EndpointReference evaluation should wait on missing AllocatedEndpoint

[karolz-ms]

Fixes #12823

This was my mistake when implementing context-aware EndpointReference evaluation

[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 -- 13074

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 13074"

[Copilot]

Pull Request Overview

This PR fixes an issue where EndpointReference evaluation would return null immediately when an AllocatedEndpoint for a specific network context was missing, instead of properly waiting for it to be allocated. The fix ensures that a ValueSnapshot is created and added to the collection for the missing network context, so that the evaluation will wait (as intended) until the endpoint is allocated.

Key Changes:

• Modified EndpointReferenceExpression.GetValueAsync() to create a new NetworkEndpointSnapshot with an empty ValueSnapshot when no snapshot exists for the requested network context, enabling proper waiting behavior
• Added a test to verify that expression resolution waits (and times out) when an allocated endpoint for a specific network context is missing

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Aspire.Hosting/ApplicationModel/EndpointReference.cs	Fixed the logic to create and add a NetworkEndpointSnapshot with an empty ValueSnapshot when none exists for the network context, instead of returning null immediately
tests/Aspire.Hosting.Tests/ExpressionResolverTests.cs	Added test ExpressionResolutionShouldWaitOnMissingAllocatedEndpoint and helper class TestHostResource to verify the fix works correctly

[karolz-ms]

/backport to release/13.0

[github-actions]

Started backporting to release/13.0: https://github.com/dotnet/aspire/actions/runs/19548391113

[github-actions]

@karolz-ms backporting to "release/13.0" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Patch format detection failed.
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!