# Galaxy backend parity matrix

This document tracks the scenario × result matrix that the
`Driver.Galaxy.ParityTests` suite drives against both Galaxy backends —
the legacy out-of-process **Galaxy.Host** (.NET 4.8 x86 + MXAccess COM,
fronted by `GalaxyProxyDriver`) and the new in-process **mxgateway**
backend (`GalaxyDriver`, .NET 10 + gRPC against `mxaccessgw`).

Maintained alongside Phase 5 (PR 5.W). The Phase 7 default flip
(PR 7.1) consumes this matrix as its go/no-go gate — every row must be
either green or carry an explicit *accepted-delta* justification.

## Reading the matrix

- **Status: green** — the scenario asserts strict parity and passes
  (or skips cleanly when the rig isn't up).
- **Status: yellow** — soft pin only (count or shape parity, not value
  parity) — acceptable when the underlying COM/gRPC stacks have known
  divergences in raw payloads but the surface presented to the
  DriverNodeManager is equivalent.
- **Status: red** — divergence detected. Row carries a fix or a
  follow-up task ID.

## Scenarios

Last verified end-to-end on the dev parity rig: **2026-04-30**
(legacy `OtOpcUaGalaxyHost` mxaccess backend; mxaccessgw v1.x at
`http://localhost:5120`; sandbox `OtOpcUaParityTest_001` deployed in
the `ZB` galaxy; 13 passed / 1 skipped / 0 failed in 19 minutes).

| PR | Test class | Scenario | Status | Notes |
|----|-----------|----------|--------|-------|
| 5.2 | `BrowseAndReadParityTests` | Same variable set | green | symmetric set diff on full-reference set, after `[]` array-suffix workaround in `GalaxyDiscoverer` |
| 5.2 | `BrowseAndReadParityTests` | Same DataType / SecurityClass / IsHistorized | green | per-attribute meta triple parity |
| 5.2 | `BrowseAndReadParityTests` | Same StatusCode-class on a sampled read | yellow | pins status class (Bad/Uncertain/Good); CLR type intentionally not asserted — see "Accepted deltas" #6 |
| 5.3 | `SubscribeAndEventRateParityTests` | Subscribe returns a handle on each backend | green | symmetric Unsubscribe cleanup |
| 5.3 | `SubscribeAndEventRateParityTests` | Event rate within ±50% over 3s | yellow | both backends fed by the same upstream MXAccess subscriptions; tolerance absorbs scheduler jitter |
| 5.4 | `WriteByClassificationParityTests` | FreeAccess / Operate write status-class parity | yellow | pins status class only; legacy flat-maps every failure to BadInternalError, mxgw distinguishes (BadCommunicationError, BadDeviceFailure, etc.) — see "Accepted deltas" #7 |
| 5.4 | `WriteByClassificationParityTests` | Configure / Tune routes via secured-write | yellow | same status-class pin |
| 5.5 | `AlarmTransitionParityTests` | Same alarm-condition source-node-id set | green | one-way invariant on sub-attribute refs (legacy populated → mxgw matches; legacy null → mxgw free to populate per AlarmRefBuilder) |
| 5.5 | `AlarmTransitionParityTests` | IsAlarm-marked variable count parity | green | soft pin — count must match, doesn't have to be non-zero |
| 5.6 | `HistoryReadParityTests` | Same historized attribute set | green | what HistoryRouter consumes when routing to the Wonderware sidecar |
| 5.6 | `HistoryReadParityTests` | New mxgw GalaxyDriver does not implement `IHistoryProvider` | green | architectural pin from Phase 1 (PR 1.3) on the *new* path; legacy `GalaxyProxyDriver` keeps the interface for back-compat until PR 7.2 — see "Accepted deltas" #8 |
| 5.7 | `ReconnectParityTests` | Reinitialize → both Healthy + reads succeed | green | recovery latency is *not* pinned (legacy: pipe + COM client; mxgw: re-Register gw session) |
| 5.7 | `ReconnectParityTests` | Health diverges only when one side recovers | yellow | soft pin until a toxiproxy-style fault injector lands |
| 5.8 | `ScanStateProbeParityTests` | Same per-platform host set | n/a — deferred | dev rig is licensed for one `$WinPlatform` only; multi-platform parity deferred to a customer rig (PR 4.7's unit tests pin the state-decoder + member-tracking logic) |
| 5.8 | `ScanStateProbeParityTests` | Same `HostState` per overlapping platform | n/a — deferred | same single-platform constraint |

## Accepted deltas

These are intentional differences between the two backends — the parity
suite skips or tolerates them by design.

1. **Transport-entry host name.** The legacy backend's
   `IHostConnectivityProbe` surface includes a host entry named after
   the Galaxy.Host process identity; the mxgw backend uses the
   configured `MxAccess.ClientName`. The names differ, but both are
   correct for their respective sessions — the parity test compares
   only the platform-host subset.

