Name the step's deadline, not a bound never set, when an unbounded command is cut (issue 1497)

go/forgekey/runner.go

@@ -56,7 +56,10 @@ func execRun(ctx context.Context, bound time.Duration, env []string, name string
 	var exitErr *exec.ExitError
 	switch {
 	case errors.Is(ctx.Err(), context.DeadlineExceeded):
-		r.Status, r.Err = 124, fmt.Sprintf("no answer within %d s", int(bound/time.Second))
+		r.Status, r.Err = 124, "ended by its step's deadline"
+		if bound > 0 {
+			r.Err = fmt.Sprintf("no answer within %d s", int(bound/time.Second))
+		}
 	case errors.Is(err, exec.ErrNotFound):
 		r.Status, r.Err = 127, "ENOENT"
 	case errors.As(err, &exitErr):

go/forgekey/runner_test.go

@@ -36,6 +36,9 @@ func TestExecRunnerForZeroIsCutByItsContext(t *testing.T) {
 	defer cancel()
 	began := time.Now()
 	r := ExecRunnerFor(0)(ctx, nil, "sleep", "2")
+	if r.Err != "ended by its step's deadline" {
+		t.Errorf("Err = %q, want the step's deadline named, not a bound that was never set", r.Err)
+	}
 	if r.Status == 0 || time.Since(began) > time.Second {
 		t.Errorf("ran = %+v after %v, want it cut", r, time.Since(began))
 	}