Add Aspire.Hosting.Dotnet integration package

[Karol Zadora-Przylecki (karolz-ms)]

Description

Adds Aspire.Hosting.Dotnet language integration package (making C# a sibling of Go/Python/Javascript). This is first part of "Project V2" workstream.

Fixes # (issue)

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No

[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://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 18442

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 18442"

[Copilot]

Pull request overview

This PR introduces a new experimental Aspire.Hosting.Dotnet language-integration package, making C# a sibling of the existing Go/Python/JavaScript language packages. It relocates CSharpAppResource and the AddCSharpApp extension methods out of core Aspire.Hosting, rebases CSharpAppResource from ProjectResource onto ExecutableResource (launched as dotnet run --project|--file), and extracts a shared internal IProjectLaunchDefaultsResource interface so the project-defaults wiring (Kestrel endpoints, launch-profile environment, ASPNETCORE URLs) can be reused by both core ProjectResource and the relocated CSharpAppResource. This is described as the first part of the "Project V2" workstream, with debug and publish/compute parity explicitly deferred.

Changes:

• New Aspire.Hosting.Dotnet package: CSharpAppResource (now an ExecutableResource) and AddCSharpApp overloads that build the dotnet run command line, validate the path/SDK version, and apply project defaults.
• New internal IProjectLaunchDefaultsResource abstraction implemented explicitly by both ProjectResource and CSharpAppResource; WithProjectDefaults and LaunchProfileExtensions generalized from ProjectResource to the interface/IResource.
• Blazor gateway and its tests migrated to CSharpAppResource; CSharpApp tests relocated to a new Aspire.Hosting.Dotnet.Tests project (no test coverage lost).

Reviewed changes

Copilot reviewed 28 out of 28 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Aspire.Hosting.Dotnet/CSharpAppHostingExtensions.cs	New relocated AddCSharpApp + polyglot dispatcher; builds dotnet run args and validation.
src/Aspire.Hosting.Dotnet/CSharpAppResource.cs	Rebased resource on ExecutableResource; explicit IProjectLaunchDefaultsResource state impl.
src/Aspire.Hosting/ApplicationModel/IProjectLaunchDefaultsResource.cs	New internal abstraction shared by core and the new package.
src/Aspire.Hosting/ApplicationModel/ProjectResource.cs	Implements the new interface via private fields + explicit members.
src/Aspire.Hosting/ProjectResourceBuilderExtensions.cs	WithProjectDefaults/helpers generalized to the interface; GetConfiguration uses .Single().
src/Shared/LaunchProfiles/LaunchProfileExtensions.cs	Signatures widened ProjectResource → IResource (complete and consistent).
src/Aspire.Hosting.Blazor/BlazorGatewayExtensions.cs	Gateway return/param types changed to CSharpAppResource.
src/Aspire.Hosting.Blazor/Aspire.Hosting.Blazor.csproj	Adds Aspire.Hosting.Dotnet project reference.
src/Aspire.Hosting.Dotnet/README.md	New package README following language-integration conventions.
tests/Aspire.Hosting.Dotnet.Tests/*	New test project with relocated + new coverage (args, metadata, debugging, launch-profile, guards).
tests/Aspire.Hosting.Tests/ProjectResourceTests.cs, ResourceCommandAnnotationTests.cs	Remove CSharpApp tests (relocated) and unused suppression pragma.
tests/Aspire.Hosting.Blazor.Tests/*	Gateways switched to AddCSharpApp; add Aspire.Hosting.Dotnet reference + suppression.
Aspire.slnx	Registers the new source and test projects.
docs/plans/project-v2-csharpprogram-watch.md	Planning doc describing the staged workstream and intentional deferrals.

[Karol Zadora-Przylecki (karolz-ms)]

Found 3 issues: 3 correctness/behavior regressions.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 2 comments.

[github-actions]

Retrying the failed CI jobs for this pull request from the CI run attempt. The rerun is being tracked in the rerun attempt.

[github-actions]

Retrying the failed CI jobs for this pull request from the CI run attempt. The rerun is being tracked in the rerun attempt.

[github-actions]

Retrying the failed CI jobs for this pull request from the CI run attempt. The rerun is being tracked in the rerun attempt.

[Alex Crome (afscrome)]

Probably not in scope for this PR, but would you expect the DotnetToolResource. (And maybe also EF) to move into this new Aspire.Hosting.Dotnet package?

[Copilot]

Pull request overview

Copilot reviewed 31 out of 31 changed files in this pull request and generated 3 comments.

[github-actions]

Retrying the failed CI jobs for this pull request from the CI run attempt. The rerun is being tracked in the rerun attempt.

[github-actions]

Retrying the failed CI jobs for this pull request from the CI run attempt. The rerun is being tracked in the rerun attempt.

[github-actions]

Retrying the failed CI jobs for this pull request from the CI run attempt. The rerun is being tracked in the rerun attempt.

[Copilot]

Pull request overview

Copilot reviewed 25 out of 25 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 25 out of 25 changed files in this pull request and generated 1 comment.

[github-actions]

Tests selector (audit mode)

The full test matrix and all jobs still run in audit mode. The tests and jobs below are what selective CI would run under enforcement.

Runs the full test matrix + all jobs (ALL) — run-all fallback: '.markdownlintignore' is neither Layer-1-owned nor matched by a Layer 2 rule

---

Selection computed for commit 5a85faf.

[Copilot]

Pull request overview

Copilot reviewed 25 out of 25 changed files in this pull request and generated no new comments.

[github-actions]

Retrying the failed CI jobs for this pull request from the CI run attempt. The rerun is being tracked in the rerun attempt.

[Karol Zadora-Przylecki (karolz-ms)]

I have done multiple rounds of AI code reviews and PR testing for this PR and believe all issues have been addressed.

[David Fowler (davidfowl)]

We need a playground sample that uses this new resoruce type.

[Karol Zadora-Przylecki (karolz-ms)]

We need a playground sample that uses this new resource type.

I will add the playground sample and new .NET Functions resource to the feature plan in my next PR.

[aspire-repo-bot]

⚠️ Documentation was required for this change, but a docs PR could not be drafted automatically.

Documentation was required and all content was authored and committed to branch docs/aspire-hosting-dotnet-integration on microsoft/aspire.dev, but the create_pull_request safe-output tool failed twice with "Pinned SHA ... failed to generate patch: ERR_SYSTEM: Git command failed with status 1" — a shallow-clone infrastructure error that prevented the draft PR from being opened.

Triggered signals (6): new_hosting_integration_project, new_package_added, new_public_type, integration_readme_changed, experimental_attribute_added, target_framework_changed — all pointing to the new Aspire.Hosting.Dotnet package and its AddDotnetProject / DotnetProjectResource public API.

Documentation authored (needs manual PR):

• src/frontend/src/content/docs/integrations/dotnet/dotnet-project-hosting.mdx — new reference page for AddDotnetProject (package install, C# & TypeScript examples, path types, file-based app prerequisites, dependencies, launch profile config, diagnostic suppression, comparison table)
• src/frontend/src/content/docs/diagnostics/aspiredotnetproject001.mdx — diagnostics reference for ASPIREDOTNETPROJECT001
• src/frontend/config/sidebar/integrations.topics.ts — sidebar entry for the new page

See the workflow run for details: https://github.com/microsoft/aspire/actions/runs/28605119390