go/cli: an outcome not known is not a refusal; the Go binding is checked in the Go toolchain

Review of hq ADR 0272: a line whose answer did not come in time may have
run, and saying "nothing ran" there is a lie. Answer.Unknown and NotKnown
say it may have run and name the call to look at.

The SDK's repo-check ran in the TypeScript toolchain only and said
"NOT TESTED HERE: go/". go/merge-check.sh now runs the Go binding in the Go
toolchain, declared by the root check (mesh-check-also), as the lab does.

Released as go/v0.1.9 (go/v0.1.8 is mesh-sdk #12's).

go/cli/cli.go

@@ -54,11 +54,24 @@ type Answer struct {
 	Refused string `json:"refused,omitempty"`
 	// Cut says the output was longer than one bus message and was cut there.
 	Cut bool `json:"cut,omitempty"`
+	// Unknown says the line was asked and its outcome is not known: no answer came in time, and it may have
+	// run. Never said as a refusal, which means nothing ran.
+	Unknown string `json:"unknown,omitempty"`
 }
 
 // Refusal is an answer saying that nothing ran, and why.
 func Refusal(why string) Answer { return Answer{Exit: 1, Refused: why} }
 
+// NotKnown is an answer saying the line was asked and what came of it is not known: it may have run. call is
+// the controller's call the line runs as, when it is known, which `calls` answers.
+func NotKnown(call, why string) Answer {
+	where := "the controller's `calls` lists what came of each line"
+	if call != "" {
+		where = "see the call " + call + " (`calls " + call + "`)"
+	}
+	return Answer{Exit: 1, Unknown: why + "; the line may have run — " + where}
+}
+
 // ErrTooLong is a request or an answer over its bound.
 var ErrTooLong = errors.New("longer than the protocol allows")