feat(deployment-manager): resolve DeploymentManager-006 — query site deployment state before redeploy and reconcile

Adds DeploymentStateQuery request/response contracts (Commons), a site-side
handler (SiteRuntime), a CommunicationService query method (Communication), and
reconciliation in DeploymentService: when a prior record is InProgress or
Failed-on-timeout, query the site; if it already holds the target revision hash
mark the record Success without re-sending; on query failure fall through to a
normal deploy (site-side stale-rejection is the safety net).

src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs

@@ -78,6 +78,12 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         Receive<EnableInstanceCommand>(HandleEnable);
         Receive<DeleteInstanceCommand>(HandleDelete);
 
+        // DeploymentManager-006: query-the-site-before-redeploy idempotency.
+        // Central asks for the instance's currently-applied deployment identity
+        // before re-sending a deployment whose prior record is stuck InProgress
+        // or Failed due to a timeout.
+        Receive<DeploymentStateQueryRequest>(HandleDeploymentStateQuery);
+
         // WP-33: Handle system-wide artifact deployment
         Receive<DeployArtifactsCommand>(HandleDeployArtifacts);
 
@@ -446,6 +452,44 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         _logger.LogInformation("Instance {Instance} deleted", instanceName);
     }
 
+    /// <summary>
+    /// DeploymentManager-006: answers a central query for the instance's
+    /// currently-applied deployment identity. The site's deployed-config store
+    /// (SQLite) is the authoritative record — it covers both enabled and
+    /// disabled instances, and survives node restart/failover. If the instance
+    /// has no stored config, the response reports <c>IsDeployed = false</c> with
+    /// null identity so central falls through to a normal deploy.
+    /// </summary>
+    private void HandleDeploymentStateQuery(DeploymentStateQueryRequest request)
+    {
+        var sender = Sender;
+        var instanceName = request.InstanceUniqueName;
+
+        _storage.GetAllDeployedConfigsAsync().ContinueWith(t =>
+        {
+            if (!t.IsCompletedSuccessfully)
+            {
+                _logger.LogError(
+                    t.Exception?.GetBaseException(),
+                    "Failed to read deployed configs for deployment state query of {Instance}",
+                    instanceName);
+                // Treat a storage read failure as "unknown" — central falls
+                // through to a normal deploy and relies on site-side
+                // stale-rejection as the safety net.
+                return new DeploymentStateQueryResponse(
+                    request.CorrelationId, instanceName, false, null, null, DateTimeOffset.UtcNow);
+            }
+
+            var config = t.Result.FirstOrDefault(c => c.InstanceUniqueName == instanceName);
+            return config == null
+                ? new DeploymentStateQueryResponse(
+                    request.CorrelationId, instanceName, false, null, null, DateTimeOffset.UtcNow)
+                : new DeploymentStateQueryResponse(
+                    request.CorrelationId, instanceName, true,
+                    config.DeploymentId, config.RevisionHash, DateTimeOffset.UtcNow);
+        }).PipeTo(sender);
+    }
+
     // ── DCL connection management ──
 
     private readonly HashSet<string> _createdConnections = new();