.Net: fix: address three static analysis issues (audio format, text search, KernelProcess) (#13925)

Fixes #13922

## Problem
Three static analysis issues identified by PVS-Studio in the .NET
codebase:

1. **`ClientCore.ChatCompletion.cs`** — `GetAudioOutputMimeType`
contained a duplicate `ChatOutputAudioFormat.Wav` check (lines 985 and
1000) making the second branch unreachable. The `Aac` audio format
supported by the OpenAI SDK was silently unhandled, causing a
`NotSupportedException` at runtime.

2. **`TextSearchStore.cs`** — `GetTextSearchResultsAsync` assigned a
LINQ expression to a `results` variable (deferred execution) that was
never iterated. The return statement duplicated the projection. The
unused variable was dead code.

3. **`KernelProcess.cs`** — The constructor accepted a `threads`
parameter but never assigned it to the `Threads` property, silently
discarding all threads passed by callers.

## Solution
1. Replace the second `Wav` branch with an `Aac` branch and update the
error message to list `'aac'` as a supported format.
2. Reuse the `results` variable in the `return` statement instead of
duplicating the `Select` projection.
3. Assign the `threads` parameter to `this.Threads` when it is not null.

## Testing
- Changes are logic-only with no new external dependencies.
- Existing unit tests for `OpenAIChatCompletionService` and
`TextSearchStore` continue to apply.
- No new runtime behaviour is introduced for the `Wav` fix (it was
already handled earlier in the method); `Aac` now maps to `"audio/aac"`
as expected.

---------

Co-authored-by: octo-patch <[email protected]>
Co-authored-by: Roger Barreto <[email protected]>

dotnet/src/Connectors/Connectors.OpenAI.UnitTests/Services/OpenAIChatCompletionServiceTests.cs

@@ -1981,6 +1981,16 @@ public sealed class OpenAIChatCompletionServiceTests : IDisposable
         { "{\"voice\":\"echo\",\"format\":\"opus\"}", "{\"voice\":\"echo\",\"format\":\"opus\"}" },
     };
 
+    public static TheoryData<ChatOutputAudioFormat, string> AudioMimeTypeMappingData => new()
+    {
+        { ChatOutputAudioFormat.Wav, "audio/wav" },
+        { ChatOutputAudioFormat.Aac, "audio/aac" },
+        { ChatOutputAudioFormat.Mp3, "audio/mp3" },
+        { ChatOutputAudioFormat.Opus, "audio/opus" },
+        { ChatOutputAudioFormat.Flac, "audio/flac" },
+        { ChatOutputAudioFormat.Pcm16, "audio/pcm16" },
+    };
+
 #pragma warning disable CS8618, CA1812
     private sealed class MathReasoning
     {
@@ -2191,6 +2201,56 @@ public sealed class OpenAIChatCompletionServiceTests : IDisposable
         // The ExpiresAt value is converted to a DateTime object, so we can't directly compare it to the Unix timestamp
     }
 
+    [Theory]
+    [MemberData(nameof(AudioMimeTypeMappingData))]
+    public async Task ItMapsAudioOutputFormatToCorrectMimeTypeAsync(ChatOutputAudioFormat format, string expectedMimeType)
+    {
+        // Arrange
+        var chatCompletion = new OpenAIChatCompletionService(modelId: "gpt-4o", apiKey: "NOKEY", httpClient: this._httpClient);
+
+        var responseJson = """
+        {
+            "model": "gpt-4o",
+            "choices": [
+                {
+                    "message": {
+                        "role": "assistant",
+                        "content": "This is the text response.",
+                        "audio": {
+                            "data": "AQIDBA=="
+                        }
+                    },
+                    "finish_reason": "stop"
+                }
+            ],
+            "usage": {
+                "prompt_tokens": 10,
+                "completion_tokens": 20,
+                "total_tokens": 30
+            }
+        }
+        """;
+
+        this._messageHandlerStub.ResponseToReturn = new HttpResponseMessage(HttpStatusCode.OK)
+        { Content = new StringContent(responseJson) };
+
+        var settings = new OpenAIPromptExecutionSettings
+        {
+            Modalities = ChatResponseModalities.Text | ChatResponseModalities.Audio,
+            Audio = new ChatAudioOptions(ChatOutputAudioVoice.Alloy, format)
+        };
+
+        // Act
+        var result = await chatCompletion.GetChatMessageContentAsync(this._chatHistoryForTest, settings);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(2, result.Items.Count);
+        var audioContent = result.Items[1] as AudioContent;
+        Assert.NotNull(audioContent);
+        Assert.Equal(expectedMimeType, audioContent.MimeType);
+    }
+
     [Fact]
     public async Task GetChatMessageContentsThrowsExceptionWithEmptyBinaryContentAsync()
     {

dotnet/src/Connectors/Connectors.OpenAI/Core/ClientCore.ChatCompletion.cs

@@ -1006,9 +1006,9 @@ internal partial class ClientCore
             return "audio/opus";
         }
 
-        if (audioOptions.OutputAudioFormat == ChatOutputAudioFormat.Wav)
+        if (audioOptions.OutputAudioFormat == ChatOutputAudioFormat.Aac)
         {
-            return "audio/wav";
+            return "audio/aac";
         }
 
         if (audioOptions.OutputAudioFormat == ChatOutputAudioFormat.Flac)
@@ -1021,7 +1021,7 @@ internal partial class ClientCore
             return "audio/pcm16";
         }
 
