Merge branch 'main' into features/foundry-hosting-it-msb3026-fix

CI publish step: gate the BuildProjectReferences=false fast-path on an explicit -UsePrebuiltProjectReferences switch (passed by the workflow) instead of marker detection. Adds a preflight error when stale obj/Release/net10.0 outputs would cause CS0579, with actionable recovery instructions.

Telemetry UT flake: AgentFrameworkResponseHandlerTelemetryTests was using a plain List<Activity> for OTel's InMemoryExporter. The exporter writes from background Activity completion callbacks while parallel tests on the same global ActivitySource feed every listener, racing against the assertion's enumeration and throwing 'Collection was modified'. Replaced with a small thread-safe ConcurrentActivityList that locks add/enumerate and returns a snapshot for assertions.

.github/workflows/dotnet-build-and-test.yml

@@ -379,6 +379,14 @@ jobs:
       # We rebuild and push the test container image on every IT run so framework code changes
       # are picked up; the image tag is content-hashed across the test container source AND its
       # framework project references, so identical content is a no-op push.
+      #
+      # `-UsePrebuiltProjectReferences` opts into the no-rebuild fast path: publish skips
+      # rebuilding ProjectReferences and consumes the DLLs the prior "Build Foundry hosted IT
+      # (and its deps)" step already produced. This avoids MSB3026 ("file is being used by
+      # another process") collisions caused by the previous build's shared-compilation server
+      # still holding file handles to those DLLs. Safe in CI because the prebuild step ran in
+      # the same job against the same source. Do not remove the prebuild step (the subsequent
+      # `dotnet test --no-build` step depends on it too).
       - name: Build and push Foundry Hosted Agents test container
         id: build-foundry-hosted-image
         shell: pwsh
@@ -388,7 +396,7 @@ jobs:
           if ([string]::IsNullOrWhiteSpace($registry)) {
             throw "IT_HOSTED_AGENT_REGISTRY not set in the integration environment."
           }
-          & "${{ github.workspace }}/dotnet/tests/Foundry.Hosting.IntegrationTests/scripts/it-build-image.ps1" -Registry $registry | Tee-Object -FilePath $env:GITHUB_ENV -Append
+          & "${{ github.workspace }}/dotnet/tests/Foundry.Hosting.IntegrationTests/scripts/it-build-image.ps1" -Registry $registry -UsePrebuiltProjectReferences | Tee-Object -FilePath $env:GITHUB_ENV -Append
 
       - name: Run Foundry Hosted Agents Integration Tests
         shell: pwsh

dotnet/tests/Foundry.Hosting.IntegrationTests/scripts/it-build-image.ps1

@@ -41,7 +41,14 @@ param(
 
     [string] $Repository = "foundry-hosting-it",
 
-    [string] $TestContainerProject = "dotnet/tests/Foundry.Hosting.IntegrationTests.TestContainer"
+    [string] $TestContainerProject = "dotnet/tests/Foundry.Hosting.IntegrationTests.TestContainer",
+
+    # Explicit opt-in for the no-rebuild fast path. CI sets this after running the
+    # "Build Foundry hosted IT (and its deps)" step, which guarantees the prebuilt
+    # library DLLs match current source. Off by default so local invocations always
+    # let publish rebuild ProjectReferences and never produce an image whose tag is
+    # computed from current source while the contents come from a stale build.
+    [switch] $UsePrebuiltProjectReferences
 )
 
 $ErrorActionPreference = "Stop"
@@ -100,7 +107,60 @@ if (Test-Path $out) {
     Remove-Item -Recurse -Force $out
 }
 
