Phase 3 PR 38 — DriverNodeManager HistoryRead override (LMX #1 finish). Wires the OPC UA HistoryRead service through CustomNodeManager2's four protected per-kind hooks — HistoryReadRawModified / HistoryReadProcessed / HistoryReadAtTime / HistoryReadEvents — each dispatching to the driver's IHistoryProvider capability (PR 35 for ReadAtTime + ReadEvents on top of PR 19-era ReadRaw + ReadProcessed). Was the last missing piece of the end-to-end HistoryRead path: PR 10 + PR 11 shipped the Galaxy.Host IPC contracts, PR 35 surfaced them on IHistoryProvider + GalaxyProxyDriver, but no server-side handler bridged OPC UA HistoryRead service requests onto the capability interface. Now it does.

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>

docs/v2/lmx-followups.md

@@ -7,24 +7,50 @@ Basic256Sha256 endpoints and alarms are observable through
 specific before the stack can fully replace the v1 deployment, in
 rough priority order.
 
-## 1. Proxy-side `IHistoryProvider` for `ReadAtTime` / `ReadEvents`
-
-**Status**: Capability surface complete (PR 35). OPC UA HistoryRead service-handler
-wiring in `DriverNodeManager` remains as the next step; integration-test still
-pending.
+## 1. Proxy-side `IHistoryProvider` for `ReadAtTime` / `ReadEvents` — **DONE (PRs 35 + 38)**
 
 PR 35 extended `IHistoryProvider` with `ReadAtTimeAsync` + `ReadEventsAsync`
 (default throwing implementations so existing impls keep compiling), added the
-`HistoricalEvent` + `HistoricalEventsResult` records to
-`Core.Abstractions`, and implemented both methods in `GalaxyProxyDriver` on top
-of the PR 10 / PR 11 IPC messages. Wire-to-domain mapping (`ToHistoricalEvent`)
-is unit-tested for field fidelity, null-preservation, and `DateTimeKind.Utc`.
+`HistoricalEvent` + `HistoricalEventsResult` records to `Core.Abstractions`,
+and implemented both methods in `GalaxyProxyDriver` on top of the PR 10 / PR 11
+IPC messages.
 
-**Remaining**:
-- `DriverNodeManager` wires the new capability methods onto `HistoryRead`
-  `AtTime` + `Events` service handlers.
-- Integration test: OPC UA client calls `HistoryReadAtTime` / `HistoryReadEvents`,
-  value flows through IPC to the Host's `HistorianDataSource`, back to the client.
+PR 38 wired the OPC UA HistoryRead service-handler through
+`DriverNodeManager` by overriding `CustomNodeManager2`'s four per-kind hooks —
+`HistoryReadRawModified` / `HistoryReadProcessed` / `HistoryReadAtTime` /
+`HistoryReadEvents`. Each walks `nodesToProcess`, resolves the driver-side
+full reference from `NodeId.Identifier`, dispatches to the right
+`IHistoryProvider` method, and populates the paired results + errors lists
+(both must be set — the MasterNodeManager merges them and a Good result with
+an unset error slot serializes as `BadHistoryOperationUnsupported` on the
+wire). Historized variables gain `AccessLevels.HistoryRead` so the stack
+dispatches; the driver root folder gains `EventNotifiers.HistoryRead` so
+`HistoryReadEvents` can target it.
+
+Aggregate translation uses a small `MapAggregate` helper that handles
+`Average` / `Minimum` / `Maximum` / `Total` / `Count` (the enum surface the
+driver exposes) and returns null for unsupported aggregates so the handler
+can surface `BadAggregateNotSupported`. Raw+Processed+AtTime wrap driver
+samples as `HistoryData` in an `ExtensionObject`; Events emits a
+`HistoryEvent` with the standard BaseEventType field list (EventId /
+SourceName / Message / Severity / Time / ReceiveTime) — custom
+`SelectClause` evaluation is an explicit follow-up.
+
+**Tests**:
+
+- `DriverNodeManagerHistoryMappingTests` — 12 unit cases pinning
+  `MapAggregate`, `BuildHistoryData`, `BuildHistoryEvent`, `ToDataValue`.
+- `HistoryReadIntegrationTests` — 5 end-to-end cases drive a real OPC UA
+  client (`Session.HistoryRead`) against a fake `IHistoryProvider` driver
+  through the running stack. Covers raw round-trip, processed with Average
+  aggregate, unsupported aggregate → `BadAggregateNotSupported`, at-time
+  timestamp forwarding, and events field-list shape.
+
+**Deferred**:
+- Continuation-point plumbing via `Session.Save/RestoreHistoryContinuationPoint`.
+  Driver returns null continuations today so the pass-through is fine.
+- Per-`SelectClause` evaluation in HistoryReadEvents — clients that send a
+  custom field selection currently get the standard BaseEventType layout.
 
 ## 2. Write-gating by role — **DONE (PR 26)**