Files: Move… opens a folder picker, and a move across filesystems copies then removes

The picker walks the machine like the tab does — back, forward, up, breadcrumbs, a path
box, a new folder — and "Move here" puts the file or folder in the folder being looked
at; it says why it can't when it can't (already here, into itself, a name clash). POST
/api/files/move is a rename when the two ends share a filesystem and otherwise a task:
on a NAS every move between datasets is a different filesystem, and a rename there is
EXDEV. The copy is built under a hidden temporary name beside its destination, renamed
into place once complete, and only then is the original removed, so a failure or a
cancel leaves the original as it was. Modes, times, symlinks and, as root, owners are kept.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/files/files.go

@@ -15,6 +15,7 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"os/signal"
 	"os/user"
 	"path/filepath"
 	"sort"
@@ -62,6 +63,7 @@ type FS interface {
 	Mkdir(ctx context.Context, path string) error
 	Touch(ctx context.Context, path string) error
 	Rename(ctx context.Context, from, to string) error
+	Move(ctx context.Context, from, to string, progress io.Writer) error // Rename, or across filesystems a copy and a removal; long, so callers run it as a task
 	Delete(ctx context.Context, path string, recursive bool) error
 	Chmod(ctx context.Context, path string, perm os.FileMode) error
 }
@@ -385,6 +387,30 @@ func (s Sudo) Touch(ctx context.Context, path string) error {
 func (s Sudo) Rename(ctx context.Context, from, to string) error {
 	return s.runJSON(ctx, nil, "rename", from, to)
 }
+
+// Move as root: the helper does the copying and talks on stdout.
+func (s Sudo) Move(ctx context.Context, from, to string, progress io.Writer) error {
+	c := s.cmd(ctx, "move", from, to)
+	c.Stdout = progress
+	var errb strings.Builder
+	c.Stderr = &errb
+	if err := c.Run(); err != nil {
+		if msg := strings.TrimSpace(errb.String()); msg != "" {
+			return errors.New(msg)
+		}
+		return err
+	}
+	return nil
+}
+
+// MoveCmd is the command a task runs for a long move: this binary's helper, as root when
+// the backend is.
+func MoveCmd(ctx context.Context, fsys FS, self, from, to string) *exec.Cmd {
+	if s, ok := fsys.(Sudo); ok {
+		return s.cmd(ctx, "move", from, to)
+	}
+	return exec.CommandContext(ctx, self, "fs", "move", from, to)
+}
 func (s Sudo) Delete(ctx context.Context, path string, recursive bool) error {
 	if recursive {
 		return s.runJSON(ctx, nil, "delete", "-r", path)
@@ -399,7 +425,7 @@ func (s Sudo) Chmod(ctx context.Context, path string, perm os.FileMode) error {
 func Helper(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer) int {
 	fail := func(err error) int { fmt.Fprintln(stderr, err.Error()); return 1 }
 	if len(args) < 2 {
-		return fail(errors.New("usage: hamlab fs <list|stat|read|write|mkdir|touch|rename|delete|chmod> …"))
+		return fail(errors.New("usage: hamlab fs <list|stat|read|write|mkdir|touch|rename|move|delete|chmod> …"))
 	}
 	ctx := context.Background()
 	var l Local
@@ -452,7 +478,7 @@ func Helper(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer)
 				return fail(err)
 			}
 		}
-	case "rename":
+	case "rename", "move":
 		from, err := clean(1)
 		if err != nil {
 			return fail(err)
@@ -461,6 +487,15 @@ func Helper(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer)
 		if err != nil {
 			return fail(err)
 		}
+		if op == "move" {
+			// A cancelled task is a SIGTERM: stop copying and take the partial copy away.
+			mctx, stop := signal.NotifyContext(ctx, syscall.SIGTERM, syscall.SIGINT)
+			defer stop()
+			if err := l.Move(mctx, from, to, stdout); err != nil {
+				return fail(err)
+			}
+			return 0
+		}
 		if err := l.Rename(ctx, from, to); err != nil {
 			return fail(err)
 		}