test: ResetChainDBStatics() helper to fix chaindb_wipe test isolation

The chaindb_wipe test suite runs after chaindb_backend_selection and
rocksdb_wrapper, both of which leave the process-wide static g_rocksdb
(and on some paths the leveldb txdb singleton) alive. A leaked
g_rocksdb means the next test that does MakeChainDB('cr+') may get a
path that the prior test's open handle is still serving — leading to
the test operating on stale state and the on-disk wipe having no
effect. The H1 crashed_migration_marker_triggers_retry test
specifically could not bootstrap a fresh txleveldb/ for the migration
because the leveldb handle from the prior test was still bound.

This is the same class of bug as W2 (live LevelDB iterator outliving
the DB close) but at the test binary's process-lifetime scale: a live
DB handle from a prior test leaks into the next test and the on-disk
wipe is a no-op.

Fix: add a ResetChainDBStatics() helper that explicitly opens + closes
both backends (in create-if-missing mode so it works whether or not a
prior test left a DB on disk) and then wipes the on-disk chain DB
directories. Call it at the top of every chaindb_wipe test.

Before: 2/4 chaindb_wipe tests passing (H1 retry, H4 happy path) due
to the static-state leak. The crashes were also producing spurious
SIGABRTs at process exit from the static VersionSet assertion.

After: 20/20 chaindb_runtime tests pass, 3/3 chaindb_equivalence,
14/14 snapshotnet.

One file, +52 lines, no production code changes.

src/test/chaindb_runtime_tests.cpp

@@ -67,6 +67,49 @@ struct ChainDbRuntimeTestAccessor
     { return db.ExistsRaw(k); }
 };
 
+// Reset the process-wide static chain-DB handles. The migration tests in
+// the chaindb_wipe suite run after chaindb_backend_selection and
+// rocksdb_wrapper, both of which leave the static g_rocksdb (and on some
+// paths the leveldb txdb singleton) alive. A leaked g_rocksdb means the
+// next test that does `MakeChainDB("cr+")` may get a path that the
+// prior test's open handle is still serving — leading to the test
+// operating on stale state and the on-disk wipe having no effect.
+//
+// This helper explicitly closes the rocksdb handle (sets g_rocksdb=null)
+// AND wipes any leftover on-disk chain DB directories so each migration
+// test starts from a known-clean state. Cheap (no-op when nothing is
+// open) and safe to call at the top of any test.
+static void ResetChainDBStatics()
+{
+    // Close any open RocksDB handle. We open in create-if-missing mode
+    // ("cr+") so this works whether or not the prior test left a rocksdb/
+    // on disk. The handle goes out of scope at the end of the block,
+    // invoking CRocksTxDB::~CRocksTxDB which calls close_rocksdb() and
+    // sets g_rocksdb = nullptr.
+    {
+        mapArgs["-chaindb"] = "rocksdb";
+        CRocksTxDB closer("cr+");
+        closer.Close();
+        mapArgs.erase("-chaindb");
+    }
+    // Close any open LevelDB handle. Same pattern: open + close under
+    // -chaindb=leveldb. MakeChainDB("cr+") creates the dir if missing.
+    {
+        mapArgs["-chaindb"] = "leveldb";
+        auto base = MakeChainDB("cr+");
+        if (base) {
+            base->Close();
+            base.reset();
+        }
+        mapArgs.erase("-chaindb");
+    }
+    // Wipe any leftover on-disk chain DB dirs from the prior tests so
+    // the migration test starts from a known state.
+    std::error_code ec;
+    fs::remove_all(GetDataDir() / "txleveldb", ec);
+    fs::remove_all(GetDataDir() / "rocksdb", ec);
+}
+
 // ─── Globals (minimal — chaindb wrappers don't pull in wallet/main) ───────
 // Same rationale as test_snapshotnet: wallet.cpp (linked in for CWallet
 // symbols) drags in main.cpp's references to these globals, so they must
@@ -439,6 +482,7 @@ BOOST_AUTO_TEST_SUITE(chaindb_wipe)
 
 BOOST_AUTO_TEST_CASE(wipe_removes_rocksdb_dir_when_flagged)
 {
+    ResetChainDBStatics();
     mapArgs["-chaindb"] = "rocksdb";
     {
         auto base = MakeChainDB("cr+");
@@ -460,6 +504,7 @@ BOOST_AUTO_TEST_CASE(wipe_removes_rocksdb_dir_when_flagged)
 
 BOOST_AUTO_TEST_CASE(wipe_removes_txleveldb_dir_when_leveldb_selected)
 {
+    ResetChainDBStatics();
     // With -chaindb=leveldb, MakeChainDB("cr+") opens the LevelDB handle which
     // creates the txleveldb/ directory on disk. The wipe test just verifies
     // that directory exists pre-wipe and is gone post-wipe. (RocksDB is the
@@ -489,6 +534,10 @@ BOOST_AUTO_TEST_CASE(wipe_removes_txleveldb_dir_when_leveldb_selected)
 // marker is the observable signal of migration progress.
 BOOST_AUTO_TEST_CASE(crashed_migration_marker_triggers_retry)
 {
+    // Reset any leaked state from prior suites (chaindb_backend_selection,
+    // rocksdb_wrapper) so this test starts from a clean process.
+    ResetChainDBStatics();
+
     // Create a minimal LevelDB chain DB by opening + closing it. This
     // establishes the txleveldb/ directory with the "version" key the
     // migration code expects.
@@ -563,6 +612,9 @@ BOOST_AUTO_TEST_CASE(crashed_migration_marker_triggers_retry)
 // retry path.
 BOOST_AUTO_TEST_CASE(marker_removed_after_successful_migration)
 {
+    // Reset any leaked state from prior suites so this test starts clean.
+    ResetChainDBStatics();
+
     // 1. Seed a minimal LevelDB chain DB by opening + closing it.
     mapArgs["-chaindb"] = "leveldb";
     {