perf(central): set-based ingest, aligned partition purge, KPI query shapes, EF hygiene

docs/components/ConfigurationDatabase.md

@@ -78,13 +78,15 @@ builder.Property(e => e.ExecutionId)
         "CAST(JSON_VALUE(DetailsJson,'$.executionId') AS uniqueidentifier)", stored: true)
     .ValueGeneratedOnAddOrUpdate();
 
-// Composite PK includes OccurredAtUtc for partition alignment
+// Composite PK includes OccurredAtUtc for partition alignment — and is the ONLY
+// EventId uniqueness enforcement (WP2.2 / AlignAuditLogEventIdUniqueness). EventId
+// is a GUID minted once at the site alongside OccurredAtUtc, so a given EventId
+// always lands in one partition and pair-uniqueness is EventId-uniqueness.
 builder.HasKey(e => new { e.EventId, e.OccurredAtUtc });
-
-builder.HasIndex(e => e.EventId).IsUnique()
-    .HasDatabaseName("UX_AuditLog_EventId");
 ```
 
+The predecessor `UX_AuditLog_EventId` — a single-column unique index on `[PRIMARY]`, deliberately NOT partition-aligned — was dropped: a non-aligned index blocks `ALTER TABLE … SWITCH PARTITION`, so the retention purge had to drop it, switch, and rebuild it offline inside the switch transaction on every run.
+
 **`TemplateConfiguration`** (representative of the domain-area configs) sets up the self-referencing parent FK, folder FK, cascade-delete relationships to attributes/alarms/scripts/compositions/native alarm sources, and the filtered unique index that enforces name uniqueness only on non-derived (base) templates.
 
 **`SiteCallEntityTypeConfiguration`** maps `SiteCall` to `dbo.SiteCalls` with a `TrackedOperationId` PK stored as `varchar(36)` (GUID in `"D"` format) so the column shape matches the wire format and the site SQLite store — one consistent format for operational debugging.
@@ -108,11 +110,13 @@ VALUES
 
 `FormattableString` interpolation parameterises every value so there is no injection surface. SQL error numbers `2601` and `2627` (unique-index violation) are swallowed as no-ops because the IF NOT EXISTS check has a race window; both the check-loser and the retrying telemetry path are semantically correct duplicates.
 
+`InsertManyIfNotExistsAsync` is the set-based form the ingest hot path uses: one `INSERT … SELECT … FROM (VALUES …) WHERE NOT EXISTS` per chunk of 100 rows (ten bound parameters per row against SQL Server's 2,100-parameter ceiling), so a telemetry packet costs one round trip instead of one per event. Because the anti-semi-join only sees committed rows, the packet is de-duplicated by `EventId` in C# first (first-write-wins, matching the single-row contract); a duplicate-key fault from a concurrent writer falls back to the per-row path so the batch is never a correctness dependency. It uses raw ADO.NET with explicitly typed `SqlParameter`s — the `VALUES` constructor derives its column types from the first row's parameters, so an untyped null would give the derived column the wrong type — and enlists in the DbContext's ambient transaction when one is open (the cached-telemetry dual-write).
+
 `QueryAsync` builds LINQ predicates over `AuditLogRow` using `AsNoTracking()`, translating filter dimensions (`Channels`, `Kinds`, `Statuses`, `SourceSiteIds`, `SourceNodes`, `ExecutionId`, `ParentExecutionId`, time range) to server-side SQL IN/equality predicates and using keyset pagination on `(OccurredAtUtc DESC, EventId DESC)`.
 
 `GetExecutionTreeAsync` walks the `ParentExecutionId` graph in two phases: a loop climbs to the root (bounded at 32 levels), then a recursive CTE descends the full tree and LEFT JOINs back to `AuditLog` so stub nodes (purged or row-less executions) still appear with `RowCount = 0`.
 
-`SwitchOutPartitionAsync` executes a drop-and-rebuild dance — dropping `UX_AuditLog_EventId`, creating a byte-identical staging table (including the computed-column definitions), switching the target partition to staging, dropping staging, and rebuilding the unique index — all inside a single `BEGIN TRY / BEGIN CATCH` block that guarantees the index is present whether the switch succeeds or rolls back.
+`SwitchOutPartitionAsync` creates a byte-identical staging table (including the computed-column definitions), switches the target partition to staging, and drops staging, inside a single `BEGIN TRY / BEGIN CATCH` block whose CATCH cleans up the staging table on any failure. No index is dropped or rebuilt: uniqueness rides the partition-aligned clustered PK, so the switch is metadata-only. A guarded defensive `DROP INDEX UX_AuditLog_EventId` remains at the head of the batch purely so a database restored from a pre-alignment backup still purges.
 
 ### IAuditService — config-change audit
 
@@ -241,7 +245,7 @@ The host is running in production mode and `GetPendingMigrationsAsync` found una
 
 ### AuditLog partition switch fails mid-operation
 
-`SwitchOutPartitionAsync` wraps the drop-and-rebuild dance in `BEGIN TRY / BEGIN CATCH`. On failure the CATCH block drops the staging table if it exists and rebuilds `UX_AuditLog_EventId` if it was dropped before the failure. The original exception is re-thrown so the Audit Log purge actor logs it and retries on the next daily tick. Verify that the `scadabridge_audit_purger` role still holds `ALTER ON SCHEMA::dbo` if the operation fails with a permissions error.
+`SwitchOutPartitionAsync` wraps the staging/switch batch in `BEGIN TRY / BEGIN CATCH`. On failure the CATCH block drops the staging table if it exists, so no orphaned `AuditLog_Staging_*` object is left behind. There is no index to repair — uniqueness lives on the clustered PK, which the switch never touches. The original exception is re-thrown so the Audit Log purge actor logs it and retries on the next daily tick. Verify that the `scadabridge_audit_purger` role still holds `ALTER ON SCHEMA::dbo` if the operation fails with a permissions error.
 
 ### Design-time `dotnet ef` tooling cannot find a connection string