test: cover CoinJoin client lifecycle handling

Add functional coverage for CoinJoin session startup, participant restart, wallet unload/reload, and live stop/reset cleanup. Add a focused manager unit test that verifies removeWallet cannot erase a client while doForClient is using it, and isolate peers synchronously before testing the live session.

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

Author: thepastaclaw

src/wallet/test/coinjoin_tests.cpp

@@ -32,6 +32,10 @@
 
 #include <boost/test/unit_test.hpp>
 
+#include <chrono>
+#include <future>
+#include <thread>
+
 namespace wallet {
 BOOST_FIXTURE_TEST_SUITE(coinjoin_tests, BasicTestingSetup)
 
@@ -394,6 +398,38 @@ BOOST_FIXTURE_TEST_CASE(coinjoin_pending_observation_reload_tests, CTransactionB
     SetMockTime(0);
 }
 
+BOOST_FIXTURE_TEST_CASE(coinjoin_wallet_manager_remove_during_client_access_tests, CTransactionBuilderTestSetup)
+{
+    std::promise<void> client_entered;
+    auto client_entered_future{client_entered.get_future()};
+    std::promise<void> release_client;
+    auto release_client_future{release_client.get_future()};
+    bool client_found{false};
+
+    std::thread client_thread([&] {
+        client_found = m_node.cj_walletman->doForClient(wallet->GetName(), [&](CCoinJoinClientManager&) {
+            client_entered.set_value();
+            release_client_future.wait();
+        });
+    });
+
+    client_entered_future.wait();
+    auto remove_future{std::async(std::launch::async, [&] { m_node.cj_walletman->removeWallet(wallet->GetName()); })};
+
+    // doForClient holds the manager-map lock while the callback uses the
+    // client, so removal must wait until the callback has released it.
+    BOOST_CHECK_EQUAL(remove_future.wait_for(std::chrono::milliseconds{100}), std::future_status::timeout);
+
+    release_client.set_value();
+    client_thread.join();
+    BOOST_CHECK(client_found);
+    BOOST_CHECK_EQUAL(remove_future.wait_for(std::chrono::seconds{1}), std::future_status::ready);
+    remove_future.get();
+
+    // Restore the fixture's manager for its teardown.
+    m_node.cj_walletman->addWallet(wallet);
+}
+
 BOOST_FIXTURE_TEST_CASE(coinjoin_pending_observation_unreadable_tests, CTransactionBuilderTestSetup)
 {
     // 0.100001 DASH, a valid CoinJoin denomination

test/functional/test_runner.py

@@ -101,6 +101,7 @@
     # Longest test should go first, to favor running tests in parallel
     'feature_llmq_data_recovery.py',
     # vv Tests less than 5m vv
+    'wallet_coinjoin_mixing.py',
     'feature_fee_estimation.py',
     'feature_block.py', # NOTE: needs dash_hash to pass
     # vv Tests less than 2m vv