feat(historian): advertise only the backend's aggregates under AggregateFunctions (#682)

IHistorianDataSource.SupportedAggregates (default: every HistoryAggregateType)
is the one authority for both ServerCapabilities/AggregateFunctions (i=2997) and
HistoryServerCapabilities/AggregateFunctions (i=11201) and for the up-front
BadAggregateNotSupported in HistoryRead-Processed. Gateway declares
AggregateModeMapper.Served (4), SqlServer/QuestDB AggregateFamilies.Served (17),
Null none. Only the folder references are trimmed; the SDK's calculator
factories stay so live AggregateFilter subscriptions keep working.

Co-Authored-By: Claude <noreply@anthropic.com>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests/Mapping/AggregateModeMapperTests.cs

@@ -38,6 +38,21 @@ public sealed class AggregateModeMapperTests
     public void Average_and_Count_are_not_supported(HistoryAggregateType a)
         => Assert.Throws<HistoryAggregateNotSupportedException>(() => AggregateModeMapper.ToRetrievalMode(a));
 
+    [Fact] // #682: the served (= advertised) set is exactly what the mapper maps, and the data source returns it
+    public void Served_is_exactly_the_mapped_members_and_the_data_source_declares_it()
+    {
+        Assert.Equal(
+            new[] { HistoryAggregateType.Minimum, HistoryAggregateType.Maximum, HistoryAggregateType.Total, HistoryAggregateType.TimeAverage }
+                .OrderBy(a => a),
+            AggregateModeMapper.Served.OrderBy(a => a));
+        foreach (var a in Enum.GetValues<HistoryAggregateType>().Where(a => !AggregateModeMapper.Served.Contains(a)))
+            Assert.Throws<HistoryAggregateNotSupportedException>(() => AggregateModeMapper.ToRetrievalMode(a));
+
+        var source = new GatewayHistorianDataSource(
+            new FakeHistorianGatewayClient(), Microsoft.Extensions.Logging.Abstractions.NullLogger<GatewayHistorianDataSource>.Instance);
+        Assert.Same(AggregateModeMapper.Served, source.SupportedAggregates);
+    }
+
     [Fact]
     public void Undefined_value_is_a_programming_error_not_a_not_supported()
         => Assert.Throws<ArgumentOutOfRangeException>(() => AggregateModeMapper.ToRetrievalMode((HistoryAggregateType)9999));

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Sql.Common.Tests/ProcessedReadTests.cs

@@ -19,4 +19,13 @@ public sealed class ProcessedReadTests
                 HistoryAggregateType.PercentGood, HistoryAggregateType.PercentBad, HistoryAggregateType.TimeAverage2,
                 HistoryAggregateType.Total2]);
     }
+
+    [Fact]
+    public void Served_is_exactly_the_members_with_a_family()
+    {
+        // #682: the advertised set and the dispatch are one definition — a member is served iff it has a family.
+        AggregateFamilies.Served.Count.ShouldBe(17);
+        foreach (var a in Enum.GetValues<HistoryAggregateType>())
+            AggregateFamilies.Served.Contains(a).ShouldBe(AggregateFamilies.FamilyOf(a) is not null, a.ToString());
+    }
 }