-        throw new NotSupportedException($"Unsupported audio output format '{audioOptions.OutputAudioFormat}'. Supported formats are 'wav', 'mp3', 'opus', 'flac' and 'pcm16'.");
+        throw new NotSupportedException($"Unsupported audio output format '{audioOptions.OutputAudioFormat}'. Supported formats are 'wav', 'mp3', 'opus', 'aac', 'flac' and 'pcm16'.");
     }
 
     private OpenAIChatMessageContent CreateChatMessageContent(ChatMessageRole chatRole, string content, ChatToolCall[] toolCalls, FunctionCallContent[]? functionCalls, IReadOnlyDictionary<string, object?>? metadata, string? authorName)

dotnet/src/Experimental/Process.Abstractions/KernelProcess.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using Microsoft.SemanticKernel.Process.Internal;
 using Microsoft.SemanticKernel.Process.Models;
 
@@ -50,5 +51,9 @@ public sealed record KernelProcess : KernelProcessStepInfo
         Verify.NotNullOrWhiteSpace(state.Name);
 
         this.Steps = [.. steps];
+        if (threads is not null)
+        {
+            this.Threads = threads.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
+        }
     }
 }

dotnet/src/Experimental/Process.UnitTests/KernelProcessTests.cs

@@ -0,0 +1,60 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using Xunit;
+
+namespace Microsoft.SemanticKernel.Process.UnitTests;
+
+/// <summary>
+/// Unit tests for <see cref="KernelProcess"/>.
+/// </summary>
+public class KernelProcessTests
+{
+    /// <summary>
+    /// Verifies that the <see cref="KernelProcess"/> constructor assigns the supplied
+    /// <c>threads</c> dictionary to the <see cref="KernelProcess.Threads"/> property
+    /// instead of silently discarding it.
+    /// </summary>
+    [Fact]
+    public void Constructor_AssignsThreadsParameter_WhenProvided()
+    {
+        // Arrange
+        var state = new KernelProcessState(name: "TestProcess", version: "v1", id: "p1");
+        var steps = new List<KernelProcessStepInfo>();
+        var threads = new Dictionary<string, KernelProcessAgentThread>
+        {
+            ["main"] = new KernelProcessAgentThread { ThreadName = "main", ThreadId = "t-1" },
+            ["aux"] = new KernelProcessAgentThread { ThreadName = "aux", ThreadId = "t-2" },
+        };
+
+        // Act
+        var process = new KernelProcess(state, steps, edges: null, threads: threads);
+
+        // Assert
+        Assert.Equal(2, process.Threads.Count);
+        Assert.True(process.Threads.ContainsKey("main"));
+        Assert.True(process.Threads.ContainsKey("aux"));
+        Assert.Equal("t-1", process.Threads["main"].ThreadId);
+        Assert.Equal("t-2", process.Threads["aux"].ThreadId);
+    }
+
+    /// <summary>
+    /// Verifies that the <see cref="KernelProcess"/> constructor leaves
+    /// <see cref="KernelProcess.Threads"/> as an empty dictionary when the
+    /// <c>threads</c> argument is null.
+    /// </summary>
+    [Fact]
+    public void Constructor_DefaultsThreadsToEmptyDictionary_WhenNull()
+    {
+        // Arrange
+        var state = new KernelProcessState(name: "TestProcess", version: "v1", id: "p2");
+        var steps = new List<KernelProcessStepInfo>();
+
+        // Act
+        var process = new KernelProcess(state, steps, edges: null, threads: null);
+
+        // Assert
+        Assert.NotNull(process.Threads);
+        Assert.Empty(process.Threads);
+    }
+}

dotnet/src/SemanticKernel.Core/Data/TextSearchStore/TextSearchStore.cs

@@ -202,12 +202,7 @@ public sealed partial class TextSearchStore<TKey> : ITextSearch, IDisposable
         var searchResult = await this.SearchInternalAsync(query, searchOptions, cancellationToken).ConfigureAwait(false);
 
         var results = searchResult.Select(x => new TextSearchResult(x.Text ?? string.Empty) { Name = x.SourceName, Link = x.SourceLink });
-        return new(searchResult.Select(x =>
-            new TextSearchResult(x.Text ?? string.Empty)
-            {
-                Name = x.SourceName,
-                Link = x.SourceLink
-            }).ToAsyncEnumerable());
+        return new(results.ToAsyncEnumerable());
     }
 
     /// <inheritdoc/>

dotnet/src/SemanticKernel.UnitTests/Data/TextSearchStoreTests.cs

@@ -245,6 +245,37 @@ public class TextSearchStoreTests
         Assert.Equal("Sample text", actualResultsList[0]);
     }
 
+    [Fact]
+    public async Task GetTextSearchResultsAsyncReturnsTextSearchResults()
+    {
+        // Arrange
+        var mockResults = new List<VectorSearchResult<TextSearchStore<string>.TextRagStorageDocument<string>>>
+        {
+            new(new TextSearchStore<string>.TextRagStorageDocument<string>
+            {
+                Text = "Sample text",
+                SourceName = "src-name",
+                SourceLink = "src-link",
+            }, 0.9f)
+        };
+
+        this._recordCollectionMock
+            .Setup(r => r.SearchAsync("query", 3, It.IsAny<VectorSearchOptions<TextSearchStore<string>.TextRagStorageDocument<string>>>(), It.IsAny<CancellationToken>()))
+            .Returns(mockResults.ToAsyncEnumerable());
+
+        using var store = new TextSearchStore<string>(this._vectorStoreMock.Object, "testCollection", 128);
+
+        // Act
+        var actualResults = await store.GetTextSearchResultsAsync("query");
+
+        // Assert
+        var actualResultsList = await actualResults.Results.ToListAsync();
+        Assert.Single(actualResultsList);
+        Assert.Equal("Sample text", actualResultsList[0].Value);
+        Assert.Equal("src-name", actualResultsList[0].Name);
+        Assert.Equal("src-link", actualResultsList[0].Link);
+    }
+
     [Fact]
     public async Task SearchAsyncWithHybridReturnsSearchResults()
     {