fix(rank-battle): route ai-start through the queue-time MatchContext

Live-smoke bug 2026-06-02: queued Bloodcraft (deck #5), wire showed
classId=2 (Swordcraft) for self_info on the /ai_unlimited_rank_battle/start
response — client rendered the wrong leader.

Two layers of the same bug:

1. MatchContextBuilder.BuildForRankBattleAsync hardcoded deckNo=1 instead
   of taking it from the do_matching request — verified against
   data_dumps/captures/traffic.ndjson L17 where deck_no=5 was on the wire.
   Signature changes to (viewerId, format, deckNo); DoMatchingInternal
   passes req.DeckNo.

2. AiStartInternal rebuilt MatchContext from scratch — but the /ai_*/start
   request body is BaseRequest only, no deck_no on the wire. The fix uses
   the MatchContext the bridge already stored at do_matching resolution time
   (in the Bot PendingBattle), so deck/cosmetic data is consistent end-to-end.
   New IBattleSessionStore.TryFindPendingForViewer(viewerId) finds the
   viewer's pending battle for lookup. The store entry persists across
   ai_start (idempotent reads are fine — the WS handler removes on connect).
   No-pending sentinel: ai_id=-1 surfaces the "no AI assigned" error in the
   client.

Tests: 936 → 939 passing.
- MatchContextBuilderTests.BuildForRankBattle_uses_the_caller_supplied_deck_number
  seeds deck #1 (class 1) and deck #5 (class 6) and asserts the deckNo
  argument picks the right one.
- RankBattleControllerTests.AiStart_self_info_class_matches_queued_deck_number
  is the end-to-end regression: register Bot battle with deck #5, hit
  /ai_unlimited_rank_battle/start, assert self_info.classId == 6.
- RankBattleControllerTests.AiStart_without_pending_battle_returns_neg1_sentinel
  locks the defensive ai_id=-1 path.
- Existing AiStart_* tests bypass do_matching, so adapted to call a new
  RegisterBotBattleAsync helper that mirrors what InProcessPairUp does on
  AI-fallback resolution.

SeedDeckAsync gains an optional classId so test cases can differentiate
decks by class (was always picking Classes.First()).

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

SVSim.BattleNode/Sessions/IBattleSessionStore.cs

@@ -8,6 +8,16 @@ public interface IBattleSessionStore
     /// <summary>Look up the pending battle. Returns null if not present.</summary>
     PendingBattle? TryGetPending(string battleId);
 
+    /// <summary>
+    /// Find a pending battle this viewer is a participant in (P1 or P2). Used by the
+    /// HTTP-side <c>/ai_&lt;fmt&gt;/start</c> endpoint to retrieve the deck/cosmetic
+    /// context the viewer registered at <c>do_matching</c> time — the <c>/start</c>
+    /// request body carries no <c>deck_no</c> of its own. Returns null if the viewer
+    /// has no pending battle (already consumed by WS connect, never registered, or
+    /// evicted by timeout).
+    /// </summary>
+    PendingBattle? TryFindPendingForViewer(long viewerId);
+
     /// <summary>Mark a battle as no longer pending (e.g. on successful connect or explicit close).</summary>
     bool RemovePending(string battleId);
 }

SVSim.BattleNode/Sessions/InMemoryBattleSessionStore.cs

@@ -12,6 +12,21 @@ public sealed class InMemoryBattleSessionStore : IBattleSessionStore
     public PendingBattle? TryGetPending(string battleId) =>
         _pending.TryGetValue(battleId, out var b) ? b : null;
 
+    public PendingBattle? TryFindPendingForViewer(long viewerId)
+    {
+        // Linear scan — _pending is bounded by concurrent in-flight matches (low
+        // double digits at most), so this stays cheap. Returns whichever match the
+        // dictionary's enumerator yields first; in practice a viewer has at most one
+        // pending battle since each /do_matching either pairs/falls-back the existing
+        // slot or parks without registering.
+        foreach (var b in _pending.Values)
+        {
+            if (b.P1.ViewerId == viewerId) return b;
+            if (b.P2 is not null && b.P2.ViewerId == viewerId) return b;
+        }
+        return null;
+    }
+
     public bool RemovePending(string battleId) =>
         _pending.TryRemove(battleId, out _);
 }

