begin prepping policy refactor manually

tcp/policy.go

@@ -0,0 +1,15 @@
+package tcp
+
+type Policy interface {
+	Reset()
+	// PreTx is called before writing to a frame.
+	// The outgoing frame options can be set by the Policy and will be respected if Frame offset >5.
+	PreTx(h *Handler, outgoingOpts Frame) (rtxFrom Value, retransmit, holdNew bool)
+	// PreRx is called by [Handler] on every incoming segment.
+	// PreRx can choose to drop segment if it returns keep=false.
+	PreRx(h *Handler, incoming Frame) (keep bool)
+	// PostRx is called by [Handler] after accepting an incoming segment.
+	PostRx(h *Handler, prevState State, accepted Frame)
+	// PostTx called on leaving the transmit path.
+	PostTx(h *Handler, outgoing Frame)
+}