Implement publisher advertisement and CLI integration

[mitchdenny]

Introduce publisher advertisement events and enhance CLI functionality to retrieve publishers. Update the application to handle different execution modes and improve backchannel connection handling.

We now fire an event when the CLI asks the AppHost for publishers to advertise themselves. This is currently hooked up inside the AddPublisher method, and this will probably be where publishers declare the arguments that they accept and their mapping to options.

At the moment the GetPublishersAsync RPC call just returns an array of strings but once I start working on option mapping it will be a richer set of objects that are returned.

aspire-build-prompting.mp4

[Copilot]

Pull Request Overview

This pull request implements publisher advertisement events and enhances CLI integration by adding new publisher-related functionality, updating the backchannel connection, and adjusting Azure provisioning modes. Key changes include:

• Adding new tests and publisher advertisement events to support publisher discovery.
• Updating backchannel and CLI components to enable fetching publishers via RPC calls.
• Adjusting execution mode checks in Azure infrastructure and provisioners.

Reviewed Changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/Aspire.Hosting.Tests/Backchannel/AppHostBackchannelTests.cs	Introduces tests for backchannel connectivity, ping responses, resource streaming, and publisher requests.
src/Aspire.Hosting/Publishing/PublisherAdvertisementEvent.cs	Implements publisher advertisement event and related types.
src/Aspire.Cli/Program.cs	Adds CLI integration for retrieving publishers asynchronously.
src/Aspire.Hosting/Backchannel/AppHostRpcTarget.cs	Updates to include a new GetPublishersAsync method using publisher advertisement events.
src/Aspire.Cli/Backchannel/AppHostBackchannel.cs	Adds IDisposable support and integrates process management for backchannel connections.
src/Aspire.Hosting/PublisherDistributedApplicationBuilderExtensions.cs	Subscribes to publisher advertisement events when adding a publisher.
src/Aspire.Hosting.Azure.*	Adjusts execution mode conditions in Azure infrastructure and provisioners.
playground/publishers/Publishers.AppHost/docker-compose.yaml	Updates connection string for SQL Server configuration.
src/Aspire.Hosting.Azure/AzureResourcePreparer.cs	Skips Azure resource preparation in inspect mode.
src/Aspire.Cli/DotNetCliRunner.cs	Updates backchannel connection startup to include process information.

Files not reviewed (1)

• playground/publishers/Publishers.AppHost/Properties/launchSettings.json: Language not supported

[davidfowl]

Conflcits!

[maddymontaquila]

Fit n finish things either for this PR or a follow up issue -

• When you don't specify a publisher, we shouldn't show the warning that " ' ' " wasn't found
• When you do specify, it should prob be "Finding publisher..." or "Getting publisher..." instead of available ones because it makes me feel like you're searching for the whole list again
• are you planning on caching so we don't have to look up every time?