SVSim.EmulatedEntrypoint/Controllers/RankBattleController.cs

@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Sessions;
 using SVSim.Database.Enums;
 using SVSim.EmulatedEntrypoint.Constants;
 using SVSim.EmulatedEntrypoint.Matching;
@@ -24,6 +25,7 @@ public sealed class RankBattleController : ControllerBase
 {
     private readonly IMatchingPairUpService _pairUp;
     private readonly IMatchingBridge _bridge;
+    private readonly IBattleSessionStore _sessionStore;
     private readonly IMatchContextBuilder _ctxBuilder;
     private readonly IBotRoster _botRoster;
     private readonly ILogger<RankBattleController> _log;
@@ -31,12 +33,14 @@ public sealed class RankBattleController : ControllerBase
     public RankBattleController(
         IMatchingPairUpService pairUp,
         IMatchingBridge bridge,
+        IBattleSessionStore sessionStore,
         IMatchContextBuilder ctxBuilder,
         IBotRoster botRoster,
         ILogger<RankBattleController> log)
     {
         _pairUp = pairUp;
         _bridge = bridge;
+        _sessionStore = sessionStore;
         _ctxBuilder = ctxBuilder;
         _botRoster = botRoster;
         _log = log;
@@ -120,14 +124,14 @@ public sealed class RankBattleController : ControllerBase
         MatchContext ctx;
         try
         {
-            ctx = await _ctxBuilder.BuildForRankBattleAsync(vid, format);
+            ctx = await _ctxBuilder.BuildForRankBattleAsync(vid, format, req.DeckNo);
         }
         catch (InvalidOperationException ex)
         {
-            // Most likely cause: viewer has no deck for this format. Surface as 3001
+            // Most likely cause: viewer has no deck at that slot for this format. Surface
-            // RC_BATTLE_MATCHING_ILLEGAL — the client shows the standard matchmaking-error
+            // as 3001 RC_BATTLE_MATCHING_ILLEGAL — the client shows the standard
-            // dialog rather than retrying forever.
+            // matchmaking-error dialog rather than retrying forever.
-            _log.LogWarning(ex, "BuildForRankBattleAsync failed for viewer {Vid} format {Fmt}; returning 3001.", vid, format);
+            _log.LogWarning(ex, "BuildForRankBattleAsync failed for viewer {Vid} format {Fmt} deckNo {DeckNo}; returning 3001.", vid, format, req.DeckNo);
             return Ok(new DoMatchingResponseDto { MatchingState = 3001, NodeServerUrl = "" });
         }
 
@@ -167,18 +171,19 @@ public sealed class RankBattleController : ControllerBase
     {
         if (!TryGetViewerId(out var vid)) return Unauthorized();
 
-        MatchContext selfCtx;
+        // The /ai_<fmt>/start request body is BaseRequest only — it carries no deck_no.
-        try
+        // The deck the viewer queued with was captured in the PendingBattle's MatchContext
+        // at /do_matching resolution time (when InProcessPairUp called bridge.RegisterBattle).
+        // Reuse that context so SelfInfo's classId/charaId/sleeveId match what the user
+        // actually picked. Rebuilding from deck #1 was the 2026-06-02 wire-bug — surfaced
+        // as "queued Bloodcraft, saw Swordcraft leader."
+        var pending = _sessionStore.TryFindPendingForViewer(vid);
+        if (pending is null)
         {
-            selfCtx = await _ctxBuilder.BuildForRankBattleAsync(vid, format);
+            _log.LogWarning("AiStart for viewer {Vid} format {Fmt} has no pending battle; returning ai_id=-1.", vid, format);
-        }
-        catch (InvalidOperationException ex)
-        {
-            // No deck → can't build a self profile. Surface as the "no AI assigned"
-            // sentinel; the client treats ai_id=-1 as a fallback/error condition.
-            _log.LogWarning(ex, "AiStart failed for viewer {Vid} format {Fmt}; returning ai_id=-1.", vid, format);
             return Ok(new AiBattleStartResponseDto { AiId = -1 });
         }
+        var selfCtx = pending.P1.Context;
 
         var bot = await _botRoster.PickAsync(selfCtx, ct);
 

SVSim.EmulatedEntrypoint/Services/IMatchContextBuilder.cs

@@ -18,13 +18,10 @@ public interface IMatchContextBuilder
     Task<MatchContext> BuildForTwoPickAsync(long viewerId);
 
