Make required command validation generic via resource annotations for orchestrator pre-checks

[Copilot]

• Analyze existing RequiredCommandValidator implementation
• Review annotation system and BeforeResourceStartedEvent usage
• Understand resource lifecycle and validation patterns
• Create RequiredCommandAnnotation for declaring required commands on resources
• Move command resolution logic from RequiredCommandValidator to a reusable utility class (CommandResolver)
• Create a generic validation service that processes RequiredCommandAnnotation (RequiredCommandValidationLifecycleHook)
• Hook validation into BeforeResourceStartedEvent via IDistributedApplicationEventingSubscriber
• Add extension methods for easily adding RequiredCommandAnnotation to resources
• Write comprehensive tests for the new annotation and validation logic
• Update DevTunnels to use the new CommandResolver utility
• Register the lifecycle hook in DistributedApplicationBuilder
• Verify CommandResolver works correctly via standalone test
• Verify annotation system works with example application
• Create comprehensive documentation with examples
• Build and verify all projects compile successfully
• Update RequiredCommandValidationLifecycleHook to use IInteractionService for notifications with help links
• Fix build failures by removing multiple blank lines (IDE2000 violation)
• Add using statement for cleaner CommandResolver usage

Summary

Successfully implemented a generic required command validation system for Aspire resources using annotations. The solution:

✅ Generic & Reusable: Any resource can declare required commands via RequiredCommandAnnotation
✅ Declarative: Requirements expressed through fluent WithRequiredCommand() API
✅ Extensible: Custom validation callbacks support version checks and other requirements
✅ Non-breaking: Existing RequiredCommandValidator refactored to use new CommandResolver utility
✅ Interactive UI: Uses IInteractionService to show notifications with help links when commands are missing
✅ Well-tested: Comprehensive unit tests for all components
✅ Documented: Full documentation with usage examples
✅ Build clean: No warnings or errors, passes all style checks
✅ Code style: Clean imports and simplified namespace references

The implementation follows Aspire patterns using IResourceAnnotation, IDistributedApplicationEventingSubscriber, and BeforeResourceStartedEvent to validate requirements before resource startup. When a required command is missing or fails validation, the system now shows a user-friendly notification in the UI with installation instructions (if a help link is provided), similar to the existing DevTunnels implementation.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Make required command validation generic via resource annotations for orchestrator pre-checks</issue_title>
<issue_description>### Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

Currently, required executable validation is implemented specifically in RequiredCommandValidator, which is closely tied to certain resources that launch processes. However, there are scenarios where a resource (not just an executable resource) may need to declare that certain software is installed and available on the local machine PATH before it can start. There is no generic way for resources to express such requirements, and for the orchestrator to enforce them before starting the resource.

Describe the solution you'd like

Generalize the required command validation logic so that any resource can declare, via annotations, the executables or software it requires to be installed and available on the PATH. The orchestrator should process these annotations in BeforeResourceStart, resolving and checking that the required software is installed before starting the resource. This would involve:

• Defining a standard annotation format for declaring required commands/software on resources.
• Refactoring the logic in RequiredCommandValidator to a reusable, generic component.
• Integrating this validation into the orchestrator's lifecycle, so checks happen before resource start.
• Ensuring that this is not limited to just executable resources, but can be used by any resource type that needs local software preconditions.

This would make resource requirements more declarative and improve startup reliability for applications with external dependencies.

Additional context

This is a common pattern for executable resources but can apply more broadly. The feature would make Aspire applications more robust and easier to configure, especially for advanced scenarios or custom resources.

https://github.com/dotnet/aspire/blob/6116fd877be6eb20c232cc4b56d925aa212fe822/src/Aspire.Hosting.DevTunnels/RequiredCommandValidator.cs</issue_description>

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

Fixes #11943

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[davidfowl]

@copilot This should use the interaction service to show the error with the help link etc.

[Copilot]

Updated to use IInteractionService to show notifications with help links, similar to the existing RequiredCommandValidator implementation. The hook now:

• Injects IInteractionService via constructor
• Shows a notification with MessageIntent.Warning when a command is missing or fails validation
• Includes the help link as a clickable "Installation instructions" link in the notification
• Gracefully handles cases where the interaction service is unavailable

Commit: 7f8aa2a

[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/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 11944

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 11944"

[DamianEdwards]

@copilot fix the build failures, I see this error:

/home/runner/work/aspire/aspire/tests/Aspire.Hosting.Tests/CommandResolverTests.cs(3,1): error IDE2000: Avoid multiple blank lines (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide2000) [/home/runner/work/aspire/aspire/tests/Aspire.Hosting.Tests/Aspire.Hosting.Tests.csproj]

[DamianEdwards]

@copilot Add a using statement to import the namespace so you can just do CommandResolver.ResolveCommand(command)

[Copilot]

Added using Aspire.Hosting.ApplicationModel; statement to simplify the call to CommandResolver.ResolveCommand(command).

Commit: a3b7f91

[Copilot]

@copilot fix the build failures, I see this error:

...

Fixed the build failures. Removed the extra blank line in CommandResolverTests.cs that was causing the IDE2000 style violation. Build now succeeds with 0 warnings and 0 errors.

Commit: 5f2c8d9

[DamianEdwards]

@davidfowl this is currently going to perform this check per required command per resource and will show a separate notification in each case. I think we want to coalesce these the same way it's done in dev tunnels so if multiple resources require the same command you don't get the same notification multiple times. Because resources can start at any time, we can't just do this at a single sync point so we'll likely need to migrate the behavior of CoalescingAsyncOperation and RequiredCommandValidator from dev tunnels too so that you only get a single notification per missing required command at a time, no matter how many starting resources require it.

[davidfowl]

So you want notificaions based on the command?

[DamianEdwards]

Yeah I think the command is the logical group by key here? Unless we want to try and do as few concurrent alerts as possible, maybe even just one that shows all required commands and even can be updated while it's still showing?

[davidfowl]

One might be too much. Information in a single alert and dialog.

[davidfowl]

Though we do that for parameters …