diff --git a/docker/build.sh b/docker/build.sh
index 52957617..a8919b5b 100755
--- a/docker/build.sh
+++ b/docker/build.sh
@@ -23,10 +23,12 @@ fi
 
 # Build from repo root (so COPY paths in Dockerfile resolve correctly)
 echo "Building scadabridge:latest image..."
+# Note: ${NUGET_ARGS[@]+...} guards against the "unbound variable" error that
+# set -u raises on bash 3.2 (macOS default) when expanding an empty array.
 docker build \
     -t scadabridge:latest \
     -f "$SCRIPT_DIR/Dockerfile" \
-    "${NUGET_ARGS[@]}" \
+    ${NUGET_ARGS[@]+"${NUGET_ARGS[@]}"} \
     "$REPO_ROOT"
 
 echo "Build complete: scadabridge:latest"
diff --git a/docker/seed-sites.sh b/docker/seed-sites.sh
index 7c2c9d89..2139b347 100755
--- a/docker/seed-sites.sh
+++ b/docker/seed-sites.sh
@@ -63,6 +63,35 @@ $CLI $URL $AUTH notification create \
     --emails "engineer@company.com" \
 || echo "  (Engineering Alerts may already exist)"
 
+echo ""
+echo "Creating MxGateway data connections (shared gateway) on each site..."
+# A shared MxGateway data connection pointing at the MxAccess Gateway. Data
+# connections are site-scoped (the DCL runs on site clusters only — central
+# nodes do not host data connections), so one is created per site. The same
+# gateway endpoint + API key is reused across all sites.
+#
+# Config is the typed MxGatewayEndpointConfig JSON (camelCase keys), matching
+# MxGatewayEndpointConfigSerializer.
+MXGW_ENDPOINT="http://10.100.0.48:5120"
+MXGW_APIKEY="mxgw_scadabridgeshared_O193yRm28zftUAcL-HPkTjAuE-vPz86MUtNLFWpcbOY"
+MXGW_CONFIG="{\"endpoint\":\"${MXGW_ENDPOINT}\",\"apiKey\":\"${MXGW_APIKEY}\",\"clientName\":\"\",\"writeUserId\":0,\"useTls\":false,\"caFile\":\"\",\"serverName\":\"\",\"readTimeoutMs\":5000}"
+
+for ident in site-a site-b site-c; do
+    SITE_ID=$($CLI $URL $AUTH --format json site list \
+        | python3 -c "import sys,json; print(next((s['id'] for s in json.load(sys.stdin) if s.get('siteIdentifier')=='$ident'), ''))" 2>/dev/null)
+    if [ -z "$SITE_ID" ]; then
+        echo "  ($ident not found — skipping MxGateway connection)"
+        continue
+    fi
+    echo "  $ident (id=$SITE_ID): creating 'MxGateway Shared'..."
+    $CLI $URL $AUTH data-connection create \
+        --site-id "$SITE_ID" \
+        --name "MxGateway Shared" \
+        --protocol "MxGateway" \
+        --primary-config "$MXGW_CONFIG" \
+    || echo "    (MxGateway connection may already exist on $ident)"
+done
+
 echo ""
 echo "Seeding LDAP group mappings (Design + Deployment)..."
 # SecurityConfiguration.HasData declares 4 mappings but the InitialSchema
@@ -82,9 +111,18 @@ IF NOT EXISTS (SELECT 1 FROM LdapGroupMappings WHERE Id = 4)
 SET IDENTITY_INSERT LdapGroupMappings OFF;
 "
 
+echo ""
+echo "Deploying artifacts to all sites (pushes data connections so the sites"
+echo "establish them — the MxGateway DataConnectionActor connects eagerly)..."
+$CLI $URL $AUTH deploy artifacts \
+|| echo "  (artifact deploy reported an issue — check 'deploy status')"
+
 echo ""
 echo "=== Site seeding complete ==="
 echo ""
 echo "Verify with: $CLI $URL $AUTH site list"
+echo "Verify connections: $CLI $URL $AUTH data-connection list"
+echo "Verify MxGateway is live (per site container):"
+echo "  docker logs scadabridge-site-a-a 2>&1 | grep -i mxgateway"
 echo "Multi-role test user has Admin + Design + Deployment."
 echo "Sign out and back in to refresh session role claims."
diff --git a/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/DeploymentManagerActor.cs b/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/DeploymentManagerActor.cs
index d53212e4..55ca8163 100644
--- a/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/DeploymentManagerActor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/DeploymentManagerActor.cs
@@ -1002,6 +1002,11 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
             "Deploying system artifacts, deploymentId={DeploymentId}", command.DeploymentId);
 
         var sender = Sender;
+        // Capture Self before entering Task.Run: the Self/Sender/Context properties
+        // are backed by the ambient ActorCell, which is null on a thread-pool thread,
+        // so reading Self *inside* the lambda throws "no active ActorContext". The
+        // data-connections branch below dispatches via this captured ref.
+        var self = Self;
 
         Task.Run(async () =>
         {
@@ -1071,7 +1076,7 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
                     // helper's hash cache skips unchanged definitions, so
                     // the push is idempotent for re-deploys of the same
                     // artifact bundle.
-                    Self.Tell(new ApplyArtifactDataConnectionsToDcl(command.DataConnections));
+                    self.Tell(new ApplyArtifactDataConnectionsToDcl(command.DataConnections));
                 }
 
                 // Store SMTP configurations