.NET: Fix filter combine logic for ChatHistoryMemoryProvider (#4501)

* Fix filter combine logic for ChatHistoryMemoryProvider

* Replace var with explicit types in filter building code and test

Address PR review nit: use explicit types instead of var for better
readability in the filter-building logic and the new combined filter
compilation test.

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

* Fix style issues

---------

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

Author: westey-m

dotnet/src/Microsoft.Agents.AI/Memory/ChatHistoryMemoryProvider.cs

@@ -350,36 +350,38 @@ private async Task<string> SearchTextAsync(string userQuestion, ChatHistoryMemor
         string? userId = searchScope.UserId;
         string? sessionId = searchScope.SessionId;
 
-        Expression<Func<Dictionary<string, object?>, bool>>? filter = null;
+        // Build a combined filter using a single shared parameter to avoid expression tree
+        // scoping issues when multiple filters are combined with AndAlso.
+        ParameterExpression parameter = Expression.Parameter(typeof(Dictionary<string, object?>), "x");
+        Expression? filterBody = null;
+
         if (applicationId != null)
         {
-            filter = x => (string?)x[ApplicationIdField] == applicationId;
+            filterBody = RebindFilterBody(x => (string?)x[ApplicationIdField] == applicationId, parameter);
         }
 
         if (agentId != null)
         {
-            Expression<Func<Dictionary<string, object?>, bool>> agentIdFilter = x => (string?)x[AgentIdField] == agentId;
-            filter = filter == null ? agentIdFilter : Expression.Lambda<Func<Dictionary<string, object?>, bool>>(
-                Expression.AndAlso(filter.Body, agentIdFilter.Body),
-                filter.Parameters);
+            Expression body = RebindFilterBody(x => (string?)x[AgentIdField] == agentId, parameter);
+            filterBody = filterBody == null ? body : Expression.AndAlso(filterBody, body);
         }
 
         if (userId != null)
         {
-            Expression<Func<Dictionary<string, object?>, bool>> userIdFilter = x => (string?)x[UserIdField] == userId;
-            filter = filter == null ? userIdFilter : Expression.Lambda<Func<Dictionary<string, object?>, bool>>(
-                Expression.AndAlso(filter.Body, userIdFilter.Body),
-                filter.Parameters);
+            Expression body = RebindFilterBody(x => (string?)x[UserIdField] == userId, parameter);
+            filterBody = filterBody == null ? body : Expression.AndAlso(filterBody, body);
         }
 
         if (sessionId != null)
         {
-            Expression<Func<Dictionary<string, object?>, bool>> sessionIdFilter = x => (string?)x[SessionIdField] == sessionId;
-            filter = filter == null ? sessionIdFilter : Expression.Lambda<Func<Dictionary<string, object?>, bool>>(
-                Expression.AndAlso(filter.Body, sessionIdFilter.Body),
-                filter.Parameters);
+            Expression body = RebindFilterBody(x => (string?)x[SessionIdField] == sessionId, parameter);
+            filterBody = filterBody == null ? body : Expression.AndAlso(filterBody, body);
         }
 
+        Expression<Func<Dictionary<string, object?>, bool>>? filter = filterBody != null
+            ? Expression.Lambda<Func<Dictionary<string, object?>, bool>>(filterBody, parameter)
+            : null;
+
         // Use search to find relevant messages
         var searchResults = collection.SearchAsync(
             queryText,
@@ -467,6 +469,27 @@ public void Dispose()
 
     private string? SanitizeLogData(string? data) => this._enableSensitiveTelemetryData ? data : "<redacted>";
 
