feat(suidhelper): mix suidhelper.install wrapping cargo xtask install

Author: markovejnovic

lib/mix/tasks/suidhelper.install.ex

@@ -0,0 +1,40 @@
+defmodule Mix.Tasks.Suidhelper.Install do
+  @shortdoc "Build, stamp, and install the setuid helper (wraps `cargo xtask install`)"
+  @moduledoc """
+  Builds, stamps, and installs the Rust setuid helper by wrapping
+  `cargo xtask install` in `native/suidhelper`.
+
+      mix suidhelper.install
+
+  The xtask first stamps the release binary (BLAKE3 self-checksum into
+  `.note.sum`, the same step the `:suidhelper_stamp` compiler runs) and then
+  installs it setuid-root to `/usr/local/bin/hyper-suidhelper` via `sudo
+  install`. `sudo` may prompt for a password on the controlling terminal.
+
+  This is the privileged counterpart to `mix suidhelper.stamp`: that one only
+  rebuilds, stamps, and re-captures the embedded build identity; this one also
+  places the binary on `PATH` setuid-root. `cargo` and the helper's toolchain
+  (see `native/suidhelper/rust-toolchain.toml`) must be installed.
+  """
+
+  use Mix.Task
+
+  @helper_dir "native/suidhelper"
+
+  @impl Mix.Task
+  def run(argv) do
+    {_, 0} =
+      System.cmd("cargo", ["xtask", "install" | argv],
+        cd: @helper_dir,
+        into: IO.stream(:stdio, :line)
+      )
+  rescue
+    MatchError ->
+      Mix.raise("""
+      `cargo xtask install` failed installing the suidhelper.
+
+      Ensure `cargo` and the helper's toolchain (see #{@helper_dir}/rust-toolchain.toml)
+      are installed, and that `sudo` is available for the setuid install step.
+      """)
+  end
+end