ipc: Add MakeBasicInit function

Add a MakeBasicInit() function so simpler standalone IPC clients like
bitcoin-mine in #30437 and bitcoin-cli in #32297 that only initiate IPC
connections without exposing any IPC interfaces themselves can to avoid needing
to implement their own specialized interfaces::Init subclasses.

src/init/basic.cpp

@@ -0,0 +1,26 @@
+// Copyright (c) 2025 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <interfaces/init.h>
+#include <interfaces/ipc.h>
+
+namespace init {
+namespace {
+class BitcoinBasicInit : public interfaces::Init
+{
+public:
+    BitcoinBasicInit(const char* exe_name, const char* process_argv0) : m_ipc(interfaces::MakeIpc(exe_name, process_argv0, *this)) {}
+    interfaces::Ipc* ipc() override { return m_ipc.get(); }
+private:
+    std::unique_ptr<interfaces::Ipc> m_ipc;
+};
+} // namespace
+} // namespace init
+
+namespace interfaces {
+std::unique_ptr<Init> MakeBasicInit(const char* exe_name, const char* process_argv0)
+{
+    return std::make_unique<init::BitcoinBasicInit>(exe_name, process_argv0);
+}
+} // namespace interfaces

src/interfaces/init.h

@@ -55,6 +55,25 @@ std::unique_ptr<Init> MakeWalletInit(int argc, char* argv[], int& exit_status);
 
 //! Return implementation of Init interface for the gui process.
 std::unique_ptr<Init> MakeGuiInit(int argc, char* argv[]);
+
+//! Return implementation of Init interface for a basic IPC client that doesn't
+//! provide any IPC services itself.
+//!
+//! When an IPC client connects to a socket or spawns a process, it gets a pointer
+//! to an Init object allowing it to create objects and threads on the remote
+//! side of the IPC connection. But the client also needs to provide a local Init
+//! object to allow the remote side of the connection to create objects and
+//! threads on this side. This function just returns a basic Init object
+//! allowing remote connections to only create local threads, not other objects
+//! (because its Init::make* methods return null.)
+//!
+//! @param exe_name Current executable name, which is just passed to the IPC
+//!     system and used for logging.
+//!
+//! @param process_argv0 Optional string containing argv[0] value passed to
+//!     main(). This is passed to the IPC system and used to locate binaries by
+//!     relative path if subprocesses are spawned.
+std::unique_ptr<Init> MakeBasicInit(const char* exe_name, const char* process_argv0="");
 } // namespace interfaces
 
 #endif // BITCOIN_INTERFACES_INIT_H