config(battle-node): require NodeServerUrl from appsettings, no fallback

Move the localhost default off BattleNodeOptions and out of Program.cs
into an appsettings.json "BattleNode" section, and make AddBattleNode
throw at startup if the value is missing or blank. Deployments now must
set the URL explicitly, and dev keeps working via the checked-in value.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleNode/Bridge/BattleNodeOptions.cs

@@ -1,13 +1,25 @@
 namespace SVSim.BattleNode.Bridge;
 
 /// <summary>
-/// DI-injected options for the battle node. NodeServerUrl matches the prod
-/// do_matching wire format: <c>host:port/socket.io/</c>, no scheme prefix.
-/// BestHTTP's SocketManager parses it as the Socket.IO v2 endpoint URL.
+/// DI-injected options for the battle node.
 /// </summary>
 public sealed class BattleNodeOptions
 {
-    public string NodeServerUrl { get; set; } = "localhost:5148/socket.io/";
+    /// <summary>
+    /// The Socket.IO v2 endpoint URL echoed back to the client on <c>/*/do_matching</c>
+    /// success (matching_state 3004/3007/3011). Matches the prod do_matching wire format:
+    /// <c>host[:port]/socket.io/</c> — no scheme prefix, must end with <c>/socket.io/</c>.
+    /// The client's BestHTTP <c>SocketManager</c> parses this string directly; a leading
+    /// <c>http://</c>/<c>https://</c> or a missing trailing slash will make the client
+    /// fail to connect. Host may be an IP, hostname, or FQDN.
+    /// <para>
+    /// Deployment-time value — no hardcoded fallback. Must be provided via the
+    /// <c>"BattleNode:NodeServerUrl"</c> key in <c>appsettings.json</c> (or an
+    /// equivalently-named env var); <see cref="Hosting.BattleNodeExtensions.AddBattleNode"/>
+    /// validates presence at startup and throws if empty.
+    /// </para>
+    /// </summary>
+    public string NodeServerUrl { get; set; } = "";
 
     /// <summary>
     /// How long the first arriver's WS waits for a partner before disconnecting.

SVSim.BattleNode/Hosting/BattleNodeExtensions.cs

@@ -18,15 +18,26 @@ public static class BattleNodeExtensions
     /// instance the WebSocket handler constructs on connect.
     /// </summary>
     /// <param name="configure">
-    /// Optional callback to override <see cref="BattleNodeOptions"/> defaults. The default
-    /// <c>NodeServerUrl</c> assumes the EmulatedEntrypoint host on
-    /// <c>http://localhost:5148</c> and shares the port for the Socket.IO endpoint. Override
-    /// when the node runs on a different port/host or behind a reverse proxy.
+    /// Callback to populate <see cref="BattleNodeOptions"/>. Must set
+    /// <see cref="BattleNodeOptions.NodeServerUrl"/> — there is no hardcoded fallback; the
+    /// value is a deployment concern (localhost during dev, a real host[:port]/socket.io/
+    /// when the node runs behind a reverse proxy or on a separate box). Startup throws
+    /// <see cref="InvalidOperationException"/> if it's still empty after the callback runs.
     /// </param>
+    /// <exception cref="InvalidOperationException">
+    /// <see cref="BattleNodeOptions.NodeServerUrl"/> is null, empty, or whitespace after
+    /// <paramref name="configure"/> runs.
+    /// </exception>
     public static IServiceCollection AddBattleNode(this IServiceCollection services, Action<BattleNodeOptions>? configure = null)
     {
         var options = new BattleNodeOptions();
         configure?.Invoke(options);
+        if (string.IsNullOrWhiteSpace(options.NodeServerUrl))
+        {
+            throw new InvalidOperationException(
+                "BattleNode:NodeServerUrl is not configured. Set it in appsettings.json under " +
+                "the \"BattleNode\" section (format: \"host[:port]/socket.io/\", no scheme prefix).");
+        }
         services.AddSingleton(options);
         services.AddSingleton<IBattleSessionStore, InMemoryBattleSessionStore>();
         services.AddSingleton<IMatchingBridge, MatchingBridge>();

SVSim.EmulatedEntrypoint/Program.cs

@@ -165,11 +165,10 @@ public class Program
 
         builder.Services.AddBattleNode(opt =>
         {
-            // Matches the prod do_matching wire format: host:port/socket.io/, no scheme prefix.
-            // BestHTTP's SocketManager parses this as the Socket.IO v2 endpoint URL.
-            opt.NodeServerUrl = "localhost:5148/socket.io/";
-            // Any field in BattleNodeOptions can be overridden via the "BattleNode" section
-            // in appsettings*.json — see appsettings.Development.json for DiagnosticLogging.
+            // Every field on BattleNodeOptions is populated from the "BattleNode" section in
+            // appsettings*.json. NodeServerUrl has no hardcoded fallback — AddBattleNode
+            // throws at startup if it's missing/blank. See BattleNodeOptions.NodeServerUrl
+            // for the required wire format.
             builder.Configuration.GetSection("BattleNode").Bind(opt);
         });
         // In-process FCFS pair-up for TK2 PvP /do_matching, plus rank-battle's AI-fallback

SVSim.EmulatedEntrypoint/appsettings.json

@@ -27,5 +27,13 @@
   "Deck": {
     "MaxDeckSlots": 36
   },
+  "BattleNode": {
+    // Socket.IO v2 endpoint URL echoed to the client on /*/do_matching success.
+    // Wire format: "host[:port]/socket.io/" — no scheme prefix, trailing slash REQUIRED.
+    // Host may be an IP, hostname, or FQDN. BestHTTP's SocketManager parses this string
+    // directly; a leading http:// or https:// will make the client fail to connect.
+    // Startup throws if this value is missing or blank; there is no hardcoded fallback.
+    "NodeServerUrl": "localhost:5148/socket.io/"
+  },
   "AllowedHosts": "*"
 }