Remove what an earlier delivery of a check left before raising its store again

An ask redelivered after the build agent stopped mid-check (the rollout it was checking updated it)
found its own throwaway store under its name, and the check said it could not run (mesh-controller#105,
build-1791331512096605198).

internal/builder/check.go

@@ -298,6 +298,13 @@ func Check(ctx context.Context, run Runner, spec CheckSpec, workspace, registry
 	say("check", "the facts of %s (%s): %d machine(s), the bus at %s, the store at %s", f.Taken.Format(time.RFC3339),
 		short(strings.TrimPrefix(digest, "sha256:")), len(f.Machines), f.Versions.Bus, f.Versions.Store)
 
+	// **What an earlier delivery of this same ask left is removed first** (novox/hq issue 285): an ask is
+	// redelivered when the holder that took it stopped mid-check — the build agent itself updated by the
+	// rollout it is checking — and its containers, named by the ask's id, are still there. Raising the
+	// store again under that name was refused, and the check said it could not run.
+	if n, err := RemoveContainersOf(ctx, run, spec.ID); err == nil && n > 0 {
+		say("check", "removed %d throwaway container(s) an earlier delivery of this check left", n)
+	}
 	// The throwaway store and bus, of the versions the mesh runs, removed whatever happens.
 	defer func() {
 		removing, done := context.WithTimeout(context.Background(), time.Minute)

internal/builder/check_test.go

@@ -457,3 +457,26 @@ func TestTheSeatCallsAGateThatRaisedNoMachineAnError(t *testing.T) {
 		t.Error("a failing verdict is the change's, and stands")
 	}
 }
+
+// **Issue 285**: an ask redelivered after its holder stopped mid-check found its own throwaway store still
+// there under its name, and the check said it could not run. What an earlier delivery left goes first.
+func TestARedeliveredCheckRemovesWhatItsEarlierDeliveryLeft(t *testing.T) {
+	registry := checkEnvironment(t)
+	repo, head := aCheckedRepository(t, map[string]string{CheckScript: "echo checked\n"})
+	id := fmt.Sprintf("check-again-%d", time.Now().UnixNano())
+	if out, err := exec.Command("docker", "run", "-d", "--rm", "--label", BuildLabel+"="+id, "--name", id+"-store",
+		"postgres:17-alpine", "sleep", "300").CombinedOutput(); err != nil {
+		t.Skipf("no container for the earlier delivery: %v %s", err, out)
+	}
+	v, err := Check(t.Context(), Command, CheckSpec{ID: id, Repository: repo, Ref: head, Owner: "novox",
+		Repo: "hq", Number: 7, Toolchain: goToolchain}, t.TempDir(), registry, GitCredential{}, nil)
+	if err != nil {
+		t.Fatalf("a redelivered check could not run: %v", err)
+	}
+	if v.Repo == nil || v.Repo.Verdict != "pass" {
+		t.Errorf("the repository's check answered %+v", v.Repo)
+	}
+	if left := labelled(id); len(left) > 0 {
+		t.Errorf("the check left %d container(s) behind", len(left))
+	}
+}