[WIP] Fix issue with global semantics not producing errors

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Semantic qualifiers on a global semantics without in should error</issue_title>
<issue_description># Issue Description
I had a variable definition on global scope with a semantic qualifier:

static int2 group_thread_id: SV_GroupThreadID

This compiles without error, but the variable does not hold the correct value. This was a very hard to find bug.

Reproducer Code

See above.

Expected Behavior

The variable should either contain the correct value or error when compiling.

Actual Behavior

The shader compiled without error but the variable did not contain the correct value

Environment

• Slang Version 2025.14.3
• OS Arch Linux 6.16.4
• GPU/Driver version AMD / Mesa 1:25.2.2-2 / vulkan-radeon 1:25.2.2-2

Additional context

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Semantic qualifiers on a global semantics without in should error #8435

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.