fix(historian): map Boolean historization to Int2, not degenerate Int1 (#441)

The historian's Int1 analog-tag creation path is server-degenerate:
EnsureTags(Int1) stores an unusable stub (live-probed on the deployed
2023 R2 historian; root-caused + documented gateway-side in
HistorianGateway #11 / PR #16). HistorianTypeMapper mapped
DriverDataType.Boolean -> HistorianDataType.Int1, so Boolean historized
tags failed auto-provisioning.

Map Boolean -> Int2 instead (store 0/1). Int2 is a proven-creatable
analog type, and the value-write path already sends every value as a
double on WriteLiveValues regardless of tag type, so Boolean 0.0/1.0
round-trips cleanly. Both Float and Int2 are supported, so a
pre-existing Float Boolean tag retypes cleanly on its next deploy.

- HistorianTypeMapper: Boolean => Int2 (+ remarks)
- Unit pins: HistorianTypeMapperTests, GatewayTagProvisionerTests
  (Boolean_definition_carries_explicit_Int2_presence)
- Live gate: EnsureTags_boolean_sandbox_provisions_as_Int2 (was _Int1);
  retype probe reframed Float->Int2 (drops the dead Int1 leg)
- Docs: docs/Historian.md 'Boolean historization maps to Int2', CLAUDE.md,
  archreview STATUS.md (R2-06 live gate -> 6/6)

Resolves #441.

docs/Historian.md

@@ -141,48 +141,44 @@ for this node), which is the signal to check that `ServerHistorian:Enabled=true`
 > so a HistoryRead on it runs to the full `CallTimeout` (~30 s) before erroring. Auto-provisioning on deploy
 > keeps freshly-historized tags from hitting that slow path. See the `CallTimeout` row above.
 
-### 0.2.0 DataType provisioning delta (archreview 06/U-7)
+### Boolean historization maps to Int2 (issue #441)
 
-`EnsureTags` is contract-documented (HistorianGateway 0.2.0) as an **upsert** — *"creates or updates
+`EnsureTags` is contract-documented (HistorianGateway 0.2.0+) as an **upsert** — *"creates or updates
 historian tags according to the given definitions"* — that maps per-tag onto AVEVA's
 `HistorianClient.EnsureTagAsync(definition) -> bool`. It is **not idempotent** (not routed through the
 idempotent retry pipeline) and **not skip-if-exists**.
 
-The 0.1.0→0.2.0 client bump made `HistorianTagDefinition.DataType` **proto3-optional** (explicit presence).
-Under 0.1.0, the provisioner's `Boolean → Int1` mapping sent wire value `0`, indistinguishable from unset, so
-the gateway defaulted such tags to the SDK-default **Float**. Under 0.2.0 the same call carries explicit
-presence, so Boolean tags now provision as **Int1** (the pre-existing intent of `HistorianTypeMapper` — no
-mapper code change is needed or wanted). Consequences:
+`HistorianTypeMapper` maps **`DriverDataType.Boolean → HistorianDataType.Int2`** and Boolean values
+historize as a small **0/1 integer**. Int2 is used rather than the semantically-exact `Int1` because the
+historian's **`Int1` analog-tag creation path is server-degenerate** — `EnsureTags(Int1)` stores an
+unusable stub, so a Boolean tag mapped to `Int1` never becomes historizable. This is an evidence-based
+decision from a live probe against the deployed 2023 R2 historian; the root cause and gateway-side
+resolution are tracked in [issue #441](https://gitea.dohertylan.com/dohertj2/lmxopcua/issues/441) and
+HistorianGateway [#11](https://gitea.dohertylan.com/dohertj2/historiangw/issues/11) / PR #16 (which
+documents `Int1` as an explicit, evidence-based exclusion). The value-write path is unaffected: the
+recorder sends every value as a `double` on `WriteLiveValues` regardless of tag type, so a Boolean
+`0.0/1.0` round-trips cleanly into the Int2 tag.
 
-1. **New Boolean tags provision correctly as Int1.** This is the fix arriving as a silent, zero-diff
-   semantic change from the bump.
-2. **Pre-bump Boolean tags exist historian-side as Float.** On the next deploy that dispatches provisioning
-   for such a tag, the gateway is asked (via the upsert) to update it to Int1.
+**Observed live (2026-07-13, real 0.2.0 gateway → real AVEVA historian on `wonder-sql-vd03`, probed via
+`grpcurl` — archreview R2-06 T12):**
+- `EnsureTags` is a **real create-or-update upsert** — re-`EnsureTags` of an existing tag at the same type
+  returns `Success=true`.
+- An **in-place retype between SUPPORTED types is ACCEPTED** — `Float→Double` on an existing tag returns
+  `Success=true`.
+- A type sweep confirmed **`Int2/UInt2/Int4/UInt4/Float/Double` all provision `Success=true`; only `Int1`
+  fails** (`Success=false, Error="ProtocolEvidenceMissingException"` — the vendored client's "no capture
+  evidence for this type" guard → gRPC `Unimplemented`), both for a fresh tag and as a retype target. Mapping
+  Boolean to `Int2` sidesteps that gap entirely.
 
