Windows addon loaders are unreachable and swallow load errors

packages/host/cpp/CxxNodeApiHostModule.hpp と AddonLoaders.hpp から開始し、その後 CxxNodeApiHostModule.cpp の loader 呼び出し元と Logger.hpp の logging API を調査します。プラットフォーム固有の loader alias を確認し、Windows における 4 つの失敗経路を追跡します。Windows が適切な loader を選択し、捕捉したロードエラーまたはシンボルエラーを握りつぶさずに報告すれば完了です。

Grouping the FIXME/HACK in CxxNodeApiHostModule.hpp with the four TODOs in AddonLoaders.hpp. Both halves of the Windows story are incomplete, and the first makes the second unobservable.

The loader policy is hardcoded to POSIX

https://github.com/callstackincubator/react-native-node-api/blob/29a527d87fa8cb965b0048b1b4c1cff2b0eab281/packages/host/cpp/CxxNodeApiHostModule.hpp#L45-L46

Win32Loader and WinRTLoader exist in AddonLoaders.hpp and are compiled behind #if defined(_WIN32), but nothing ever selects them — LoaderPolicy is unconditionally PosixLoader. The alias should be chosen by platform (_WIN32 → Win32Loader, with WinRT distinguished by the appropriate API-family macro, POSIX otherwise), which is a compile-time #if rather than a design question.

The Windows loaders discard the reason for every failure

All four failure paths detect the error and then do nothing with it:

https://github.com/callstackincubator/react-native-node-api/blob/29a527d87fa8cb965b0048b1b4c1cff2b0eab281/packages/host/cpp/AddonLoaders.hpp#L52-L57

https://github.com/callstackincubator/react-native-node-api/blob/29a527d87fa8cb965b0048b1b4c1cff2b0eab281/packages/host/cpp/AddonLoaders.hpp#L63-L68

https://github.com/callstackincubator/react-native-node-api/blob/29a527d87fa8cb965b0048b1b4c1cff2b0eab281/packages/host/cpp/AddonLoaders.hpp#L84-L89

https://github.com/callstackincubator/react-native-node-api/blob/29a527d87fa8cb965b0048b1b4c1cff2b0eab281/packages/host/cpp/AddonLoaders.hpp#L95-L100

LoadLibrary/LoadPackagedLibrary/GetProcAddress all return null and leave the reason in GetLastError(). Returning null without capturing it means the caller in CxxNodeApiHostModule.cpp can only report "Failed to load library" — the distinction between "file not found", "a transitive dependency is missing" and "wrong architecture" is lost, and those are precisely the three things a developer needs to tell apart. PosixLoader has the same shape of gap but at least has dlerror() available; the commented-out NSLog there suggests it was once wired up.

Suggested minimum: format the DWORD via FormatMessageA and route it through log_error/log_debug from Logger.hpp, matching how the POSIX path should report dlerror().

Both were listed in the original permalinks on #30. Relevant to #305 (Windows test app on CI) — without a Windows test app these paths stay unexercised whichever way they are fixed.