# Architecture Review 06 — Gateway Integrations (Galaxy Driver + Historian Gateway Driver)

- **Date:** 2026-07-12
- **Commit:** `f6eaa267` (master, clean tree)
- **Updates:** the 2026-07-08 review at `9cad9ed0`. Since then the arch-review remediation branches merged to master (none targeted this domain's code), plus two in-domain deltas: the docker-dev `ServerHistorian` stale-keys fix (`7233e2ba`) and the `ZB.MOM.WW.HistorianGateway` Client + Contracts **0.1.0 → 0.2.0** bump (`f6eaa267`). Both `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy*` and `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway` (and their test projects) are **byte-identical** to `9cad9ed0` — all prior file:line citations remain exact.
- **Scope:**
  - `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy` (+ `.Contracts`, `.Browser`)
  - `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway`
  - Test coverage: `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests`, `.Galaxy.Browser.Tests`, `.Historian.Gateway.Tests`
  - Peripheral (read for context, not reviewed in depth): `Runtime/Historian/*` (recorder, options), `AddressSpaceApplier` provisioning/subscription hooks, `OtOpcUaNodeManager` tie-cluster paging, Host `Program.cs` historian wiring, `docker-dev/docker-compose.yml`.
- **Dimensions:** Stability, Performance, Conventions, Underdeveloped Areas.

---

## Prior-finding status (9cad9ed0 → f6eaa267)

| ID | One-liner | Status @ f6eaa267 |
|---|---|---|
| S-1 (High) | Galaxy write success is optimistic; committed-write failure can never surface | **STILL OPEN** — `GatewayGalaxyDataWriter.cs:281-302` unchanged (empty-statuses ⇒ `Good`; advise-failure path `:234-243` still proceeds). STATUS.md lists "06/S-1 (Galaxy fail-closed)" under *suggested next*, not done. |
| S-2 (Med) | EventPump saturation drops the newest events (inverted staleness bias) | **STILL OPEN** — `EventPump.cs:128-140` unchanged. |
| S-3 (Med) | `ReadViaSubscribeOnceAsync` can wait forever on a non-cancellable token | **STILL OPEN** — `GalaxyDriver.cs:738-755` unchanged. |
| S-4 (Med) | Transport-failure detection is EventPump-only; subscription-less driver never degrades | **STILL OPEN** — `ReportTransportFailure` still has the single pump-fault caller (`GalaxyDriver.cs:929-949`). |
| S-5 (Med) | Outbox `RemoveAsync` truncates the FIFO prefix; out-of-order acks silently drop | **STILL OPEN** — `FasterLogHistorizationOutbox.cs:158-182` unchanged. |
| S-6 (Med) | `RefreshConnectionStateAsync` has no production caller; snapshot flags dormant | **STILL OPEN** — verified by grep: only `GatewayHealthSnapshotTests` (3 call sites) invokes it; no hosted-service was added. |
| S-7 (Low) | Alarm feed reconnect has no backoff (fixed 5 s) | **STILL OPEN** — `GatewayGalaxyAlarmFeed.cs:102-148` unchanged. |
| S-8 (Low) | `GalaxyMxSession` state unsynchronized across reopen (accepted, emergent safety) | **STILL OPEN** — unchanged; still un-documented invariant. |
| S-9 / S-10 (Positive) | Store-and-forward discipline; TLS/API-key posture | **Unchanged** — and S-10 strengthened for free by the 0.2.0 client (PEM-bundle trust anchors; see bump assessment). |
| P-1 (Med) | Galaxy Read = 3 round-trips + publish wait | **STILL OPEN** — gateway-constrained, unchanged. |
| P-2 (Med) | Alarm drain is one unary `SendEvent` per event | **STILL OPEN** — 0.2.0 ships no batched `SendEvents`; client surface for events unchanged. |
| P-3 (Low) | Four channels to the historian sidecar (deliberate) | **Unchanged** — trade-off still argued in-source. |
| P-4 (Positive) | Fan-in/fan-out indexed, bounded, metered | **Unchanged.** |
| P-5 (Low) | HistoryRead buffers whole replies; `maxEvents <= 0` unbounded | **STILL OPEN** — 0.2.0 `ReadEventsAsync` signature is identical (no wire-side cap param); adapter still drops `maxEvents` (`HistorianGatewayClientAdapter.cs:76-89`). |
| P-6 (Low) | Outbox peek holds the state lock across disk I/O | **STILL OPEN** — unchanged, still negligible at 64-entry batches. |
| C-1 / C-2 (Positive) | Secret handling; seam quality | **Unchanged.** |
| C-3 (Med) | Historian seam leaks wire types by design; keep contained | **STILL OPEN** — `IHistorianGatewayClient.cs` doc unchanged; no guard note added. The 0.2.0 bump is a live demonstration of the risk: contract-semantics changes now flow straight into driver behavior (see U-7). |
| C-4 (Low) | Options-validation styles diverge | **STILL OPEN** — unchanged; and the warnings-only style's sharp edge materialized live (see S-11). |
| C-5 (Low) | Retired Wonderware project directories still on disk | **STILL OPEN** — all five dirs (`src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware{,.Client,.Client.Contracts}` + 2 test dirs) still present, still absent from the slnx. |
| C-6 (Low) | EventPump silently drops unknown event families with no metric | **STILL OPEN** — `EventPump.cs:192-207` unchanged. |
| U-1 (High, doc-drift) | CLAUDE.md KNOWN LIMITATION 2 stale (ref feed wired but doc said empty-set) | **FIXED** — the docs branch (`9fadead6`, merged to master via `b67bd9e8`) rewrote LIMITATION 2 to "value-capture wired; live end-to-end verification still pending", matching the code. The remaining *live verification* half was never part of the drift finding — it lives on under U-2. |
| U-2 (Med) | Live-validation gate built but only partially run | **STILL OPEN** — no live run since; the arch-review #12 rig session ran with the historian **disabled** (that's what surfaced `7233e2ba`). The 0.2.0 bump adds fresh reason to re-run it (see U-7). |
| U-3 (Med) | WriteSecured / VerifiedWrite user identity stubbed at zero | **STILL OPEN** — `GatewayGalaxyDataWriter.cs:263-264` unchanged. |
| U-4 (Med) | Dormant-paths inventory (refresh, batched replay, footprint, client-side event cap/filter) | **STILL OPEN** — all four items unchanged; 0.2.0 fixes none of the gateway gaps (no wire-side `maxEvents`, no batched replay/`SendEvents`). |
| U-5 (Low) | Outbox serializer has no version/format byte | **STILL OPEN** — `HistorizationOutboxEntrySerializer.cs:14-16` unchanged. |
| U-6 | Test-coverage thin spots (advise-failure status, out-of-order `RemoveAsync`, S-3 hang, pump filter) | **STILL OPEN** — zero test changes in the three gateway test projects since `9cad9ed0`. |

