Clear setgid when hardening Windows VM directories

A numeric chmod keeps setuid/setgid on a directory, so a setgid ~/Windows
stayed 2700 and failed the exact 700 privacy check, aborting the launch.
dockur marks an initially empty /shared setgid (chmod 2777) on first boot,
so this hits fresh installs the next time the bind anchors are recreated.

bin/omarchy-windows-vm

@@ -580,7 +580,9 @@ prepare_caller_mounts() {
   # Privacy is an explicit preflight step for both already-pinned sources, not
   # a side effect halfway through the two-mount transaction. Old umask-022
   # installs are hardened together before either Docker-facing anchor changes.
-  chmod 0700 -- "/proc/$BASHPID/fd/$storage_fd" "/proc/$BASHPID/fd/$shared_fd" || {
+  # The mode is symbolic because a numeric chmod keeps setuid/setgid on a
+  # directory, and dockur marks an initially empty /shared setgid (2777).
+  chmod u=rwx,go=,a-s -- "/proc/$BASHPID/fd/$storage_fd" "/proc/$BASHPID/fd/$shared_fd" || {
     exec {storage_fd}<&-
     exec {shared_fd}<&-
     return 1
@@ -1015,7 +1017,7 @@ prepare_user_mount_sources() {
     echo "omarchy-windows-vm: storage and shared must be different directories" >&2
     return 1
   }
-  chmod 0700 -- "$storage" "$shared"
+  chmod u=rwx,go=,a-s -- "$storage" "$shared"
 }
 
 storage_space_path() {

test/shell.d/windows-vm-compose-test.sh

@@ -112,6 +112,8 @@ pass "pkexec target is only the canonical packaged regular file, never a PATH sy
 reset_case
 external_shared="$TMPDIR/external-shared"
 mkdir -m 0755 -p "$HOME/.windows" "$external_shared" "$HOME/.config/windows"
+# dockur leaves an initially empty share setgid, which a numeric chmod keeps.
+chmod 2777 "$external_shared"
 ln -s "$external_shared" "$HOME/Windows"
 touch "$HOME/.windows/existing-disk" "$external_shared/existing-shared-file"
 LEGACY_COMPOSE_FILE="$HOME/.config/windows/docker-compose.yml"

test/shell.d/windows-vm-mount-boundary-test.sh

@@ -143,6 +143,23 @@ chown root:root "$USERS_DIR"
 mounts_ready || fail "restored production boundaries were rejected"
 pass "root rejects wrong-owned and group-writable production mount boundaries without mutation"
 
+# dockur marks an empty /shared setgid (chmod 2777) on first boot, and a numeric
+# chmod keeps setuid/setgid on directories. Hardening has to clear the special
+# bits behind live anchors and again when the binds are recreated after reboot.
+chmod 2777 /home/shared-target
+chmod 6755 /home/storage-target
+with_vm_lock prepare_caller_mounts || fail "root rejected setgid sources behind live anchors"
+mounts_ready || fail "final guard rejected re-hardened setgid sources"
+umount "$EXPECTED_SHARED"
+umount "$EXPECTED_STORAGE"
+chmod 2777 /home/shared-target
+chmod 6755 /home/storage-target
+with_vm_lock prepare_caller_mounts || fail "root could not rebind setgid sources"
+[[ $(command stat -Lc '%u:%a' "$EXPECTED_STORAGE") == 1000:700 &&
+  $(command stat -Lc '%u:%a' "$EXPECTED_SHARED") == 1000:700 ]] || fail "setgid sources were not hardened to 0700"
+mounts_ready || fail "final guard rejected rebound setgid sources"
+pass "hardening clears the setuid/setgid bits a numeric chmod keeps on directories"
+
 expected_space=$(command df -P -- /home/storage-target | awk 'NR==2 {print int($4/1024/1024)}')
 actual_space=$(available_storage_gb)
 [[ $actual_space == "$expected_space" ]] || fail "disk-space helper did not measure the storage target filesystem"