+    /// <summary>
+    /// Rebinds a filter expression's body to use the specified shared parameter,
+    /// replacing the original lambda parameter so that multiple filters can be safely
+    /// combined with <see cref="Expression.AndAlso(Expression, Expression)"/>.
+    /// </summary>
+    private static Expression RebindFilterBody(
+        Expression<Func<Dictionary<string, object?>, bool>> filter,
+        ParameterExpression sharedParameter)
+    {
+        return new ParameterReplacer(filter.Parameters[0], sharedParameter).Visit(filter.Body);
+    }
+
+    /// <summary>
+    /// An <see cref="ExpressionVisitor"/> that replaces one <see cref="ParameterExpression"/> with another.
+    /// </summary>
+    private sealed class ParameterReplacer(ParameterExpression original, ParameterExpression replacement) : ExpressionVisitor
+    {
+        protected override Expression VisitParameter(ParameterExpression node)
+            => node == original ? replacement : base.VisitParameter(node);
+    }
+
     /// <summary>
     /// Represents the state of a <see cref="ChatHistoryMemoryProvider"/> stored in the <see cref="AgentSession.StateBag"/>.
     /// </summary>

dotnet/tests/Microsoft.Agents.AI.UnitTests/Memory/ChatHistoryMemoryProviderTests.cs

@@ -454,6 +454,77 @@ public async Task InvokedAsync_CreatesFilter_WhenSearchScopeProvidedAsync()
             Times.Once);
     }
 
+    [Fact]
+    public async Task InvokedAsync_CombinedFilterCanBeCompiled_WhenMultipleScopeFiltersProvidedAsync()
+    {
+        // Arrange
+        // This test reproduces a bug where combining multiple scope filters
+        // (e.g. userId + sessionId) produces an expression tree with dangling
+        // ParameterExpression references that fails at compile time.
+        ChatHistoryMemoryProviderOptions providerOptions = new()
+        {
+            SearchTime = ChatHistoryMemoryProviderOptions.SearchBehavior.BeforeAIInvoke,
+            MaxResults = 2,
+            ContextPrompt = "Here is the relevant chat history:\n"
+        };
+
+        ChatHistoryMemoryProviderScope searchScope = new()
+        {
+            ApplicationId = "app1",
+            AgentId = "agent1",
+            SessionId = "session1",
+            UserId = "user1"
+        };
+
+        System.Linq.Expressions.Expression<Func<Dictionary<string, object?>, bool>>? capturedFilter = null;
+
+        this._vectorStoreCollectionMock
+            .Setup(c => c.SearchAsync(
+                It.IsAny<string>(),
+                It.IsAny<int>(),
+                It.IsAny<VectorSearchOptions<Dictionary<string, object?>>>(),
+                It.IsAny<CancellationToken>()))
+            .Callback((string query, int maxResults, VectorSearchOptions<Dictionary<string, object?>> options, CancellationToken ct) =>
+                capturedFilter = options.Filter)
+            .Returns(ToAsyncEnumerableAsync(new List<VectorSearchResult<Dictionary<string, object?>>>()));
+
+        ChatHistoryMemoryProvider provider = new(
+            this._vectorStoreMock.Object,
+            TestCollectionName,
+            1,
+            _ => new ChatHistoryMemoryProvider.State(searchScope, searchScope),
+            options: providerOptions);
+
+        ChatMessage requestMsg = new(ChatRole.User, "requesting relevant history");
+        AIContextProvider.InvokingContext invokingContext = new(s_mockAgent, new TestAgentSession(), new AIContext { Messages = new List<ChatMessage> { requestMsg } });
+
+        // Act
+        await provider.InvokingAsync(invokingContext, CancellationToken.None);
+
+        // Assert - The filter must be compilable and executable without expression tree scoping errors
+        Assert.NotNull(capturedFilter);
+        Func<Dictionary<string, object?>, bool> compiledFilter = capturedFilter!.Compile();
+
+        Dictionary<string, object?> matchingRecord = new()
+        {
+            ["ApplicationId"] = "app1",
+            ["AgentId"] = "agent1",
+            ["SessionId"] = "session1",
+            ["UserId"] = "user1"
+        };
+
+        Dictionary<string, object?> nonMatchingRecord = new()
+        {
+            ["ApplicationId"] = "app1",
+            ["AgentId"] = "agent1",
+            ["SessionId"] = "other-session",
+            ["UserId"] = "user1"
+        };
+
+        Assert.True(compiledFilter(matchingRecord));
+        Assert.False(compiledFilter(nonMatchingRecord));
+    }
+
     [Theory]
     [InlineData(false, false, 2)]
     [InlineData(true, false, 2)]