What & why

Closes #

How it was verified

• mvn verify is green (JDK 17+)
• Documentation-only — nothing to build

Checklist

• The issue was claimed with a comment before starting (see CONTRIBUTING — didn't claim it? Open the PR anyway, just say so)
• One logical change (unrelated fixes belong in their own PR)
• Behavior changes arrive with the test that demanded them; bug fixes start from a failing test
• No golden-file test changed — st/1 is a public API. If a golden test did change, that is a deliberate format change: say so below, and update docs/FORMAT.md
• New config property? It has a setter (Joran naming), a default that preserves current behavior, coverage in LogbackXmlConfigTest, and a row in the README config table

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