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).

tests/ScadaLink.SiteRuntime.Tests/Actors/DeploymentManagerActorTests.cs

@@ -187,6 +187,46 @@ public class DeploymentManagerActorTests : TestKit, IDisposable
         Assert.DoesNotContain(configs, c => c.InstanceUniqueName == "LifecyclePump");
     }
 
+    // ── DeploymentManager-006: query-the-site-before-redeploy ──
+
+    [Fact]
+    public async Task DeploymentStateQuery_DeployedInstance_ReturnsAppliedIdentity()
+    {
+        // A deployed instance must report its currently-applied deployment ID
+        // and revision hash so central can reconcile before a re-deploy.
+        await _storage.StoreDeployedConfigAsync(
+            "QueriedPump", MakeConfigJson("QueriedPump"), "dep-applied", "sha256:applied", true);
+
+        var actor = CreateDeploymentManager();
+        await Task.Delay(2000); // allow startup to load configs
+
+        actor.Tell(new DeploymentStateQueryRequest("corr-q1", "QueriedPump", DateTimeOffset.UtcNow));
+
+        var response = ExpectMsg<DeploymentStateQueryResponse>(TimeSpan.FromSeconds(5));
+        Assert.Equal("corr-q1", response.CorrelationId);
+        Assert.Equal("QueriedPump", response.InstanceUniqueName);
+        Assert.True(response.IsDeployed);
+        Assert.Equal("dep-applied", response.AppliedDeploymentId);
+        Assert.Equal("sha256:applied", response.AppliedRevisionHash);
+    }
+
+    [Fact]
+    public async Task DeploymentStateQuery_UnknownInstance_ReturnsNotDeployed()
+    {
+        // An instance the site has never received a deployment for must report
+        // IsDeployed=false with null applied identity.
+        var actor = CreateDeploymentManager();
+        await Task.Delay(500);
+
+        actor.Tell(new DeploymentStateQueryRequest("corr-q2", "NeverDeployed", DateTimeOffset.UtcNow));
+
+        var response = ExpectMsg<DeploymentStateQueryResponse>(TimeSpan.FromSeconds(5));
+        Assert.Equal("corr-q2", response.CorrelationId);
+        Assert.False(response.IsDeployed);
+        Assert.Null(response.AppliedDeploymentId);
+        Assert.Null(response.AppliedRevisionHash);
+    }
+
     [Fact]
     public void DeploymentManager_SupervisionStrategy_ResumesOnException()
     {