Add opt-in Timeout to PurgeInstancesFilter for partial purge

src/Client/Core/PurgeInstancesFilter.cs

@@ -14,4 +14,14 @@
     DateTimeOffset? CreatedTo = null,
     IEnumerable<OrchestrationRuntimeStatus>? Statuses = null)
 {
+    /// <summary>
+    /// Gets or sets the maximum amount of time to spend purging instances in a single call.
+    /// If <c>null</c> (default), all matching instances are purged with no time limit.
+    /// When set, the purge stops accepting new instances after this duration elapses.
+    /// The value of <see cref="PurgeResult.IsComplete"/> depends on the backend implementation:
+    /// it may be <c>false</c> if the purge timed out, <c>true</c> if all instances were purged,
+    /// or <c>null</c> if the backend does not support reporting completion status.
+    /// Not all backends support this property; those that do not will ignore it.
+    /// </summary>
+    public TimeSpan? Timeout { get; init; }
 }

src/Client/Grpc/GrpcDurableTaskClient.cs

@@ -488,6 +488,19 @@ public override Task<PurgeResult> PurgeAllInstancesAsync(
             request.PurgeInstanceFilter.RuntimeStatus.AddRange(filter.Statuses.Select(x => x.ToGrpcStatus()));
         }
 
+        if (filter?.Timeout is not null)
+        {
+            if (filter.Timeout.Value <= TimeSpan.Zero)
+            {
+                throw new ArgumentOutOfRangeException(
+                    nameof(filter),
+                    filter.Timeout.Value,
+                    "Timeout must be a positive TimeSpan.");
+            }
+
+            request.PurgeInstanceFilter.Timeout = Google.Protobuf.WellKnownTypes.Duration.FromTimeSpan(filter.Timeout.Value);
+        }
+
         return this.PurgeInstancesCoreAsync(request, cancellation);
     }
 

src/Grpc/orchestrator_service.proto

@@ -517,6 +517,7 @@ message PurgeInstanceFilter {
     google.protobuf.Timestamp createdTimeFrom = 1;
     google.protobuf.Timestamp createdTimeTo = 2;
     repeated OrchestrationStatus runtimeStatus = 3;
+    google.protobuf.Duration timeout = 4;
 }
 
 message PurgeInstancesResponse {

test/Client/Grpc.Tests/GrpcDurableTaskClientTests.cs

@@ -127,5 +127,44 @@ public async Task ScheduleNewOrchestrationInstanceAsync_ValidDedupeStatus_DoesNo
         var exception = await act.Should().ThrowAsync<Exception>();
         exception.Which.Should().NotBeOfType<ArgumentException>();
     }
+
+    [Fact]
+    public async Task PurgeAllInstancesAsync_NegativeTimeout_ThrowsArgumentOutOfRangeException()
+    {
+        // Arrange
+        var client = this.CreateClient();
+        var filter = new PurgeInstancesFilter { Timeout = TimeSpan.FromSeconds(-1) };
+
+        // Act & Assert
+        Func<Task> act = async () => await client.PurgeAllInstancesAsync(filter);
+        var exception = await act.Should().ThrowAsync<ArgumentOutOfRangeException>();
+        exception.Which.Message.Should().Contain("Timeout must be a positive TimeSpan.");
+    }
+
+    [Fact]
+    public async Task PurgeAllInstancesAsync_ZeroTimeout_ThrowsArgumentOutOfRangeException()
+    {
+        // Arrange
+        var client = this.CreateClient();
+        var filter = new PurgeInstancesFilter { Timeout = TimeSpan.Zero };
+
+        // Act & Assert
+        Func<Task> act = async () => await client.PurgeAllInstancesAsync(filter);
+        var exception = await act.Should().ThrowAsync<ArgumentOutOfRangeException>();
+        exception.Which.Message.Should().Contain("Timeout must be a positive TimeSpan.");
+    }
+
+    [Fact]
+    public async Task PurgeAllInstancesAsync_PositiveTimeout_DoesNotThrowValidationError()
+    {
+        // Arrange
+        var client = this.CreateClient();
+        var filter = new PurgeInstancesFilter { Timeout = TimeSpan.FromSeconds(30) };
+
+        // Act & Assert - validation should pass; the call will fail at gRPC level, not validation
+        Func<Task> act = async () => await client.PurgeAllInstancesAsync(filter);
+        var exception = await act.Should().ThrowAsync<Exception>();
+        exception.Which.Should().NotBeOfType<ArgumentOutOfRangeException>();
+    }
 }