R-5: a kept call is asked again only while its key is open and not replaced

busretry.Open and DoKept, process.Conn.CallKeptWhileOpen.

Builds: design 47 G §351, §425, §460

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

go/process/call.go

@@ -76,6 +76,20 @@ func (c *Conn) CallKeptOn(node, key string, body any) (json.RawMessage, error) {
 	return c.callKeptOn(called, fallback, body)
 }
 
+// CallKeptWhileOpen is CallKept for an ask the asker can close or replace: it is asked again only while open says its
+// key is still open (design 47 G §351, §460).
+func (c *Conn) CallKeptWhileOpen(open busretry.Open, key string, body any) (json.RawMessage, error) {
+	called, fallback, err := callSubjectsOn(key, "", c.callerToken())
+	if err != nil {
+		return nil, err
+	}
+	data, err := json.Marshal(body)
+	if err != nil {
+		return nil, err
+	}
+	return busretry.DoKept("the call on "+fallback, open, askBoth(c.request, called, fallback, data), nil)
+}
+
 func (c *Conn) callKeptOn(called, fallback string, body any) (json.RawMessage, error) {
 	data, err := json.Marshal(body)
 	if err != nil {