init: custom init process inside sandbox

Bubblewrap as init is a bit awkward and don't support a few setup actions fortify will need, such as starting/supervising nscd.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

internal/init/payload.go

@@ -0,0 +1,15 @@
+package init0
+
+const EnvInit = "FORTIFY_INIT"
+
+type Payload struct {
+	// target full exec path
+	Argv0 string
+	// child full argv
+	Argv []string
+	// wayland fd, -1 to disable
+	WL int
+
+	// verbosity pass through
+	Verbose bool
+}