Fix semantic tokens for fully qualified component names

[Copilot]

Problem

Fully qualified component names were displaying with incorrect colorization in the editor. When using components like <Microsoft.AspNetCore.Components.Web.PageTitle>, the C# semantic tokens (namespace, operator, class) were showing through instead of being overridden by Razor's component element token:

Root Cause

The issue was in the SemanticRange.CompareTo sorting logic. When multiple semantic tokens started at the same position, the sort order was:

1. Start line
2. Start character
3. End line
4. End character ← Problem: Shorter tokens sorted first
5. FromRazor flag ← Never reached when end positions differ

This caused shorter C# tokens (e.g., "Microsoft" at chars 1-10) to be sorted before the longer Razor token (chars 1-46), preventing the Razor token from overriding the C# tokens.

Solution

Modified SemanticRange.CompareTo: Moved the FromRazor check to occur immediately after comparing start positions, before comparing end positions. This ensures Razor tokens at the same start position always sort first, regardless of length.

Added containment filtering in TryWriteToken: Added logic to skip C# tokens that are fully contained within a Razor token on the same line, providing an additional safeguard.

Testing

Added comprehensive test coverage with the new FullyQualifiedComponent test that verifies:

• Fully qualified component names display as single razorComponentElement tokens
• Both component and non-component (miscellaneous file) scenarios work correctly
• Background color variations work as expected

All existing semantic tokens tests continue to pass with no regressions.

Fixes #11480 (if applicable - replace with actual issue number)

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• 2kmvsblobprodcus39.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• 2zrvsblobprodcus388.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• 7devsblobprodcus323.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• 7tjvsblobprodcus341.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• bcnvsblobprodcus378.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• frdvsblobprodcus327.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• ibzvsblobprodcus369.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• imzvsblobprodcus368.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• josvsblobprodcus372.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• kgfvsblobprodcus314.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• kh4vsblobprodcus325.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• kijvsblobprodcus387.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• l49vsblobprodcus358.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• mobile.events.data.microsoft.com
  • Triggering command: /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/Microsoft.VisualStudioCode.RazorExtension.Test.runtimeconfig.json --depsfile /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/Microsoft.VisualStudioCode.RazorExtension.Test.deps.json /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/testhost.dll --port 46623 --endpoint 127.0.0.1:046623 --role client --parentprocessid 6323 --telemetryoptedin false (dns block)
  • Triggering command: /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/Microsoft.VisualStudioCode.RazorExtension.Test.runtimeconfig.json --depsfile /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/Microsoft.VisualStudioCode.RazorExtension.Test.deps.json /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/testhost.dll --port 40259 --endpoint 127.0.0.1:040259 --role client --parentprocessid 6599 --telemetryoptedin false (dns block)
  • Triggering command: /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/Microsoft.VisualStudioCode.RazorExtension.Test.runtimeconfig.json --depsfile /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/Microsoft.VisualStudioCode.RazorExtension.Test.deps.json /home/REDACTED/work/razor/razor/artifacts/bin/Microsoft.VisualStudioCode.RazorExtension.Test/Debug/net9.0/testhost.dll --port 42535 --endpoint 127.0.0.1:042535 --role client --parentprocessid 11560 --telemetryoptedin false (dns block)
• s4uvsblobprodcus326.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)
• u3hvsblobprodcus371.vsblob.vsassets.io
  • Triggering command: dotnet build src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Microsoft.VisualStudioCode.RazorExtension.Test.csproj (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Fully qualified components look bad</issue_title>
<issue_description>Presumably broken by my start tag mapping:

Razor semantic tokens is supposed to override C# semantic tokens, but clearly that doesn't happen if there is a fully qualified component name. We probably don't have any test coverage for that.</issue_description>

<agent_instructions>New tests should be in CohostSemanticTokensRangeEndpointTest</agent_instructions>

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

Fixes #12330

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