     /// <summary>
-    /// Build a context for a rank-battle viewer + format (rotation / unlimited). Pulls the
+    /// Build a context for a rank-battle viewer + format (rotation / unlimited) + the
-    /// viewer's deck #1 for that format + viewer cosmetics. Throws if the viewer has no
+    /// caller-selected deck number (from <c>do_matching</c>'s <c>deck_no</c>). Pulls the
-    /// deck registered for the format.
+    /// viewer's deck for that format/number + viewer cosmetics. Throws if the viewer has
+    /// no deck at that slot.
     /// </summary>
-    /// <remarks>
+    Task<MatchContext> BuildForRankBattleAsync(long viewerId, Format format, int deckNo);
-    /// Deck-selection persistence (which deck number is "current" for this format) is a
-    /// separate concern; deck #1 is a placeholder until that lands.
-    /// </remarks>
-    Task<MatchContext> BuildForRankBattleAsync(long viewerId, Format format);
 }

SVSim.EmulatedEntrypoint/Services/MatchContextBuilder.cs

@@ -70,17 +70,17 @@ public class MatchContextBuilder : IMatchContextBuilder
             BattleType: 11);
     }
 
-    public async Task<MatchContext> BuildForRankBattleAsync(long viewerId, Format format)
+    public async Task<MatchContext> BuildForRankBattleAsync(long viewerId, Format format, int deckNo)
     {
         var viewer = await _viewers.LoadForMatchContextAsync(viewerId)
             ?? throw new InvalidOperationException($"viewer {viewerId} not found");
 
-        // Per spec, deck-selection persistence (which deck number is "current" for this
+        // IDeckRepository is the right path here — viewer-graph nav refs (DeckCard.Card)
-        // format) is a separate concern; #1 is a placeholder until that lands. IDeckRepository
+        // don't auto-load (see project_ef_nav_include_pitfall memory), which would
-        // is the right path here — viewer-graph nav refs (DeckCard.Card) don't auto-load
+        // silently ship card_id=0.
-        // (see project_ef_nav_include_pitfall memory), which would silently ship card_id=0.
+        var deck = await _decks.GetDeck(viewerId, format, deckNo)
-        var deck = await _decks.GetDeck(viewerId, format, deckNo: 1)
+            ?? throw new InvalidOperationException(
-            ?? throw new InvalidOperationException($"viewer {viewerId} has no deck for format {format}");
+                $"viewer {viewerId} has no deck #{deckNo} for format {format}");
 
         var defaults = _config.Get<DefaultLoadoutConfig>();
         var emblemId = viewer.Info.SelectedEmblem.Id != 0

SVSim.UnitTests/BattleNode/Integration/BattleNodeFlowTests.cs

@@ -418,7 +418,7 @@ public class BattleNodeFlowTests
         var bridge = factory.Services.GetRequiredService<IMatchingBridge>();
         using var scope = factory.Services.CreateScope();
         var builder = scope.ServiceProvider.GetRequiredService<SVSim.EmulatedEntrypoint.Services.IMatchContextBuilder>();
-        var ctx = await builder.BuildForRankBattleAsync(vid, SVSim.Database.Enums.Format.Rotation);
+        var ctx = await builder.BuildForRankBattleAsync(vid, SVSim.Database.Enums.Format.Rotation, deckNo: 1);
         var pending = bridge.RegisterBattle(
             new SVSim.BattleNode.Bridge.BattlePlayer(vid, ctx),
             p2: null,

SVSim.UnitTests/Controllers/RankBattleControllerTests.cs

@@ -2,7 +2,10 @@ using System.Net.Http.Json;
 using System.Text.Json;
 using Microsoft.Extensions.DependencyInjection;
 using NUnit.Framework;
+using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Sessions;
 using SVSim.Database.Enums;
+using SVSim.EmulatedEntrypoint.Services;
 using SVSim.UnitTests.Infrastructure;
 
 namespace SVSim.UnitTests.Controllers;
@@ -44,6 +47,21 @@ public class RankBattleControllerTests
         steam_session_ticket = "",
     };
 
