fix(alarms): Severity runs one direction, higher = more urgent; raw priority kept (#129)

AlarmConditionState.Severity mixed two conventions: OPC UA rows carried Part 9
Severity (higher = more severe) while MxGateway native alarms and computed
alarms carried a raw AVEVA-style priority (1 = most urgent). Every consumer
ranks higher as worse, so Worst Severity, the severity filter/sort and the
site event-log Error threshold picked the LEAST urgent MxGateway/computed
alarms.

- AlarmPriorityBands: the OtOpcUa GalaxyAlarmPriority table (lmxopcua#887,
  b61f3e05), value for value: 1-250 -> 1000, 251-500 -> 750, 501-750 -> 500,
  751-999 -> 250; <= 0 clamps to Critical, > 999 to Low.
- MxGatewayAlarmMapper bands the gateway severity (= AVEVA priority);
  AlarmConditionStateFactory.ForComputed bands PriorityLevel. OPC UA unchanged.
- AlarmConditionState gains trailing Priority (int?): the raw source number,
  exactly the pre-#129 Severity. AlarmStateChanged.Priority and the wire
  AlarmStateUpdate.priority keep that meaning (no proto change); central derives
  Severity by kind (SeverityFromPriority), so an older site decodes correctly.
- ScriptAlarm gains trailing Priority. The native MES 900-999 band and the MES
  API Severity/MinSeverity/MaxSeverity key off Priority; rig seed scripts moved
  from a.Severity to a.Priority, so MES output is unchanged.
- AlarmActor raise logs Error when the banded severity >= 700 (same threshold
  as NativeAlarmActor): priority 1-500 Error, 501+ Warning (was raw >= 700).
- NativeAlarmActor upgrades pre-#129 native_alarm_state rows on rehydrate.
- Debug snapshot decode restores Condition.Priority from the row's priority.
- Docs: Commons, DCL, SiteRuntime, Communication, CentralUI, InboundAPI,
  HighLevelReqs, MES alarm-status plan, CLAUDE.md.

Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi

tests/ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Tests/MxGatewayAlarmMapperTests.cs

@@ -33,7 +33,8 @@ public class MxGatewayAlarmMapperTests
         Assert.Equal(CommonsTransitionKind.Acknowledge, t.Kind);
         Assert.True(t.Condition.Active);
         Assert.True(t.Condition.Acknowledged);
-        Assert.Equal(600, t.Condition.Severity);
+        Assert.Equal(500, t.Condition.Severity);   // AVEVA priority 600 = Medium → 500 (#129)
+        Assert.Equal(600, t.Condition.Priority);   // raw priority kept
         Assert.Equal("operator1", t.OperatorUser);
         Assert.Equal("Tank01", t.SourceObjectReference);
     }
@@ -45,7 +46,8 @@ public class MxGatewayAlarmMapperTests
         var c = MxGatewayAlarmMapper.MapConditionState(ProtoConditionState.ActiveAcked, severity: 600);
         Assert.True(c.Active);
         Assert.True(c.Acknowledged);
-        Assert.Equal(600, c.Severity);
+        Assert.Equal(500, c.Severity);
+        Assert.Equal(600, c.Priority);
     }
 
     /// <summary>Verifies that an active, unacknowledged snapshot maps to the snapshot kind.</summary>
@@ -58,7 +60,7 @@ public class MxGatewayAlarmMapperTests
             SourceObjectReference = "Tank01",
             AlarmTypeName = "AnalogLimitAlarm.Hi",
             CurrentState = ProtoConditionState.Active,
-            Severity = 1500 // out of range — must clamp
+            Severity = 1500 // out of range — Priority clamps, Severity reads AVEVA Low
         };
 
         var t = MxGatewayAlarmMapper.MapSnapshot(snap);
@@ -66,7 +68,8 @@ public class MxGatewayAlarmMapperTests
         Assert.Equal(CommonsTransitionKind.Snapshot, t.Kind);
         Assert.True(t.Condition.Active);
         Assert.False(t.Condition.Acknowledged);
-        Assert.Equal(1000, t.Condition.Severity);
+        Assert.Equal(250, t.Condition.Severity);
+        Assert.Equal(1000, t.Condition.Priority);
     }
 
     /// <summary>Verifies that the source reference is object-relative rather than the full provider reference.</summary>
@@ -334,4 +337,63 @@ public class MxGatewayAlarmMapperTests
         // The end-of-snapshot sentinel has no condition payload at all.
         Assert.Null(MxGatewayAlarmMapper.SnapshotComplete().AckTime);
     }
+
+    // ── Gitea #129: one Severity direction, raw priority kept ──
+
+    /// <summary>
+    /// The gateway's <c>severity</c> field is the AVEVA priority (1 = most urgent). Severity uses OtOpcUa's
+    /// band table (lmxopcua#887), so priority 1 is the MOST severe — on a live transition and a snapshot alike.
+    /// </summary>
+    [Theory]
+    [InlineData(1, 1000)]
+    [InlineData(250, 1000)]
+    [InlineData(251, 750)]
+    [InlineData(500, 750)]
+    [InlineData(501, 500)]
+    [InlineData(750, 500)]
+    [InlineData(751, 250)]
+    [InlineData(999, 250)]
+    [InlineData(0, 1000)]
+    [InlineData(-100, 1000)]
+    [InlineData(1000, 250)]
+    [InlineData(int.MaxValue, 250)]
+    public void Severity_follows_the_AVEVA_priority_bands(int rawPriority, int expectedSeverity)
+    {
+        var live = MxGatewayAlarmMapper.MapTransition(new OnAlarmTransitionEvent
+        {
+            AlarmFullReference = "Galaxy!Area.Tank01.Hi", SourceObjectReference = "Tank01.Hi",
+            TransitionKind = ProtoTransitionKind.Raise, Severity = rawPriority
+        });
+        var snap = MxGatewayAlarmMapper.MapSnapshot(new ActiveAlarmSnapshot
+        {
+            AlarmFullReference = "Galaxy!Area.Tank01.Hi", SourceObjectReference = "Tank01.Hi",
+            CurrentState = ProtoConditionState.Active, Severity = rawPriority
+        });
+
+        Assert.Equal(expectedSeverity, live.Condition.Severity);
+        Assert.Equal(expectedSeverity, snap.Condition.Severity);
+    }
+
+    /// <summary>
+    /// The MES 900–999 band must select exactly the alarms it selected before #129, which tested the old
+    /// Severity — the gateway value clamped to 0–1000. Priority carries exactly that value for every input.
+    /// </summary>
+    [Fact]
+    public void Priority_is_the_pre_129_Severity_so_the_MES_band_is_unchanged()
+    {
+        foreach (var raw in new[] { int.MinValue, -1, 0, 1, 250, 251, 750, 751, 899, 900, 950, 999, 1000, 1001, 1500, int.MaxValue })
+        {
+            var t = MxGatewayAlarmMapper.MapTransition(new OnAlarmTransitionEvent
+            {
+                AlarmFullReference = "A", SourceObjectReference = "A",
+                TransitionKind = ProtoTransitionKind.Raise, Severity = raw
+            });
+            var preFixSeverity = Math.Clamp(raw, 0, 1000);
+            Assert.Equal(preFixSeverity, t.Condition.Priority);
+
+            var inBandBefore = preFixSeverity is >= 900 and <= 999;
+            var inBandNow = t.Condition.Priority is >= 900 and <= 999;
+            Assert.Equal(inBandBefore, inBandNow);
+        }
+    }
 }