[cehojac]

Summary

Ports the Dokan user-mode filesystem binding (go/kbfs/dokan) from the Dokan 1.2 API to the Dokan 2.3.1 API (dokan2.dll/dokan2.sys).

Dokan 1.x is unmaintained and has no signed ARM64 driver — the Dokany 1.5.x arm64 binaries shipped unsigned in the zip and fail to load, which is why KBFS is completely broken on Windows on ARM64 devices (Surface Pro/Laptop ARM, Snapdragon X, etc). Dokany 2.2+ ships an official signed Dokan_ARM64.msi. This port fixes #27989 and also moves Windows off the legacy API for x64.

Changes

• Vendor Dokan 2.3.1.1000 headers in dokan_header/ (the same UNICODE_STRING-in-mingw comment-out is re-applied)
• loaddll.go: load DOKAN2.DLL, require DokanVersion() >= 200, resolve DokanInit/DokanShutdown
• bridge.c: call DokanInit() before DokanMain and DokanShutdown() after it returns (required by the 2.x library)
• Mounted callback updated to the 2.x signature (LPCWSTR MountPoint added)
• DOKAN_FILE_INFO.DeleteOnClose → DeletePending (2.x rename)

Everything else is unchanged: all 25 DOKAN_OPERATIONS keep identical names/signatures, DOKAN_OPTION_* flags keep the same values, and the 2.x delete semantics already match the existing code (DeleteFile/DeleteDirectory stay check-only; the real delete still happens in Cleanup when DeletePending is set).

Important packaging note

This PR makes kbfsdokan require Dokan 2.x at runtime — a system with only Dokan 1.x installed will fail the version check. The Windows installer currently bundles DokanSetup_redist.exe 1.4.0.1000, which must be updated to a 2.x redistributable for the GUI "install Dokan" flow to keep working (see the upgrade process in packaging/windows/readme.md). Note that Dokany 2.x no longer publishes DokanSetup_redist.exe — releases ship per-arch MSIs (Dokan_x64.msi, Dokan_ARM64.msi), so the packaging may need to switch bundling mechanism. A full ARM64 installer (Electron --arch=arm64, WiX Platform=arm64) is out of scope here.

Test plan

• go test ./kbfs/dokan — TestEmptyFS mounts a real filesystem on T:\ against the signed Dokany 2.3.1 ARM64 driver; all callbacks exercised
• Real KBFS mount on Windows 11 ARM64: kbfsdokan.exe K:\ → Dokan version: 231 driver 400 → K:\private/K:\public serve real encrypted folders
• x64 Windows sanity check against Dokan 2.x would be appreciated from a maintainer with an x64 box

Generated with Devin

[cehojac]

@chrisnojima ping for review — this makes KBFS work on Windows ARM64 (fixes #27989). Tested on a Surface Laptop 7: service + Dokan 2.3.1 driver + K: mount verified end-to-end, MSI install persists across reboot.