Document framework assembly access rule

[PureWeen]

Documents the framework-wide rule against adding InternalsVisibleTo or [UnsafeAccessor] in shipping framework code to reach non-public members in another framework assembly. The assembly boundary should be redesigned instead; if that requires a public API, the repository API-review and baseline process applies.

This makes the guidance from #68365 (comment) durable for future contributors and coding agents, while clarifying that existing uses are not precedent for new ones.

[Copilot]

Pull request overview

Documents a framework-wide guideline in the repo’s Copilot instructions to avoid new cross-assembly access to non-public members via InternalsVisibleTo or UnsafeAccessor, and to prefer explicit public APIs via the API review/baseline process. This helps keep the guidance from #68365 durable and discoverable for future contributors and coding agents.

Changes:

• Adds a new “Framework assembly boundaries” section to .github/copilot-instructions.md.
• Explicitly states the rule against InternalsVisibleTo/UnsafeAccessor for new cross-assembly access.
• Directs contributors to design public APIs and follow the API review/baseline process instead.

Show a summary per file

File	Description
.github/copilot-instructions.md	Adds durable guidance on respecting ASP.NET Core framework assembly boundaries and avoiding new cross-assembly non-public access bridges.

Review details

💡 Add a code-review agent skill for context-aware, tailored reviews. Learn more in the docs.

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite