restic: restore a single kept file, not only a directory

The first restore of an arr app refused its settings file with "not a directory": restic restores
a snapshot's subfolder, not a file. A file is restored with its full path into a scratch directory
beside the target, moved into place, and the scratch removed.

modules/restic/cmd/restic-backups/backups.go

@@ -440,7 +440,7 @@ func (b *Backups) Restore(ctx context.Context, module, snapshot, path string) (*
 		if b.exists(ctx, target) {
 			return nil, fmt.Errorf("%s already exists; nothing is restored over anything", target)
 		}
-		if _, err := b.restic(ctx, "restore", chosen.ID+":"+p, "--target", target); err != nil {
+		if err := b.restoreOne(ctx, chosen.ID, p, target); err != nil {
 			return nil, err
 		}
 		r.Restored = append(r.Restored, target)
@@ -449,6 +449,51 @@ func (b *Backups) Restore(ctx context.Context, module, snapshot, path string) (*
 	return r, nil
 }
 
+// restoreOne puts one kept path at target. A directory is restored as the snapshot's subfolder, so
+// its contents land directly in target; a single file cannot be — restic restores a subfolder, not a
+// file (a settings file refused with "not a directory" on the first restore of an app, 2026-10-05) —
+// so it is restored with its full path into a scratch directory beside target, moved into place, and
+// the scratch directory removed.
+func (b *Backups) restoreOne(ctx context.Context, id, path, target string) error {
+	file, err := b.isFile(ctx, id, path)
+	if err != nil {
+		return err
+	}
+	if !file {
+		_, err := b.restic(ctx, "restore", id+":"+path, "--target", target)
+		return err
+	}
+	scratch := target + ".partial"
+	if _, err := b.restic(ctx, "restore", id, "--target", scratch, "--include", path); err != nil {
+		return err
+	}
+	if _, err := b.Run(ctx, "mv", scratch+path, target); err != nil {
+		return err
+	}
+	_, err = b.Run(ctx, "rm", "-rf", scratch)
+	return err
+}
+
+// isFile is whether a kept path is a single file in the snapshot, as restic lists it.
+func (b *Backups) isFile(ctx context.Context, id, path string) (bool, error) {
+	out, err := b.restic(ctx, "ls", "--json", id, path)
+	if err != nil {
+		return false, err
+	}
+	scanner := bufio.NewScanner(strings.NewReader(out))
+	scanner.Buffer(make([]byte, 1024*1024), 16*1024*1024)
+	for scanner.Scan() {
+		var node struct {
+			Type string `json:"type"`
+			Path string `json:"path"`
+		}
+		if json.Unmarshal(scanner.Bytes(), &node) == nil && node.Path == path {
+			return node.Type == "file", nil
+		}
+	}
+	return false, fmt.Errorf("restore point %s does not list %s", id, path)
+}
+
 // Check is the weekly look at the repository's own integrity, with a sample of the data read back.
 func (b *Backups) Check(ctx context.Context) error {
 	b.mu.Lock()

modules/restic/cmd/restic-backups/backups_test.go

@@ -187,7 +187,9 @@ func TestWithTheRealResticAMistakeIsUndoneBesideTheLiveData(t *testing.T) {
 	must(t, os.Mkdir(store, 0o700))
 	must(t, os.Mkdir(dumps, 0o700))
 	must(t, os.WriteFile(filepath.Join(store, "mailbox"), []byte("the only copy of a letter\n"), 0o600))
-	where := placed(t, "# mail\npath "+store+"\n# pg\nrun echo 'every row' > "+dumps+"/all.dump\npath "+dumps+"\n")
+	settings := filepath.Join(root, "settings.xml")
+	must(t, os.WriteFile(settings, []byte("<Config>kept</Config>\n"), 0o600))
+	where := placed(t, "# mail\npath "+store+"\npath "+settings+"\n# pg\nrun echo 'every row' > "+dumps+"/all.dump\npath "+dumps+"\n")
 	// As whoever runs the test, against its own repository: no sudo.
 	run := func(ctx context.Context, name string, args ...string) (string, error) {
 		out, err := exec.CommandContext(ctx, name, args...).Output()
@@ -217,14 +219,36 @@ func TestWithTheRealResticAMistakeIsUndoneBesideTheLiveData(t *testing.T) {
 		t.Fatalf("listed %+v", listed)
 	}
 
+	// The mistake to a single file, too.
+	must(t, os.WriteFile(settings, []byte("<Config>overwritten</Config>\n"), 0o600))
+
 	restored, err := b.Restore(ctx, "mail", "", "")
 	must(t, err)
-	if len(restored.Restored) != 1 || !strings.HasSuffix(restored.Restored[0], "store.restored-20261006-030000") {
+	if len(restored.Restored) != 2 {
 		t.Fatalf("restored %+v", restored)
 	}
-	if raw, _ := os.ReadFile(filepath.Join(restored.Restored[0], "mailbox")); string(raw) != "the only copy of a letter\n" {
+	var dir, file string
+	for _, r := range restored.Restored {
+		switch {
+		case strings.HasSuffix(r, "store.restored-20261006-030000"):
+			dir = r
+		case strings.HasSuffix(r, "settings.xml.restored-20261006-030000"):
+			file = r
+		}
+	}
+	if raw, _ := os.ReadFile(filepath.Join(dir, "mailbox")); string(raw) != "the only copy of a letter\n" {
 		t.Fatalf("the restored letter: %q", raw)
 	}
+	// A single file comes back as a file beside the live one, and nothing of the scratch remains.
+	if raw, _ := os.ReadFile(file); string(raw) != "<Config>kept</Config>\n" {
+		t.Fatalf("the restored settings: %q", raw)
+	}
+	if raw, _ := os.ReadFile(settings); string(raw) != "<Config>overwritten</Config>\n" {
+		t.Fatalf("the restore wrote over the live settings: %q", raw)
+	}
+	if _, err := os.Stat(file + ".partial"); err == nil {
+		t.Fatal("the scratch directory was left behind")
+	}
 	if _, err := os.Stat(filepath.Join(store, "mailbox")); err == nil {
 		t.Fatal("the restore wrote into the live directory")
 	}