Upgrade to .NET 10

[feO2x]

Rationale

The repository is pinned to the .NET 8 SDK and C# 12, its runnable projects and automation use .NET 8, and the source-export pipeline models .NET 8 as its modern target. Upgrade the development and execution baseline to the .NET 10 LTS toolchain, replace the net8.0 product asset with net10.0, and retain the existing .NET Standard compatibility floor.

The upgrade must also keep the compiler-loaded analyzer safe after the RS1038 assembly split, align Roslyn with the pinned SDK, and accommodate .NET 10 package pruning without suppressing warnings or changing guard-clause behavior.

Acceptance Criteria

• global.json selects the .NET SDK 10.0.300 feature band with latestPatch, and local builds, CI, and release packaging use that SDK selection as their single source of truth.
• The repository uses C# 14; runnable tools and test projects target net10.0, benchmarks target net10.0 and net48, and the product package contains exactly netstandard2.0, netstandard2.1, and net10.0 assets with no net8.0 asset.
• The net10.0 product asset is Native AOT-compatible and exposes the existing modern API surface without behavioral or source-level regressions, including the span, memory, and generic-math overloads.
• The analyzer, code-fix, and source-export projects use Roslyn 5.6.0 consistently; Release builds produce no RS1038, CS8032, or new Roslyn analyzer warnings, and analyzer and code-fix behavior remains covered by automated tests.
• Source export replaces Net8_0 with Net10_0, emits and validates the correct .NET 10 source, and preserves NetStandard2_0 as the default for the committed single-file distribution.
• Restore and build produce no NU1510 package-pruning warning, and the packed NuGet dependency groups contain only dependencies required by each target framework.
• User-facing framework documentation describes the resulting .NET 10 and .NET Standard support accurately and contains no stale .NET 8 SDK, target-framework, or support claims.
• The complete solution restores and builds without warnings in Release configuration on the pinned SDK, all automated tests pass, and a signed-equivalent package verification confirms the expected assemblies, symbols, Source Link data, documentation, icon, and target-framework dependency groups.

Technical Details

Use this target matrix:

Component	Target frameworks
Light.GuardClauses	netstandard2.0;netstandard2.1;net10.0
Main, analyzer, and source-export test projects	net10.0 by default
Source-export tool	net10.0
Source-validation harness	netstandard2.0;net10.0
Benchmarks	net10.0;net48
Analyzer and code-fix assemblies	netstandard2.0

Retain the main test project's optional TargetFrameworks.props override and enable IsAotCompatible for the net10.0 product asset. Existing NET8_0_OR_GREATER branches express the API capability boundary and are defined when targeting .NET 10; retain them rather than performing a mechanical rename to .NET 10 guards. Compile the repository with an explicit <LangVersion>14</LangVersion>. C# 14 changes overload resolution involving Span<T> conversions, so the existing string, span, memory, and generic-math tests must compile and pass without changing the public overload set unless a genuine ambiguity is found.

Pin Microsoft.CodeAnalysis.Analyzers, Microsoft.CodeAnalysis.CSharp, and Microsoft.CodeAnalysis.CSharp.Workspaces to 5.6.0, matching the compiler line in the .NET SDK 10.0.300 feature band. Remove the code-fix project's 4.11.0 VersionOverride and update the central explanatory comment, while preserving the compiler-only dependency boundary of Light.GuardClauses.InternalRoslynAnalyzers and the Workspaces dependency in Light.GuardClauses.InternalRoslynAnalyzers.CodeFixes. The source-export tool and its tests use the same Workspaces version, so syntax parsing, semantic analysis, analyzers, and code fixes all share one Roslyn line.

Account for .NET 10's framework-package pruning rather than disabling it. System.Collections.Immutable remains a package dependency only where it is required for the .NET Standard product and validation assets; net10.0 uses the framework assembly, and the source-export tool does not carry a redundant direct reference. Update the centrally managed Microsoft.Extensions.Configuration.* and System.Collections.Immutable packages to 10.0.9. Remove the explicit Microsoft.SourceLink.GitHub package because Source Link for GitHub is included and enabled by the .NET 10 SDK; retain the existing repository, symbol-package, and untracked-source properties and verify their packed output.

Replace SourceTargetFramework.Net8_0 with Net10_0. The parse-options factory uses C# 14 and defines the symbols required by the current source to select its .NET 10 branches: NET, NETCOREAPP, NET10_0, NET10_0_OR_GREATER, NET9_0_OR_GREATER, and NET8_0_OR_GREATER, but not the exact-version symbol NET8_0. Update modern-only imports, polyfill suppression, the validation project, validator mapping, configuration, and tests for the replacement target. Cover .NET 10 flattening, conditional branch selection, polyfill omission, and build validation. The committed configuration and Light.GuardClauses.SingleFile.cs remain the portable NetStandard2_0 output.

Update both GitHub Actions workflows to install the SDK through global-json-file: global.json. Remove the release workflow's independently configurable SDK-version input so an older compiler cannot load analyzers built against Roslyn 5.6.0. Preserve the existing restore/build/test and signed package flow otherwise.