Land feature 57's controller work on its release branch

The controller plans config, templates and moved providers' provisions,
hands bus accounts to the vault and judges the new manifest words, on the
feature's SDK and node-engine validator (feature 57, config and provisioning).

internal/builder/check_merge_test.go

@@ -210,3 +210,53 @@ func TestACheckMergeRunsNoHook(t *testing.T) {
 		t.Fatalf("a hook ran when the check made its merge: %s", said)
 	}
 }
+
+// What a check's tests change in the workspace never reaches what it builds for the merge (novox/hq issue 703): the
+// builds are made from a copy of the merge, outside the workspace, cloned before anything of the change runs.
+func TestWhatTheTestsChangeInTheWorkspaceNeverReachesTheBuild(t *testing.T) {
+	repo, head, _ := aTrunkAndABranch(t, map[string]string{"main.go": "package main // the merge\n"},
+		map[string]string{"trunk-only": "t"}, map[string]string{"head-only": "h"})
+	workspace := t.TempDir()
+	tree := filepath.Join(workspace, "check", "checked")
+	if out, err := exec.Command("git", "clone", "--quiet", repo, tree).CombinedOutput(); err != nil {
+		t.Fatalf("%v\n%s", err, out)
+	}
+	dir, cloned, err := checkoutForTheBuilds(t.Context(), Command, tree, head, workspace)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+	if withinDir(workspace, cloned) {
+		t.Fatalf("the builds' checkout %s is inside the workspace %s the tests mount", cloned, workspace)
+	}
+
+	// The tests rewrite the tree, its branch and every object it holds.
+	if err := os.WriteFile(filepath.Join(tree, "main.go"), []byte("package main // planted\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := filepath.WalkDir(filepath.Join(tree, ".git", "objects"), func(path string, d os.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return err
+		}
+		_ = os.Chmod(path, 0o644)
+		return os.WriteFile(path, []byte("planted"), 0o644)
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	// The build clones the merge from its own checkout, as buildForTheMerge does, and reads what the merge holds.
+	build := filepath.Join(t.TempDir(), "source")
+	if out, err := exec.Command("git", "clone", "--quiet", cloned, build).CombinedOutput(); err != nil {
+		t.Fatalf("%v\n%s", err, out)
+	}
+	if out, err := exec.Command("git", "-C", build, "checkout", "--quiet", head).CombinedOutput(); err != nil {
+		t.Fatalf("%v\n%s", err, out)
+	}
+	body, err := os.ReadFile(filepath.Join(build, "main.go"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(body) != "package main // the merge\n" {
+		t.Fatalf("the build read %q: what the tests wrote reached it", body)
+	}
+}