docs(xmldoc): fill missing XML docs + strip tracking-ID comments across src

Adds <summary>/<param>/<returns>/<inheritdoc> where missing and removes
project bookkeeping IDs (task/tracking refs) from shipped code comments,
so the docs read cleanly and CommentChecker is quiet except for known
false positives (PLC/protocol terms, event/IEqualityComparer inheritdoc).
Doc/comment-only; no logic changed; solution builds clean.

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/IHistorianDataSource.cs

@@ -28,6 +28,7 @@ public interface IHistorianDataSource : IDisposable
     /// <param name="endUtc">The end of the time range in UTC.</param>
     /// <param name="maxValuesPerNode">The maximum number of values to return per node.</param>
     /// <param name="cancellationToken">A cancellation token that can be used to cancel the operation.</param>
+    /// <returns>The raw historical samples for the tag over the requested range.</returns>
     Task<HistoryReadResult> ReadRawAsync(
         string fullReference,
         DateTime startUtc,
@@ -46,6 +47,7 @@ public interface IHistorianDataSource : IDisposable
     /// <param name="interval">The interval for bucketing samples.</param>
     /// <param name="aggregate">The aggregation function to apply to each bucket.</param>
     /// <param name="cancellationToken">A cancellation token that can be used to cancel the operation.</param>
+    /// <returns>One aggregated sample per interval bucket over the requested range.</returns>
     Task<HistoryReadResult> ReadProcessedAsync(
         string fullReference,
         DateTime startUtc,
@@ -63,6 +65,7 @@ public interface IHistorianDataSource : IDisposable
     /// <param name="fullReference">The full reference of the tag to read.</param>
     /// <param name="timestampsUtc">The list of timestamps to read values at.</param>
     /// <param name="cancellationToken">A cancellation token that can be used to cancel the operation.</param>
+    /// <returns>One sample per requested timestamp, in the same order as <paramref name="timestampsUtc"/>.</returns>
     Task<HistoryReadResult> ReadAtTimeAsync(
         string fullReference,
         IReadOnlyList<DateTime> timestampsUtc,
@@ -77,7 +80,7 @@ public interface IHistorianDataSource : IDisposable
     ///     Note on parameter types — <paramref name="maxEvents"/> is <see cref="int"/> (not
     ///     <see cref="uint"/>) so callers can pass <c>0</c> or a negative value as a "use the
     ///     backend's default cap" sentinel; see <c>WonderwareHistorianClient</c> /
-    ///     <c>HistorianDataSource</c> and Core.Abstractions-006 for the rationale. The sibling
+    ///     <c>HistorianDataSource</c> for the rationale. The sibling
     ///     <see cref="ReadRawAsync"/> / <see cref="ReadProcessedAsync"/> use
     ///     <c>uint maxValuesPerNode</c> because their OPC UA HistoryRead surface has no
     ///     equivalent "use default" sentinel.
@@ -85,8 +88,7 @@ public interface IHistorianDataSource : IDisposable
     ///     This surface declares <see cref="ReadAtTimeAsync"/> and <see cref="ReadEventsAsync"/>
     ///     as required members — a server-side historian owns the full read surface, unlike
     ///     <see cref="IHistoryProvider"/> where the same two methods are optional default-impl
-    ///     methods so legacy drivers can stay raw-only. The asymmetry is intentional
-    ///     (Core.Abstractions-008).
+    ///     methods so legacy drivers can stay raw-only. The asymmetry is intentional.
     /// </remarks>
     /// <param name="sourceName">The source name to filter events, or null to return events from all sources.</param>
     /// <param name="startUtc">The start of the time range in UTC.</param>
@@ -96,9 +98,10 @@ public interface IHistorianDataSource : IDisposable
     ///     default cap. When the backend cap truncates the result, implementations MUST set
     ///     <see cref="HistoricalEventsResult.ContinuationPoint"/> to a non-null token so
     ///     callers can detect truncation and page — a null continuation point means all
-    ///     matching events were returned. (Core.Abstractions-009.)
+    ///     matching events were returned.
     /// </param>
     /// <param name="cancellationToken">A cancellation token that can be used to cancel the operation.</param>
+    /// <returns>The matching historical event records, with a continuation point if the result was truncated.</returns>
     Task<HistoricalEventsResult> ReadEventsAsync(
         string? sourceName,
         DateTime startUtc,
@@ -110,5 +113,6 @@ public interface IHistorianDataSource : IDisposable
     ///     Point-in-time health snapshot for diagnostics and dashboards. Pure
     ///     observation; never blocks on backend I/O.
     /// </summary>
+    /// <returns>The current health snapshot for the historian backend.</returns>
     HistorianHealthSnapshot GetHealthSnapshot();
 }

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/IHistorizationOutbox.cs

@@ -16,6 +16,7 @@ public interface IHistorizationOutbox : IDisposable
     /// <summary>Appends <paramref name="entry"/> to the tail of the durable buffer.</summary>
     /// <param name="entry">The value record to buffer.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     ValueTask AppendAsync(HistorizationOutboxEntry entry, CancellationToken ct);
 
     /// <summary>
@@ -24,6 +25,7 @@ public interface IHistorizationOutbox : IDisposable
     /// </summary>
     /// <param name="max">Maximum number of entries to return; must be positive.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>Up to <paramref name="max"/> oldest un-acked entries in FIFO order.</returns>
     ValueTask<IReadOnlyList<HistorizationOutboxEntry>> PeekBatchAsync(int max, CancellationToken ct);
 
     /// <summary>
@@ -32,9 +34,11 @@ public interface IHistorizationOutbox : IDisposable
     /// </summary>
     /// <param name="id">The <see cref="HistorizationOutboxEntry.Id"/> to ack.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     ValueTask RemoveAsync(Guid id, CancellationToken ct);
 
     /// <summary>Current number of un-acked entries held in the buffer.</summary>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>The current number of un-acked entries in the buffer.</returns>
     ValueTask<int> CountAsync(CancellationToken ct);
 }

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/NullHistorianDataSource.cs

@@ -9,7 +9,7 @@ namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 ///     <para>
 ///         A process-wide singleton via <see cref="Instance"/> (private ctor): it carries no state
 ///         and is immutable, so one shared instance is safe to assign as the node-manager's
-///         <c>HistorianDataSource</c> default until the Host wires a real source post-start (Task 5).
+///         <c>HistorianDataSource</c> default until the Host wires a real source post-start.
 ///     </para>
 /// </summary>
 public sealed class NullHistorianDataSource : IHistorianDataSource
@@ -55,10 +55,7 @@ public sealed class NullHistorianDataSource : IHistorianDataSource
         int maxEvents,
         CancellationToken cancellationToken) => Task.FromResult(EmptyEvents);
 
-    /// <summary>
-    ///     Returns a fully-disabled snapshot — no connections open, every counter zero, every nullable
-    ///     field null, no cluster nodes. Pure; never blocks.
-    /// </summary>
+    /// <inheritdoc />
     public HistorianHealthSnapshot GetHealthSnapshot() => new(
         TotalQueries: 0,
         TotalSuccesses: 0,