fix(host): resolve Host-012..015 — consume DownIfAlone in HOCON, sub-second timing precision, config-driven Serilog sinks, transient-only startup retry

src/ScadaLink.Host/Actors/AkkaHostedService.cs

@@ -67,7 +67,8 @@ public class AkkaHostedService : IHostedService
         // interpolated value, so a hostname, seed node or strategy containing a quote,
         // backslash or whitespace cannot corrupt the configuration document.
         var hocon = BuildHocon(_nodeOptions, _clusterOptions, roles,
-            transportHeartbeatSec, transportFailureSec);
+            _communicationOptions.TransportHeartbeatInterval,
+            _communicationOptions.TransportFailureThreshold);
 
         var config = ConfigurationFactory.ParseString(hocon);
         _actorSystem = ActorSystem.Create("scadalink", config);
@@ -106,13 +107,21 @@ public class AkkaHostedService : IHostedService
     /// routed through <see cref="QuoteHocon"/> (string values) so a hostname,
     /// seed-node URI, role or split-brain strategy containing a quote, backslash or
     /// whitespace cannot corrupt the document or be silently misparsed (Host-006).
+    ///
+    /// Host-012: the <c>keep-oldest down-if-alone</c> flag is emitted from
+    /// <see cref="ClusterOptions.DownIfAlone"/> rather than hard-coded, so the bound
+    /// configuration value is actually consumed.
+    ///
+    /// Host-013: every duration is rendered via <see cref="DurationHocon"/> in
+    /// milliseconds, so sub-second cluster timing values (e.g. a 750ms heartbeat) are
+    /// preserved exactly instead of being rounded to whole seconds.
     /// </summary>
     public static string BuildHocon(
         NodeOptions nodeOptions,
         ClusterOptions clusterOptions,
         IEnumerable<string> roles,
-        double transportHeartbeatSec,
-        double transportFailureSec)
+        TimeSpan transportHeartbeat,
+        TimeSpan transportFailure)
     {
         var seedNodesStr = string.Join(",",
             clusterOptions.SeedNodes.Select(QuoteHocon));
@@ -132,8 +141,8 @@ akka {{
             port = {nodeOptions.RemotingPort}
         }}
         transport-failure-detector {{
-            heartbeat-interval = {transportHeartbeatSec:F0}s
-            acceptable-heartbeat-pause = {transportFailureSec:F0}s
+            heartbeat-interval = {DurationHocon(transportHeartbeat)}
+            acceptable-heartbeat-pause = {DurationHocon(transportFailure)}
         }}
     }}
     cluster {{
@@ -142,14 +151,14 @@ akka {{
         min-nr-of-members = {clusterOptions.MinNrOfMembers}
         split-brain-resolver {{
             active-strategy = {QuoteHocon(clusterOptions.SplitBrainResolverStrategy)}
-            stable-after = {clusterOptions.StableAfter.TotalSeconds:F0}s
+            stable-after = {DurationHocon(clusterOptions.StableAfter)}
             keep-oldest {{
-                down-if-alone = on
+                down-if-alone = {(clusterOptions.DownIfAlone ? "on" : "off")}
             }}
         }}
         failure-detector {{
-            heartbeat-interval = {clusterOptions.HeartbeatInterval.TotalSeconds:F0}s
-            acceptable-heartbeat-pause = {clusterOptions.FailureDetectionThreshold.TotalSeconds:F0}s
+            heartbeat-interval = {DurationHocon(clusterOptions.HeartbeatInterval)}
+            acceptable-heartbeat-pause = {DurationHocon(clusterOptions.FailureDetectionThreshold)}
         }}
         run-coordinated-shutdown-when-down = on
     }}
@@ -159,6 +168,18 @@ akka {{
 }}";
     }
 
+    /// <summary>
+    /// Renders a <see cref="TimeSpan"/> as a HOCON duration in milliseconds. Akka's
+    /// HOCON parser accepts a <c>ms</c> suffix, so emitting whole milliseconds
+    /// preserves sub-second configuration exactly — a 750ms heartbeat stays 750ms
+    /// rather than being rounded to <c>1s</c> (or, for sub-half-second values,
+    /// silently collapsing to a degenerate <c>0s</c>) — Host-013.
+    /// </summary>
+    private static string DurationHocon(TimeSpan duration)
+    {
+        return $"{(long)Math.Round(duration.TotalMilliseconds)}ms";
+    }
+
     /// <summary>
     /// Renders a value as a HOCON double-quoted string, escaping backslashes and
     /// double quotes so the resulting token cannot break out of its string literal.