Server: collect tombstones past their retention, compact superseded change entries, and refuse cursors from before a collection

src/DodoSSH.Api/Program.cs

@@ -48,6 +48,10 @@ builder.Services.AddSingleton<ICursorKeyProvider, CursorKeyProvider>();
 builder.Services.AddSingleton<VaultEventHub>();
 builder.Services.AddSingleton<IVaultEventPublisher, VaultEventFanOut>();
 
+// ADR 0003's tombstone collection, and the compaction of the change log that goes with it.
+builder.Services.AddScoped<TombstoneCollector>();
+builder.Services.AddHostedService<TombstoneCollectionService>();
+
 // The relay's services, its ticket key ring, and a shutdown long enough for its drain. See ADR 0004.
 builder.Services.AddDodoRelay();