The ssh install and ssh to commands (closes #2)

keyfunc ssh install appends the public line on a host through the system ssh, only when absent, feeding the line on standard input; keyfunc ssh to serves the derived key from an in-process agent on a private socket and runs the system ssh with it, the private key never on disk. Two review rounds; the second passed with no findings.

Model: opus-5 (implementation and review); fable-5-1 (landing)

internal/cli/cli.go

@@ -2,6 +2,7 @@
 package cli
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -37,14 +38,22 @@ func Root() *cobra.Command {
 }
 
 // Main runs the tool and returns the status the process should exit
-// with.
+// with. An error ends the tool with status 1, except when it carries a
+// status of its own, which "ssh to" uses to hand on the status ssh
+// ended with. ssh has already said whatever it had to say in that
+// case, so nothing more is printed.
 func Main() int {
 	err := Root().Execute()
-	if err != nil {
-		fmt.Fprintln(os.Stderr, "keyfunc: "+err.Error())
-
-		return 1
+	if err == nil {
+		return 0
 	}
 
-	return 0
+	var passed ssh.StatusError
+	if errors.As(err, &passed) {
+		return passed.Status
+	}
+
+	fmt.Fprintln(os.Stderr, "keyfunc: "+err.Error())
+
+	return 1
 }