarks in this post are explicitly labeled manually simulated, not agent-executed. The proposal is open as issue #75 — not yet merged, not yet a pull request. The missing data-engineering transformation AWS Transform Custom can apply agent-driven code transformations across a single repository — or thousands of them at once, via AWS Batch and Fargate. As of July 30, 2026, its public sample repository, aws-samples/aws-transform-custom-samples , contained three community-contributed transformations: an EKS version-upgrade-readiness skill, a JBoss-to-Spring-Boot migration, and a Kubernetes readiness migration. None of them touched data engineering. Given that most of my day-to-day work sits across AWS data engineering, Databricks, and Delta Lake, that gap was the obvious thing to fill. What an AWS Transform Custom "skill" looks like Before writing anything, I studied the deepest existing example, jboss-to-springboot , since the pattern it establishes is effectively an unwritten spec for the other two skills as well: README.md — the problem, what the skill does, and how to invoke it via the atx CLI. This is also where the repo draws a clear line: these are readiness transformations. They modify repository artifacts — code and infrastructure-as-code — but they don't deploy jobs, call AWS APIs to change running resources, or claim data-level equivalence. That distinction matters throughout everything below. SKILL.md — the agent-facing definition: YAML frontmatter with trigger keywords, an Objective, explicit Non-Goals , Constraints, worked before/after examples, a "signal in source code → reference file" routing table, and a numbered V