ensure invalid deltas result in new state collections (#4623)

#### Does this PR need a docs update or release note?

- [x] ⛔ No

#### Type of change

- [x] 🐛 Bugfix

#### Test Plan

- [x] ⚡ Unit test
- [x] 💚 E2E

src/internal/m365/collection/drive/collections.go

@@ -335,7 +335,7 @@ func (c *Collections) Get(
 
 		logger.Ctx(ictx).Infow(
 			"previous metadata for drive",
-			"num_paths_entries", len(oldPrevPaths))
+			"count_old_prev_paths", len(oldPrevPaths))
 
 		du, newPrevPaths, err := c.PopulateDriveCollections(
 			ctx,
@@ -368,7 +368,7 @@ func (c *Collections) Get(
 
 		logger.Ctx(ictx).Infow(
 			"persisted metadata for drive",
-			"num_new_paths_entries", len(newPrevPaths),
+			"count_new_prev_paths", len(newPrevPaths),
 			"delta_reset", du.Reset)
 
 		numDriveItems := c.NumItems - numPrevItems
@@ -762,6 +762,7 @@ func (c *Collections) PopulateDriveCollections(
 			ctx = clues.Add(ctx, "delta_reset_occurred", true)
 			newPrevPaths = map[string]string{}
 			currPrevPaths = map[string]string{}
+			seenFolders = map[string]string{}
 			c.CollectionMap[driveID] = map[string]*Collection{}
 			invalidPrevDelta = true
 		}
@@ -929,6 +930,10 @@ func (c *Collections) processItem(
 			delete(newPrevPaths, alreadyHandledFolderID)
 		}
 
+		if invalidPrevDelta {
+			prevPath = nil
+		}
+
 		seenFolders[collectionPath.String()] = itemID
 
 		col, err := NewCollection(

src/internal/m365/collection/drive/collections_test.go

@@ -2403,6 +2403,118 @@ func (suite *CollectionsUnitSuite) TestGet() {
 				fullPath(1, name(folder)): true,
 			},
 		},
+		{
+			name:   "OneDrive_OneItemPage_InvalidPrevDelta_AnotherFolderAtExistingLocation",
+			drives: []models.Driveable{drive1},
+			enumerator: mock.EnumerateItemsDeltaByDrive{
+				DrivePagers: map[string]*mock.DriveItemsDeltaPager{
+					idx(drive, 1): {
+						Pages: []mock.NextPage{
+							{
+								Items: []models.DriveItemable{
+									driveRootItem(rootID),
+									driveItem(id(folder), name(folder), parent(1), rootID, isFolder),
+									driveItem(id(file), name(file), parent(1, name(folder)), id(folder), isFile),
+								},
+							},
+							{
+								Items: []models.DriveItemable{},
+								Reset: true,
+							},
+							{
+								Items: []models.DriveItemable{
+									driveRootItem(rootID),
+									driveItem(id(folder), name(folder), parent(1), rootID, isFolder),
+									driveItem(id(file), name(file), parent(1, name(folder)), id(folder), isFile),
+								},
+							},
+						},
+						DeltaUpdate: pagers.DeltaUpdate{URL: delta, Reset: true},
+					},
+				},
+			},
+			canUsePreviousBackup: true,
+			errCheck:             assert.NoError,
+			previousPaths: map[string]map[string]string{
+				idx(drive, 1): {
+					rootID:     fullPath(1),
+					id(folder): fullPath(1, name(folder)),
+				},
+			},
+			expectedCollections: map[string]map[data.CollectionState][]string{
+				fullPath(1): {data.NewState: {}},
+				fullPath(1, name(folder)): {
+					data.NewState: {id(folder), id(file)},
+				},
+			},
+			expectedDeltaURLs: map[string]string{
+				idx(drive, 1): delta,
+			},
+			expectedPreviousPaths: map[string]map[string]string{
+				idx(drive, 1): {
+					rootID:     fullPath(1),
+					id(folder): fullPath(1, name(folder)),
+				},
+			},
+			expectedDelList: pmMock.NewPrefixMap(map[string]map[string]struct{}{}),
+			doNotMergeItems: map[string]bool{
+				fullPath(1):               true,
+				fullPath(1, name(folder)): true,
+			},
+		},
+		{
+			name:   "OneDrive_OneItemPage_ImmediateInvalidPrevDelta_MoveFolderToPreviouslyExistingPath",
+			drives: []models.Driveable{drive1},
+			enumerator: mock.EnumerateItemsDeltaByDrive{
+				DrivePagers: map[string]*mock.DriveItemsDeltaPager{
+					idx(drive, 1): {
+						Pages: []mock.NextPage{
+							{
+								Items: []models.DriveItemable{},
+								Reset: true,
+							},
+							{
+								Items: []models.DriveItemable{
+									driveRootItem(rootID),
+									driveItem(idx(folder, 2), name(folder), parent(1), rootID, isFolder),
+									driveItem(idx(file, 2), name(file), parent(1, name(folder)), idx(folder, 2), isFile),
+								},
+							},
+						},
+						DeltaUpdate: pagers.DeltaUpdate{URL: delta, Reset: true},
+					},
+				},
+			},
+			canUsePreviousBackup: true,
+			errCheck:             assert.NoError,
+			previousPaths: map[string]map[string]string{
+				idx(drive, 1): {
+					rootID:     fullPath(1),
+					id(folder): fullPath(1, name(folder)),
+				},
+			},
+			expectedCollections: map[string]map[data.CollectionState][]string{
+				fullPath(1): {data.NewState: {}},
+				fullPath(1, name(folder)): {
+					data.DeletedState: {},
+					data.NewState:     {idx(folder, 2), idx(file, 2)},
+				},
+			},
+			expectedDeltaURLs: map[string]string{
+				idx(drive, 1): delta,
+			},
+			expectedPreviousPaths: map[string]map[string]string{
+				idx(drive, 1): {
+					rootID:         fullPath(1),
+					idx(folder, 2): fullPath(1, name(folder)),
+				},
+			},
+			expectedDelList: pmMock.NewPrefixMap(map[string]map[string]struct{}{}),
+			doNotMergeItems: map[string]bool{
+				fullPath(1):               true,
+				fullPath(1, name(folder)): true,
+			},
+		},
 		{
 			name:   "OneDrive_OneItemPage_InvalidPrevDelta_AnotherFolderAtDeletedLocation",
 			drives: []models.Driveable{drive1},
@@ -2555,7 +2667,7 @@ func (suite *CollectionsUnitSuite) TestGet() {
 			},
 			expectedCollections: map[string]map[data.CollectionState][]string{
 				fullPath(1):                   {data.NewState: {}},
-				fullPath(1, name(folder)):     {data.NotMovedState: {id(folder), id(file)}},
+				fullPath(1, name(folder)):     {data.NewState: {id(folder), id(file)}},
 				fullPath(1, namex(folder, 2)): {data.DeletedState: {}},
 			},
 			expectedDeltaURLs: map[string]string{