**New findings this pass:** S-11 (Medium), U-7 (Medium), C-7 (Low) — see body. **All three REMEDIATED on `r2/06-serverhistorian-failfast` (R2-06, 2026-07-13); the U-7 live EnsureTags/retype leg is operator-gated pending a VPN run.**

---

## What changed since 2026-07-08 (in-domain delta assessment)

### The HistorianGateway 0.1.0 → 0.2.0 bump (`f6eaa267`)

One-line change to `Directory.Packages.props`; the consumed contract/client surface changed in five ways (verified by diffing the cached 0.1.0 vs 0.2.0 package XML docs + member lists):

1. **`HistorianTagDefinition.DataType` is now proto3-optional** (`HasDataType`/`ClearDataType` added). Old semantics: wire-0 (`INT1`) was indistinguishable from unset ⇒ the gateway mapped it to the SDK default **Float**. New semantics: presence is explicit, so a set `DataType` — *including* wire-0 `Int1` — is honored. **This directly changes `GatewayTagProvisioner` behavior for Boolean tags** (it maps `Boolean → HistorianDataType.Int1`, `HistorianTypeMapper.cs:28`, and always sets the field, `GatewayTagProvisioner.cs:57`): under 0.1.0 a Boolean tag was silently provisioned as Float; under 0.2.0 it provisions as Int1 (correct). The bump commit's impact analysis covered only the `opc_quality` change — this one was not assessed (see **U-7**).
2. **`HistorianHistoricalValue.OpcQuality` is now proto3-optional.** The commit's gate check is correct and verified: OtOpcUa never constructs `HistorianHistoricalValue` (no `AddHistoricalValues` caller anywhere in src/tests); all `OpcQuality` uses are the read-side `HistorianSample`/`HistorianAggregateSample`, unaffected.
3. **`HistorianLiveValue.Quality`/`QualityDetail` documented as dead inputs on `WriteLiveValues`** — the gateway's SQL live path silently discards them (server-managed quality; the SQL login is column-permission-denied). `GatewayHistorianValueWriter.cs:63` populates `Quality` anyway (see **C-7**).
4. **Client `ToUtcTimestamp` behavior fix:** a `DateTimeKind.Unspecified` timestamp is now interpreted as already-UTC instead of being shifted by the host's UTC offset. Absorbed improvement — OtOpcUa's own conversion sites already `SpecifyKind(..., Utc)` defensively (`GatewayHistorianDataSource.cs:269`, `AlarmEventMapper.cs:20`, `GatewayHistorianValueWriter.cs:70`), and UA-stack DateTimes are Utc-kinded, so no behavior change is expected here; the client-side times passed to `ReadRaw`/`ReadAggregate` are now safe even if an Unspecified kind ever leaks through.
5. **Client hardening/docs:** `LoadTrustAnchors` now honors a full PEM bundle (root + intermediates) for `CaCertificatePath` pinning (strengthens S-10); the `RawRead`/`RawWrite`/`RawAdmin` escape hatches are documented as bypassing bearer-header injection, typed-exception mapping, and the retry pipeline (the adapter uses only typed methods — unaffected); per-RPC scope requirements (`historian:read` / `historian:tags:write`) are now documented, matching CLAUDE.md's prerequisites; streaming reads documented as *not* retried (transient failures surface — consistent with how `GatewayHistorianDataSource` maps them to health failures); a new `IHistorianGatewayClientTransport` seam exists client-side (unused by OtOpcUa; `IHistorianGatewayClient` remains the repo's seam).

Wire compatibility is preserved (field numbers unchanged; the proto3-optional changes are wire-compatible). No compile-surface break: the solution builds and the gateway-driver suite passed per the bump commit. The residual risk is behavioral, not structural — captured as U-7.

### The docker-dev `ServerHistorian` stale-keys fix (`7233e2ba`)

Config-only: docker-dev compose had `ServerHistorian__Enabled=true` with the retired Wonderware `Host`/`Port`/`SharedSecret` keys, so post-cutover code read an empty `Endpoint`, and `HistorianGatewayClientAdapter.Create` threw an unhandled `UriFormatException` at every bring-up — docker-dev was unbootable against current code. The fix rewrites both centrals to the gateway-shape keys, **disabled by default**, enable via `OTOPCUA_HISTORIAN_ENABLED` + `OTOPCUA_HISTORIAN_ENDPOINT` + env `ServerHistorian__ApiKey`; central-1 verified booting clean. Correct fix for the rig — but it fixed only the config, not the code path that turns a misconfigured section into a crash-loop with a raw `UriFormatException`. That code gap is new finding **S-11**.

