Per-kind override shape: each hook receives the pre-filtered nodesToProcess list (NodeHandles for nodes this manager claimed), iterates them, resolves handle.NodeId.Identifier to the driver-side full reference string, and dispatches to the right IHistoryProvider method. Write back into the outer results + errors slots at handle.Index (not the local loop counter — nodesToProcess is a filtered subset of nodesToRead, so indexing by the loop counter lands in the wrong slot for mixed-manager batches). WriteResult helper sets both results[i] AND errors[i]; this matters because MasterNodeManager merges them and leaving errors[i] at its default (BadHistoryOperationUnsupported) overrides a Good result with Unsupported on the wire — this was the subtle failure mode that masked a correctly-constructed HistoryData response during debugging. Failure-isolation per node: NotSupportedException from a driver that doesn't implement a particular HistoryProvider method translates to BadHistoryOperationUnsupported in that slot; generic exceptions log and surface BadInternalError; unresolvable NodeIds get BadNodeIdUnknown. The batch continues unconditionally.
Aggregate mapping: MapAggregate translates ObjectIds.AggregateFunction_Average / Minimum / Maximum / Total / Count to the driver's HistoryAggregateType enum. Null for anything else (e.g. TimeAverage, Interpolative) so the handler surfaces BadAggregateNotSupported at the batch level — per Part 13, one unsupported aggregate means the whole request fails since ReadProcessedDetails carries one aggregate list for all nodes. BuildHistoryData wraps driver DataValueSnapshots as Opc.Ua.HistoryData in an ExtensionObject; BuildHistoryEvent wraps HistoricalEvents as Opc.Ua.HistoryEvent with the canonical BaseEventType field list (EventId, SourceName, Message, Severity, Time, ReceiveTime — the order OPC UA clients that didn't customize the SelectClause expect). ToDataValue preserves null SourceTimestamp (Galaxy historian rows often carry only ServerTimestamp) — synthesizing a SourceTimestamp would lie about actual sample time.
Two address-space changes were required to make the stack dispatch reach the per-kind hooks at all: (1) historized variables get AccessLevels.HistoryRead added to their AccessLevel byte — the base's early-gate check on (variable.AccessLevel & HistoryRead != 0) was rejecting requests before our override ever ran; (2) the driver-root folder gets EventNotifiers.HistoryRead | SubscribeToEvents so HistoryReadEvents can target it (the conventional pattern for alarm-history browse against a driver-owned object). Document the 'set both bits' requirement inline since it's not obvious from the surface API.
OpcHistoryReadResult alias: Opc.Ua.HistoryReadResult (service-layer per-node result) collides with Core.Abstractions.HistoryReadResult (driver-side samples + continuation point) by type name; the alias 'using OpcHistoryReadResult = Opc.Ua.HistoryReadResult' keeps the override signatures unambiguous and the test project applies the mirror pattern for its stub driver impl.
Tests — DriverNodeManagerHistoryMappingTests (12 new Category=Unit cases): MapAggregate translates each supported aggregate NodeId via reflection-backed theory (guards against the stack renaming AggregateFunction_* constants); returns null for unsupported NodeIds (TimeAverage) and null input; BuildHistoryData wraps samples with correct DataValues + SourceTimestamp preservation; BuildHistoryEvent emits the 6-element BaseEventType field list in canonical order (regression guard for a future 'respect the client's SelectClauses' change); null SourceName / Message translate to empty-string Variants (nullable-Variant refactor trap); ToDataValue preserves StatusCode + both timestamps; ToDataValue leaves SourceTimestamp at default when the snapshot omits it. HistoryReadIntegrationTests (5 new Category=Integration): drives a real OPC UA client Session.HistoryRead against a fake HistoryDriver through the running server. Covers raw round-trip (verifies per-node DataValue ordering + values); processed with Average aggregate (captures the driver's received aggregate + interval, asserting MapAggregate routed correctly); unsupported aggregate (TimeAverage → BadAggregateNotSupported); at-time (forwards the per-timestamp list); events (BaseEventType field list shape, SelectClauses populated to satisfy the stack's filter validator). Server.Tests Unit: 55 pass / 0 fail (43 prior + 12 new mapping). Server.Tests Integration: 14 pass / 0 fail (9 prior + 5 new history). Full solution build clean, 0 errors.
lmx-followups.md #1 updated to 'DONE (PRs 35 + 38)' with two explicit deferred items: continuation-point plumbing (driver returns null today so pass-through is fine) and per-SelectClause evaluation in HistoryReadEvents (clients with custom field selections get the canonical BaseEventType layout today).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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