Store rung V151: collect each Availability Group's group_id and count groups by it (#4475)

[erikdarlingdata]

Refs #4475.

Why

Since #4481, the Availability Groups count joins the cards of the same AG by name plus overlapping replica sets. That leaves one case it can't see.

• The case: two monitored SECONDARIES of one AG, with its primary not monitored.
• Why it's invisible: on a server hosting a secondary replica, sys.dm_hadr_availability_replica_states returns only local information. So each secondary reports only itself, their replica sets share nothing, and they count as 2.
• The fix: the AG's own group_id is the same GUID on every replica, so it identifies the group exactly.

What changes

• The collectors: AgReplicaStatesCollector and AgDatabaseReplicaStatesCollector select group_id = CONVERT(nvarchar(36), ag.group_id), appended as their last column.
• Store rung V151:
  • ALTER TABLE collect.ag_replica_states ADD COLUMN IF NOT EXISTS group_id text, and the same on collect.ag_database_replica_states;
  • nullable, no default, no backfill; it works on hypertables with compressed chunks;
  • StorageVersion.SchemaVersion = 151, and the Viewer's store probe gains V151's sentinel and its arm.
• Lite's twin: DuckDbInitializer.CurrentSchemaVersion = 65 adds the same column to both tables, idempotently. Fresh Lite stores get it from the collectors' column lists.
• The count (AgTopology.CountDistinctGroups):
  • members with the SAME group_id are one group, even when they share no replica name;
  • different group_ids are never one group, even with the same name and overlapping replicas;
  • members collected before the column existed use the existing name + replica-overlap rule, and join a same-named member that has an id when their replicas overlap (the same AG seen before and after the upgrade).
  • The earlier overload delegates to the new one, so existing callers are unchanged.
• The reads: group_id is carried through the store's AG state reader, the Viewer's AG view, the web/MCP get_ag_health (distinct_ag_count) and Lite's AG read.

Test plan

• The count (AgTopologyCardsTests, pure):
  • two secondaries of one AG with the same id and disjoint replica sets → 1;
  • 42 same-named AGs with 42 distinct ids → 42;
  • the id-less path is unchanged (every The Viewer counts Availability Groups by identity, shows Job History loading, and says "queries" (#4475, #4478) #4481 case stays green);
  • with-id + id-less, the same name, overlapping replicas → 1;
  • different ids with overlapping replicas → 2;
  • with-id + id-less with disjoint replicas → 2.
  • Mirrored through DarlingAgReader.Build in DarlingAgReaderTests, with the id-less companion (→ 2).
  • On dev, the id-less form of the first case gives 2.
• The live reads (AgGroupIdLiveReaderTests): two servers each report only their own replica of the same AG (the same group_id).
  • DarlingAgReader.GetAgHealthAsync gives distinct_ag_count = 1.
  • The Viewer's GetAvailabilityGroupsAsync → AgTopology.Counts gives 1 group, 2 views, 2 reporting servers.
  • RED on dev at runtime: Expected: 1 / Actual: 2.
• The rung (AgGroupIdRungTests, the new top rung):
  • ladder registration, the probe sentinel and its top arm, the schema after migrate, idempotency;
  • a real upgrade: a store at V150 whose AG chunks are compressed migrates to V151, the old rows read group_id NULL, and a write in the collector's column order carries the GUID.
  • V150's rung class and the older probe-loop facts now assert the stays-true shape.
  • The fresh-vs-upgraded schema pin covers the new column.
• Lite's twin was checked with DuckDB locally (the ALTERs run twice idempotently; an old row reads NULL; a GUID round-trips). Lite.Tests builds, and Windows CI runs it.
• Mutation: the id union disabled → the pure and live pins RED.
• Totals: 156/156 across the rung, probe, ladder, scaffold, generator, Viewer and census classes, and the count/reader classes green. The only failures are 2 pre-existing WPF-only tests that can't load on macOS. Darling.Tests and Lite.Tests build with 0 warnings.

CHANGELOG

SECTION: Changed
ENTRY:

• Darling and Lite now record each Availability Group's group_id, so two monitored secondaries of one AG count as one group even without its primary ([Store rung V151: collect each Availability Group's group_id and count groups by it (#4475) #4495]) - store rung V151 adds the column. Rows collected before it fall back to matching by name and replica.
  REF:
  [Store rung V151: collect each Availability Group's group_id and count groups by it (#4475) #4495]: Store rung V151: collect each Availability Group's group_id and count groups by it (#4475) #4495

IMPORTANT: Store rung V151 adds a group_id column to ag_replica_states and ag_database_replica_states (Lite: schema 65). Rows collected before the upgrade have it empty.