Phase 2 PR 9 — thread IsAlarm discovery flag end-to-end. GalaxyRepository.GetAttributesAsync has always emitted is_alarm alongside is_historized (CASE WHEN EXISTS with the primitive_definition join on primitive_name='AlarmExtension' per v1's Extended Attributes SQL lifted byte-for-byte into the PR 5 repository port), and GalaxyAttributeRow.IsAlarm has been populated since the port, but the flag was silently dropped at the MapAttribute helper in both MxAccessGalaxyBackend and DbBackedGalaxyBackend because GalaxyAttributeInfo on the IPC side had no field to carry it — every deployed alarm attribute arrived at the Proxy with no signal that it was alarm-bearing. This PR wires the flag through the three translation boundaries: GalaxyAttributeInfo gains [Key(6)] public bool IsAlarm { get; set; } at the end of the message to preserve wire-compat with pre-PR9 payloads that omit the key (MessagePack treats missing keys as default, so a newer Proxy talking to an older Host simply gets IsAlarm=false for every attribute); both backend MapAttribute helpers copy row.IsAlarm into the IPC shape; DriverAttributeInfo in Core.Abstractions gains a new IsAlarm parameter with default value false so the positional record signature change doesn't force every non-Galaxy driver call site to flow a flag they don't produce (the existing generic node-manager and future Modbus/etc. drivers keep compiling without modification); GalaxyProxyDriver.DiscoverAsync passes attr.IsAlarm through to the DriverAttributeInfo positional constructor. This is the discovery-side foundation — the generic node-manager can now enrich alarm-bearing variables with OPC UA AlarmConditionState during address-space build (the existing v1 LmxNodeManager pattern that subscribes to <tag>.InAlarm + .Priority + .DescAttrName + .Acked and merges them into a ConditionState) but this PR deliberately stops at discovery: the full alarm subsystem (subscription management for the 4 alarm-status attributes, state-machine tracking for Active/Unacknowledged/Confirmed/Inactive transitions, OPC UA Part 9 alarm event emission, and the write-to-AckMsg ack path) is a follow-up PR 10+ because it touches the node-manager's address-space build path — orthogonal to the IPC flow this PR covers. Tests — AlarmDiscoveryTests (new, 3 cases): GalaxyAttributeInfo_IsAlarm_round_trips_true_through_MessagePack serializes an IsAlarm=true instance and asserts the decoded flag is true + IsHistorized is true + AttributeName survives unchanged; GalaxyAttributeInfo_IsAlarm_round_trips_false_through_MessagePack covers the default path; Pre_PR9_payload_without_IsAlarm_key_deserializes_with_default_false is the wire-compat regression guard — serializes a stand-in PrePR9Shape class with only keys 0..5 (identical layout to the pre-PR9 GalaxyAttributeInfo) and asserts the newer GalaxyAttributeInfo deserializer produces IsAlarm=false without throwing, so a rolling upgrade where the Proxy ships first can talk to an old Host during the window before the Host upgrades without a MessagePack "missing key" exception. Full solution build: 0 errors, 38 warnings (existing). Galaxy.Host.Tests Unit suite: 27 pass / 0 fail (3 new alarm-discovery + 9 PR5 historian + 15 pre-existing). This PR branches off phase-2-pr5-historian because GalaxyProxyDriver's constructor signature + GalaxyHierarchyRow's IsAlarm init-only property are both ancestor state that the simpler branch bases (phase-2-pr4-findings, master) don't yet include.

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

src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverAttributeInfo.cs

@@ -19,10 +19,17 @@ namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 /// <param name="ArrayDim">Declared array length when <see cref="IsArray"/> is true; null otherwise.</param>
 /// <param name="SecurityClass">Write-authorization tier for this attribute.</param>
 /// <param name="IsHistorized">True when this attribute is expected to feed historian / HistoryRead.</param>
+/// <param name="IsAlarm">
+///     True when this attribute represents an alarm condition (Galaxy: has an
+///     <c>AlarmExtension</c> primitive). The generic node-manager enriches the variable with an
+///     OPC UA <c>AlarmConditionState</c> when true. Defaults to false so existing non-Galaxy
+///     drivers aren't forced to flow a flag they don't produce.
+/// </param>
 public sealed record DriverAttributeInfo(
     string FullName,
     DriverDataType DriverDataType,
     bool IsArray,
     uint? ArrayDim,
     SecurityClassification SecurityClass,
-    bool IsHistorized);
+    bool IsHistorized,
+    bool IsAlarm = false);