chore(go): audit transaction engine

Share change filtering between the durable and test transaction paths,
collapse repeated precondition handling, unify journal sequence parsing,
and split the subprocess worker test file.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

cmd/elydora/plugins/transaction.go

@@ -5,9 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
-	"path/filepath"
 	"runtime"
-	"strings"
 )
 
 type renameFunc func(source, destination string) error
@@ -165,84 +163,60 @@ func writeChangesWithFileOps(
 	if ops.moveNoReplace == nil {
 		return fmt.Errorf("%s is missing atomic file operations", label)
 	}
-	filtered := make([]fileChange, 0, len(changes))
-	targets := map[string]bool{}
-	for _, change := range changes {
-		if change == nil || (change.existed && !change.remove &&
-			bytes.Equal(change.original, change.next) &&
-			sameManagedFileMode(change.originalMode, change.mode)) {
-			continue
-		}
-		target := filepath.Clean(change.filePath)
-		if runtime.GOOS == "windows" {
-			target = strings.ToLower(target)
-		}
-		if targets[target] {
-			return fmt.Errorf("%s contains duplicate file target %s", label, change.filePath)
-		}
-		targets[target] = true
-		filtered = append(filtered, *change)
+	filtered, err := filterDurableChanges(changes, label)
+	if err != nil {
+		return err
 	}
-	if err := assertFilePreconditions(preconditions, label); err != nil {
-		return fmt.Errorf("%s: %w", label, err)
+	checkPreconditions := func() error {
+		if err := assertFilePreconditions(preconditions, label); err != nil {
+			return fmt.Errorf("%s: %w", label, err)
+		}
+		return nil
+	}
+	if err := checkPreconditions(); err != nil {
+		return err
 	}
 	if len(filtered) == 0 {
 		return nil
 	}
 	staged := make([]stagedChange, 0, len(filtered))
+	abortStaging := func(cause error) error {
+		return joinTransactionFailure(cause, cleanupStaging(staged), "cleanup failed")
+	}
 	for _, change := range filtered {
-		if err := assertFilePreconditions(preconditions, label); err != nil {
-			cleanupErrors := cleanupStaging(staged)
-			return joinTransactionFailure(
-				fmt.Errorf("%s: %w", label, err),
-				cleanupErrors,
-				"cleanup failed",
-			)
+		if err := checkPreconditions(); err != nil {
+			return abortStaging(err)
 		}
 		item, err := stageChange(change)
 		if err != nil {
-			cleanupErrors := cleanupStaging(staged)
-			return joinTransactionFailure(fmt.Errorf("%s: %w", label, err), cleanupErrors, "cleanup failed")
+			return abortStaging(fmt.Errorf("%s: %w", label, err))
 		}
 		staged = append(staged, item)
-		if err := assertFilePreconditions(preconditions, label); err != nil {
-			cleanupErrors := cleanupStaging(staged)
-			return joinTransactionFailure(
-				fmt.Errorf("%s: %w", label, err),
-				cleanupErrors,
-				"cleanup failed",
-			)
-		}
 	}
-	if err := assertFilePreconditions(preconditions, label); err != nil {
-		cleanupErrors := cleanupStaging(staged)
-		return joinTransactionFailure(fmt.Errorf("%s: %w", label, err), cleanupErrors, "cleanup failed")
+	if err := checkPreconditions(); err != nil {
+		return abortStaging(err)
+	}
+	recoverStaged := func(cause error) error {
+		failures := rollbackChanges(staged, ops)
+		failures = append(failures, cleanupStaging(staged)...)
+		return joinTransactionFailure(cause, failures, "recovery failed")
 	}
 	for index := range staged {
-		if err := assertFilePreconditions(preconditions, label); err != nil {
-			recoveryErrors := rollbackChanges(staged, ops)
-			recoveryErrors = append(recoveryErrors, cleanupStaging(staged)...)
-			return joinTransactionFailure(fmt.Errorf("%s: %w", label, err), recoveryErrors, "recovery failed")
+		if err := checkPreconditions(); err != nil {
+			return recoverStaged(err)
 		}
 		if err := commitChange(&staged[index], ops); err != nil {
-			recoveryErrors := rollbackChanges(staged, ops)
-			recoveryErrors = append(recoveryErrors, cleanupStaging(staged)...)
-			return joinTransactionFailure(fmt.Errorf("%s: %w", label, err), recoveryErrors, "recovery failed")
+			return recoverStaged(fmt.Errorf("%s: %w", label, err))
 		}
 	}
-	if err := assertFilePreconditions(preconditions, label); err != nil {
-		recoveryErrors := rollbackChanges(staged, ops)
-		recoveryErrors = append(recoveryErrors, cleanupStaging(staged)...)
-		return joinTransactionFailure(fmt.Errorf("%s: %w", label, err), recoveryErrors, "recovery failed")
+	if err := checkPreconditions(); err != nil {
+		return recoverStaged(err)
 	}
 	if err := assertCommittedChanges(staged); err != nil {
-		recoveryErrors := rollbackChanges(staged, ops)
-		recoveryErrors = append(recoveryErrors, cleanupStaging(staged)...)
-		return joinTransactionFailure(fmt.Errorf("%s: %w", label, err), recoveryErrors, "recovery failed")
+		return recoverStaged(fmt.Errorf("%s: %w", label, err))
 	}
-	cleanupErrors := cleanupStaging(staged)
-	if len(cleanupErrors) > 0 {
-		return joinTransactionFailure(fmt.Errorf("%s cleanup failed", label), cleanupErrors, "cleanup failed")
+	if failures := cleanupStaging(staged); len(failures) > 0 {
+		return joinTransactionFailure(fmt.Errorf("%s cleanup failed", label), failures, "cleanup failed")
 	}
 	return nil
 }

