Keep a failed toolchain probe a loud refusal; only the command directory is fixed (issue 734, review round 1)

Declining an ask whose probe failed would turn a truly broken toolchain into a
wait of up to the decline bound that then fails with an empty "needs a node
with" reason. With the node-engine no longer deleting a running build and
commands started in a directory that exists, the getwd cause is gone, so the
guard's refusal stays as it was. The decline refactor goes with it.

go/buildstep/pull_test.go

@@ -139,8 +139,7 @@ func TestPullHoldsAtMostItsCapacity(t *testing.T) {
 
 // An ask that is not one, or not this seat's, is dropped and runs nowhere. And issue 890/AC1: a check ask needing
 // node-build-node is declined on a node that lacks it (its step refused as declined, naming what it lacks, the message
-// dropped for the asker to put again), and runs on a node that has it. And issue 734: an ask whose run is refused to
-// ask again (a toolchain that could not be read) is declined the same way, not refused for good.
+// dropped for the asker to put again), and runs on a node that has it.
 func TestPullDropsWhatIsNoAsk(t *testing.T) {
 	src, st := NewFakeAsks(), newSteps()
 	src.Publish(delivery.AskDelivery, []byte(`{"v":1}`))
@@ -174,21 +173,6 @@ func TestPullDropsWhatIsNoAsk(t *testing.T) {
 		Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { return nil, nil }}
 	go q.Pull(ctx)
 	waitFor(t, "the placed ask acked where its need is met", func() bool { a, _, _ := has.Fates(); return len(a) == 1 })
-
-	probe, probeSteps := NewFakeAsks(), newSteps()
-	unready := testAsk(delivery.AskCheck)
-	_ = probe.PublishAsk(unready)
-	r := &Puller{Source: probe, Language: delivery.AskGo, Node: "ace", Put: probeSteps.put, Capacity: func() int { return 1 },
-		PullWait: 10 * time.Millisecond, Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
-			return nil, &Refusal{Text: "the installed go version could not be read: getwd: no such file or directory", Again: true}
-		}}
-	go r.Pull(ctx)
-	waitFor(t, "the unready ask termed", func() bool { _, tm, _ := probe.Fates(); return len(tm) == 1 })
-	key, _ = delivery.AskStepKey("ace", unready.ID)
-	s, _ = probeSteps.get(key)
-	if _, ok := delivery.DeclinedOf(s); !ok || !strings.Contains(s.Reason, "getwd") {
-		t.Fatalf("the step of an ask its node could not run now = %+v, want it declined naming why", s)
-	}
 }
 
 // load reads the recorded steps state's raw values: the pause key is not a step, so it is kept apart.