2. **Reconnect latency cadence.** Legacy reconnect roundtrips an OS
   named pipe + an MxAccess COM client + a Galaxy.Host process restart
   if the host died. The mxgw reconnect re-Registers the gateway session
   over an existing gRPC channel. Sub-second vs multi-second recoveries
   are both correct for their own paths; only the eventual `Healthy`
   convergence is pinned.

3. **Read-value drift.** A read sampled twice on a live Galaxy can
   return different values legitimately. We pin `StatusCode`-class
   parity (Bad/Uncertain/Good); value equality is not pinned.

4. **Event-rate variance.** Both backends consume the same upstream
   MXAccess publish events but route them through different deserializers
   (LMXProxyServer COM events vs gRPC `MxEvent` protos). Scheduler
   jitter on either side can shift counts within a 3s window; we pin a
   ±50% ratio, not strict equality.

5. **`IHistoryProvider` on the new path only.** Phase 1 (PR 1.3) lifted
   history off the per-driver path onto the server-owned
   `HistoryRouter` for the *new* in-process `GalaxyDriver`. The legacy
   `GalaxyProxyDriver` still surfaces `IHistoryProvider` for back-compat
   with the legacy server bootstrap path — it's an accepted delta
   retired in PR 7.2 alongside the rest of the legacy projects. The
   pin we want to enforce is "the new path doesn't regress to per-driver
   history."

6. **Read value-CLR-type.** Legacy returns the raw VARIANT (e.g.
   `Byte[]`) for an attribute that hasn't received its first value
   cycle from MxAccess yet, while mxgw returns the typed value
   (`Single`, `Int32`, etc.). Once a real value is written or scanned,
   both converge. Pinning CLR-type equality across the uninitialized
   window adds noise without a real parity invariant — the
   `StatusCode`-class assertion already covers the
   "did the read succeed" question.

7. **Write-failure StatusCode mapping.** Legacy
   `MxAccessGalaxyBackend.WriteValuesAsync` flat-maps every failure to
   `BadInternalError` (`0x80020000`); mxgw
   `GatewayGalaxyDataWriter.TranslateReply` uses
   `MxStatusProxy.RawDetectedBy` to distinguish gw-layer faults
   (`BadCommunicationError`, `0x80050000`) from MxAccess HRESULT
   faults (`BadDeviceFailure`, `BadNotConnected`, etc.). Both yield
   Bad-status — the parity invariant is the *status class*, not the
   exact code. Tighter mapping parity isn't worth investing in: the
   legacy mapping retires alongside `GalaxyProxyDriver` in PR 7.2.

8. **Single-platform scope on the dev rig.** Two
   `ScanStateProbeParityTests` scenarios are deferred to a customer
   rig with multiple deployed `$WinPlatform` instances; this dev box
   is licensed for one. PR 4.7's unit tests (`PerPlatformProbeWatcherTests`)
   pin the state-decoder + member-tracking logic at the seam level,
   so the runtime parity check becomes a customer-rig acceptance gate
   before that customer goes live, not a precondition for retiring
   the legacy projects on this dev box.

9. **Workaround for the gw `[]` array-suffix bug.**
   `mxaccessgw/src/MxGateway.Server/Galaxy/GalaxyRepository.cs:173-175`
   appends `[]` to the `full_tag_reference` of array-typed attributes,
   which `MxAccess COM IInstance.AddItem` doesn't accept. The lmxopcua
   discoverer (`GalaxyDiscoverer.StripArraySuffix`) defensively strips
   the suffix. Tracked in `mxaccessgw/requirements-array-suffix-fix.md`;
   the workaround is removed when that gw fix lands.

## Outstanding deltas

None as of 2026-04-30. Phase 7 (PR 7.1) flipped the default to
`mxgw`; PR 7.2 (legacy project deletion) is unblocked — the matrix
gate is satisfied and no further soak/pilot precondition applies.

## Running the matrix

```bash
# Both backends must be reachable for any row to run; rows skip
# cleanly when their backend is unavailable.
dotnet test tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.ParityTests/
```

Environment overrides for the mxgw backend:

| Variable | Default | Purpose |
|----------|---------|---------|
| `OTOPCUA_PARITY_GW_ENDPOINT` | `http://localhost:5120` | mxaccessgw gRPC endpoint |
| `OTOPCUA_PARITY_GW_API_KEY` | `parity-suite-key` | API key handed to `MxGatewayClient` |
| `OTOPCUA_PARITY_CLIENT_NAME` | `OtOpcUa-Parity` | `MxAccess.ClientName` for the session |

The legacy backend reads ZB SQL on `localhost:1433` and spawns
`OtOpcUa.Driver.Galaxy.Host.exe` from
`src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host/bin/Debug/net48/` — both
must exist for the legacy half to resolve.
