Central singleton (M6-T4 Bundle C) that drives the daily AuditLog partition
purge. On a configurable timer (default 24 hours) the actor:
1. Queries IAuditLogRepository.GetPartitionBoundariesOlderThanAsync for
monthly boundaries whose latest OccurredAtUtc is older than
DateTime.UtcNow - AuditLogOptions.RetentionDays.
2. For each eligible boundary calls SwitchOutPartitionAsync, which runs
the drop-and-rebuild dance around UX_AuditLog_EventId.
3. Publishes AuditLogPurgedEvent(boundary, rowsDeleted, durationMs) on
the actor-system EventStream so the Bundle E central health collector
and ops surfaces can subscribe without coupling to this actor.
Co-changes:
* SwitchOutPartitionAsync returns long (rows deleted) — sampled BEFORE the
switch via COUNT_BIG over the per-partition filter so the count
reflects what the switch removed, not a post-purge scan of a table that
no longer exists. All stub implementations updated.
* AuditLogPurgeOptions: IntervalHours (default 24), IntervalOverride for
tests, Interval property resolving either.
* AuditLogPurgedEvent: record with MonthBoundary, RowsDeleted, DurationMs.
Behavior:
* Continue-on-error per boundary — one partition that throws does NOT
abandon the rest of the tick.
* DI scope opened per tick (IAuditLogRepository is a SCOPED EF Core
service); mirrors SiteAuditReconciliationActor and AuditLogIngestActor.
* SupervisorStrategy Resume keeps the singleton alive across leaked
exceptions.
* EventStream capture BEFORE the first await — Context is unsafe after
await in async receive handlers (same pattern as Sender-capture in
AuditLogIngestActor.OnIngestAsync).
Tests:
* Tick_Fires_OnDailyInterval — visible timer side effect.
* Tick_OldPartitions_SwitchedOut — both seeded boundaries purged.
* Tick_NewerPartitions_Untouched — empty enumerator → no switches.
* Tick_PublishesPurgedEvent_WithRowCount — AuditLogPurgedEvent carries
RowsDeleted and DurationMs.
* Tick_SwitchThrows_OtherPartitionsStillProcessed — continue-on-error.
* Threshold_UsesAuditLogOptionsRetentionDays — non-default 30-day window
computed from UtcNow - RetentionDays.
* EndToEnd_RealPartition_RowsRemoved_PurgedEventPublished — TestKit +
MsSqlMigrationFixture: real partitioned table, Jan-2026 row purged,
Apr-2026 row kept, AuditLogPurgedEvent observed via probe.
Replaces M1's NotSupportedException stub with the production drop-DROP-INDEX
→ CREATE-staging → SWITCH PARTITION → DROP-staging → CREATE-INDEX dance
documented in alog.md §4. UX_AuditLog_EventId is intentionally non-aligned
with ps_AuditLog_Month so single-column EventId uniqueness can be enforced
cheaply for InsertIfNotExistsAsync; SQL Server rejects ALTER TABLE SWITCH
while a non-aligned unique index is present, so the implementation drops
it, switches the partition data into a GUID-suffixed staging table on
[PRIMARY], drops staging (discarding the rows), and rebuilds the unique
index — all inside an explicit transaction with a CATCH that guarantees
the unique index is rebuilt regardless of failure point.
Also adds GetPartitionBoundariesOlderThanAsync to IAuditLogRepository: a
CROSS APPLY over sys.partition_range_values + per-partition MAX(OccurredAtUtc)
to enumerate retention-eligible months for the M6 purge actor (next commit).
Tests verify:
* Old partition's rows are removed; other months untouched
* UX_AuditLog_EventId is rebuilt after a successful switch
* InsertIfNotExistsAsync's first-write-wins idempotency still holds after switch
* On engineered SWITCH failure (inbound FK from a probe table), SqlException
propagates AND UX_AuditLog_EventId is still present (CATCH branch ran)
* GetPartitionBoundariesOlderThanAsync returns only boundaries whose partition's
MAX(OccurredAtUtc) is strictly older than the threshold; empty partitions
excluded
M4 Bundle B (B1) — add the central-only ICentralAuditWriter implementation
and inject it into NotificationOutboxActor so subsequent tasks (B2/B3) can
route attempt + terminal lifecycle events through the direct-write audit path.
- CentralAuditWriter: thin wrapper around IAuditLogRepository.InsertIfNotExistsAsync;
scope-per-call (matches AuditLogIngestActor / NotificationOutboxActor pattern);
stamps IngestedAtUtc; swallows all internal failures (alog.md §13).
- Registered as a singleton in AddAuditLog.
- NotificationOutboxActor ctor takes ICentralAuditWriter (validated non-null).
- Host wiring resolves the writer once from the root provider and passes it
into the singleton's Props.Create call.
- Existing TestKit fixtures updated with a NoOpCentralAuditWriter helper so
tests that don't exercise audit emission still compile and pass.