cmd/elydora/plugins/transaction_journal.go

@@ -178,8 +178,7 @@ func loadDurableJournal(directory string) (*durableJournal, error) {
 	}
 	stateNames := make([]string, 0)
 	for _, entry := range entries {
-		if !entry.IsDir() && strings.HasPrefix(entry.Name(), "state-") &&
-			strings.HasSuffix(entry.Name(), ".json") {
+		if _, state := durableJournalStateSequence(entry.Name()); state && !entry.IsDir() {
 			stateNames = append(stateNames, entry.Name())
 		}
 	}
@@ -317,11 +316,11 @@ func validateDurableJournalProgress(journal *durableJournal) error {
 	return nil
 }
 
-func durableJournalStateSequence(name string) (uint64, bool) {
-	if !strings.HasPrefix(name, "state-") || !strings.HasSuffix(name, ".json") {
+func durableJournalSequence(name, suffix string) (uint64, bool) {
+	if !strings.HasPrefix(name, "state-") || !strings.HasSuffix(name, suffix) {
 		return 0, false
 	}
-	value := strings.TrimSuffix(strings.TrimPrefix(name, "state-"), ".json")
+	value := strings.TrimSuffix(strings.TrimPrefix(name, "state-"), suffix)
 	if len(value) != 20 {
 		return 0, false
 	}
@@ -329,14 +328,10 @@ func durableJournalStateSequence(name string) (uint64, bool) {
 	return sequence, err == nil
 }
 
+func durableJournalStateSequence(name string) (uint64, bool) {
+	return durableJournalSequence(name, ".json")
+}
+
 func durableJournalPendingSequence(name string) (uint64, bool) {
-	if !strings.HasPrefix(name, "state-") || !strings.HasSuffix(name, ".pending") {
-		return 0, false
-	}
-	value := strings.TrimSuffix(strings.TrimPrefix(name, "state-"), ".pending")
-	if len(value) != 20 {
-		return 0, false
-	}
-	sequence, err := strconv.ParseUint(value, 10, 64)
-	return sequence, err == nil
+	return durableJournalSequence(name, ".pending")
 }

cmd/elydora/plugins/transaction_subprocess_test.go

@@ -13,282 +13,6 @@ import (
 	"time"
 )
 
