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/Deployment/DeployCompileValidator.cs

@@ -58,19 +58,54 @@ public sealed class DeployCompileValidator
     /// <returns>A list of compile-error messages; empty if the configuration is clean.</returns>
     public IReadOnlyList<string> Validate(string configJson, string? instanceName = null)
     {
-        FlattenedConfiguration? config;
+        if (!TryParse(configJson, out var config, out var parseError))
+            return [parseError!];
+
+        return Validate(config!, instanceName);
+    }
+
+    /// <summary>
+    /// Deserializes a flattened-configuration JSON exactly as <see cref="Validate(string, string?)"/>
+    /// does, so a caller that needs the parsed object as well (the Deployment Manager, which hands
+    /// it on to the Instance Actor — review 2026-10-21 01/SR-P5) parses once instead of once per
+    /// consumer. The error text is the one <see cref="Validate(string, string?)"/> reports.
+    /// </summary>
+    /// <param name="configJson">The flattened-configuration JSON.</param>
+    /// <param name="config">The parsed configuration, or <see langword="null"/> on failure.</param>
+    /// <param name="error">The deserialization error, or <see langword="null"/> on success.</param>
+    /// <returns><see langword="true"/> when the JSON produced a configuration.</returns>
+    public static bool TryParse(string configJson, out FlattenedConfiguration? config, out string? error)
+    {
         try
         {
             config = JsonSerializer.Deserialize<FlattenedConfiguration>(configJson);
         }
         catch (JsonException ex)
         {
-            return [$"Configuration JSON failed to deserialize: {ex.Message}"];
+            config = null;
+            error = $"Configuration JSON failed to deserialize: {ex.Message}";
+            return false;
         }
 
         if (config == null)
-            return ["Configuration JSON failed to deserialize: result was null."];
+        {
+            error = "Configuration JSON failed to deserialize: result was null.";
+            return false;
+        }
 
+        error = null;
+        return true;
+    }
+
+    /// <summary>
+    /// Validates an already-parsed flattened configuration — the same checks as
+    /// <see cref="Validate(string, string?)"/> without a second deserialization (01/SR-P5).
+    /// </summary>
+    /// <param name="config">The parsed flattened configuration.</param>
+    /// <param name="instanceName">See <see cref="Validate(string, string?)"/>.</param>
+    /// <returns>A list of error messages; empty if the configuration is clean.</returns>
+    public IReadOnlyList<string> Validate(FlattenedConfiguration config, string? instanceName = null)
+    {
         var errors = new List<string>();
 
         // Runtime names first: they are cheap, and a name Akka refuses would otherwise surface