fix(arena-tk2): park returns 3002 RETRY + empty node_server_url

Two client-crash bugs in the do_matching response when no partner is
waiting:

1. matching_state was 3001 (RC_BATTLE_MATCHING_ILLEGAL); the client's
   Matching.OnFinishedDoMatching switch maps that to an error dialog,
   not a retry. The retry state is 3002 (RC_BATTLE_MATCHING_RETRY).

2. node_server_url was omitted entirely. The client's
   DoMatchingBase.SettingDoMatchingData reads it via
   data["node_server_url"].ToString() with no Keys.Contains guard, so
   absence throws KeyNotFoundException out of NetworkManager.Connect
   before the matching_state switch is even reached. Prod RETRY
   captures send "" while waiting and the real URL only on SUCCEEDED;
   match that.

battle_id stays absent; its accessor IS guarded.

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

SVSim.EmulatedEntrypoint/Controllers/ArenaTwoPickBattleController.cs

@@ -62,10 +62,16 @@ public class ArenaTwoPickBattleController : SVSimController
                 ct);
             if (paired is null)
             {
+                // 3002 = RC_BATTLE_MATCHING_RETRY: client polls again. 3001 is ILLEGAL
+                // and shows an error dialog on the client side. node_server_url must be
+                // present (the client's DoMatchingBase.SettingDoMatchingData calls
+                // .ToString() on it without a Keys.Contains guard); prod sends "" while
+                // waiting and the real URL only on SUCCEEDED. battle_id stays absent
+                // (its accessor IS guarded).
                 return Ok(new DoMatchingResponseDto
                 {
-                    MatchingState = 3001,
-                    // BattleId / NodeServerUrl null — client polls again.
+                    MatchingState = 3002,
+                    NodeServerUrl = "",
                 });
             }
 

SVSim.UnitTests/Controllers/ArenaTwoPickBattleControllerTests.cs

@@ -40,7 +40,7 @@ public class ArenaTwoPickBattleControllerTests
     }
 
     [Test]
-    public async Task DoMatching_solo_poller_returns_3001_RETRY_with_no_BattleId()
+    public async Task DoMatching_solo_poller_returns_3002_RETRY_with_no_BattleId_but_empty_NodeServerUrl()
     {
         using var factory = new SVSimTestFactory();
         var vid = await factory.SeedViewerAsync();
@@ -58,11 +58,17 @@ public class ArenaTwoPickBattleControllerTests
         using var doc = JsonDocument.Parse(body);
         var root = doc.RootElement;
 
-        Assert.That(root.GetProperty("matching_state").GetInt32(), Is.EqualTo(3001));
-        // BattleId should be ABSENT from the JSON (WhenWritingNull) — TryGetProperty
-        // returns false when the key isn't present.
+        // 3002 = RC_BATTLE_MATCHING_RETRY (client polls again). 3001 is ILLEGAL and
+        // pops an error dialog on the client.
+        Assert.That(root.GetProperty("matching_state").GetInt32(), Is.EqualTo(3002));
+        // battle_id must be ABSENT from the JSON; the client's accessor IS guarded with
+        // Keys.Contains so absence is the safe shape (matches prod RETRY captures).
         Assert.That(root.TryGetProperty("battle_id", out _), Is.False,
-            "battle_id must be absent from the wire when matching_state==3001 RETRY.");
+            "battle_id must be absent from the wire when matching_state==3002 RETRY.");
+        // node_server_url MUST be present (empty string while waiting, the real URL on
+        // SUCCEEDED). Client's DoMatchingBase.SettingDoMatchingData calls .ToString() on
+        // it without a Keys.Contains guard, so absence throws KeyNotFoundException.
+        Assert.That(root.GetProperty("node_server_url").GetString(), Is.EqualTo(""));
     }
 
     [Test]
@@ -107,8 +113,8 @@ public class ArenaTwoPickBattleControllerTests
         // A polls first (parks).
         var respA1 = await clientA.PostAsync("/arena_two_pick_battle/do_matching", JsonContent.Create(req));
         using var docA1 = JsonDocument.Parse(await respA1.Content.ReadAsStringAsync());
-        Assert.That(docA1.RootElement.GetProperty("matching_state").GetInt32(), Is.EqualTo(3001),
-            "A's first poll parks.");
+        Assert.That(docA1.RootElement.GetProperty("matching_state").GetInt32(), Is.EqualTo(3002),
+            "A's first poll parks (3002 = RETRY).");
 
         // B polls (pairs).
         var respB = await clientB.PostAsync("/arena_two_pick_battle/do_matching", JsonContent.Create(req));