-const durableWorkerEnvironment = "ELYDORA_DURABLE_TRANSACTION_WORKER"
-
-func TestDurableTransactionSubprocessWorker(t *testing.T) {
-	mode := os.Getenv(durableWorkerEnvironment)
-	if mode == "" {
-		return
-	}
-	target := os.Getenv("ELYDORA_DURABLE_TARGET")
-	switch mode {
-	case "crash-update":
-		runDurableCrashWorker(t, target)
-	case "crash-multi-update":
-		runDurableMultiCrashWorker(t, target, os.Getenv("ELYDORA_DURABLE_SECOND_TARGET"))
-	case "crash-create":
-		runDurableCreateCrashWorker(t, target)
-	case "crash-delete":
-		runDurableDeleteCrashWorker(t, target)
-	case "crash-committed-cleanup":
-		runDurableCommittedCleanupCrashWorker(t, target)
-	case "crash-rollback-hardlink":
-		runDurableRollbackHardlinkCrashWorker(t)
-	case "crash-init-workspace-empty":
-		runDurableInitializationWorkspaceCrashWorker(t, target, false)
-	case "crash-init-workspace-owner":
-		runDurableInitializationWorkspaceCrashWorker(t, target, true)
-	case "crash-init-stage-full":
-		runDurableInitializationStageCrashWorker(t, target, false)
-	case "crash-init-stage-partial":
-		runDurableInitializationStageCrashWorker(t, target, true)
-	case "crash-init-probe":
-		runDurableInitializationProbeCrashWorker(t, target)
-	case "crash-journal-owner":
-		runDurableJournalOwnerCrashWorker(t)
-	case "crash-journal-pending-full":
-		runDurableJournalPendingCrashWorker(t, target, false)
-	case "crash-journal-pending-partial":
-		runDurableJournalPendingCrashWorker(t, target, true)
-	case "crash-workspace-marker-cleanup":
-		runDurableWorkspaceMarkerCleanupCrashWorker(t, target)
-	case "crash-journal-marker-cleanup":
-		runDurableJournalMarkerCleanupCrashWorker(t, target)
-	case "crash-torn-journal-tail":
-		runDurableTornJournalTailCrashWorker(t, target)
-	case "reader":
-		runDurableReaderWorker(t, target)
-	case "writer":
-		runDurableWriterWorker(t, target)
-	default:
-		t.Fatalf("unknown durable transaction worker %q", mode)
-	}
-}
-
-func runDurableRollbackHardlinkCrashWorker(t *testing.T) {
-	stateRoot, err := durableTransactionStateRoot()
-	if err != nil {
-		t.Fatal(err)
-	}
-	entries, err := os.ReadDir(stateRoot)
-	if err != nil {
-		t.Fatal(err)
-	}
-	journalPath := ""
-	for _, entry := range entries {
-		if entry.IsDir() && strings.HasPrefix(entry.Name(), "txn-") {
-			if journalPath != "" {
-				t.Fatal("multiple recovery journals found")
-			}
-			journalPath = filepath.Join(stateRoot, entry.Name())
-		}
-	}
-	if journalPath == "" {
-		t.Fatal("recovery journal is unavailable")
-	}
-	journal, err := loadDurableJournal(journalPath)
-	if err != nil || len(journal.Entries) != 1 {
-		t.Fatalf("load recovery journal: %v", err)
-	}
-	entry := journal.Entries[0]
-	if err := os.Link(entry.Path, entry.DiscardPath); err != nil {
-		t.Fatal(err)
-	}
-	if err := syncTransactionDirectory(filepath.Dir(entry.DiscardPath)); err != nil {
-		t.Fatal(err)
-	}
-	os.Exit(91)
-}
-
