feat: replace tiny-process-library with SDK process code (CreateProcessW)

Replace the FetchContent dependency on tiny-process-library with internal
cross-platform process code adapted from copilot-sdk-cpp. This eliminates
an external dependency that was transitively inherited by downstream
projects (libagents -> fastmcpp_core).

Win32 implementation upgraded from CreateProcessA to CreateProcessW:
- UTF-8/UTF-16 conversion via utf8_to_wide() helper
- STARTUPINFOEXW with explicit handle inheritance (PROC_THREAD_ATTRIBUTE_HANDLE_LIST)
- Job Object for automatic child cleanup
- CREATE_NO_WINDOW to prevent console popups
- Stderr redirected to NUL when not captured

StdioTransport rewritten from callback-based (deque + condition_variable)
to synchronous pipe model (direct read_line on stdout pipe), with a
background stderr reader thread in keep-alive mode to prevent pipe buffer
deadlock. Process liveness is checked during timeout polling (200ms
intervals) for fast failure detection when servers crash.

Also fixes two CI issues from PR #31:
- openapi_provider.hpp: brace-init default param -> explicit Options{}
- transports.hpp: add missing override on session_id/has_session

New tests: stdio_lifecycle, stdio_stderr, stdio_timeout.
All 89 tests pass.

Author: 0xeb

CMakeLists.txt

@@ -169,24 +169,8 @@ if(FASTMCPP_ENABLE_POST_STREAMING OR FASTMCPP_ENABLE_SAMPLING_HTTP_HANDLERS)
   endif()
 endif()
 
-# TinyProcessLib for cross-platform subprocess (header-only)
-FetchContent_Declare(
-  tiny_process_lib
-  GIT_REPOSITORY https://github.com/eidheim/tiny-process-library.git
-  GIT_TAG master
-)
-FetchContent_GetProperties(tiny_process_lib)
-if(NOT tiny_process_lib_POPULATED)
-  FetchContent_Populate(tiny_process_lib)
-endif()
-target_include_directories(fastmcpp_core PUBLIC ${tiny_process_lib_SOURCE_DIR})
-target_compile_definitions(fastmcpp_core PUBLIC TINY_PROCESS_LIB_AVAILABLE)
-target_sources(fastmcpp_core PRIVATE ${tiny_process_lib_SOURCE_DIR}/process.cpp)
-if(UNIX)
-  target_sources(fastmcpp_core PRIVATE ${tiny_process_lib_SOURCE_DIR}/process_unix.cpp)
-elseif(WIN32)
-  target_sources(fastmcpp_core PRIVATE ${tiny_process_lib_SOURCE_DIR}/process_win.cpp)
-endif()
+# Cross-platform subprocess management (replaces tiny-process-library)
+target_sources(fastmcpp_core PRIVATE src/internal/process.cpp)
 find_package(Threads REQUIRED)
 target_link_libraries(fastmcpp_core PRIVATE Threads::Threads)
 
@@ -466,6 +450,26 @@ if(FASTMCPP_BUILD_TESTS)
   target_link_libraries(fastmcpp_stdio_failure PRIVATE fastmcpp_core)
   add_test(NAME fastmcpp_stdio_failure COMMAND fastmcpp_stdio_failure)
 
+  add_executable(fastmcpp_stdio_lifecycle tests/transports/stdio_lifecycle.cpp)
+  target_link_libraries(fastmcpp_stdio_lifecycle PRIVATE fastmcpp_core)
+  add_test(NAME fastmcpp_stdio_lifecycle COMMAND fastmcpp_stdio_lifecycle)
+  set_tests_properties(fastmcpp_stdio_lifecycle PROPERTIES
+    WORKING_DIRECTORY "$<TARGET_FILE_DIR:fastmcpp_stdio_lifecycle>"
+  )
+
+  add_executable(fastmcpp_stdio_stderr tests/transports/stdio_stderr.cpp)
+  target_link_libraries(fastmcpp_stdio_stderr PRIVATE fastmcpp_core)
+  add_test(NAME fastmcpp_stdio_stderr COMMAND fastmcpp_stdio_stderr)
+  set_tests_properties(fastmcpp_stdio_stderr PROPERTIES
+    WORKING_DIRECTORY "$<TARGET_FILE_DIR:fastmcpp_stdio_stderr>"
+  )
+
+  add_executable(fastmcpp_stdio_timeout tests/transports/stdio_timeout.cpp)
+  target_link_libraries(fastmcpp_stdio_timeout PRIVATE fastmcpp_core)
+  add_test(NAME fastmcpp_stdio_timeout COMMAND fastmcpp_stdio_timeout)
+  # Timeout test can take up to ~35 seconds
+  set_tests_properties(fastmcpp_stdio_timeout PROPERTIES TIMEOUT 60)
+
   # App mounting tests
   add_executable(fastmcpp_app_mounting tests/app/mounting.cpp)
   target_link_libraries(fastmcpp_app_mounting PRIVATE fastmcpp_core)

include/fastmcpp/client/transports.hpp

@@ -132,10 +132,10 @@ class SseClientTransport : public ITransport,
     bool is_connected() const;
 
     /// Get the current MCP session ID (from the SSE "endpoint" event).
-    std::string session_id() const;
+    std::string session_id() const override;
 
     /// Check if a session ID has been set.
-    bool has_session() const;
+    bool has_session() const override;
 
     void set_server_request_handler(ServerRequestHandler handler) override;
 
@@ -195,10 +195,10 @@ class StreamableHttpTransport : public ITransport,
     fastmcpp::Json request(const std::string& route, const fastmcpp::Json& payload) override;
 
     /// Get the session ID (set after successful initialize)
-    std::string session_id() const;
+    std::string session_id() const override;
 
     /// Check if a session ID has been set
-    bool has_session() const;
+    bool has_session() const override;
 
     /// Set callback for handling server-initiated notifications during streaming responses
     void set_notification_callback(std::function<void(const fastmcpp::Json&)> callback);

include/fastmcpp/providers/openapi_provider.hpp

@@ -15,16 +15,16 @@ class OpenAPIProvider : public Provider
   public:
     struct Options
     {
-        bool validate_output{true};
+        bool validate_output = true;
         std::map<std::string, std::string> mcp_names; // operationId -> component name
     };
 
     explicit OpenAPIProvider(Json openapi_spec, std::optional<std::string> base_url = std::nullopt,
-                             Options options = {});
+                             Options options = Options{});
 
     static OpenAPIProvider from_file(const std::string& file_path,
                                      std::optional<std::string> base_url = std::nullopt,
-                                     Options options = {});
+                                     Options options = Options{});
 
     std::vector<tools::Tool> list_tools() const override;
     std::optional<tools::Tool> get_tool(const std::string& name) const override;