---

## Architecture Overview

### Galaxy driver data flow (mxaccessgw)

`GalaxyDriver` (`GalaxyDriver.cs`) is a standard Tier-A in-process Equipment-kind driver registered under type name `GalaxyMxGateway`. All Galaxy access flows over gRPC to the external **mxaccessgw** gateway (sibling repo), consumed via the Gitea-feed packages `ZB.MOM.WW.MxGateway.Client` / `.Contracts` (`MxCommand` / `MxEvent` protos — unchanged this period). The driver holds **three logical gRPC clients**:

1. **Worker session** — `GalaxyMxSession` wraps `MxGatewayClient.OpenSessionAsync` + MXAccess `Register`. All data-plane traffic rides it:
   - **Subscribe** — `GatewayGalaxySubscriber.SubscribeBulkAsync` (session-level `SetBufferedUpdateInterval` applied first, cached last-applied value), events consumed by the shared `EventPump` off the bidirectional `StreamEvents` RPC, fanned out through `SubscriptionRegistry`'s handle→subscription reverse map onto `OnDataChange`.
   - **Read** — MxAccess has no one-shot read; `ReadViaSubscribeOnceAsync` synthesises Read as SubscribeBulk → first-event wait per handle → UnsubscribeBulk.
   - **Write** — `GatewayGalaxyDataWriter`: lazy `AddItem` (or borrow a live handle from the subscription registry), `AdviseSupervisory` once per handle (required for commit under WriteUserId=0), then raw `Write` or `WriteSecured` routed on the discovery-captured per-tag `SecurityClassification`.
2. **Session-less client** (`_ownedMxClient`) — the always-on central alarm monitor: `GatewayGalaxyAlarmFeed` (StreamAlarms: active-alarm snapshot → `snapshot_complete` → live transitions, self-reconnecting) and `GatewayGalaxyAlarmAcknowledger` (unary `AcknowledgeAlarm`).
3. **Repository client** (`GalaxyRepositoryClient`) — hierarchy browse for `DiscoverAsync` (via `IGalaxyHierarchySource` → `GalaxyDiscoverer`) and the `DeployWatcher` deploy-event stream that raises `IRediscoverable.OnRediscoveryNeeded`.

Recovery is owned by `ReconnectSupervisor` (Healthy → TransportLost → Reopening → Replaying → Healthy, capped exponential backoff, never gives up): the `EventPump` stream fault feeds `ReportTransportFailure`; reopen routes through `GalaxyMxSession.RecreateAsync` (dispose stale session + client, rebuild) and invalidates the writer's handle/advise caches; replay recreates the EventPump then re-issues SubscribeBulk per tracked subscription and `Rebind`s the registry with the fresh handles. Host connectivity is surfaced through `HostStatusAggregator` (transport state from the supervisor + per-platform `ScanState` probes via `PerPlatformProbeWatcher`).

Since `9cad9ed0`, Galaxy capability dispatch from `DriverInstanceActor` is additionally wrapped by the arch-review #10 `IDriverCapabilityInvoker` seam (tier-A resilience pipeline) — a Runtime-side change outside this domain's code, noted here because Galaxy calls now flow through it.

### Historian gateway data flow (HistorianGateway sidecar)

`Driver.Historian.Gateway` is the **sole historian backend**, consuming the `ZB.MOM.WW.HistorianGateway.Client` package **0.2.0** (`historian_gateway.v1`) behind the proto-typed `IHistorianGatewayClient` seam (`HistorianGatewayClientAdapter` is a pure pass-through over the typed client methods; channels are lazy — no I/O at construction, except the eager `new Uri(Endpoint)` at `HistorianGatewayClientAdapter.cs:45`, see S-11). Four independent paths, each with **its own gRPC channel** to the same sidecar (documented deliberate trade-off, `GatewayHistorianServiceCollectionExtensions.cs:57-64`):

1. **Read** — `GatewayHistorianDataSource` (`IHistorianDataSource`): OPC UA HistoryRead Raw/Processed/AtTime/Events → `ReadRaw` / `ReadAggregate` / `ReadAtTime` / `ReadEvents`; at-time replies re-aligned one-snapshot-per-requested-timestamp; health counters under a single lock. Tie-cluster paging (`MaxTieClusterOverfetch`) lives server-side in `OtOpcUaNodeManager` (~line 2200), bound from `ServerHistorianOptions`.
2. **Alarm history write** — `GatewayAlarmHistorianWriter` (`SendEvent` per event) behind the durable `SqliteStoreAndForwardSink`; maps every outcome (ack, typed client exceptions, raw `RpcException`) to exactly one `Ack` / `RetryPlease` / `PermanentFail` per event and never throws.
3. **Continuous historization** — `ContinuousHistorizationRecorder` (Runtime actor) taps the dependency-mux value fan-out, appends to the crash-safe `FasterLogHistorizationOutbox` (PerEntry fsync or Periodic commit; bounded drop-oldest capacity; startup recovery scan), drains through `GatewayHistorianValueWriter` (`WriteLiveValues`, non-throwing bool).
4. **Tag provisioning** — `GatewayTagProvisioner` (`EnsureTags`), dispatched fire-and-forget from `AddressSpaceApplier.Apply` with a tally log; non-historizable data types skipped; can never block or fail a deploy.

---

## Findings

### 1. Stability

#### S-1 (High) — Galaxy write success is optimistic; a committed-write failure can never surface

`GatewayGalaxyDataWriter.TranslateReply` (`GatewayGalaxyDataWriter.cs:281-302`) honours the protocol status and the first MXAccess status row, **defaulting to `Good` when the statuses array is empty** — and the gateway's write execution is effectively fire-and-forget past dispatch (the reply reflects command acceptance, not the eventual COM-side commit). Two concrete consequences:

- The supervisory-advise failure path (`GatewayGalaxyDataWriter.cs:234-243`) logs a warning, forgets the handle, and **lets the write proceed anyway** — but the file's own comment (`:163-165`) states a raw Write without supervisory advise "doesn't throw (reply looks OK) but the value never reaches the galaxy". That is a silent write loss returning `Good` to the OPC UA client.
- The server's write-outcome self-correction (#5, reverts the node on a failed device write) can structurally never trigger for Galaxy, so a lost write leaves a phantom-Good node value indefinitely.

