Raise a check's store without durability and remove what earlier holders left (hq issue 306)

On the control node the store-bound packages of the controller's suite ran
five to seven times slower than on any other holder, and every controller
check that landed there ran past the suite's thirty minutes: a throwaway
store flushing to a disk the mesh's own store, bus and forge keep busy.
A store that lives for one check needs no crash safety.

A holder recreated mid-check left the check's store and bus running, and
the redelivery went to another machine, so nothing removed them: eleven
pairs across four machines. A starting holder has taken nothing, so every
container labelled with an ask of the seat is an earlier holder's.

internal/builder/kill_test.go

@@ -101,3 +101,40 @@ func TestAKillRemovesTheContainersLabelledWithTheBuild(t *testing.T) {
 		t.Errorf("ran %v", ran)
 	}
 }
+
+// **Issue 306**: a holder starting removes what earlier holders on its machine left — every container
+// labelled with an ask of the seat — and nothing labelled otherwise.
+func TestAStartingHolderRemovesWhatEarlierHoldersLeftAndNothingElse(t *testing.T) {
+	var ran [][]string
+	run := func(_ context.Context, _ string, name string, args ...string) (string, error) {
+		ran = append(ran, append([]string{name}, args...))
+		if args[0] == "ps" {
+			return "c1 build-1791418000320743455\nc2 build-1791418000320743455\n" +
+				"c3 check-here-1791418000320743455\nc4 check-test-17\nc5 build-x\nc6 build-\n\nc7 build-1791319895953076871\n", nil
+		}
+		return "", nil
+	}
+	n, err := RemoveLeftBehind(context.Background(), run)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 3 {
+		t.Errorf("removed %d", n)
+	}
+	if len(ran) != 2 || !reflect.DeepEqual(ran[1], []string{"docker", "rm", "-f", "c1", "c2", "c7"}) {
+		t.Fatalf("ran %v", ran)
+	}
+	if !strings.Contains(strings.Join(ran[0], " "), "--filter label=mesh.build") {
+		t.Errorf("listed with %v", ran[0])
+	}
+
+	// Nothing left behind: nothing removed, and no rm asked.
+	ran = nil
+	quiet := func(_ context.Context, _ string, name string, args ...string) (string, error) {
+		ran = append(ran, append([]string{name}, args...))
+		return "c3 check-here-1\n", nil
+	}
+	if n, err := RemoveLeftBehind(context.Background(), quiet); err != nil || n != 0 || len(ran) != 1 {
+		t.Errorf("with nothing of the seat's: %d %v %v", n, err, ran)
+	}
+}