fix(historian): #687 review — one bounded re-read instead of failing, raw budget unclamped, exclusive forward end

- M1/M2: when the 1 ms pre-window margin (boundary row + stored samples, e.g. a
  >16-sample tie cluster at start-1ms / lastTs-1ms) uses up the cap + 16 budget,
  re-read ONCE asking for cap + m + 16 (m = pre-window rows seen); fail
  BadTooManyOperations only if the re-read is still short because of them. The
  raw budget is no longer clamped at the gateway default ceiling (AVEVA always
  emits the boundary row, so page sizes 999,985-1,000,000 always came back
  short); the #688 clamp stays on the per-sample aggregate path only.
- Merge trap: NumValuesPerNode 0 => int.MaxValue, never through the clamp.
- L3: the forward end is exclusive ([start, end), the IHistorianDataSource
  contract); a point read (start == end, the tie-cluster over-fetch) inclusive.
- RequestStartFor never goes before the Unix epoch (#686's walk-back floor).
- L4 (docs): an Uncertain native row for an all-NULL interval is unverified live.

CLAUDE.md

@@ -1364,7 +1364,7 @@ historian tagname, which is the tag's driver `FullName`.
 
 The server dispatches all OPC UA HistoryRead to the registered `IHistorianDataSource` — the
 `GatewayHistorianDataSource` read client when enabled, else the `NullHistorianDataSource` default
-(historized nodes return `GoodNoData` for Raw/AtTime — Processed is `BadAggregateNotSupported` since #682). Supported variants: Raw (⚠️ #687, client-visible: Gateway raw reads no longer return AVEVA's synthetic start-boundary row — asked from 1 ms early with `NumValuesPerNode + 16` rows and filtered by timestamp, the #681 classification — so an empty window is `GoodNoData`, not a fabricated value at StartTime; `ReturnBounds` is ignored on every backend), Processed
+(historized nodes return `GoodNoData` for Raw/AtTime — Processed is `BadAggregateNotSupported` since #682). Supported variants: Raw (⚠️ #687, client-visible: Gateway raw reads no longer return AVEVA's synthetic start-boundary row — asked from 1 ms early (epoch-floored) with `NumValuesPerNode + 16` rows (unclamped; 0 ⇒ `int.MaxValue`) and filtered by timestamp — so an empty window is `GoodNoData`, not a fabricated value at StartTime; the forward end is now exclusive (a point read inclusive); pre-window rows that crowd the budget trigger ONE re-read with room for them, else `BadTooManyOperations`; `ReturnBounds` is ignored on every backend), Processed
 (backend-dependent: SqlServer/QuestDb serve seventeen; Gateway twelve = `GatewayHistorianDataSource.ServedAggregates` — ⚠️ #681, client-visible: the ten per-sample ones (Average, Count, Min/Max, Range, Start/End/Delta, Min/MaxActualTime) are evaluated from RAW gateway reads by the shared `Sql.Common` evaluator — identical to the SQL backends, Calculated bits, interval-start stamps, #677 reverse; Min/Max are no longer AVEVA modes, the read moves every raw sample of the window (a month of 1 Hz ⇒ `BadTooManyOperations` at the default `MaxTimeWeightedRawRows` cap), and every gateway stream is consumed to completion (an abandoned one makes the gateway evict its shared historian session) — plus TimeAverage/Total via AVEVA modes (interval-start stamped + Calculated; ⚠️ #685: AVEVA's extra pre-window row is dropped ⇒ one row per interval in `[Start, End)`, and an Uncertain (opc 64) interval keeps its value as `UncertainDataSubNormal` — AVEVA's TWA excludes NULL-gap time where the SQL backends bridge it; per-interval values still need gateway fix historiangw#27); the other time-weighted five stay `BadAggregateNotSupported` because the gateway has no prior-sample read for Part 13 bounds; `docs/Historian.md` §Aggregate set), and AtTime over historized variable nodes; Events over
 alarm-owning equipment-folder event-notifier nodes. Reads are ungated (served from any redundancy node);
 authorization uses the standard `AccessLevels.HistoryRead` bit set at materialization.