**Blast radius:** operator writes (WriteOperate-gated) to Galaxy attributes that silently don't commit, with no Bad status, no health degradation, no metric. Not scheduled in the remediation pass; STATUS.md carries it under "suggested next" as *06/S-1 (Galaxy fail-closed)*. Recommendation: (a) return `Uncertain` (not proceed-to-Good) when supervisory advise fails; (b) pursue a gateway-side `WriteComplete` correlation (the gw backlog's `OnWriteComplete` event family already exists in the proto — `EventPump.cs:200-206` filters it out) so the reply/statuses row carries the real commit outcome; (c) add a `galaxy.writes.unconfirmed` counter in the interim.

#### S-2 (Medium) — EventPump saturation drops the *newest* events (inverted staleness bias)

`EventPump.RunAsync` (`EventPump.cs:128-140`) uses `TryWrite` against a bounded channel: when the fan-out consumer stalls, the **just-arrived** event is dropped and 50 000 stale queued events are preserved. For last-value-wins OPC UA telemetry this is the wrong bias — after a stall clears, subscribers replay old values and the freshest one may be the dropped one. The drop is at least metered (`galaxy.events.dropped`). Recommendation: per-item-handle conflation (keep newest per handle) or drop-oldest ring semantics; either preserves the no-backpressure requirement while keeping recent data.

#### S-3 (Medium) — `ReadViaSubscribeOnceAsync` can wait forever on a non-cancellable token

The read synthesis (`GalaxyDriver.cs:738-755`) fills pending snapshots with `BadTimeout` **only via `cancellationToken.Register`**. If a caller passes `CancellationToken.None` (or a token that never fires) and a successfully subscribed tag never publishes an initial event (gateway hiccup between SubscribeBulk and first push), the awaits at `:753` never complete and the read hangs, holding the subscription open. Recommendation: race each pending TCS against an internal deadline derived from `DefaultCallTimeoutSeconds` / `PublishingIntervalMs` regardless of the caller's token.

#### S-4 (Medium) — Transport-failure detection is EventPump-only; a subscription-less driver never degrades

`ReconnectSupervisor.ReportTransportFailure` has exactly one production caller: the EventPump stream-fault callback (`GalaxyDriver.cs:929-949`). The pump only starts on the first subscribe/read. A driver doing only writes (or idle after discovery) whose gateway restarts will keep `GetHealth() == Healthy`; each write then fails per-request with `BadCommunicationError`, but no reopen/replay/`Degraded` transition ever runs, and the stale session persists until something subscribes. Failed unary RPCs (SubscribeBulk, Write, AcknowledgeAlarm) do not feed the supervisor either. Recommendation: report classified transport exceptions from the write/subscribe paths into the supervisor (idempotent by design, so this is cheap).

#### S-5 (Medium) — FasterLog outbox `RemoveAsync` truncates the FIFO prefix; out-of-order acks silently drop unacked entries

`FasterLogHistorizationOutbox.RemoveAsync` (`FasterLogHistorizationOutbox.cs:158-182`) removes the target **plus every older live entry** and truncates the log to the target's successor. The contract "recorder acks in FIFO order" is enforced only by comment. If the drain ever acks a mid-batch id first (e.g. per-tag partial write success in a future recorder change), all older unacked values are durably discarded without incrementing `DroppedCount`. Recommendation: count and warn when the prefix removal drops non-target entries, or make the API batch-oriented (`RemoveThroughAsync`) so the semantics are explicit at the call site.

#### S-6 (Medium) — Historian health snapshot's connection flags are dormant in production

`GatewayHistorianDataSource.RefreshConnectionStateAsync` (`GatewayHistorianDataSource.cs:219-244`) is documented as "intended to be driven by a periodic health hosted-service", but **no production caller exists** — re-verified this pass: only `GatewayHealthSnapshotTests` invokes it. `ProcessConnectionOpen` / `EventConnectionOpen` in `GetHealthSnapshot` are therefore permanently `false` in a deployed host, which any dashboard consuming the snapshot will read as "historian down" (or, if ignored, the flags are dead weight). Same shape as the memory's "register-AND-pass-into-consumer" trap that bit `GatewayTagProvisioner` in PR #423. Recommendation: add the periodic refresh hosted-service (or fold a refresh into the existing health probe cadence), or remove the flags from the snapshot.

#### S-7 (Low) — Alarm feed reconnect has no backoff

`GatewayGalaxyAlarmFeed.RunAsync` (`GatewayGalaxyAlarmFeed.cs:102-148`) re-opens on a fixed 5 s delay forever. `DeployWatcher` (capped exponential + jitter, `DeployWatcher.cs:212-233`) and `ReconnectSupervisor` both do this properly. A dead gateway gets hammered every 5 s per driver instance. Cosmetic at this scale, but inconsistent; align on capped exponential.

#### S-8 (Low) — `GalaxyMxSession` state is unsynchronized across reopen

`_session` / `_connected` (`GalaxyMxSession.cs:28-32`) are plain fields; `RecreateAsync` tears down while concurrent writers/subscribers may hold or fetch `Session`. In practice the supervisor's single-flight recovery plus the per-call try/catch (mapped to `BadCommunicationError`) contain it, and the caches are invalidated post-reopen — but the safety is emergent, not designed. Acceptable; document the invariant on `Session`.

#### S-11 (Medium, NEW) — An enabled-but-misconfigured `ServerHistorian` section crash-loops the Host with a raw `UriFormatException`; one corner gets no warning at all

> **REMEDIATED — `r2/06-serverhistorian-failfast` (R2-06, 2026-07-13; live leg operator-gated).** New fail-fast `ServerHistorianOptionsValidator` (Host, wired via `AddValidatedOptions`) consumer-gates on `ServerHistorian:Enabled` **OR** `AlarmHistorian:Enabled` (closing the zero-warning corner) and fails startup with a named, aggregated `OptionsValidationException` on an empty / non-absolute / non-http(s) `Endpoint`. Adapter defense-in-depth replaces the bare `new Uri(...)` with `Uri.TryCreate`→named `InvalidOperationException`. `Validate()` gains malformed-endpoint warning parity; an alarm-only deployment logs a startup warning. Also directly answers C-4's "give the warnings style a fail-fast tier".

