internal/pkg: cancel on scanner error

This avoids discarding output thus appearing unresponsive.

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

internal/pkg/exec.go

@@ -361,6 +361,7 @@ const (
 // scanVerbose prefixes program output for a verbose [message.Msg].
 func scanVerbose(
 	msg message.Msg,
+	cancel context.CancelFunc,
 	done chan<- struct{},
 	prefix string,
 	r io.Reader,
@@ -375,6 +376,7 @@ func scanVerbose(
 		msg.Verbose(prefix, s.Text())
 	}
 	if err := s.Err(); err != nil && !errors.Is(err, os.ErrClosed) {
+		cancel()
 		msg.Verbose("*"+prefix, err)
 	}
 }
@@ -433,8 +435,8 @@ func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
 		}()
 
 		stdoutDone, stderrDone := make(chan struct{}), make(chan struct{})
-		go scanVerbose(msg, stdoutDone, "("+a.name+":1)", stdout)
+		go scanVerbose(msg, cancel, stdoutDone, "("+a.name+":1)", stdout)
-		go scanVerbose(msg, stderrDone, "("+a.name+":2)", stderr)
+		go scanVerbose(msg, cancel, stderrDone, "("+a.name+":2)", stderr)
 		defer func() { <-stdoutDone; <-stderrDone }()
 	}