Add content fidelity/preservation rule to the What's New include SKILL file

[Copilot]

The What's New automation's content rules (.github/skills/whats-new-include-content-rules/SKILL.md) governed only formatting — headings, xrefs, links, phrasing, naming — with no directive against condensing source release notes. The agent could drop parallel examples or the rationale tying prose to code, degrading fidelity.

Changes

• New top-priority rule — added ### Content fidelity — preserve information; do not condense as the first subsection under ## Content rules. It requires transferring all substantive content (every code example, explanatory sentence, and the reasoning connecting prose to code), forbids dropping one of a set of parallel examples, mandates keeping the "why" next to code and a per-include self-containment re-read, and limits removal to genuine cross-preview duplication.
• Enforced at completion — added five matching items to the Validation checklist (every source example present, paired examples retained together, rationale preserved, each include reads correctly in isolation, removals limited to duplication).

Not included — access-restricted

The issue also asked to reinforce this in Step 1 of .github/agents/whats-new-from-release-notes.agent.md. That file lives under .github/agents, which this agent can't access, so the change wasn't made here and needs to be applied manually. Suggested Step 1 text:

Apply those rules to create one include file per feature from the source
release notes.

**Fidelity is the priority.** Transfer the source content faithfully: preserve
every code example, every explanatory sentence, and the reasoning that ties
prose to code. You may reformat, and you may combine overlapping content across
previews to avoid repetition, but do not summarize or drop information. In
particular, never drop one of a set of parallel examples, and never leave a code
sample without the explanation that made it make sense in the source. If a
source section makes sense and the resulting include does not, that is a defect.

Because the agent-file reinforcement is still outstanding, this only partially addresses the issue.

• Fixes What new agent: Improve preservation rules #37349