-func runDurableMultiCrashWorker(t *testing.T, firstTarget, secondTarget string) {
-	changes := make([]*fileChange, 0, 2)
-	for _, item := range []struct {
-		path  string
-		value string
-	}{{firstTarget, "first-next"}, {secondTarget, "second-next"}} {
-		change, err := prepareFileChange(item.path, "multi crash target", []byte(item.value), 0600)
-		if err != nil {
-			t.Fatal(err)
-		}
-		changes = append(changes, change)
-	}
-	ops := newTransactionFileOps(nil)
-	replace := ops.replaceWithBackup
-	commits := 0
-	ops.replaceWithBackup = func(current, replacement, backup string) error {
-		if err := replace(current, replacement, backup); err != nil {
-			return err
-		}
-		commits++
-		if commits == 2 {
-			os.Exit(87)
-		}
-		return nil
-	}
-	if err := writeChangesWithFileOps(changes, "multi crash transaction", ops); err != nil {
-		t.Fatal(err)
-	}
-	t.Fatal("multi crash worker completed without terminating")
-}
-
-func runDurableCreateCrashWorker(t *testing.T, target string) {
-	change, err := prepareFileChange(target, "crash create target", []byte("created"), 0600)
-	if err != nil {
-		t.Fatal(err)
-	}
-	ops := newTransactionFileOps(nil)
-	move := ops.moveNoReplace
-	ops.moveNoReplace = func(source, destination string) error {
-		if err := move(source, destination); err != nil {
-			return err
-		}
-		if sameTransactionTestPath(destination, target) {
-			os.Exit(88)
-		}
-		return nil
-	}
-	if err := writeChangesWithFileOps([]*fileChange{change}, "crash create", ops); err != nil {
-		t.Fatal(err)
-	}
-	t.Fatal("create crash worker completed without terminating")
-}
-
-func runDurableDeleteCrashWorker(t *testing.T, target string) {
-	change, err := prepareSourceChange(
-		target,
-		"crash delete target",
-		[]byte("delete-original"),
-		true,
-		nil,
-		0600,
-		true,
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-	ops := newTransactionFileOps(nil)
-	move := ops.moveNoReplace
-	ops.moveNoReplace = func(source, destination string) error {
-		if err := move(source, destination); err != nil {
-			return err
-		}
-		if sameTransactionTestPath(source, target) {
-			os.Exit(89)
-		}
-		return nil
-	}
-	if err := writeChangesWithFileOps([]*fileChange{change}, "crash delete", ops); err != nil {
-		t.Fatal(err)
-	}
-	t.Fatal("delete crash worker completed without terminating")
-}
-
-func runDurableCommittedCleanupCrashWorker(t *testing.T, target string) {
-	change, err := prepareFileChange(target, "committed cleanup target", []byte("committed"), 0600)
-	if err != nil {
-		t.Fatal(err)
-	}
-	ops := newTransactionFileOps(nil)
-	replace := ops.replaceWithBackup
-	blocker := ""
-	ops.replaceWithBackup = func(current, replacement, backup string) error {
-		if err := replace(current, replacement, backup); err != nil {
-			return err
-		}
-		blocker = filepath.Join(filepath.Dir(backup), "cleanup-blocker")
-		return os.WriteFile(blocker, []byte("block"), 0600)
