Track src/txdb-factory.cpp

This file has been built into the binary since the M1.3 chain-DB
backend split (referenced from src/CMakeLists.txt) but was never
committed. A fresh clone wouldn't build without it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/txdb-factory.cpp

@@ -0,0 +1,64 @@
+// Copyright (c) 2026 The Triangles developers.
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "txdb.h"
+#include "util.h"
+
+#include <stdexcept>
+#include <string>
+
+namespace {
+
+// Pick the backend once per process. -chaindb is a startup flag; switching at
+// runtime would require reopening every CTxDB instance, which the codebase
+// doesn't currently support. We cache the resolved choice so subsequent
+// MakeChainDB calls don't re-parse the argument.
+enum class ChainDbKind { LevelDB, RocksDB };
+
+ChainDbKind ResolveChainDbKind()
+{
+    static const ChainDbKind kKind = []() {
+        std::string s = GetArg("-chaindb", std::string("leveldb"));
+        for (auto& c : s) c = std::tolower(static_cast<unsigned char>(c));
+
+        if (s == "leveldb")
+            return ChainDbKind::LevelDB;
+
+        if (s == "rocksdb") {
+#ifdef BUILD_ROCKSDB
+            return ChainDbKind::RocksDB;
+#else
+            throw std::runtime_error(
+                "-chaindb=rocksdb requested but this binary was built without "
+                "BUILD_ROCKSDB. Rebuild with -DBUILD_ROCKSDB=ON, or use "
+                "-chaindb=leveldb.");
+#endif
+        }
+
+        throw std::runtime_error(
+            "-chaindb=" + s + " is not a recognized backend. "
+            "Valid values: leveldb"
+#ifdef BUILD_ROCKSDB
+            ", rocksdb"
+#endif
+            ".");
+    }();
+    return kKind;
+}
+
+} // anonymous namespace
+
+std::unique_ptr<CTxDBBase> MakeChainDB(const char* pszMode)
+{
+    switch (ResolveChainDbKind()) {
+    case ChainDbKind::LevelDB:
+        return std::unique_ptr<CTxDBBase>(new CTxDB(pszMode));
+#ifdef BUILD_ROCKSDB
+    case ChainDbKind::RocksDB:
+        return std::unique_ptr<CTxDBBase>(new CRocksTxDB(pszMode));
+#endif
+    }
+    // Unreachable — ResolveChainDbKind throws on bad input.
+    return nullptr;
+}