-dotnet publish $TestContainerProject -c Release -f net10.0 -r linux-musl-x64 --self-contained false -o $out --tl:off | Out-Host
+# Conditionally tell publish to skip rebuilding ProjectReferences and consume the
+# prebuilt library DLLs in place. This avoids two failure modes that arise when
+# the CI workflow runs a `dotnet build` of the same library projects immediately
+# before this script:
+#   1) MSB3026 "file is being used by another process" when publish's MSBuild
+#      tries to overwrite src/<lib>/bin/Release/net10.0/<lib>.dll while the
+#      previous build's shared-compilation server still holds a file handle.
+#   2) Publish needlessly rebuilding identical managed (RID-agnostic) library
+#      DLLs that prebuild already produced.
+# Gated on -UsePrebuiltProjectReferences (a strict opt-in) instead of marker
+# detection, because a developer machine may have a stale Release build of the
+# libraries from days ago; using those would silently produce an image whose
+# content is older than the source the tag is computed from.
+$publishExtraArgs = @()
+if ($UsePrebuiltProjectReferences) {
+    Write-Host "-UsePrebuiltProjectReferences: skipping ProjectReference rebuild." -ForegroundColor DarkGray
+    $publishExtraArgs += "-p:BuildProjectReferences=false"
+} else {
+    # Preflight: in default (rebuild) mode, publish propagates RuntimeIdentifier=linux-musl-x64
+    # to library ProjectReferences and writes their intermediates to a RID-suffixed obj path
+    # (e.g. obj/Release/net10.0/linux-musl-x64/). DefaultItemExcludes follows the new
+    # IntermediateOutputPath, so any *.AssemblyInfo.cs left in obj/Release/net10.0/ from a
+    # prior `dotnet build` is no longer excluded and gets picked up by the **/*.cs Compile
+    # glob, producing CS0579 "duplicate attribute" errors. Detect that state up front and
+    # tell the user exactly how to recover.
+    $staleObjProbes = @(
+        "dotnet/src/Microsoft.Agents.AI.Foundry.Hosting/obj/Release/net10.0",
+        "dotnet/src/Microsoft.Agents.AI.Foundry/obj/Release/net10.0",
+        "dotnet/src/Microsoft.Agents.AI/obj/Release/net10.0",
+        "dotnet/src/Microsoft.Agents.AI.Abstractions/obj/Release/net10.0"
+    )
+    $stale = @($staleObjProbes | Where-Object { Test-Path (Join-Path $_ "*.AssemblyInfo.cs") })
+    if ($stale.Count -gt 0) {
+        $msg = @(
+            "Detected prior Release/net10.0 build outputs in:"
+            ($stale | ForEach-Object { "  - $_" })
+            ""
+            "Publish would propagate -r linux-musl-x64 to those ProjectReferences and the"
+            "leftover obj/Release/net10.0/*.AssemblyInfo.cs files would cause CS0579 duplicate"
+            "attribute errors. Pick one:"
+            "  (a) Pass -UsePrebuiltProjectReferences (skips ProjectReference rebuild and"
+            "      uses the existing src/<lib>/bin/Release/net10.0/*.dll outputs in place)."
+            "      Only safe when you know those DLLs match current source - this is the path"
+            "      CI uses immediately after its 'Build Foundry hosted IT (and its deps)' step."
+            "  (b) Remove the stale obj/Release trees, e.g.:"
+            "        Remove-Item -Recurse -Force dotnet/src/Microsoft.Agents.AI*/obj/Release"
+            "      and re-run."
+        ) -join "`n"
+        throw $msg
+    }
+    Write-Host "Letting publish build ProjectReferences (pass -UsePrebuiltProjectReferences in CI to skip)." -ForegroundColor DarkGray
+}
+
+dotnet publish $TestContainerProject -c Release -f net10.0 -r linux-musl-x64 --self-contained false -o $out @publishExtraArgs --tl:off | Out-Host
 if ($LASTEXITCODE -ne 0) {
     throw "dotnet publish failed with exit code $LASTEXITCODE."
 }

dotnet/tests/Microsoft.Agents.AI.Foundry.Hosting.UnitTests/AgentFrameworkResponseHandlerTelemetryTests.cs

@@ -37,7 +37,7 @@ public class AgentFrameworkResponseHandlerTelemetryTests
     public async Task CreateAsync_DefaultAgent_EmitsInvokeAgentSpanAsync()
     {
         // Arrange
-        var activities = new List<Activity>();
+        var activities = new ConcurrentActivityList();
         using var tracerProvider = Sdk.CreateTracerProviderBuilder()
             .AddSource(ResponsesSourceName)
             .AddInMemoryExporter(activities)
@@ -56,7 +56,7 @@ public class AgentFrameworkResponseHandlerTelemetryTests
         await foreach (var _ in handler.CreateAsync(request, context, CancellationToken.None)) { }
 
         // Assert — filter by agent name to isolate this test's span from any parallel test spans
-        var mySpan = Assert.Single(activities.Where(a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name"))).ToList());
+        var mySpan = Assert.Single(activities.Snapshot().Where(a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name"))).ToList());
         Assert.Equal("invoke_agent", mySpan.GetTagItem("gen_ai.operation.name"));
         Assert.NotNull(mySpan.GetTagItem("gen_ai.agent.id"));
     }
@@ -65,7 +65,7 @@ public class AgentFrameworkResponseHandlerTelemetryTests
     public async Task CreateAsync_KeyedAgent_EmitsInvokeAgentSpanAsync()
     {
         // Arrange
-        var activities = new List<Activity>();
+        var activities = new ConcurrentActivityList();
         using var tracerProvider = Sdk.CreateTracerProviderBuilder()
             .AddSource(ResponsesSourceName)
             .AddInMemoryExporter(activities)
@@ -84,7 +84,7 @@ public class AgentFrameworkResponseHandlerTelemetryTests
         await foreach (var _ in handler.CreateAsync(request, context, CancellationToken.None)) { }
 