-   **Observed live (2026-07-13, real 0.2.0 gateway → real AVEVA historian on `wonder-sql-vd03`, probed via
-   `grpcurl` — archreview R2-06 T12):**
-   - `EnsureTags` is a **real create-or-update upsert** — re-`EnsureTags` of an existing tag at the same type
-     returns `Success=true`.
-   - An **in-place retype between SUPPORTED types is ACCEPTED** — `Float→Double` on an existing tag returns
-     `Success=true` (hypothesis **(ii) accepted as a plain retype**, not rejected).
-   - **BUT `Int1` — the 0.2.0 Boolean target — is *not a creatable type* on this historian's histsdk:**
-     `EnsureTags(Int1)` returns `Success=false, Error="ProtocolEvidenceMissingException"` (the vendored client's
-     "no capture evidence for this type" guard → gRPC `Unimplemented`), both for a fresh tag and as a retype
-     target. A type sweep confirmed it is **Int1-specific**: `Int2/UInt2/Int4/UInt4/Float/Double` all provision
-     `Success=true`; only `Int1` fails.
-   - **Net for a pre-bump Float Boolean tag asked to become Int1:** the provision **fails** (per-tag
-     `Success=false` → `failed=N` tally). It is **neither silently retyped nor data-lost** — the tag stays Float
-     and remains readable; the Int1 provision simply doesn't land until the gateway's histsdk gains `Int1`
-     create-evidence — filed as
-     [historiangw#11](https://gitea.dohertylan.com/dohertj2/historiangw/issues/11). (Prerequisite for reaching this
-     outcome at all: the provisioner must stamp a **positive
-     `StorageRateMs`** — a `0` made `EnsureTags` throw `ArgumentOutOfRangeException` and fail *every* provision;
-     fixed in `GatewayTagProvisioner`, PR #439.)
-3. **The failure mode is bounded and observable either way.** Provisioning is fire-and-forget and never
-   blocks/fails a deploy; a per-tag rejection surfaces only as the tally's `failed` count. Values written to
-   a still-Float tag by the recorder remain readable (Float supersets Int1's 0/1 range); nothing is lost
-   pending a reconcile. A bulk retype sweep is **not** done in code — assess via the probe first, then decide
-   whether reconciliation is a one-time operator action.
+> **Prerequisite for provisioning to land at all:** the provisioner must stamp a **positive `StorageRateMs`**
+> — a `0` made `EnsureTags` throw `ArgumentOutOfRangeException` and fail *every* provision (fixed in
+> `GatewayTagProvisioner`, PR #439).
+
+**Migration note for pre-existing Boolean tags.** A Boolean tag historian-side as Float (e.g. from the
+0.1.0-era default) is asked, on its next deploy, to upsert to Int2. Both are supported analog types, so the
+retype is accepted. Provisioning is fire-and-forget and never blocks/fails a deploy; a per-tag rejection (if
+any) surfaces only as the tally's `failed` count, and values written to a still-Float tag remain readable
+(Float supersets the 0/1 range) pending reconcile. A bulk retype sweep is **not** done in code.
 
 ---
 
@@ -407,11 +403,11 @@ The gateway-backed driver also ships an env-gated live suite (`Category=LiveInte
 `HISTGW_GATEWAY_ENDPOINT` / `HISTGW_GATEWAY_APIKEY` / `HISTGW_TEST_TAG` / `HISTGW_WRITE_SANDBOX_TAG` /
 `HISTGW_BOOL_SANDBOX_TAG` / `HISTGW_ALARM_SOURCE` env vars (it skips cleanly when they are absent).
 `HISTGW_BOOL_SANDBOX_TAG` (e.g. `HistGW.LiveTest.BoolSandbox`, a **dedicated** writable Boolean tag —
-never the shared Float write sandbox) drives the 0.2.0 Boolean `EnsureTags` leg
-(`EnsureTags_boolean_sandbox_provisions_as_Int1`) and the retype probe
-(`EnsureTags_type_change_outcome_is_observable`) that resolve the
-[0.2.0 DataType provisioning delta](#020-datatype-provisioning-delta-archreview-06u-7) open question. Running
-the full suite against a **0.2.0** gateway (all six tests, none skipped) also discharges 06/U-2's
+never the shared Float write sandbox) drives the Boolean historization leg
+(`EnsureTags_boolean_sandbox_provisions_as_Int2`) and the retype probe
+(`EnsureTags_type_change_outcome_is_observable`) that back the
+[Boolean historization maps to Int2](#boolean-historization-maps-to-int2-issue-441) decision. Running
+the full suite against the gateway (all six tests, none skipped) also discharges 06/U-2's
 "full documented run" for the historian suite.
 
 See [AlarmHistorian.md](AlarmHistorian.md) for the alarm write path and