perf(site-runtime): deserialize a deploy's flattened config once and hand the parsed object down (review 2026-10-21 01/SR-P5)

The deploy compile warm parses once off-thread; the parsed FlattenedConfiguration
rides DeployCompileWarmed to the gate (new Validate(FlattenedConfiguration)
overload), the redeploy buffer, CreateInstanceActor's DCL ensure and a new
InstanceActor constructor overload. Stored-row paths parse once inside
CreateInstanceActor; an unparseable stored row still fails init via S6.

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/InstanceActor.cs

@@ -262,6 +262,50 @@ public class InstanceActor : ReceiveActor
         IServiceProvider? serviceProvider = null,
         TimeSpan? staticOverrideFlushInterval = null,
         Task? staticStateResetGate = null)
+        : this(
+            instanceUniqueName,
+            JsonSerializer.Deserialize<FlattenedConfiguration>(configJson),
+            storage, compilationService, sharedScriptLibrary, streamManager, options, logger,
+            dclManager, healthCollector, serviceProvider, staticOverrideFlushInterval,
+            staticStateResetGate)
+    {
+    }
+
+    /// <summary>
+    /// Initializes the instance actor from an ALREADY-PARSED flattened configuration (review
+    /// 2026-10-21 01/SR-P5). The Deployment Manager parses each config once — the deploy compile
+    /// warm, the gate, the DCL-connection ensure and this actor all used to deserialize the same
+    /// JSON separately — and hands the object over. The configuration is read-only here, so
+    /// sharing the instance the Deployment Manager parsed is safe. Parameters are as for the
+    /// JSON overload.
+    /// </summary>
+    /// <param name="instanceUniqueName">System-wide unique name identifying this instance.</param>
+    /// <param name="configuration">The parsed flattened configuration (null = empty instance).</param>
+    /// <param name="storage">Site storage service for loading and persisting static overrides.</param>
+    /// <param name="compilationService">Service used to compile instance scripts.</param>
+    /// <param name="sharedScriptLibrary">Library of shared scripts available to instance scripts.</param>
+    /// <param name="streamManager">Optional site stream manager for publishing attribute/alarm changes.</param>
+    /// <param name="options">Site runtime configuration options.</param>
+    /// <param name="logger">Logger for this actor.</param>
+    /// <param name="dclManager">Optional Data Connection Layer manager actor reference.</param>
+    /// <param name="healthCollector">Optional health collector for reporting metrics.</param>
+    /// <param name="serviceProvider">Optional DI service provider for script execution services.</param>
+    /// <param name="staticOverrideFlushInterval">Coalescing window for buffered static-override writes.</param>
+    /// <param name="staticStateResetGate">See the JSON overload.</param>
+    public InstanceActor(
+        string instanceUniqueName,
+        FlattenedConfiguration? configuration,
+        SiteStorageService storage,
+        ScriptCompilationService compilationService,
+        SharedScriptLibrary sharedScriptLibrary,
+        SiteStreamManager? streamManager,
+        SiteRuntimeOptions options,
+        ILogger logger,
+        IActorRef? dclManager = null,
+        ISiteHealthCollector? healthCollector = null,
+        IServiceProvider? serviceProvider = null,
+        TimeSpan? staticOverrideFlushInterval = null,
+        Task? staticStateResetGate = null)
     {
         _instanceUniqueName = instanceUniqueName;
         _storage = storage;
@@ -277,8 +321,7 @@ public class InstanceActor : ReceiveActor
         _staticOverrideFlushInterval = staticOverrideFlushInterval ?? TimeSpan.FromMilliseconds(100);
         _staticStateResetGate = staticStateResetGate;
 
-        // Deserialize the flattened configuration
-        _configuration = JsonSerializer.Deserialize<FlattenedConfiguration>(configJson);
+        _configuration = configuration;
 
         // Load default attribute values from the flattened configuration
         // Data-sourced attributes start with Uncertain quality until the first DCL value arrives.