diff --git a/internal/sync/annotations.go b/internal/sync/annotations.go
index 2ad0f12b..b012fc91 100644
--- a/internal/sync/annotations.go
+++ b/internal/sync/annotations.go
@@ -95,6 +95,18 @@ type SaveHighlightResult struct {
 	Conflict  bool
 }
 
+// coalesce returns fallback when v is the zero value — the LWW-apply
+// "an omitted field preserves the stored value" primitive. Zeroes matter
+// here because pgFloat8/pgInt4 turn them into NULLs: an uncoalesced
+// partial payload would erase stored locators on every re-save.
+func coalesce[T comparable](v, fallback T) T {
+	var zero T
+	if v == zero {
+		return fallback
+	}
+	return v
+}
+
 // idTargetOwnership verifies an id-targeted edit's ownership: the URL row
 // must belong to the requesting user and media item.
 func idTargetOwnership(rowUser, rowItem, reqUser, reqItem pgtype.UUID, kind string, id pgtype.UUID) error {
@@ -238,35 +250,23 @@ func (s *AnnotationService) applyLWW(
 	// xpointer) and may carry no CFI either: keep the stored ones so
 	// device-native serve-back and round-trip identity survive a web-side
 	// note/color edit instead of being wiped to empty.
-	startPosition := req.StartPosition
-	if startPosition == "" {
-		startPosition = existing.StartPosition.String
-	}
-	endPosition := req.EndPosition
-	if endPosition == "" {
-		endPosition = existing.EndPosition.String
-	}
-	epubcfiStart := req.EpubcfiStart
-	if epubcfiStart == "" {
-		epubcfiStart = existing.EpubcfiStart.String
-	}
-	epubcfiEnd := req.EpubcfiEnd
-	if epubcfiEnd == "" {
-		epubcfiEnd = existing.EpubcfiEnd.String
-	}
+	startPosition := coalesce(req.StartPosition, existing.StartPosition.String)
+	endPosition := coalesce(req.EndPosition, existing.EndPosition.String)
+	epubcfiStart := coalesce(req.EpubcfiStart, existing.EpubcfiStart.String)
+	epubcfiEnd := coalesce(req.EpubcfiEnd, existing.EpubcfiEnd.String)
 
 	highlight, err := s.db.UpdateMediaHighlightForSync(ctx, database.UpdateMediaHighlightForSyncParams{
 		ID:                 existing.ID,
 		SelectionText:      req.SelectionText,
 		StartPosition:      pgText(startPosition),
 		EndPosition:        pgText(endPosition),
-		Color:              pgText(req.Color),
-		NoteText:           pgText(req.NoteText),
-		PercentageStart:    pgFloat8(req.PercentageStart),
-		PercentageEnd:      pgFloat8(req.PercentageEnd),
+		Color:              pgText(coalesce(req.Color, existing.Color.String)),
+		NoteText:           pgText(coalesce(req.NoteText, existing.NoteText.String)),
+		PercentageStart:    pgFloat8(coalesce(req.PercentageStart, existing.PercentageStart.Float64)),
+		PercentageEnd:      pgFloat8(coalesce(req.PercentageEnd, existing.PercentageEnd.Float64)),
 		EpubcfiStart:       pgText(epubcfiStart),
 		EpubcfiEnd:         pgText(epubcfiEnd),
-		ChapterReference:   pgInt4(req.ChapterReference),
+		ChapterReference:   pgInt4(coalesce(req.ChapterReference, existing.ChapterReference.Int32)),
 		LastModifiedAt:     pgtype.Timestamptz{Time: modifiedAt, Valid: true},
 		LastModifiedSource: pgtype.Text{String: req.Source, Valid: req.Source != ""},
 		DeviceSyncData:     deviceData,
@@ -561,24 +561,6 @@ func (s *AnnotationService) SaveNote(ctx context.Context, req SaveNoteRequest) (
 			if dedupKey == "" {
 				dedupKey = byID.DedupKey.String
 			}
-			if req.EpubcfiLocation == "" {
-				req.EpubcfiLocation = byID.EpubcfiLocation.String
-			}
-			if req.PercentageLocation == 0 {
-				req.PercentageLocation = byID.PercentageLocation.Float64
-			}
-			if req.CharacterStart == 0 {
-				req.CharacterStart = byID.CharacterStart.Int32
-			}
-			if req.CharacterEnd == 0 {
-				req.CharacterEnd = byID.CharacterEnd.Int32
-			}
-			if req.ChapterReference == 0 {
-				req.ChapterReference = byID.ChapterReference.Int32
-			}
-			if req.ParagraphReference == 0 {
-				req.ParagraphReference = byID.ParagraphReference.Int32
-			}
 			if tombstoneWins(byID.Deleted.Bool, byID.DeletedAt, byID.LastModifiedAt, req.ModifiedAt) {
 				return &SaveNoteResult{Note: byID, Outcome: SaveOutcomeDeleted}, nil
 			}
@@ -663,17 +645,21 @@ func (s *AnnotationService) applyNoteLWW(ctx context.Context, req SaveNoteReques
 
 	deviceData := mergeDeviceSyncData(existing.DeviceSyncData, req.Source, req.DeviceSyncData)
 
