Merge fix/669-event-continuation: event HistoryRead continuation points + open-ended reads (#669)

docs/Historian.md

@@ -618,6 +618,23 @@ are disposed when the session closes). Resuming an unknown / evicted / released
 `BadContinuationPointInvalid`. `releaseContinuationPoints` drops the stored cursors without reading
 data.
 
+### Continuation-point paging (Events) (#669)
+
+A capped event read (`NumValuesPerNode > 0`) pages exactly like Raw, with one difference: the trigger is the **source's
+truncation flag** (`HistoricalEventsResult.ContinuationPoint != null`), never the page count, so a cap-sized page the source
+says is complete carries no continuation point. `NumValuesPerNode == 0` stays unbounded and never pages.
+
+- The cursor is `(source, next start, end, boundary skip, cap)` in the same session-bound store as Raw (flagged as an events
+  cursor — a Raw point presented to an events read, or the reverse, is `BadContinuationPointInvalid`). The next page reads from
+  the last event's `EventTimeUtc` **inclusive** and drops the events at that timestamp already emitted.
+- A tie cluster larger than the cap is paged within by over-fetching the half-open window `[T, T + resolution)` up to
+  `MaxTieClusterOverfetch`; beyond that bound the node answers `BadHistoryOperationUnsupported` (raise the bound).
+- **Tie exactness depends on the backend.** SqlServer and QuestDB order by `(EventTimeUtc, EventId)`, so the skip count is exact.
+  The Gateway backend has no stable intra-timestamp order (and only a truncation flag), so ties at a page boundary are
+  best-effort there.
+- Reverse event reads (`start > end`) are not paged server-side; no continuation point is issued for them.
+- No session on the request (in-process callers) degrades to single-shot, as for Raw.
+
 ### Total aggregate
 
 The OPC UA `Total` aggregate is **supported** over the HistorianGateway backend. The gateway exposes a
@@ -760,8 +777,8 @@ result never has both.
 
 `[start, end)` by `EventTimeUtc`; **a reversed window (`end < start`) is swapped and returned ascending**. A null `sourceName` means all
 sources, otherwise `SourceName = @source`. Ordered `(EventTimeUtc, EventId)` ascending. A bounded read fetches `maxEvents + 1` rows and
-returns a non-null continuation point when the extra row exists; the node manager does not currently issue or resume event
-continuation points, so a client-capped read returns only the first page.
+returns a non-null continuation point when the extra row exists; the node manager turns that flag into an OPC UA continuation
+point (see [Continuation-point paging (Events)](#continuation-point-paging-events-669)).
 
 ### Aggregates (Processed reads)