feat(s3/lifecycle): emit MPU init records from FilerListFunc

Last gap in the filer-backed ListFunc. A directory at .uploads/<id>
carrying ExtMultipartObjectKey is the MPU init record; emit one
bootstrap.Entry with IsMPUInit=true and DestKey set to the user's
intended path. The walker's MatchPath uses DestKey for prefix
matching; the WalkerDispatcher uses it for the LifecycleDelete RPC's
ObjectPath. .uploads/<id> directories without the extended key are
mid-write before metadata landed and stay skipped.

isMPUInitDir is upgraded from the path-shape-only stub to the full
shape + extended-attr check that mirrors router.mpuInitInfo and
scheduler/bootstrap.go's same-named helper.

Tests pin: valid init record emits with the right DestKey, missing
ExtMultipartObjectKey skips the directory.

weed/s3api/s3lifecycle/dailyrun/filer_list_func.go

@@ -28,9 +28,9 @@ func init() { listPageSize.Store(1024) }
 // IsLatest / NumVersions / NoncurrentIndex / SuccessorModTime so the
 // walker's NoncurrentDays evaluation has the same per-version state
 // the streaming bootstrap injects via reader.Event.BootstrapVersion.
-//
-// MPU init records at .uploads/<id> are skipped here; the follow-up
-// commit emits one Entry per init with IsMPUInit and DestKey set.
+// MPU init records at .uploads/<id> with ExtMultipartObjectKey set
+// are emitted whole with IsMPUInit=true and DestKey carrying the
+// user's intended path.
 func FilerListFunc(client filer_pb.SeaweedFilerClient, bucketsPath string) bootstrap.ListFunc {
 	return func(ctx context.Context, bucket, start string, cb func(*bootstrap.Entry) error) error {
 		if client == nil {
@@ -78,9 +78,18 @@ func walkBucketTree(ctx context.Context, client filer_pb.SeaweedFilerClient, dir
 		full := dir + "/" + e.Name
 		key := strings.TrimPrefix(full, bucketRoot+"/")
 		if e.IsDirectory {
-			if isMPUInitDirShape(key) {
-				// TODO(phase4b): emit MPU init as a single Entry.
-				return nil
+			if isMPUInitDir(key, e) {
+				if start != "" && key <= start {
+					return nil
+				}
+				destKey := string(e.Extended[s3_constants.ExtMultipartObjectKey])
+				return cb(&bootstrap.Entry{
+					Path:      key,
+					DestKey:   destKey,
+					IsMPUInit: true,
+					ModTime:   time.Unix(e.Attributes.Mtime, int64(e.Attributes.MtimeNs)),
+					Size:      int64(e.Attributes.FileSize),
+				})
 			}
 			return walkBucketTree(ctx, client, full, bucketRoot, start, cb)
 		}
@@ -282,14 +291,20 @@ func isVersionsDir(entry *filer_pb.Entry) bool {
 	return entry.IsDirectory && strings.HasSuffix(entry.Name, s3_constants.VersionsFolder)
 }
 
-// isMPUInitDirShape mirrors scheduler/bootstrap.go's isMPUInitDir but
-// checks the path shape only; the Extended-attr verification lives in
-// the eventual full-MPU emission path.
-func isMPUInitDirShape(key string) bool {
+// isMPUInitDir mirrors router.mpuInitInfo: a directory at
+// .uploads/<id> carrying the destination key in Extended is the MPU
+// init record. Verified shape + presence of ExtMultipartObjectKey;
+// directories at .uploads/<id> without the key are mid-write before
+// metadata landed and stay out of the dispatch path.
+func isMPUInitDir(key string, entry *filer_pb.Entry) bool {
 	uploadsPrefix := s3_constants.MultipartUploadsFolder + "/"
 	if !strings.HasPrefix(key, uploadsPrefix) {
 		return false
 	}
 	rest := key[len(uploadsPrefix):]
-	return rest != "" && !strings.ContainsRune(rest, '/')
+	if rest == "" || strings.ContainsRune(rest, '/') {
+		return false
+	}
+	v, ok := entry.Extended[s3_constants.ExtMultipartObjectKey]
+	return ok && len(v) > 0
 }

weed/s3api/s3lifecycle/dailyrun/filer_list_func_test.go

@@ -143,17 +143,54 @@ func TestFilerListFunc_RecursesIntoSubdirs(t *testing.T) {
 	assert.Equal(t, []string{"logs/2026/b.log", "logs/a.log", "root.txt"}, paths)
 }
 
-func TestFilerListFunc_SkipsUploadsDirsForNow(t *testing.T) {
-	// Phase 4b-pre: `.uploads/<id>/` MPU init records are skipped
-	// here. The follow-up commit emits one IsMPUInit Entry per init.
+func TestFilerListFunc_MPUInitEmitsWithDestKey(t *testing.T) {
+	// .uploads/<id>/ with ExtMultipartObjectKey is the MPU init record.
+	// One Entry per init, IsMPUInit=true, DestKey = the user's path.
 	mtime := time.Now()
+	mpuDir := dir("upload-id-1")
+	mpuDir.Extended = map[string][]byte{
+		s3_constants.ExtMultipartObjectKey: []byte("user/path/object"),
+	}
 	client := &fakeFiler{tree: map[string][]*filer_pb.Entry{
 		"/buckets/bkt": {
 			file("regular.txt", mtime, 1),
 			dir(s3_constants.MultipartUploadsFolder),
 		},
 		"/buckets/bkt/" + s3_constants.MultipartUploadsFolder: {
-			dir("upload-id-1"),
+			mpuDir,
+		},
+	}}
+	listFn := FilerListFunc(client, "/buckets")
+	var got []*bootstrap.Entry
+	require.NoError(t, listFn(context.Background(), "bkt", "", func(e *bootstrap.Entry) error {
+		got = append(got, e)
+		return nil
+	}))
+	require.Len(t, got, 2)
+	byPath := map[string]*bootstrap.Entry{}
+	for _, e := range got {
+		byPath[e.Path] = e
+	}
+	require.NotNil(t, byPath["regular.txt"])
+	require.NotNil(t, byPath[s3_constants.MultipartUploadsFolder+"/upload-id-1"])
+	mpu := byPath[s3_constants.MultipartUploadsFolder+"/upload-id-1"]
+	assert.True(t, mpu.IsMPUInit)
+	assert.Equal(t, "user/path/object", mpu.DestKey)
+}
+
+func TestFilerListFunc_MPUInitWithoutDestKeyIsSkipped(t *testing.T) {
+	// A `.uploads/<id>` directory missing ExtMultipartObjectKey is
+	// mid-write before metadata landed; the dispatcher would error
+	// on empty DestKey. Skip it so the walk doesn't halt.
+	mtime := time.Now()
+	mpuDir := dir("upload-id-2") // no Extended
+	client := &fakeFiler{tree: map[string][]*filer_pb.Entry{
+		"/buckets/bkt": {
+			file("regular.txt", mtime, 1),
+			dir(s3_constants.MultipartUploadsFolder),
+		},
+		"/buckets/bkt/" + s3_constants.MultipartUploadsFolder: {
+			mpuDir,
 		},
 	}}
 	listFn := FilerListFunc(client, "/buckets")
@@ -162,7 +199,7 @@ func TestFilerListFunc_SkipsUploadsDirsForNow(t *testing.T) {
 		paths = append(paths, e.Path)
 		return nil
 	}))
-	assert.Equal(t, []string{"regular.txt"}, paths, ".uploads/ must not surface raw children")
+	assert.Equal(t, []string{"regular.txt"}, paths)
 }
 
 // fileWithExt is a versioned-file entry helper.