-	}
-	err = writeChangesWithFileOps([]*fileChange{change}, "committed cleanup", ops)
-	if err == nil || !strings.Contains(err.Error(), "committed; durable cleanup failed") {
-		t.Fatalf("committed cleanup error = %v", err)
-	}
-	if err := os.Remove(blocker); err != nil {
-		t.Fatal(err)
-	}
-	os.Exit(90)
-}
-
-func runDurableCrashWorker(t *testing.T, target string) {
-	change, err := prepareFileChange(target, "crash target", []byte("next"), 0600)
-	if err != nil {
-		t.Fatal(err)
-	}
-	ops := newTransactionFileOps(nil)
-	replace := ops.replaceWithBackup
-	absoluteTarget, err := filepath.Abs(target)
-	if err != nil {
-		t.Fatal(err)
-	}
-	ops.replaceWithBackup = func(current, replacement, backup string) error {
-		if err := replace(current, replacement, backup); err != nil {
-			return err
-		}
-		if sameTransactionTestPath(current, absoluteTarget) {
-			os.Exit(86)
-		}
-		return nil
-	}
-	if err := writeChangesWithFileOps([]*fileChange{change}, "crash transaction", ops); err != nil {
-		t.Fatal(err)
-	}
-	t.Fatal("crash worker completed without terminating")
-}
-
-func runDurableReaderWorker(t *testing.T, target string) {
-	stop := os.Getenv("ELYDORA_DURABLE_STOP")
-	for {
-		if _, err := os.Lstat(stop); err == nil {
-			return
-		} else if !errors.Is(err, os.ErrNotExist) {
-			t.Fatal(err)
-		}
-		content, err := os.ReadFile(target)
-		if err != nil {
-			if errors.Is(err, os.ErrNotExist) {
-				t.Fatalf("reader observed missing target: %v", err)
-			}
-			if _, statErr := os.Lstat(target); statErr != nil {
-				t.Fatalf("reader observed unavailable target: %v; stat=%v", err, statErr)
-			}
-			time.Sleep(time.Millisecond)
-			continue
-		}
-		if string(content) != "value-a" && string(content) != "value-b" {
-			t.Fatalf("reader observed partial value %q", content)
-		}
-		time.Sleep(time.Millisecond)
-	}
-}
-
-func runDurableWriterWorker(t *testing.T, target string) {
-	value := os.Getenv("ELYDORA_DURABLE_VALUE")
-	ready := os.Getenv("ELYDORA_DURABLE_READY")
-	start := os.Getenv("ELYDORA_DURABLE_START")
-	change, err := prepareFileChange(target, "writer target", []byte(value), 0600)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if err := os.WriteFile(ready, []byte("ready"), 0600); err != nil {
-		t.Fatal(err)
-	}
-	deadline := time.Now().Add(15 * time.Second)
-	for {
-		if _, err := os.Lstat(start); err == nil {
-			break
-		} else if !errors.Is(err, os.ErrNotExist) {
-			t.Fatal(err)
-		}
-		if time.Now().After(deadline) {
-			t.Fatal("writer start barrier timed out")
-		}
-		time.Sleep(time.Millisecond)
-	}
-	if err := writeChanges([]*fileChange{change}, "subprocess writer", nil); err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(23)
-	}
-}
-
 func TestDurableTransactionRecoversAfterProcessTermination(t *testing.T) {
 	home := filepath.Join(t.TempDir(), "home")
 	if err := createPrivateTransactionDirectory(home); err != nil {

cmd/elydora/plugins/transaction_subprocess_worker_test.go

@@ -0,0 +1,287 @@
+package plugins
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+const durableWorkerEnvironment = "ELYDORA_DURABLE_TRANSACTION_WORKER"
+
+func TestDurableTransactionSubprocessWorker(t *testing.T) {
+	mode := os.Getenv(durableWorkerEnvironment)
+	if mode == "" {
+		return
+	}
+	target := os.Getenv("ELYDORA_DURABLE_TARGET")
+	switch mode {
+	case "crash-update":
+		runDurableCrashWorker(t, target)
+	case "crash-multi-update":
+		runDurableMultiCrashWorker(t, target, os.Getenv("ELYDORA_DURABLE_SECOND_TARGET"))
+	case "crash-create":
+		runDurableCreateCrashWorker(t, target)
+	case "crash-delete":
+		runDurableDeleteCrashWorker(t, target)
+	case "crash-committed-cleanup":
+		runDurableCommittedCleanupCrashWorker(t, target)
+	case "crash-rollback-hardlink":
+		runDurableRollbackHardlinkCrashWorker(t)
+	case "crash-init-workspace-empty":
+		runDurableInitializationWorkspaceCrashWorker(t, target, false)
+	case "crash-init-workspace-owner":
+		runDurableInitializationWorkspaceCrashWorker(t, target, true)
+	case "crash-init-stage-full":
+		runDurableInitializationStageCrashWorker(t, target, false)
+	case "crash-init-stage-partial":
+		runDurableInitializationStageCrashWorker(t, target, true)
+	case "crash-init-probe":
+		runDurableInitializationProbeCrashWorker(t, target)
+	case "crash-journal-owner":
+		runDurableJournalOwnerCrashWorker(t)
+	case "crash-journal-pending-full":
+		runDurableJournalPendingCrashWorker(t, target, false)
+	case "crash-journal-pending-partial":
+		runDurableJournalPendingCrashWorker(t, target, true)
+	case "crash-workspace-marker-cleanup":
+		runDurableWorkspaceMarkerCleanupCrashWorker(t, target)
+	case "crash-journal-marker-cleanup":
+		runDurableJournalMarkerCleanupCrashWorker(t, target)
+	case "crash-torn-journal-tail":
+		runDurableTornJournalTailCrashWorker(t, target)
+	case "reader":
+		runDurableReaderWorker(t, target)
+	case "writer":
+		runDurableWriterWorker(t, target)
+	default:
+		t.Fatalf("unknown durable transaction worker %q", mode)
+	}
+}
+
+func runDurableRollbackHardlinkCrashWorker(t *testing.T) {
+	stateRoot, err := durableTransactionStateRoot()
+	if err != nil {
+		t.Fatal(err)
+	}
+	entries, err := os.ReadDir(stateRoot)
+	if err != nil {
+		t.Fatal(err)
+	}
+	journalPath := ""
+	for _, entry := range entries {
+		if entry.IsDir() && strings.HasPrefix(entry.Name(), "txn-") {
+			if journalPath != "" {
+				t.Fatal("multiple recovery journals found")
+			}
+			journalPath = filepath.Join(stateRoot, entry.Name())
+		}
+	}
+	if journalPath == "" {
+		t.Fatal("recovery journal is unavailable")
+	}
+	journal, err := loadDurableJournal(journalPath)
+	if err != nil || len(journal.Entries) != 1 {
+		t.Fatalf("load recovery journal: %v", err)
+	}
+	entry := journal.Entries[0]
+	if err := os.Link(entry.Path, entry.DiscardPath); err != nil {
+		t.Fatal(err)
+	}
+	if err := syncTransactionDirectory(filepath.Dir(entry.DiscardPath)); err != nil {
+		t.Fatal(err)
+	}
+	os.Exit(91)
+}
+
+func runDurableMultiCrashWorker(t *testing.T, firstTarget, secondTarget string) {
+	changes := make([]*fileChange, 0, 2)
+	for _, item := range []struct {
+		path  string
+		value string
+	}{{firstTarget, "first-next"}, {secondTarget, "second-next"}} {
+		change, err := prepareFileChange(item.path, "multi crash target", []byte(item.value), 0600)
+		if err != nil {
+			t.Fatal(err)
+		}
+		changes = append(changes, change)
+	}
+	ops := newTransactionFileOps(nil)
+	replace := ops.replaceWithBackup
+	commits := 0
+	ops.replaceWithBackup = func(current, replacement, backup string) error {
+		if err := replace(current, replacement, backup); err != nil {
+			return err
+		}
+		commits++
+		if commits == 2 {
+			os.Exit(87)
+		}
+		return nil
+	}
+	if err := writeChangesWithFileOps(changes, "multi crash transaction", ops); err != nil {
+		t.Fatal(err)
+	}
+	t.Fatal("multi crash worker completed without terminating")
+}
+
+func runDurableCreateCrashWorker(t *testing.T, target string) {
+	change, err := prepareFileChange(target, "crash create target", []byte("created"), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ops := newTransactionFileOps(nil)
+	move := ops.moveNoReplace
+	ops.moveNoReplace = func(source, destination string) error {
+		if err := move(source, destination); err != nil {
