Scope markdown 4-backtick fence rule to true nested-fence cases

[Copilot]

The markdown guidance was too broad and caused models to emit 4-backtick fences for standalone blocks (e.g., mermaid), which breaks GitHub rendering. This change narrows the rule so 4-backticks are only used when block content literally includes triple-backtick fences.

• Problem refinement

  • Reworded the markdown generation rule in actions/setup/md/markdown.md to remove ambiguous “outer nested code block” interpretation.
  • Added explicit conditional behavior: 4-backticks only for literal embedded fences; otherwise use standard fences.

• Prompt contract update

  • Kept GitHub Flavored Markdown requirement unchanged.
  • Clarified fence selection behavior in one sentence to reduce partial/incorrect fence upgrades (e.g., opening-only changes).

<markdown-generation>
<rule>Only use 4-backtick fences when the block literally contains triple-backtick fences inside it; otherwise use standard 3-backtick fences. Use GitHub Flavored Markdown.</rule>
</markdown-generation>

[Copilot]

Pull request overview

Narrows the markdown fence selection guidance so models only emit 4-backtick fences when a code block literally contains embedded triple-backtick fences, avoiding GitHub rendering issues for standalone fenced blocks (e.g., mermaid).

Changes:

• Replaced the overly broad “outer blocks containing nested code blocks” guidance with an explicit conditional rule for when to use 4-backtick vs 3-backtick fences.

Show a summary per file

File	Description
actions/setup/md/markdown.md	Refines the markdown-generation rule to use 4-backtick fences only for true literal nested-fence cases.

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