         // Assert — filter by agent name to isolate this test's span
-        var mySpan = Assert.Single(activities.Where(a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name"))).ToList());
+        var mySpan = Assert.Single(activities.Snapshot().Where(a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name"))).ToList());
         Assert.Equal("invoke_agent", mySpan.GetTagItem("gen_ai.operation.name"));
     }
 
@@ -95,8 +95,8 @@ public class AgentFrameworkResponseHandlerTelemetryTests
         // If ApplyOpenTelemetry double-wraps, an extra span would appear on ResponsesSourceName.
         // If it correctly skips wrapping, only the pre-wrap's unique source emits spans.
         var preWrapSource = Guid.NewGuid().ToString();
-        var preWrapActivities = new List<Activity>();
-        var responsesActivities = new List<Activity>();
+        var preWrapActivities = new ConcurrentActivityList();
+        var responsesActivities = new ConcurrentActivityList();
 
         using var preWrapProvider = Sdk.CreateTracerProviderBuilder()
             .AddSource(preWrapSource)
@@ -125,18 +125,19 @@ public class AgentFrameworkResponseHandlerTelemetryTests
         await foreach (var _ in handler.CreateAsync(request, context, CancellationToken.None)) { }
 
         // Assert — pre-wrap source emits exactly 1 span (agent ran)
-        Assert.Single(preWrapActivities);
-        Assert.Equal("invoke_agent", preWrapActivities[0].GetTagItem("gen_ai.operation.name"));
+        var preWrapSnapshot = preWrapActivities.Snapshot();
+        Assert.Single(preWrapSnapshot);
+        Assert.Equal("invoke_agent", preWrapSnapshot[0].GetTagItem("gen_ai.operation.name"));
 
         // ResponsesSourceName emits 0 spans — ApplyOpenTelemetry skipped wrapping the pre-instrumented agent
-        Assert.DoesNotContain(responsesActivities, a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name")));
+        Assert.DoesNotContain(responsesActivities.Snapshot(), a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name")));
     }
 
     [Fact]
     public async Task CreateAsync_DefaultAgent_SpanDisplayNameContainsAgentNameAsync()
     {
         // Arrange
-        var activities = new List<Activity>();
+        var activities = new ConcurrentActivityList();
         using var tracerProvider = Sdk.CreateTracerProviderBuilder()
             .AddSource(ResponsesSourceName)
             .AddInMemoryExporter(activities)
@@ -155,7 +156,7 @@ public class AgentFrameworkResponseHandlerTelemetryTests
         await foreach (var _ in handler.CreateAsync(request, context, CancellationToken.None)) { }
 
         // Assert — display name follows "invoke_agent {Name}({Id})" convention; filter by agent name to isolate
-        var mySpan = Assert.Single(activities.Where(a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name"))).ToList());
+        var mySpan = Assert.Single(activities.Snapshot().Where(a => TelemetryTestAgent.AgentName.Equals(a.GetTagItem("gen_ai.agent.name"))).ToList());
         Assert.Contains("invoke_agent", mySpan.DisplayName, StringComparison.Ordinal);
         Assert.Contains(TelemetryTestAgent.AgentName, mySpan.DisplayName, StringComparison.Ordinal);
     }
@@ -231,4 +232,35 @@ public class AgentFrameworkResponseHandlerTelemetryTests
     }
 
     private sealed class TelemetryAgentSession : AgentSession;
+
+    /// <summary>
+    /// Thread-safe <see cref="ICollection{Activity}"/> used by OTel's InMemoryExporter to capture
+    /// activities emitted on globally-listened sources. Required because the exporter writes into
+    /// the supplied collection from background Activity completion callbacks while the test thread
+    /// may be enumerating it for assertions, and other tests in the same assembly may emit on the
+    /// same source concurrently. A plain <see cref="List{Activity}"/> trips
+    /// "Collection was modified; enumeration operation may not execute." in that scenario.
+    /// </summary>
+    private sealed class ConcurrentActivityList : ICollection<Activity>
+    {
+        private readonly List<Activity> _items = new();
+        private readonly object _gate = new();
+
+        public int Count { get { lock (this._gate) { return this._items.Count; } } }
+        public bool IsReadOnly => false;
+
+        public void Add(Activity item) { lock (this._gate) { this._items.Add(item); } }
+        public void Clear() { lock (this._gate) { this._items.Clear(); } }
+        public bool Contains(Activity item) { lock (this._gate) { return this._items.Contains(item); } }
+        public void CopyTo(Activity[] array, int arrayIndex) { lock (this._gate) { this._items.CopyTo(array, arrayIndex); } }
+        public bool Remove(Activity item) { lock (this._gate) { return this._items.Remove(item); } }
+
+        public Activity[] Snapshot()
+        {
+            lock (this._gate) { return this._items.ToArray(); }
+        }
+
+        public IEnumerator<Activity> GetEnumerator() => ((IEnumerable<Activity>)this.Snapshot()).GetEnumerator();
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => this.GetEnumerator();
+    }
 }