Initial implementation of arca, a LUKS volume manager.

Go CLI using cobra with mount, unmount, status, and init subcommands.
Unlocks via udisks2 D-Bus (passphrase/keyfile) or cryptsetup (FIDO2/TPM2)
with ordered method fallback. Includes NixOS-specific LD_LIBRARY_PATH
injection for systemd cryptsetup token plugins.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/golang.org/x/sys/unix/fdset.go

@@ -0,0 +1,27 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos
+
+package unix
+
+// Set adds fd to the set fds.
+func (fds *FdSet) Set(fd int) {
+	fds.Bits[fd/NFDBITS] |= (1 << (uintptr(fd) % NFDBITS))
+}
+
+// Clear removes fd from the set fds.
+func (fds *FdSet) Clear(fd int) {
+	fds.Bits[fd/NFDBITS] &^= (1 << (uintptr(fd) % NFDBITS))
+}
+
+// IsSet returns whether fd is in the set fds.
+func (fds *FdSet) IsSet(fd int) bool {
+	return fds.Bits[fd/NFDBITS]&(1<<(uintptr(fd)%NFDBITS)) != 0
+}
+
+// Zero clears the set fds.
+func (fds *FdSet) Zero() {
+	clear(fds.Bits[:])
+}