Fleet overview: an Azure master's deadlock last-seen comes from its own databases, and the Viewer card shows no sibling's Last

[erikdarlingdata]

Follow-up to #4925.

What was wrong

#4925 scoped an Azure SQL Database master's blocking and deadlock counts to its own databases, but left the "last seen" times alone. A master whose own databases had no deadlocks still showed "0 deadlocks, last seen minutes ago" on the fleet card (/api/fleet, MCP get_fleet_overview), because the time came from a separately monitored database's deadlock. The Darling Viewer's Overview card did the same: under 0 blocking and 0 deadlocks it read "Last: 2m ago" from a sibling's event.

The fix

• The fleet card: PgFactCollector.CountAndNewestDeadlocksSkippingSeparateAsync returns the scoped deadlock count AND the newest deadlock that count includes, in ONE pass, with the count's own rule: the outside rows give COUNT(*) and MAX(deadlock_time) in SQL, and each graph that counts (not every process in a separately monitored database) adds to the count and to the newest. Its statements have the same predicates, window, collection floor and parameters as the count-only statements, so the count is unchanged. CountDeadlocksSkippingSeparateAsync is unchanged (the anomaly detector uses it).
• DarlingFleetReader.ReadAzureMasterScopedCountsAsync makes that one call, and the fleet card's deadlock_last_seen takes the scoped time. The counts and the time come from the same read, so a failure can't separate them: a throw keeps that master's whole unscoped row, as before. MCP get_server_summary (which has no last-seen field) now makes one graph pass instead of two.
• The Darling Viewer: a master with separately monitored databases shows NO "Last: N ago" on its Overview card, for blocking (the extended-events and DMV sides) or deadlocks. That time looks back over all stored history, and a master's own-database newest would need an all-history read or a cache on every refresh. Its counts stay scoped, and its Blocking and Deadlocks lists keep every row, with the note saying where those databases' events are counted. Every other server, a master with no separately monitored databases, and a master whose list lookup fails keep today's "Last".
• The fleet card has no blocking last-seen field. MCP get_server_summary has no last-seen field. Lite's card shows no "Last", so Lite is unchanged. The web fleet page shows a last-seen only when the count is above 0.

Pins

• FleetOverviewAzureMasterScopeLiveTests.MasterCard_DeadlockLastSeen_IsTheNewestOfItsOwnDatabases: with a sibling's deadlock newer than master's own, master's card shows its own newest (and null when it has none).
• TheCombinedDeadlockPass_AgreesWithTheCountOnlyPass_AndFindsTheNewestCounted: an outside row, an all-in graph, a mixed graph, a graph with no database and a row with no event time; the count equals the count-only method's, the newest is the newest counted row, and a newer all-in graph is skipped.
• TheScopedCounts_MakeOneDeadlockPass: the scoped reads call the combined method once.
• ViewerFleetAzureMasterScopeLiveTests.TheMastersCard_ShowsNoLastForBlockingOrDeadlocks: a scoped master under 0/0 with newer sibling events has no "Last" in either detail, also when a scoped read fails; after a failed list lookup it keeps the unscoped "Last"; a plain server and a master with no siblings keep theirs; the counts are unchanged.
• The two throw tests also assert that a failure keeps the unscoped last-seen.
• The fleet pin failed at the tests commit (the card carried the sibling's newer time). On dev the Viewer's master shows a "Last" about 5 minutes ago from the sibling's rows, so the Viewer pin's no-"Last" assertions cannot pass there.

Tests run

• Lite.Tests and Darling.Tests build with 0 warnings and 0 errors.
• Darling.Tests in-process, on a live PostgreSQL store, all passing: ViewerFleetAzureMasterScopeLiveTests (12), FleetOverviewAzureMasterScopeLiveTests (12), AzureMasterAnalysisScopeLiveTests (21), DarlingMcpHealthToolsLivePostgresTests (2), DarlingFleetReaderSqlTests (33), DarlingFleetDeadlockCoverageTests (23), ViewerOverviewSqlTests (11), ViewerFleetDeadlockCoverageTests (29), McpPayloadContractCensusTests (68), ViewerDailySummaryAzureMasterScopeLiveTests (3), StorageCommandTimeoutTests, McpReadCommandTimeoutTests, and the T-SQL, doc-comment, repo-file and deadline-scanner guards.

CHANGELOG

None: part of the fleet overview's Azure master entry (#4925).