parity: triage 3 false-positives from first-rig run (2026-04-30)

After running the matrix end-to-end against the live rig for the
first time, three of the nine failures were false positives — bugs in
the harness and test invariants, not real backend deltas:

1. ParityHarness configured the legacy backend with
   OTOPCUA_GALAXY_BACKEND=db, which is Discover-only. Reads, writes,
   and reinits all returned "MXAccess code lift pending — DB-backed
   backend covers Discover only". Switched to mxaccess backend; the
   ZB connection string still drives the discovery path.

2. HistoryReadParityTests asserted "neither backend implements
   IHistoryProvider" — but the legacy GalaxyProxyDriver still does
   (it's an accepted back-compat delta retired in PR 7.2). The
   architectural pin we *want* is "the new path doesn't regress to
   per-driver history", so the test now asserts only the mxgw side.

3. AlarmTransitionParityTests strict-pinned the five sub-attribute
   refs (InAlarmRef, etc.) on the legacy condition. PR 2.1 added
   those refs specifically so the new mxgw driver could populate them
   via AlarmRefBuilder; legacy pre-dates PR 2.1 and leaves them null
   — that's correct, not a regression. Test now asserts a one-way
   invariant: when legacy populated a ref, mxgw must match. When
   legacy is null, mxgw is free to populate (the mxgw → server-side
   AlarmConditionService direction).

The six remaining failures are real:

- 2 from the gw-side `[]` array suffix (filed in
  mxaccessgw/requirements-array-suffix-fix.md)
- 2 write-StatusCode mapping deltas (0x80050000 vs 0x80020000) —
  Bad-status both ways but mapped to different OPC UA codes
- 1 event-rate ratio of 5x (mxgw dispatches 5x legacy in the same
  3s window)
- (Plus the 2 ScanState scenarios that skip cleanly — single-platform
  rig as documented)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.ParityTests/HistoryReadParityTests.cs

@@ -50,17 +50,20 @@ public sealed class HistoryReadParityTests
     }
 
     [Fact]
-    public async Task Neither_Galaxy_backend_implements_IHistoryProvider_directly()
+    public async Task The_new_Galaxy_backend_does_not_implement_IHistoryProvider_directly()
     {
         // Pinning the architectural decision from Phase 1 (PR 1.3): per-driver
-        // IHistoryProvider was retired in favor of the server-owned HistoryRouter.
-        // If a regression brings IHistoryProvider back on either Galaxy driver,
-        // this test fires.
+        // IHistoryProvider was retired in favor of 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 — the legacy driver retires in
+        // PR 7.2 alongside the rest of the legacy projects). The architectural
+        // pin we want to enforce is "the *new* path doesn't regress to per-driver
+        // history".
         _h.RequireBoth();
 
-        (_h.LegacyDriver as IHistoryProvider).ShouldBeNull(
-            "legacy GalaxyProxyDriver must not surface IHistoryProvider — history routes through HistoryRouter");
         (_h.MxGatewayDriver as IHistoryProvider).ShouldBeNull(
             "in-process GalaxyDriver must not surface IHistoryProvider — history routes through HistoryRouter");
+        await Task.CompletedTask;
     }
 }