.NET: Foundry.Hosting IT - avoid MSB3026 in publish step

[Roger Barreto (rogerbarreto)]

Problem

CI run https://github.com/microsoft/agent-framework/actions/runs/25446865848/job/74653338378 failed in the dotnet-foundry-hosted-it job with:

error MSB3026: Could not copy "obj/Release/net10.0/Microsoft.Agents.AI.Abstractions.dll"
to "bin/Release/net10.0/Microsoft.Agents.AI.Abstractions.dll".
The process cannot access the file ... because it is being used by another process.

Root cause

Job run two MSBuild back to back on same tree:

1. Build Foundry hosted IT (and its deps) fill dotnet/src/<lib>/bin/Release/net10.0/*.dll. Helper process (VBCSCompiler) keep file handle open.
2. it-build-image.ps1 run dotnet publish for linux-musl-x64. Publish rebuild same lib DLL into same path. First build still hold handle. Boom: MSB3026.

Fix

In it-build-image.ps1 add explicit opt-in switch -UsePrebuiltProjectReferences. CI pass switch -> publish skip ProjectReference rebuild, eat prebuilt DLL in place. No file lock fight, no extra rebuild.

Local default = no switch = publish rebuild as normal. If user have stale obj/Release/net10.0 from old build, preflight throw clear error: tell user to pass switch OR delete old obj. No silent stale image.

CI keep prebuild step. Test --no-build need it too.

Bonus: fix flaky UT

Same PR run hit flaky test AgentFrameworkResponseHandlerTelemetryTests.CreateAsync_AlreadyInstrumentedAgent_EmitsSingleSpanPerRunAsync:

System.InvalidOperationException : Collection was modified; enumeration operation may not execute.

Test use plain List<Activity> for OTel AddInMemoryExporter. Exporter write from background Activity stop callback. Parallel test on same global ActivitySource feed every listener. Add race with assertion enumerate. Boom.

Fix: tiny ConcurrentActivityList : ICollection<Activity> wrapper. Lock add/enumerate. Test call Snapshot() for assertion (lock + copy). All 4 telemetry test use it.

Verification

Local repro on Windows, three path:

Path	Setup	Switch	Result
A	clean checkout	none	publish + docker build OK
B	prebuild done	-UsePrebuiltProjectReferences	skip rebuild, Abstractions.dll ticks unchanged before/after
C	prebuild done	none	preflight throw with recovery instructions

Telemetry UT: 30 isolated runs + 5 full assembly runs (216 test each), 0 fail.

[Copilot]

Pull request overview

Addresses intermittent dotnet publish failures (MSB3026 file-in-use) in the Foundry.Hosting integration-test container build by avoiding a second rebuild of referenced libraries when they were already built by the job’s prebuild step.

Changes:

• Updated it-build-image.ps1 to detect prebuilt library outputs and conditionally add -p:BuildProjectReferences=false to dotnet publish.
• Added workflow documentation explaining why the prebuild step exists and why publish is configured to avoid rebuilding project references.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
dotnet/tests/Foundry.Hosting.IntegrationTests/scripts/it-build-image.ps1	Adds conditional logic to skip ProjectReference rebuild during publish when prebuilt outputs exist.
.github/workflows/dotnet-build-and-test.yml	Documents the CI rationale for the publish behavior to prevent MSB3026 collisions.

[github-actions]

Automated Code Review

Reviewers: 4 | Confidence: 93% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Design Approach

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Automated review by rogerbarreto's agents