system/dispatcher: wrap syscall helper functions

This allows tests to stub all kernel behaviour, like in the container package.

Signed-off-by: Ophestra <cat@gensokyo.uk>

system/dispatcher.go

@@ -0,0 +1,30 @@
+package system
+
+import "hakurei.app/system/acl"
+
+// syscallDispatcher provides methods that make state-dependent system calls as part of their behaviour.
+// syscallDispatcher is embedded in [I], so all methods must be unexported.
+type syscallDispatcher interface {
+	// new starts a goroutine with a new instance of syscallDispatcher.
+	// A syscallDispatcher must never be used in any goroutine other than the one owning it,
+	// just synchronising access is not enough, as this is for test instrumentation.
+	new(f func(k syscallDispatcher))
+
+	// aclUpdate provides [acl.Update].
+	aclUpdate(name string, uid int, perms ...acl.Perm) error
+
+	verbose(v ...any)
+	verbosef(format string, v ...any)
+}
+
+// direct implements syscallDispatcher on the current kernel.
+type direct struct{}
+
+func (k direct) new(f func(k syscallDispatcher)) { go f(k) }
+
+func (k direct) aclUpdate(name string, uid int, perms ...acl.Perm) error {
+	return acl.Update(name, uid, perms...)
+}
+
+func (direct) verbose(v ...any)                 { msg.Verbose(v...) }
+func (direct) verbosef(format string, v ...any) { msg.Verbosef(format, v...) }