+    /// <summary>
+    /// AiStart in the real client flow always follows a do_matching call that resolved
+    /// to 3011 (AI fallback) — that's when the PendingBattle is registered with the
+    /// viewer's queue-time MatchContext (deck/cosmetics). Tests bypass do_matching's
+    /// time-threshold to register a Bot PendingBattle directly via the bridge.
+    /// </summary>
+    private static async Task RegisterBotBattleAsync(SVSimTestFactory factory, long viewerId, Format format, int deckNo)
+    {
+        var bridge = factory.Services.GetRequiredService<IMatchingBridge>();
+        using var scope = factory.Services.CreateScope();
+        var builder = scope.ServiceProvider.GetRequiredService<IMatchContextBuilder>();
+        var ctx = await builder.BuildForRankBattleAsync(viewerId, format, deckNo);
+        bridge.RegisterBattle(new BattlePlayer(viewerId, ctx), p2: null, BattleType.Bot);
+    }
+
     [Test]
     public async Task DoMatching_rotation_first_poll_returns_3002_RETRY_with_empty_node_server_url()
     {
@@ -102,6 +120,7 @@ public class RankBattleControllerTests
         var viewerId = await factory.SeedViewerAsync(displayName: "TestViewer");
         await factory.SeedGlobalsAsync();
         await factory.SeedDeckAsync(viewerId, Format.Rotation, 1);
+        await RegisterBotBattleAsync(factory, viewerId, Format.Rotation, deckNo: 1);
         var client = factory.CreateAuthenticatedClient(viewerId);
 
         var resp = await client.PostAsJsonAsync("/ai_rotation_rank_battle/start", EmptyAuthedBody);
@@ -140,6 +159,7 @@ public class RankBattleControllerTests
         var viewerId = await factory.SeedViewerAsync(displayName: "Alice");
         await factory.SeedGlobalsAsync();
         await factory.SeedDeckAsync(viewerId, Format.Rotation, 1);
+        await RegisterBotBattleAsync(factory, viewerId, Format.Rotation, deckNo: 1);
         var client = factory.CreateAuthenticatedClient(viewerId);
 
         var resp = await client.PostAsJsonAsync("/ai_rotation_rank_battle/start", EmptyAuthedBody);
@@ -156,6 +176,7 @@ public class RankBattleControllerTests
         var viewerId = await factory.SeedViewerAsync(displayName: "PlayerA");
         await factory.SeedGlobalsAsync();
         await factory.SeedDeckAsync(viewerId, Format.Rotation, 1);
+        await RegisterBotBattleAsync(factory, viewerId, Format.Rotation, deckNo: 1);
         var client = factory.CreateAuthenticatedClient(viewerId);
 
         var resp = await client.PostAsJsonAsync("/ai_rotation_rank_battle/start", EmptyAuthedBody);
@@ -167,6 +188,48 @@ public class RankBattleControllerTests
         Assert.That(oppoInfo.GetProperty("classId").GetInt32(), Is.InRange(1, 8));
     }
 
+    [Test]
+    public async Task AiStart_self_info_class_matches_queued_deck_number()
+    {
+        // Regression for the 2026-06-02 "queued Bloodcraft, saw Swordcraft leader" wire bug.
+        // The original impl rebuilt MatchContext from deck #1 inside AiStart; the fix routes
+        // it through the PendingBattle the bridge stored at do_matching time (which carries
+        // the queue-time deck_no). Seed two distinct-class decks and confirm /ai_*/start
+        // returns the right class for a viewer registered with deck #5.
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync(displayName: "Ranker");
+        await factory.SeedGlobalsAsync();
+        await factory.SeedDeckAsync(viewerId, Format.Unlimited, number: 1, classId: 1);
+        await factory.SeedDeckAsync(viewerId, Format.Unlimited, number: 5, classId: 6);
+        await RegisterBotBattleAsync(factory, viewerId, Format.Unlimited, deckNo: 5);
+        var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var resp = await client.PostAsJsonAsync("/ai_unlimited_rank_battle/start", EmptyAuthedBody);
+        using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync());
+        var selfInfo = doc.RootElement.GetProperty("self_info");
+
+        Assert.That(selfInfo.GetProperty("classId").GetInt32(), Is.EqualTo(6),
+            "Self class must reflect the deck the viewer queued with (deck #5 = Bloodcraft, class 6).");
+    }
+
+    [Test]
+    public async Task AiStart_without_pending_battle_returns_neg1_sentinel()
+    {
+        // Defensive: clients always do_matching before ai_start, but if /ai_*/start is hit
+        // without a registered PendingBattle (server restart, expired match, ...), the spec
+        // sentinel ai_id=-1 surfaces the "no AI assigned" error in the client.
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync();
+        await factory.SeedGlobalsAsync();
+        await factory.SeedDeckAsync(viewerId, Format.Rotation, 1);
+        var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var resp = await client.PostAsJsonAsync("/ai_rotation_rank_battle/start", EmptyAuthedBody);
+        using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync());
+
+        Assert.That(doc.RootElement.GetProperty("ai_id").GetInt32(), Is.EqualTo(-1));
+    }
+
     [Test]
     public async Task Finish_emits_stubbed_zeros_with_battle_result_echo()
     {