`HistorianGatewayClientAdapter.Create` eagerly does `new Uri(options.Endpoint)` (`HistorianGatewayClientAdapter.cs:45`). `ServerHistorianOptions.Validate()` produces exactly the right warning for an empty Endpoint (`ServerHistorianOptions.cs:78-79`) — but it is **warnings-only**: registration proceeds (`Runtime/ServiceCollectionExtensions.cs:135-139`, `Host/Program.cs:123-127`) and the first DI resolution throws an unhandled `UriFormatException`, crashing the Host at bring-up. This is not theoretical — it made docker-dev unbootable until the config-side fix `7233e2ba` (whose commit message documents the exact failure). The code path is untouched.

The sharper corner: **`AddAlarmHistorian` gates only on `AlarmHistorian:Enabled`** (`Runtime/ServiceCollectionExtensions.cs:87`) but sources its connection from the `ServerHistorian` section (`Program.cs:127`). With `AlarmHistorian:Enabled=true` and `ServerHistorian:Enabled=false` (Endpoint legitimately empty), `Validate()` early-returns on `!Enabled` (`ServerHistorianOptions.cs:77`) — so the operator gets **zero warning**, then the same `UriFormatException` out of `CreateAlarmWriter` when the sink singleton is built. Same exposure for the continuous-historization writer (`Program.cs:187`, though that one is co-gated on `ServerHistorian.Enabled`, so only a *malformed* non-empty Endpoint reaches it).

A hard fail at startup on misconfiguration is defensible — but it should be a deliberate, named failure, not an incidental `UriFormatException` from deep inside a DI factory. Recommendation: (a) validate `Endpoint` parses as an absolute URI in `Validate()`; (b) when the section is Enabled (or *consumed* by an enabled AlarmHistorian) and Endpoint is empty/invalid, fail fast with an `InvalidOperationException` naming the configuration key — or force-disable and keep the Null defaults; (c) make `AddAlarmHistorian` also run `ServerHistorianOptions.Validate()`-equivalent checks on the connection section it actually depends on.

#### S-9 (Positive) — Store-and-forward + outbox crash-safety discipline is strong

- `GatewayAlarmHistorianWriter` (`GatewayAlarmHistorianWriter.cs:66-118`) short-circuits remaining batch entries to `RetryPlease` on shutdown, classifies auth failures as retryable (an auth blip never dead-letters), and defaults unknowns to `PermanentFail` so poison events cannot loop.
- `FasterLogHistorizationOutbox` PerEntry mode fsyncs before append returns; recovery rebuilds the index from `BeginAddress`; the capacity-overflow-after-crash convergence case is analysed in-source (`FasterLogHistorizationOutbox.cs:200-204`).
- Partial-open recovery in `GalaxyMxSession.ConnectAsync` (`GalaxyMxSession.cs:95-101`) tears down half-open state so retry rebuilds cleanly.

#### S-10 (Positive) — TLS / API-key posture

Both integrations support TLS with CA pinning (`CaCertificatePath`), the historian's `AllowUntrustedServerCertificate` inversion is explicitly documented at the mapping site (`HistorianGatewayClientAdapter.cs:49-52`), and keys are never logged. The 0.2.0 client strengthens this for free: `CaCertificatePath` now honours a full PEM bundle (root + intermediates) as trust anchors, and the raw-client escape hatches are documented as bypassing bearer injection (the adapter uses only typed methods, so no exposure). See C-1 for the resolver.

### 2. Performance

#### P-1 (Medium) — Galaxy Read costs three gateway round-trips plus a publish wait per OPC UA Read

`ReadViaSubscribeOnceAsync` = SubscribeBulk + first-event wait (up to `PublishingIntervalMs`) + UnsubscribeBulk, with server-side AddItem/RemoveItem churn per read (`GalaxyDriver.cs:644-780`). This is forced by MxAccess (no one-shot read RPC) and is correctly batched per request, but a client polling via Read instead of subscribing multiplies gateway/COM load ~3×. Recommendation: document "subscribe, don't poll" as the supported pattern; consider a short-lived read-through cache keyed on full reference if polling clients appear.

#### P-2 (Medium) — Alarm-history drain is one unary `SendEvent` per event

`GatewayAlarmHistorianWriter.WriteBatchAsync` (`GatewayAlarmHistorianWriter.cs:66-80`) serializes the batch — deliberate poison-event isolation, but an alarm storm of N events costs N sequential RPC round-trips out of the SQLite drain worker. The 0.2.0 client still has no batched `SendEvents` with per-event status rows; when the gateway grows one, adopt it. Until then this is an accepted, well-documented ceiling.

#### P-3 (Low) — Four channels to the historian sidecar; two-plus to mxaccessgw

Each historian path owns its channel (read / alarm-write / provisioner / value-writer) and the Galaxy driver holds a session client, a session-less client, and a repository client. All are lazy, HTTP/2-multiplexed, and the trade-off (clean independent dispose ownership over channel sharing) is argued in-source (`GatewayHistorianServiceCollectionExtensions.cs:57-64`). No action; noted so nobody "optimizes" it into a shared-singleton dispose bug.

#### P-4 (Positive) — Fan-in/fan-out paths are indexed, bounded, and metered

- `SubscriptionRegistry` maintains a handle→subscriptions reverse map with a per-entry handle→fullRef index, so `ResolveSubscribers` is O(subscribers), not O(bindings) (`SubscriptionRegistry.cs:97-111`), and `TryResolveItemHandle` lets the writer skip AddItem for subscribed tags with a stale-entry cross-check (`:128-142`).
- Subscribe/replay correlation uses a one-pass result index (`GalaxyDriver.BuildResultIndex`, fixing a former O(n²) on the 50k-tag path).
- EventPump decouples network read from dispatch via a bounded channel (default 50 000, configurable) with received/dispatched/dropped counters.

