.NET - Fix missing id on function_call_output in Foundry Hosting (#6246)

* Fix missing id on function_call_output in Foundry Hosting

The Foundry storage layer was rejecting responses with
"ID cannot be null or empty (Parameter 'id')" because
function_call_output items emitted by OutputConverter had no id on
the wire.

OutputItemFunctionToolCallOutput's public ctor only sets CallId and
Output; Id is read-only and only the SDK's internal ctor populates
it. OutputItemBuilder<T>.ApplyAutoStamps fills ResponseId and
AgentReference but not Id, so the itemId passed to
AddOutputItem<T>(itemId) was used only for event sequencing and the
serialized item went out with id=null.

Switch to stream.OutputItemFunctionCallOutput(callId, output), the
SDK convenience method that uses the internal ctor and stamps the
id. Add a regression test asserting the added/done events carry a
non-empty matching Id.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* ci: free disk space and relocate NuGet cache on ubuntu runners

The ubuntu-latest dotnet-build/test jobs were hitting No space left on device because the runner image only ships ~14 GB free on /. The full multi-TFM build plus the dotnet pack + console-app install-check exhausts that easily.

Add a reusable composite action .github/actions/free-runner-disk-space that runs on Linux runners only and:

* removes pre-installed toolchains we never use here (Android SDK, GHC/Haskell, CodeQL, PyPy, Ruby, Go, boost, vcpkg, etc.), prunes docker images, and disables swap (reclaims ~25-30 GB on /)

* relocates the NuGet package cache to /mnt/nuget via NUGET_PACKAGES env, since /mnt has ~75 GB free on hosted runners

Wire the action into the four ubuntu-touching jobs in dotnet-build-and-test.yml (dotnet-build, dotnet-test, dotnet-foundry-hosted-it, dotnet-test-functions). The action self-guards with runner.os == 'Linux' so the matrix legs that run on windows are unaffected.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: alliscode <25218250+alliscode@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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

@@ -121,6 +121,9 @@ jobs:
               python
               declarative-agents
 
+      - name: Free runner disk space
+        uses: ./.github/actions/free-runner-disk-space
+
       - name: Setup dotnet
         uses: actions/setup-dotnet@c2fa09f4bde5ebb9d1777cf28262a3eb3db3ced7 # v5.2.0
         with:
@@ -191,6 +194,9 @@ jobs:
               python
               declarative-agents
 
+      - name: Free runner disk space
+        uses: ./.github/actions/free-runner-disk-space
+
       # Start Cosmos DB Emulator for all integration tests and only for unit tests when CosmosDB changes happened)
       - name: Start Azure Cosmos DB Emulator
         if: ${{ runner.os == 'Windows' && (needs.paths-filter.outputs.cosmosDbChanges == 'true' || (github.event_name != 'pull_request' && matrix.integration-tests)) }}
@@ -365,6 +371,9 @@ jobs:
             dotnet
             python
 
+      - name: Free runner disk space
+        uses: ./.github/actions/free-runner-disk-space
+
       - name: Setup dotnet
         uses: actions/setup-dotnet@c2fa09f4bde5ebb9d1777cf28262a3eb3db3ced7 # v5.2.0
         with:
@@ -452,6 +461,9 @@ jobs:
             python
             declarative-agents
 
+      - name: Free runner disk space
+        uses: ./.github/actions/free-runner-disk-space
+
       - name: Setup dotnet
         uses: actions/setup-dotnet@c2fa09f4bde5ebb9d1777cf28262a3eb3db3ced7 # v5.2.0
         with: