diff --git a/.claude/rules/cleanup.md b/.claude/rules/cleanup.md
index befc6e0..5836c1c 100644
--- a/.claude/rules/cleanup.md
+++ b/.claude/rules/cleanup.md
@@ -2,4 +2,4 @@
 paths: ["internal/cleaner/**", "internal/fstree/**", "internal/classifier/**"]
 ---
 Changing what gets deleted, protected or traversed: read docs/SPEC.md § Classification and docs/ARCHITECTURE.md § Deletion Strategy first.
-Traversal rules: docs/decisions/symlink-no-follow.md, docs/decisions/one-filesystem.md.
+Traversal rules: docs/decisions/symlink-no-follow.md, docs/decisions/one-filesystem.md, docs/decisions/skip-dataless.md.
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index 2ccfb92..6f35d05 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -38,7 +38,6 @@ Three invariants keep the figures honest:
 - **Hard links** (`Nlink>1`) are counted once per artifact, keyed by `(dev, ino)`, so shared blocks net out across artifacts.
 - **APFS clones** in a `CloneAware` artifact count once; clone groups split across artifacts go to `CloneShares` so `DedupedTotal` counts them once.
 - **Hugging Face shared blobs** referenced by several models go to `BlobShares` so `DedupedTotal` counts them once.
-- **Shared traversal**: sizing walks with `fstree`, so it counts what finding reports and deletion removes.
 
 Neither scanner family sizes inline. Each collects its artifacts first — the walk during its single pass, stat scanners via `stat` — then sizes them through one shared bounded worker pool (`sizePending`, `min(NumCPU, 8)`) so the tree-walk I/O overlaps.
 
@@ -49,6 +48,7 @@ Finding, sizing and the pre-delete check walk through one package, so they cover
 - **Read each directory once.**
 - **Never follow symlinks.** Only the root is read through, and only for `--path` — [decision](decisions/symlink-no-follow.md)
 - **Stay on the root's filesystem** (like `du -x`); a directory on another device, of unknown device, or unreadable is returned as skipped — [decision](decisions/one-filesystem.md)
+- **Never read a dataless directory** (cloud placeholder whose content is not on disk); it is returned as skipped — [decision](decisions/skip-dataless.md)
 
 ### Walk engine
 
@@ -89,7 +89,7 @@ Use this pattern when a single ecosystem produces directories whose names alone
 
 Reclaiming is not always `os.RemoveAll` on a path — Docker images or simulator devices are reclaimed through vendor commands or API calls. Each `ScanResult` carries an optional `Delete *model.DeleteMethod` (kind path/command/api + display + `Run`); nil means path removal.
 
-The cleaner applies its policy gates (protected refusal, dry-run) uniformly, then executes: `Delete.Run(ctx)` when a method is attached, otherwise path removal (trash or permanent). A method with a nil `Run` is refused rather than falling back to path removal — a misconfigured item must never delete a path its method didn't intend. Trash/permanent choice only applies to path removal. Path removal (including dry-run) is refused when `fstree` skips any directory in the item: a recursive delete does not stop at mounts. Example: the global scanner's Homebrew item (`brew cleanup`).
+The cleaner applies its policy gates (protected refusal, dry-run) uniformly, then executes: `Delete.Run(ctx)` when a method is attached (example: the global scanner's Homebrew item, `brew cleanup`), otherwise path removal (trash or permanent). A method with a nil `Run` is refused rather than falling back to path removal — a misconfigured item must never delete a path its method didn't intend. Trash/permanent choice only applies to path removal. Path removal (including dry-run) is refused when `fstree` skipped any directory in the item: a mount ([decision](decisions/one-filesystem.md)), a cloud placeholder ([decision](decisions/skip-dataless.md)) or an unreadable directory.
 
 After path removal the cleaner runs the item's `Release`, if any, with the same trash/permanent removal; dry-run skips it.
 
diff --git a/docs/SPEC.md b/docs/SPEC.md
index 35c4eda..f423ed4 100644
--- a/docs/SPEC.md
+++ b/docs/SPEC.md
@@ -218,6 +218,15 @@ List supported ecosystems, categories, activity statuses, and safety levels.
 devclean list
 ```
 
+## Traversal
+
+Finding, sizing and the pre-delete check of `clean` read the same directories:
+
+- Symlinks are never followed; only the `--path` root is read through ([decision](decisions/symlink-no-follow.md)).
+- A mount under the scan root is not entered; pass it as `--path` to scan it ([decision](decisions/one-filesystem.md)).
+- A cloud placeholder directory (iCloud Drive, Dropbox or another File Provider folder whose content is not on disk) is not read, so a scan never downloads cloud content; a placeholder file adds nothing to `size`, only its logical size to `apparent_size` ([decision](decisions/skip-dataless.md)).
+- `clean`, including `--dry-run`, refuses an artifact containing a directory it did not read (a mount, a cloud placeholder, or an unreadable directory); a dry run marks it "would fail".
+
 ## Classification
 
 ### Categories
diff --git a/docs/decisions/skip-dataless.md b/docs/decisions/skip-dataless.md
new file mode 100644
index 0000000..06cc67c
--- /dev/null
+++ b/docs/decisions/skip-dataless.md
@@ -0,0 +1,18 @@
+# Do not read cloud placeholders
+
+## Decision
+
+`fstree` does not read a directory whose `st_flags` has `SF_DATALESS` (a File Provider placeholder: iCloud Drive, Dropbox, …). It returns the directory as skipped, so the pre-delete check treats it like a directory on another filesystem ([one-filesystem.md](one-filesystem.md)).
+
+## Rationale
+
+- Reading a dataless directory makes macOS download its content and blocks the read until the download ends. One scan sat 8 minutes in a single read under `~/Library/Mobile Documents`, and scans downloaded evicted iCloud items, using the disk space devclean is meant to free.
+- A placeholder takes no space on this disk, so skipping it hides nothing reclaimable.
+- The flag is in the `lstat` result the walk already has, so the check adds no system call.
+- Dataless files need no flag check: they have 0 allocated blocks (measured), and sizing never opens a file without blocks.
+
+## Rejected alternatives
+
+- **Excluding cloud folders by path** (`~/Library/Mobile Documents`, `~/Library/CloudStorage`): this misses Desktop and Documents synced to iCloud, and providers that sync other folders.
+- **Asking Foundation whether an item is in iCloud**: this needs cgo or an external command. An iCloud item that is already downloaded reads without blocking, so the flag is the exact condition.
+- **Turning materialization off for the process** (`setiopolicy_np` with `IOPOL_MATERIALIZE_DATALESS_FILES_OFF`): measured on macOS 27, an iCloud directory read still downloaded for 17 s and a file open still downloaded the file.
diff --git a/internal/fstree/dataless_darwin.go b/internal/fstree/dataless_darwin.go
new file mode 100644
index 0000000..a9a6fac
--- /dev/null
+++ b/internal/fstree/dataless_darwin.go
@@ -0,0 +1,15 @@
+package fstree
+
+import (
+	"io/fs"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// isDataless reports whether info is a File Provider placeholder (iCloud
+// Drive, Dropbox, ...) whose content is not on this disk.
+func isDataless(info fs.FileInfo) bool {
+	sys, ok := info.Sys().(*syscall.Stat_t)
+	return ok && sys.Flags&unix.SF_DATALESS != 0
+}
diff --git a/internal/fstree/dataless_other.go b/internal/fstree/dataless_other.go
new file mode 100644
index 0000000..c1499b9
--- /dev/null
+++ b/internal/fstree/dataless_other.go
@@ -0,0 +1,7 @@
+//go:build !darwin
+
+package fstree
+
+import "io/fs"
+
+func isDataless(fs.FileInfo) bool { return false }
diff --git a/internal/fstree/fstree.go b/internal/fstree/fstree.go
index 51f2f6f..d57ce51 100644
--- a/internal/fstree/fstree.go
+++ b/internal/fstree/fstree.go
@@ -1,7 +1,8 @@
 // Package fstree is the one tree traversal shared by finding artifacts,
 // sizing them and checking them before deletion, so all three cover the same
 // files. It never follows symlinks (only the root, when asked) and stays on
-// the root's filesystem, like du -x.
+// the root's filesystem, like du -x. It never reads a dataless directory, whose
+// content is in a cloud provider and would be downloaded by the read.
 package fstree
 
 import (
@@ -28,6 +29,10 @@ var deviceOf = func(_ string, info fs.FileInfo) (uint64, bool) {
 	return uint64(sys.Dev), true //nolint:unconvert // Dev is int32 on darwin, uint64 on linux
 }
 
+// dataless is indirected so a test can mark a directory dataless without a
+// cloud provider.
+var dataless = isDataless
+
 // Walker walks a tree depth-first, reading each directory once. Every hook is
 // optional.
 type Walker struct {
@@ -46,8 +51,9 @@ type Walker struct {
 }
 
 // Walk walks the tree under root and returns the directories it could not
-// check: on another filesystem, of unknown filesystem, or unreadable. A root
-// that does not exist is an empty tree. The only error is ctx's.
+// check: on another filesystem, of unknown filesystem, dataless, or
+// unreadable. A root that does not exist is an empty tree. The only error is
+// ctx's.
 func (w Walker) Walk(ctx context.Context, root string) ([]string, error) {
 	statRoot := os.Lstat
 	if w.FollowRoot {
@@ -57,7 +63,7 @@ func (w Walker) Walk(ctx context.Context, root string) ([]string, error) {
 	if errors.Is(err, fs.ErrNotExist) {
 		return nil, nil
 	}
-	if err != nil {
+	if err != nil || (info.IsDir() && dataless(info)) {
 		return []string{root}, nil
 	}
 	rootDev, rootDevOK := deviceOf(root, info)
@@ -95,6 +101,10 @@ func (w Walker) Walk(ctx context.Context, root string) ([]string, error) {
 				skipped = append(skipped, child)
 				continue
 			}
+			if dataless(childInfo) {
+				skipped = append(skipped, child)
+				continue
+			}
 			if rootDevOK {
 				if dev, ok := deviceOf(child, childInfo); !ok || dev != rootDev {
 					skipped = append(skipped, child)
@@ -120,13 +130,13 @@ type UncheckedError struct {
 }
 
 func (e *UncheckedError) Error() string {
-	return fmt.Sprintf("refusing to delete %s: contains directories on another filesystem or unreadable (%s)",
+	return fmt.Sprintf("refusing to delete %s: contains directories on another filesystem, not downloaded from a cloud provider, or unreadable (%s)",
 		e.Path, strings.Join(e.Dirs, ", "))
 }
 
 // CheckOneFilesystem returns an *UncheckedError when the tree at path has
 // directories Walk could not check. A recursive delete does not stop at
-// mounts, so it would remove files that were never sized or shown.
+// them, so it would remove files that were never sized or shown.
 func CheckOneFilesystem(ctx context.Context, path string) error {
 	skipped, err := Walker{}.Walk(ctx, path)
 	if err != nil {
diff --git a/internal/fstree/fstree_test.go b/internal/fstree/fstree_test.go
index 4391fc7..0f86cf8 100644
--- a/internal/fstree/fstree_test.go
+++ b/internal/fstree/fstree_test.go
@@ -80,6 +80,46 @@ func TestWalk_DoesNotEnterDirWithoutDevice(t *testing.T) {
 	}
 }
 
+// fakeDataless marks directories with the given base name dataless.
+func fakeDataless(t *testing.T, name string) {
+	t.Helper()
+	orig := dataless
+	dataless = func(info fs.FileInfo) bool { return info.Name() == name }
+	t.Cleanup(func() { dataless = orig })
+}
+
+func TestWalk_DoesNotReadDatalessDir(t *testing.T) {
+	root := t.TempDir()
+	cloud := filepath.Join(root, "cloud")
+	mkdirAll(t, filepath.Join(cloud, "inner"))
+	mkdirAll(t, filepath.Join(root, "local"))
+	fakeDataless(t, "cloud")
+
+	got, skipped := entered(t, Walker{}, root)
+
+	if want := []string{root, filepath.Join(root, "local")}; !slices.Equal(got, want) {
+		t.Errorf("entered = %v, want %v", got, want)
+	}
+	if want := []string{cloud}; !slices.Equal(skipped, want) {
+		t.Errorf("skipped = %v, want %v", skipped, want)
+	}
+}
+
+func TestWalk_DatalessRootIsUnchecked(t *testing.T) {
+	root := filepath.Join(t.TempDir(), "cloud")
+	mkdirAll(t, filepath.Join(root, "inner"))
+	fakeDataless(t, "cloud")
+
+	got, skipped := entered(t, Walker{}, root)
+
+	if len(got) != 0 {
+		t.Errorf("entered = %v, want none", got)
+	}
+	if want := []string{root}; !slices.Equal(skipped, want) {