#### P-5 (Low) — HistoryRead buffers whole replies; `maxEvents <= 0` is unbounded

`ReadRawAsync` / `ReadProcessedAsync` / `ReadEventsAsync` (`GatewayHistorianDataSource.cs:59-182`) drain the stream into a list before mapping. Raw reads are capped by `maxValuesPerNode`, but an events read with `maxEvents <= 0` collects without limit (the gateway's `RuntimeDb:EventReadMaxRows` is the only cap, and it's a remote deployment knob). Re-checked against 0.2.0: `ReadEventsAsync`'s client signature is unchanged — still no wire-side cap, so the adapter still cannot forward `maxEvents` (`HistorianGatewayClientAdapter.cs:76-89`). The tie-cluster paging bound (`MaxTieClusterOverfetch`, validated > 0 in `ServerHistorianOptions.Validate`, enforced at `OtOpcUaNodeManager.cs:2200-2214`) is well-designed. Recommendation: clamp events reads to a server-side default cap when the caller passes 0.

#### P-6 (Low) — Outbox peek holds the state lock across disk I/O

`PeekBatchAsync` scans FasterLog from the logical head under `_state` (`FasterLogHistorizationOutbox.cs:140-155`), blocking a concurrent `AppendAsync`'s index update for the duration of a (mostly page-cached) disk scan. At the recorder's 64-entry default batch this is negligible; revisit only if drain batches grow.

### 3. Conventions

#### C-1 (Positive) — Secret handling is a model for the other drivers

`GalaxySecretRef` (`Galaxy.Contracts/GalaxySecretRef.cs`) resolves `env:` / `file:` / `dev:` / literal with fail-fast on unset env vars and a startup warning on unprefixed cleartext; it lives in Contracts so the runtime driver and the AdminUI browser share one implementation (`GalaxyDriverBrowser.cs:125`). The historian side takes `ServerHistorian__ApiKey` via env with a "never commit" doc contract and an empty-key `Validate()` warning; the docker-dev rewrite (`7233e2ba`) follows the same discipline (`${ServerHistorian__ApiKey:-}` pass-through, key never committed). No key value is ever logged on either path.

#### C-2 (Positive) — Seam quality and driver-family consistency

- `IHistorianGatewayClient` is a clean single seam: every consumer (`GatewayHistorianDataSource`, `GatewayAlarmHistorianWriter`, `GatewayTagProvisioner`, `GatewayHistorianValueWriter`) depends only on it; `FakeHistorianGatewayClient` backs the offline suite; the adapter is a zero-translation pass-through. (The 0.2.0 client's new `IHistorianGatewayClientTransport` seam is package-internal plumbing — correctly not adopted; the repo seam stays `IHistorianGatewayClient`.)
- The Galaxy capability seams (`IGalaxyHierarchySource`, `IGalaxyDataReader/Writer`, `IGalaxySubscriber`, `IGalaxyAlarmFeed/Acknowledger`) plus the internal test ctor mirror the protocol-driver pattern; tracing decorators (`Traced*`) wrap the production seams without an OpenTelemetry dependency.
- `GalaxyDriverFactoryExtensions.CreateInstance` throws precise, instance-named errors on missing required fields (`GalaxyDriverFactoryExtensions.cs:56-75`), and `GalaxyDriverProbe` uses `JsonStringEnumConverter` (the FB-9/FB-10 enum-serialization lesson applied).

#### C-3 (Medium) — The historian seam leaks wire types by design; keep it contained

`IHistorianGatewayClient` signatures use `HistorianGateway.Contracts.Grpc` types (`HistorianSample`, `RetrievalMode`, `WriteAck`, ...) — documented as deliberate (`IHistorianGatewayClient.cs:5-11`). This is fine while the driver is the only consumer, but the pure `Mapping/` layer is the real anti-corruption boundary: any future consumer must sit **above** `GatewayHistorianDataSource`, never on the seam. The 0.2.0 bump demonstrated the flip side concretely: a *semantics* change in a contract type (`HistorianTagDefinition.DataType` presence, U-7) flowed straight into driver behavior with no compile signal. Worth a one-line guard note in the interface doc, plus a bump-checklist habit of diffing the contract XML (this pass's method) rather than relying on green builds.

#### C-4 (Low) — Options-validation styles diverge

Galaxy: throw-on-construct for required fields; DataAnnotations attributes on the records are decorative (nothing runs `Validator`). Historian: `Validate()` returns operator warnings and never throws (registration logs them). Both are defensible, but the repo now has two idioms for "driver-adjacent options validation" — and the warnings-only historian style's sharp edge materialized live this period (the docker-dev crash, see S-11): the operator got the correct warning immediately followed by an opaque crash. Pick one idiom for new sections, and give the warnings style a fail-fast tier for configurations that will provably crash anyway.

#### C-5 (Low) — Retired Wonderware project directories still on disk

`src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware{,.Client,.Client.Contracts}` (and their test dirs) remain in the tree but are absent from `ZB.MOM.WW.OtOpcUa.slnx` (0 references) — re-verified this pass. Dead directories invite grep noise and accidental resurrection; delete them (git history preserves the code).

#### C-6 (Low) — EventPump silently drops unknown event families with no metric

`Dispatch` (`EventPump.cs:192-207`) returns without counting on any non-`OnDataChange` family. The rationale comment is good, but a gateway version emitting `OnBufferedDataChange` (or a new family) would silently discard data with zero observability — the alarm feed counts its decode drops (`AlarmTransitionsDecodingFailures`); the pump should count filtered/unknown families the same way.

