review(Configuration): fix LiteDB global BsonMapper cross-instance race (High)

Re-review at 7286d320. Configuration-012 (High): LiteDbConfigCache/GenerationSealedCache built
LiteDatabase on the process-wide BsonMapper.Global whose lazy member resolution races across
concurrently-constructed DBs (NotSupportedException/duplicate-key under contention; also caused
intermittent suite flakiness). Fix: per-cache fresh BsonMapper + pre-registered entity + TDD.
-013 (dead ValidateClusterTopology, ControlPlane) / -014 (collation case-sensitivity, needs
migration) deferred. No migration touched.

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/LocalCache/GenerationSealedCache.cs

@@ -28,6 +28,18 @@ public sealed class GenerationSealedCache
     private const string CurrentPointerFileName = "CURRENT";
     private readonly string _cacheRoot;
 
+    // Private per-database BsonMapper with the entity pre-registered. LiteDB's default
+    // BsonMapper.Global is a process-wide singleton whose lazy per-type member registration is
+    // not thread-safe across concurrently-constructed LiteDatabase instances; a seal racing a
+    // read (or this cache racing LiteDbConfigCache) corrupts the global mapper, surfacing as
+    // "Member … not found on BsonMapper" or a bogus duplicate-_id insert — Configuration-012.
+    private static BsonMapper BuildMapper()
+    {
+        var mapper = new BsonMapper();
+        mapper.Entity<GenerationSnapshot>();
+        return mapper;
+    }
+
     /// <summary>Root directory for all clusters' sealed caches.</summary>
     public string CacheRoot => _cacheRoot;
 
@@ -68,7 +80,7 @@ public sealed class GenerationSealedCache
         var tmpPath = sealedPath + ".tmp";
         try
         {
-            using (var db = new LiteDatabase(new ConnectionString { Filename = tmpPath, Upgrade = false }))
+            using (var db = new LiteDatabase(new ConnectionString { Filename = tmpPath, Upgrade = false }, BuildMapper()))
             {
                 var col = db.GetCollection<GenerationSnapshot>(CollectionName);
                 col.Insert(snapshot);
@@ -126,7 +138,7 @@ public sealed class GenerationSealedCache
 
         try
         {
-            using var db = new LiteDatabase(new ConnectionString { Filename = sealedPath, ReadOnly = true });
+            using var db = new LiteDatabase(new ConnectionString { Filename = sealedPath, ReadOnly = true }, BuildMapper());
             var col = db.GetCollection<GenerationSnapshot>(CollectionName);
             var snapshot = col.FindAll().FirstOrDefault()
                 ?? throw new GenerationCacheUnavailableException(

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/LocalCache/LiteDbConfigCache.cs

@@ -11,6 +11,21 @@ namespace ZB.MOM.WW.OtOpcUa.Configuration.LocalCache;
 public sealed class LiteDbConfigCache : ILocalConfigCache, IDisposable
 {
     private const string CollectionName = "generations";
+
+    // LiteDB's default BsonMapper.Global is a process-wide singleton whose per-type member
+    // registration is lazy and NOT thread-safe across concurrently-constructed LiteDatabase
+    // instances. When several caches (this one + GenerationSealedCache) initialise in parallel
+    // the global mapper races, surfacing as "Member ClusterId not found on BsonMapper" or a
+    // bogus "duplicate key _id = 0" (the int auto-id mapping was lost so Insert writes a literal
+    // 0 twice) — Configuration-012. Give each database a private, pre-registered mapper so member
+    // resolution happens once, single-threaded, at construction and never touches the global.
+    private static BsonMapper BuildMapper()
+    {
+        var mapper = new BsonMapper();
+        mapper.Entity<GenerationSnapshot>();
+        return mapper;
+    }
+
     private readonly LiteDatabase _db;
     private readonly ILiteCollection<GenerationSnapshot> _col;
     // PutAsync is a find-then-insert/update; without serialization, two concurrent puts for the
@@ -28,7 +43,7 @@ public sealed class LiteDbConfigCache : ILocalConfigCache, IDisposable
         // the header and "recover"), so we force a write + read probe to fail fast on real corruption.
         try
         {
-            _db = new LiteDatabase(new ConnectionString { Filename = dbPath, Upgrade = true });
+            _db = new LiteDatabase(new ConnectionString { Filename = dbPath, Upgrade = true }, BuildMapper());
             _col = _db.GetCollection<GenerationSnapshot>(CollectionName);
             _col.EnsureIndex(s => s.ClusterId);
             _col.EnsureIndex(s => s.GenerationId);