+			return err
+		}
+		if sameTransactionTestPath(destination, target) {
+			os.Exit(88)
+		}
+		return nil
+	}
+	if err := writeChangesWithFileOps([]*fileChange{change}, "crash create", ops); err != nil {
+		t.Fatal(err)
+	}
+	t.Fatal("create crash worker completed without terminating")
+}
+
+func runDurableDeleteCrashWorker(t *testing.T, target string) {
+	change, err := prepareSourceChange(
+		target,
+		"crash delete target",
+		[]byte("delete-original"),
+		true,
+		nil,
+		0600,
+		true,
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ops := newTransactionFileOps(nil)
+	move := ops.moveNoReplace
+	ops.moveNoReplace = func(source, destination string) error {
+		if err := move(source, destination); err != nil {
+			return err
+		}
+		if sameTransactionTestPath(source, target) {
+			os.Exit(89)
+		}
+		return nil
+	}
+	if err := writeChangesWithFileOps([]*fileChange{change}, "crash delete", ops); err != nil {
+		t.Fatal(err)
+	}
+	t.Fatal("delete crash worker completed without terminating")
+}
+
+func runDurableCommittedCleanupCrashWorker(t *testing.T, target string) {
+	change, err := prepareFileChange(target, "committed cleanup target", []byte("committed"), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ops := newTransactionFileOps(nil)
+	replace := ops.replaceWithBackup
+	blocker := ""
+	ops.replaceWithBackup = func(current, replacement, backup string) error {
+		if err := replace(current, replacement, backup); err != nil {
+			return err
+		}
+		blocker = filepath.Join(filepath.Dir(backup), "cleanup-blocker")
+		return os.WriteFile(blocker, []byte("block"), 0600)
+	}
+	err = writeChangesWithFileOps([]*fileChange{change}, "committed cleanup", ops)
+	if err == nil || !strings.Contains(err.Error(), "committed; durable cleanup failed") {
+		t.Fatalf("committed cleanup error = %v", err)
+	}
+	if err := os.Remove(blocker); err != nil {
+		t.Fatal(err)
+	}
+	os.Exit(90)
+}
+
+func runDurableCrashWorker(t *testing.T, target string) {
+	change, err := prepareFileChange(target, "crash target", []byte("next"), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ops := newTransactionFileOps(nil)
+	replace := ops.replaceWithBackup
+	absoluteTarget, err := filepath.Abs(target)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ops.replaceWithBackup = func(current, replacement, backup string) error {
+		if err := replace(current, replacement, backup); err != nil {
+			return err
+		}
+		if sameTransactionTestPath(current, absoluteTarget) {
+			os.Exit(86)
+		}
+		return nil
+	}
+	if err := writeChangesWithFileOps([]*fileChange{change}, "crash transaction", ops); err != nil {
+		t.Fatal(err)
+	}
+	t.Fatal("crash worker completed without terminating")
+}
+
+func runDurableReaderWorker(t *testing.T, target string) {
+	stop := os.Getenv("ELYDORA_DURABLE_STOP")
+	for {
+		if _, err := os.Lstat(stop); err == nil {
+			return
+		} else if !errors.Is(err, os.ErrNotExist) {
+			t.Fatal(err)
+		}
+		content, err := os.ReadFile(target)
+		if err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				t.Fatalf("reader observed missing target: %v", err)
+			}
+			if _, statErr := os.Lstat(target); statErr != nil {
+				t.Fatalf("reader observed unavailable target: %v; stat=%v", err, statErr)
+			}
+			time.Sleep(time.Millisecond)
+			continue
+		}
+		if string(content) != "value-a" && string(content) != "value-b" {
+			t.Fatalf("reader observed partial value %q", content)
+		}
+		time.Sleep(time.Millisecond)
+	}
+}
+
+func runDurableWriterWorker(t *testing.T, target string) {
+	value := os.Getenv("ELYDORA_DURABLE_VALUE")
+	ready := os.Getenv("ELYDORA_DURABLE_READY")
+	start := os.Getenv("ELYDORA_DURABLE_START")
+	change, err := prepareFileChange(target, "writer target", []byte(value), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(ready, []byte("ready"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	deadline := time.Now().Add(15 * time.Second)
+	for {
+		if _, err := os.Lstat(start); err == nil {
+			break
+		} else if !errors.Is(err, os.ErrNotExist) {
+			t.Fatal(err)
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("writer start barrier timed out")
+		}
+		time.Sleep(time.Millisecond)
+	}
+	if err := writeChanges([]*fileChange{change}, "subprocess writer", nil); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(23)
+	}
+}