#### C-7 (Low, NEW) — The live-value writer populates a documented-dead `Quality` field

> **REMEDIATED — `r2/06-serverhistorian-failfast` (R2-06, 2026-07-13).** Decision: **keep populating** the field (the "stop populating so it's visible" alternative was rejected — proto3 sends `0` = Bad when unset, planting a future bug the instant a gateway version honors the field, whereas the recorder's `192` is correct). Visibility achieved with doc comments instead: `GatewayHistorianValueWriter` `<remarks>` + inline note at the mapping, `ContinuousHistorizationRecorder.GoodQuality` guard note, and a `docs/Historian.md` sentence — all citing 0.2.0 Contracts C-002.

`GatewayHistorianValueWriter` maps `HistorizationValue.Quality` onto `HistorianLiveValue.Quality` (`GatewayHistorianValueWriter.cs:63`), but the 0.2.0 contract now documents that field (and `QualityDetail`) as **silently discarded on the `WriteLiveValues` SQL path** — the gateway's SQL login is column-permission-denied on the server-managed Quality column, so the value is accepted on the wire and dropped. Harmless today because the recorder hardcodes `GoodQuality = 192` for every captured value (`ContinuousHistorizationRecorder.cs:45,256` — the outbox round-trips it, `:419`), so nothing meaningful is lost. The hazard is forward-looking: if the recorder is ever extended to capture *real* node quality (a natural next step), it will appear to work and silently persist nothing — quality will remain server-stamped. Add a comment at the mapping site citing the 0.2.0 contract note (Contracts C-002), or stop populating the field so the dead input is visible.

### 4. Underdeveloped Areas

#### U-2 (Medium) — KNOWN LIMITATION 1: the live-validation gate is built but still not fully run

The `Category=LiveIntegration` suite is complete and skip-clean: `GatewayLiveFixture` env-gates on `HISTGW_GATEWAY_ENDPOINT`/`APIKEY` (+ per-test `HISTGW_TEST_TAG`, `HISTGW_WRITE_SANDBOX_TAG`, `HISTGW_ALARM_SOURCE`) with a bounded 3 s TCP probe so a down VPN skips instead of hanging (`Live/GatewayLiveFixture.cs`). Four live tests cover read, EnsureTags+write, alarm SendEvent→ReadEvents round-trip, and a SendEvent contract check. The alarm leg has been run live at least once (merge `245316d8`); nothing further has run since the prior review — the arch-review #12 rig session ran with the historian **disabled**. The 0.2.0 bump raises the stakes: the suite has never executed against a 0.2.0 gateway with the 0.2.0 client, and the DataType presence change (U-7) is precisely the kind of semantics shift only the live EnsureTags leg can validate. A full documented run of the suite is the remaining work — the infrastructure is not the gap.

#### U-3 (Medium) — WriteSecured / VerifiedWrite user identity is stubbed at zero

`InvokeWriteSecuredAsync` hardcodes `CurrentUserId = 0, VerifierUserId = 0` (`GatewayGalaxyDataWriter.cs:263-264`). ArchestrA secured/verified writes exist precisely to attribute and dual-authorize the operation; user 0 will be rejected or unattributed by any galaxy that actually classifies tags SecuredWrite/VerifiedWrite. There is no mapping from the OPC UA session identity (the LDAP-authenticated principal is available server-side) to an ArchestrA user id. Until that lands, writes to secured-classification tags are effectively unsupported — document it, or fail fast with a clear status instead of sending user 0.

#### U-4 (Medium) — Dormant paths inventory

- `GatewayHistorianDataSource.RefreshConnectionStateAsync` — no production caller (see S-6).
- Replay still fans out per-subscription `SubscribeBulk`; the gateway's batched `ReplaySubscriptionsCommand` remains a "PR 6.x can swap this" note (`GalaxyDriver.cs:314-316`).
- `GalaxyDriver.FlushOptionalCachesAsync` is a no-op and `GetMemoryFootprint` is a constants-based estimate (`GalaxyDriver.cs:561-575`) — fine, but the server's cache-flush heuristic gets synthetic data from this driver.
- `HistorianGatewayClientAdapter.ReadEventsAsync` never forwards `maxEvents` on the wire (client-side cap only, documented at `IHistorianGatewayClient.cs:58-63`) and the source filter is re-applied client-side defensively (`GatewayHistorianDataSource.cs:152-157`) because the gateway-side filter "may not be present" — re-checked against 0.2.0: neither gap is addressed (the `ReadEventsAsync` client signature is unchanged). Both remain polite workarounds for gateway gaps that should be tracked against the sidecar repo.

#### U-5 (Low) — Outbox serializer has no version/format byte

`HistorizationOutboxEntrySerializer` writes a fixed positional layout with no version prefix (`HistorizationOutboxEntrySerializer.cs:14-16`). Any future field addition breaks recovery of pre-existing on-disk entries with an undiagnosable deserialization failure mid-`RecoverState`. One reserved byte now is free; a migration later is not.

#### U-7 (Medium, NEW) — The 0.2.0 bump's impact analysis missed the `DataType` presence change that alters Boolean tag provisioning

> **REMEDIATED (code + docs) — `r2/06-serverhistorian-failfast` (R2-06, 2026-07-13); LIVE LEG OPERATOR-GATED.** Pinned the 0.2.0 Boolean→Int1 explicit-presence semantics at two levels (`GatewayTagProvisionerTests.Boolean_definition_carries_explicit_Int1_presence` asserts `DataType==Int1` **and** `HasDataType` — the 0.2.0 presence witness; a package downgrade breaks the compile, a dropped-presence contract change breaks the assert). Added a written upsert/retype migration note to `docs/Historian.md` (three retype hypotheses + `failed=N` tally observability). Added the env-gated live Boolean EnsureTags leg + a **retype probe** (`HISTGW_BOOL_SANDBOX_TAG`) that records the deployed historian's in-place-retype policy. **Pending:** the live VPN run on a 0.2.0 gateway (feeds the observed retype answer back into the doc note; also discharges U-2's full documented run).

