Notify-and-fetch follow-ups:
- PendingDeploymentPurgeActor: a central cluster singleton (not
readiness-gated, best-effort) that sweeps expired PendingDeployment
staging rows on CommunicationOptions.PendingDeploymentPurgeInterval
(default 1h). Modeled on the kpi-history-recorder pattern: self-scheduling
timer, per-tick DI scope -> IDeploymentManagerRepository, continue-on-error.
Wired in AkkaHostedService.RegisterCentralActors (manager + proxy + drain);
resolves the deferred TODO in DeploymentService. Correctness never depends
on it (supersession bounds rows to <=1/instance; the fetch endpoint enforces
the TTL), so it is deliberately absent from RequiredSingletonsHealthCheck.
- SQL Server integration test for StagePendingIfAbsentAsync re-staging an
instance's OWN DeploymentId over an expired row against the real UNIQUE
index on DeploymentId — confirms EF orders DELETE before INSERT in one
SaveChanges (SQLite's constraint timing differs from SQL Server's). Plus
a same-instance supersession variant on real SQL Server.
Tests: 2 TestKit actor tests + 2 SQL Server integration tests (both ran
green against the infra MSSQL container); 235 Communication + 15
PendingDeployment tests pass; Host builds 0 warnings.