SVSim.UnitTests/Infrastructure/SVSimTestFactory.cs

@@ -369,13 +369,16 @@ internal sealed class SVSimTestFactory : WebApplicationFactory<Program>
     /// path. Picks the first seeded class/sleeve/leader-skin from the master tables; tests
     /// that need specific ids should hit the DB directly.
     /// </summary>
-    public async Task SeedDeckAsync(long viewerId, Format format, int number, string name = "Test Deck")
+    public async Task SeedDeckAsync(long viewerId, Format format, int number, string name = "Test Deck", int? classId = null)
     {
         using var scope = Services.CreateScope();
         var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
         var repo = scope.ServiceProvider.GetRequiredService<IDeckRepository>();
 
-        var cls = await db.Classes.FirstAsync();
+        var cls = classId is null
+            ? await db.Classes.FirstAsync()
+            : await db.Classes.FindAsync(classId.Value)
+                ?? throw new InvalidOperationException($"SeedDeckAsync: class {classId} not found");
         var sleeve = await db.Sleeves.FirstAsync();
         var skin = await db.LeaderSkins.FirstAsync();
 

SVSim.UnitTests/Services/MatchContextBuilderTests.cs

@@ -128,7 +128,7 @@ public class MatchContextBuilderTests
         using var scope = factory.Services.CreateScope();
         var builder = scope.ServiceProvider.GetRequiredService<IMatchContextBuilder>();
 
-        var ctx = await builder.BuildForRankBattleAsync(viewerId, Format.Rotation);
+        var ctx = await builder.BuildForRankBattleAsync(viewerId, Format.Rotation, deckNo: 1);
 
         Assert.That(ctx.UserName, Is.EqualTo("Ranker"));
         Assert.That(ctx.BattleType, Is.EqualTo(11), "BattleType=11 matches the prod rank-battle wire value (same as TK2).");
@@ -148,10 +148,33 @@ public class MatchContextBuilderTests
         using var scope = factory.Services.CreateScope();
         var builder = scope.ServiceProvider.GetRequiredService<IMatchContextBuilder>();
 
-        Assert.That(async () => await builder.BuildForRankBattleAsync(viewerId, Format.Rotation),
+        Assert.That(async () => await builder.BuildForRankBattleAsync(viewerId, Format.Rotation, deckNo: 1),
             Throws.Exception);
     }
 
+    [Test]
+    public async Task BuildForRankBattle_uses_the_caller_supplied_deck_number()
+    {
+        // Regression for the 2026-06-02 "queued Bloodcraft, saw Swordcraft leader"
+        // wire bug — MatchContextBuilder.BuildForRankBattleAsync hardcoded deckNo=1.
+        // Seed two decks for different classes (1 and 6) and confirm the deckNo
+        // argument picks the right one.
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync(displayName: "Ranker");
+        await factory.SeedGlobalsAsync();
+        await factory.SeedDeckAsync(viewerId, Format.Unlimited, number: 1, name: "Deck 1", classId: 1);
+        await factory.SeedDeckAsync(viewerId, Format.Unlimited, number: 5, name: "Deck 5", classId: 6);
+
+        using var scope = factory.Services.CreateScope();
+        var builder = scope.ServiceProvider.GetRequiredService<IMatchContextBuilder>();
+
+        var deck1Ctx = await builder.BuildForRankBattleAsync(viewerId, Format.Unlimited, deckNo: 1);
+        var deck5Ctx = await builder.BuildForRankBattleAsync(viewerId, Format.Unlimited, deckNo: 5);
+
+        Assert.That(deck1Ctx.ClassId, Is.EqualTo("1"), "deckNo=1 → class 1.");
+        Assert.That(deck5Ctx.ClassId, Is.EqualTo("6"), "deckNo=5 → class 6 (the wire-bug case).");
+    }
+
     [Test]
     public async Task BuildForTwoPick_falls_back_to_default_loadout_when_unequipped()
     {