The bump commit (`f6eaa267`) gates only on the M3 `opc_quality` change ("checked and CLEAR" — correct, verified: OtOpcUa never writes `HistorianHistoricalValue`). But 0.2.0 also made **`HistorianTagDefinition.DataType` proto3-optional** (contracts review M-2), and that one lands squarely on `GatewayTagProvisioner`:

- The provisioner always sets `DataType` explicitly (`GatewayTagProvisioner.cs:57`), and `Boolean → HistorianDataType.Int1` (`HistorianTypeMapper.cs:28`) — where **Int1 is wire value 0**.
- Under 0.1.0 the gateway could not distinguish wire-0 from unset and mapped it to the SDK default **Float** — i.e. every Boolean tag EnsureTags'd to date was silently provisioned as a Float historian tag.
- Under 0.2.0 presence is explicit, so the same call now provisions **Int1** — the intended behavior, arriving as a silent semantic change with zero code diff on our side.

Two consequences need closing out: (1) any Boolean tags provisioned under 0.1.0 exist in the historian as Float, and what the gateway's `EnsureTags` does when the existing tag's type mismatches the (now-honored) requested type is unverified — per-tag failure outcomes would surface only in the provisioner's tally log (`failed=N`); (2) the live EnsureTags gate (U-2) has never run under 0.2.0 semantics. Recommendation: re-run the `Category=LiveIntegration` EnsureTags leg including a Boolean tag; check historian-side types for any previously provisioned Boolean tags; and adopt "diff the contract XML between package versions" (this review's method — both versions sit in the local NuGet cache) as the standing bump-gate checklist, since green builds cannot catch presence-semantics changes.

#### U-6 — Test coverage assessment

Zero test changes in the three gateway test projects since `9cad9ed0`; the assessment stands verbatim:

- **Galaxy** (~250 test methods across 34 files): strong unit coverage of the hard parts — reconnect orchestration (`GalaxyMxSessionReconnectTests`, `ReconnectSupervisorTests`), pump fault/bounded-channel behaviour, registry rebind/handle-resolve, writer caches, alarm feed decode, value encode/decode, status mapping, probe, factory. Three skip-gated live smokes (`GatewayGalaxyLiveReopenAndWriteTests` — proven 2/2 against `10.100.0.48:5120` per project memory — and `GatewayGalaxyAlarmFeedLiveTests`) gated on `MXGW_ENDPOINT` + `GALAXY_MXGW_API_KEY`.
- **Historian.Gateway** (~15 files): mappers fully covered, writer/provisioner/data-source outcome classification covered via `FakeHistorianGatewayClient`, outbox recovery/capacity covered, plus the 4-test live suite.
- **Thin spots:** no test drives `GalaxyDriver` write-through the supervisory-advise *failure* branch asserting the returned status (S-1's blast radius is untested); no test exercises out-of-order `RemoveAsync` on the outbox (S-5); nothing covers the read-hang case in S-3; `EventPump` unknown-family filtering has no assertion (C-6). New this pass: nothing asserts the misconfigured-Enabled crash shape (S-11), and no test pins the Boolean→Int1 provisioning expectation against a 0.2.0-semantics fake (U-7).

---

## Maturity Ratings

| Dimension | Rating (1-5) | Prior | Justification |
|---|---|---|---|
| Stability | **4** | 4 | Layered recovery (supervisor, self-reconnecting feeds, backoff, partial-open teardown) and disciplined never-throw write sinks are unchanged; still docked for the Galaxy silent-write-loss blast radius (S-1 — explicitly deferred by the remediation pass), EventPump-only fault detection (S-4), the dormant health refresh (S-6), and now the proven-live misconfiguration crash-loop (S-11, fixed only config-side). |
| Performance | **4** | 4 | No in-domain code change; bounded channels with drop metering, O(1) fan-out indexes, handle borrowing, and a bounded tie-cluster over-fetch stand; still docked for the 3-round-trip read synthesis (P-1) and serial alarm sends (P-2), both documented and still gateway-constrained in 0.2.0. |
| Conventions | **4** | 4 | Exemplary seams, shared secret resolver, consistent driver-family shape and tracing decorators; still docked for the dual options-validation idiom (whose sharp edge now has a live incident attached), the on-disk retired Wonderware dirs, the unmetered pump filter, and the new dead-Quality-input mapping (C-7). |
| Underdeveloped areas | **3** | 3 | The U-1 doc drift is fixed (the one prior finding closed this period), but the live gates net widened: the historian live suite has still never fully run, and the 0.2.0 bump added unverified semantics on the provisioning path (U-7) that only the live EnsureTags leg can retire. WriteSecured identity remains stubbed; the gateway-gap workarounds remain. |

---

## Cross-Cutting Themes

1. **"Wired but never invoked" is this codebase's recurring failure mode** — the provisioner (PR #423), the F10b sink forwarding, and `RefreshConnectionStateAsync` (S-6, still open). Any new capability interface or hook needs an explicit production-caller check plus a live `/run`, not just unit tests. (The arch-review pass built the reflection forwarding guard for the sink family; the health-refresh instance in this domain remains unguarded.)
2. **Optimistic-Good on fire-and-forget writes** — Galaxy structurally cannot report a failed commit (S-1, deferred by the remediation pass); reviewers of the node-write router / write-outcome self-correction should not assume driver parity here.
3. **Green builds cannot gate contract-semantics changes** — the 0.2.0 bump was wire-compatible and compile-clean yet silently changed Boolean tag provisioning (U-7) and dead-lettered the live-value Quality field (C-7). The bump gate for gateway packages should include a contract-XML diff (both versions are always in the local NuGet cache) and a live-suite run, not just `dotnet test`.
4. **Warnings-only validation defers the crash, it doesn't prevent it** — the docker-dev incident (S-11) logged the exact right warning milliseconds before an opaque `UriFormatException` crash-loop. Configurations that will provably fail should fail fast, by name.
5. **Gateway-gap workarounds accrue client-side** — defensive source filters, client-side event caps, missing batched replay/`SendEvents`; 0.2.0 closed none of them. These belong on the sister repos' backlogs with links from the in-source comments.