+	// Coalesce omitted fields with the stored row (same doctrine as the
+	// highlight apply): a partial payload — a web PUT carrying only
+	// content/position, a device echo without percentages — must not
+	// wipe the locators it didn't mention (see coalesce).
 	note, err := s.db.UpdateMediaNoteForSync(ctx, database.UpdateMediaNoteForSyncParams{
 		ID:                 existing.ID,
 		UserID:             req.UserID,
 		Content:            req.Content,
-		Position:           pgText(req.Position),
-		PercentageLocation: pgFloat8(req.PercentageLocation),
-		CharacterStart:     pgInt4(req.CharacterStart),
-		CharacterEnd:       pgInt4(req.CharacterEnd),
-		EpubcfiLocation:    pgText(req.EpubcfiLocation),
-		ChapterReference:   pgInt4(req.ChapterReference),
-		ParagraphReference: pgInt4(req.ParagraphReference),
+		Position:           pgText(coalesce(req.Position, existing.Position.String)),
+		PercentageLocation: pgFloat8(coalesce(req.PercentageLocation, existing.PercentageLocation.Float64)),
+		CharacterStart:     pgInt4(coalesce(req.CharacterStart, existing.CharacterStart.Int32)),
+		CharacterEnd:       pgInt4(coalesce(req.CharacterEnd, existing.CharacterEnd.Int32)),
+		EpubcfiLocation:    pgText(coalesce(req.EpubcfiLocation, existing.EpubcfiLocation.String)),
+		ChapterReference:   pgInt4(coalesce(req.ChapterReference, existing.ChapterReference.Int32)),
+		ParagraphReference: pgInt4(coalesce(req.ParagraphReference, existing.ParagraphReference.Int32)),
 		LastModifiedAt:     pgtype.Timestamptz{Time: modifiedAt, Valid: true},
 		LastModifiedSource: pgtype.Text{String: req.Source, Valid: req.Source != ""},
 		DeviceSyncData:     deviceData,
@@ -778,24 +764,6 @@ func (s *AnnotationService) SaveBookmark(ctx context.Context, req SaveBookmarkRe
 			if dedupKey == "" {
 				dedupKey = byID.DedupKey.String
 			}
-			if req.CFIPosition == "" {
-				req.CFIPosition = byID.CfiPosition.String
-			}
-			if req.EpubcfiLocation == "" {
-				req.EpubcfiLocation = byID.EpubcfiLocation.String
-			}
-			if req.PercentageLoc == 0 {
-				req.PercentageLoc = byID.PercentageLocation.Float64
-			}
-			if req.PageNumber == 0 {
-				req.PageNumber = byID.PageNumber.Int32
-			}
-			if req.ChapterNumber == 0 {
-				req.ChapterNumber = byID.ChapterNumber.Int32
-			}
-			if req.ChapterReference == 0 {
-				req.ChapterReference = byID.ChapterReference.Int32
-			}
 			if tombstoneWins(byID.Deleted.Bool, byID.DeletedAt, byID.LastModifiedAt, req.ModifiedAt) {
 				return &SaveBookmarkResult{Bookmark: byID, Outcome: SaveOutcomeDeleted}, nil
 			}
@@ -898,16 +866,18 @@ func (s *AnnotationService) applyBookmarkLWW(ctx context.Context, req SaveBookma
 	}
 
 	bm, err := s.db.UpdateMediaBookmarkForSync(ctx, database.UpdateMediaBookmarkForSyncParams{
-		ID:                 existing.ID,
-		PageNumber:         pgInt4(req.PageNumber),
-		ChapterNumber:      pgInt4(req.ChapterNumber),
-		CfiPosition:        pgText(cfiPosition),
-		Title:              req.Title,
-		Position:           pgText(position),
-		Notes:              pgText(req.Notes),
-		PercentageLocation: pgFloat8(req.PercentageLoc),
-		EpubcfiLocation:    pgText(req.EpubcfiLocation),
-		ChapterReference:   pgInt4(req.ChapterReference),
+		ID:            existing.ID,
+		PageNumber:    pgInt4(coalesce(req.PageNumber, existing.PageNumber.Int32)),
+		ChapterNumber: pgInt4(coalesce(req.ChapterNumber, existing.ChapterNumber.Int32)),
+		CfiPosition:   pgText(cfiPosition),
+		Title:         req.Title,
+		Position:      pgText(position),
+		Notes:         pgText(req.Notes),
+		// Locator fields a partial payload omits must survive: zeroes
+		// become NULLs (pgFloat8/pgInt4) and would erase stored values.
+		PercentageLocation: pgFloat8(coalesce(req.PercentageLoc, existing.PercentageLocation.Float64)),
+		EpubcfiLocation:    pgText(coalesce(req.EpubcfiLocation, existing.EpubcfiLocation.String)),
+		ChapterReference:   pgInt4(coalesce(req.ChapterReference, existing.ChapterReference.Int32)),
 		LastModifiedAt:     pgtype.Timestamptz{Time: modifiedAt, Valid: true},
 		LastModifiedSource: pgtype.Text{String: req.Source, Valid: req.Source != ""},
 		DeviceSyncData:     deviceData,