Docs: Add new Spark version support skill

[manuzhang]

About this PR

Adds a repo-local, agent-neutral skill for introducing support for a new Spark minor version in Iceberg.

The skill generalizes the Spark 4.2 preview workflow and documents how to:

• preserve source history with separate move and copy-back commits;
• back up an existing target branch before rewriting its history;
• update the current Gradle, CI, benchmark, and publication integration points;
• keep preview source support separate from default build and release publication decisions; and
• validate the new modules and an older Spark line when shared resolution logic changes.

Testing

• quick_validate.py .agents/skills/add-spark-version
• git diff --check upstream/main...HEAD

---

AI Disclosure

• Model: GPT-5
• Platform/Tool: OpenAI Codex
• Human Oversight: partially reviewed
• Prompt Summary: Create a reusable, agent-neutral Iceberg skill based on the Spark 4.2 preview workflow for adding support for new Spark versions, including backup of an existing target branch.

[anuragmantri]

This rg pattern doesn't match sparkScalaVersions, the map inside project(':iceberg-bom') in root build.gradle that controls which Scala variants of a Spark line get included in the BOM. I checked: echo "sparkScalaVersions" | grep -E 'knownSparkVersions|defaultSparkVersions|sparkVersions|spark[0-9]+' exits 1. Could the pattern (and the "Wire the new line" file list below) include it?

[anuragmantri]

This section separates preview support from release publication decisions, which is the right distinction, but nothing here or in the discovery command above mentions .gitattributes. The export-ignore entries there are what actually gate whether a preview version tree is included in git archive source releases. #18024, "Include Spark 4.2 in source releases," was entirely about removing /spark/v4.2 and /spark/v4.2/** from .gitattributes. Could this get called out explicitly, and could .gitattributes be added to the discovery search paths in "Establish the target"?

[anuragmantri]

Thanks @manuzhang. Generally, this looks like a useful skill but .claude/ is already gitignored here (#16533), and #16778 proposed the same treatment for .github/copilot-instructions.md, .github/agents/, and .github/skills/, on the reasoning that these are workspace-local, not shared repo content.

It's worth a quick dev@ thread before this comes out of draft, so the directory choice isn't decided by default?

[github-actions]

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