+		t.Errorf("skipped = %v, want %v", skipped, want)
+	}
+}
+
 func TestWalk_ReadsEachDirOnce(t *testing.T) {
 	root := t.TempDir()
 	mkdirAll(t, filepath.Join(root, "a", "b"))
diff --git a/internal/scanner/clone.go b/internal/scanner/clone.go
index cc52ad9..3b7e0a2 100644
--- a/internal/scanner/clone.go
+++ b/internal/scanner/clone.go
@@ -30,9 +30,9 @@ type cloneInfo struct {
 }
 
 type cloneGroup struct {
-	model.CloneShare        // Blocks: st_blocks of one member
-	path             string // one member, for reading its extents
-	size             int64
+	model.CloneShare             // Blocks: st_blocks of one member
+	path             string      // one member, for reading its extents
+	info             fs.FileInfo // of path
 }
 
 // extent is a physical byte range [start, end) on a device.
@@ -129,7 +129,7 @@ func (c *cloneSources) get(ctx context.Context, path string) (extents []extent,
 						continue
 					}
 					if info, err := e.Info(); err == nil {
-						if fx, ok := fileExtents(filepath.Join(dir, e.Name()), info.Size()); ok {
+						if fx, ok := fileExtents(filepath.Join(dir, e.Name()), info); ok {
 							xs = append(xs, fx...)
 						}
 					}
diff --git a/internal/scanner/clone_darwin.go b/internal/scanner/clone_darwin.go
index e96b95e..6cfb3cf 100644
--- a/internal/scanner/clone_darwin.go
+++ b/internal/scanner/clone_darwin.go
@@ -2,6 +2,8 @@ package scanner
 
 import (
 	"encoding/binary"
+	"io/fs"
+	"syscall"
 	"unsafe"
 
 	"golang.org/x/sys/unix"
@@ -13,9 +15,12 @@ const (
 )
 
 // fileExtents returns a file's physical extents via fcntl(F_LOG2PHYS_EXT). ok
-// is false when a lookup fails (e.g. a compressed file).
-func fileExtents(path string, size int64) (xs []extent, ok bool) {
-	if size == 0 {
+// is false when a lookup fails (e.g. a compressed file). A file with no
+// allocated blocks has none and is not opened: opening a cloud placeholder
+// would download it.
+func fileExtents(path string, info fs.FileInfo) (xs []extent, ok bool) {
+	size := info.Size()
+	if sys, isStat := info.Sys().(*syscall.Stat_t); size == 0 || (isStat && sys.Blocks == 0) {
 		return nil, true
 	}
 	fd, err := unix.Open(path, unix.O_RDONLY|unix.O_CLOEXEC, 0)
diff --git a/internal/scanner/clone_other.go b/internal/scanner/clone_other.go
index bfafd21..552502b 100644
--- a/internal/scanner/clone_other.go
+++ b/internal/scanner/clone_other.go
@@ -2,10 +2,12 @@
 
 package scanner
 
+import "io/fs"
+
 // cloneSizingSupported is false off macOS: APFS clones are macOS-only, and
 // other filesystems' shared extents (btrfs, XFS reflinks) are not read.
 const cloneSizingSupported = false
 
-func fileExtents(string, int64) ([]extent, bool) { return nil, false }
+func fileExtents(string, fs.FileInfo) ([]extent, bool) { return nil, false }
 
 func fileCloneInfo(string) (cloneInfo, bool) { return cloneInfo{}, false }
diff --git a/internal/scanner/scanner.go b/internal/scanner/scanner.go
index 882c90b..14ec725 100644
--- a/internal/scanner/scanner.go
+++ b/internal/scanner/scanner.go
@@ -237,13 +237,13 @@ func measure(ctx context.Context, path string, clones *cloneSources, source stri
 					if groups == nil {
 						groups = make(map[uint64]*cloneGroup)
 					}
-					g = &cloneGroup{CloneShare: model.CloneShare{Refcnt: ci.refcnt, Blocks: blocks}, path: full, size: info.Size()}
+					g = &cloneGroup{CloneShare: model.CloneShare{Refcnt: ci.refcnt, Blocks: blocks}, path: full, info: info}
 					groups[ci.id] = g
 				}
 				g.Seen++
 				groupBlocks += blocks
 			case !ok || ci.mayShare:
-				if xs, ok := fileExtents(full, info.Size()); ok {
+				if xs, ok := fileExtents(full, info); ok {
 					extents = append(extents, xs...)
 					extentBlocks += blocks
 				}
@@ -288,7 +288,7 @@ func measure(ctx context.Context, path string, clones *cloneSources, source stri
 		}
 		// A partly rewritten copy may overlap the group: count by extent.
 		if len(extents) > 0 {
-			if xs, ok := fileExtents(g.path, g.size); ok {
+			if xs, ok := fileExtents(g.path, g.info); ok {
 				extents = append(extents, xs...)
 				continue
 			}