init(00_tmp): idempotent mkdir -p, drop rm that failed on fresh boot

init.d/00_tmp

@@ -1,4 +1,10 @@
-# FIXME change this to a service unit
-# clear and recreate tmpdir with 0o1777 permission
-rm -rf /tmp
-mkdir -m a=rwxt /tmp
+# Ensure the tmpdir exists with sticky 0o1777 permission.
+#
+# init runs each line as a standalone Oneshot command (no shell), so we cannot
+# `rm -rf /tmp || true`. The previous `rm -rf /tmp` followed by a bare
+# `mkdir /tmp` broke on a fresh boot: Redox's uutils `rm -f` errors on a
+# missing operand ("cannot remove '/tmp': No such file or directory") — which
+# POSIX says -f must ignore — and the subsequent non-`-p` mkdir then errors if
+# /tmp already exists. A live boot has a fresh ramfs /tmp with nothing to
+# clean, so just create it idempotently; `mkdir -p` is a no-op when present.
+mkdir -p -m a=rwxt /tmp