feat(workspace): implement Yjs CRDT real-time collaborative editing (resolves FLAW-01)

internal/storage/sqlite.go

@@ -232,6 +232,25 @@ func (s *Store) migrate() error {
 		PRIMARY KEY(user_id, tag)
 	);
 
+	CREATE TABLE IF NOT EXISTS document_crdt_state (
+		doc_id TEXT PRIMARY KEY,
+		state_blob BLOB NOT NULL,
+		updated_at TEXT NOT NULL,
+		updated_by TEXT NOT NULL DEFAULT '',
+		FOREIGN KEY(doc_id) REFERENCES documents(id) ON DELETE CASCADE
+	);
+
+	CREATE TABLE IF NOT EXISTS document_crdt_updates (
+		id INTEGER PRIMARY KEY AUTOINCREMENT,
+		doc_id TEXT NOT NULL,
+		update_blob BLOB NOT NULL,
+		created_at TEXT NOT NULL,
+		created_by TEXT NOT NULL DEFAULT '',
+		FOREIGN KEY(doc_id) REFERENCES documents(id) ON DELETE CASCADE
+	);
+
+	CREATE INDEX IF NOT EXISTS idx_doc_crdt_updates_doc ON document_crdt_updates(doc_id);
+
 	CREATE TABLE IF NOT EXISTS lists (
 		id TEXT PRIMARY KEY,
 		user_id TEXT NOT NULL,
@@ -1559,6 +1578,59 @@ func (s *Store) PatchDocumentBlocks(userID, docID string, req domain.DocBlocksPa
 	return doc, mergedOrder, nil
 }
 
+// GetDocumentCRDTState returns the compacted CRDT state blob and any pending updates for a document.
+func (s *Store) GetDocumentCRDTState(docID string) ([]byte, [][]byte, error) {
+	var stateBlob []byte
+	err := s.db.QueryRow(`SELECT state_blob FROM document_crdt_state WHERE doc_id = ?`, docID).Scan(&stateBlob)
+	if err != nil && err != sql.ErrNoRows {
+		return nil, nil, err
+	}
+
+	rows, err := s.db.Query(`SELECT update_blob FROM document_crdt_updates WHERE doc_id = ? ORDER BY id ASC`, docID)
+	if err != nil {
+		return stateBlob, nil, nil
+	}
+	defer rows.Close()
+
+	var updates [][]byte
+	for rows.Next() {
+		var u []byte
+		if err := rows.Scan(&u); err == nil && len(u) > 0 {
+			updates = append(updates, u)
+		}
+	}
+	return stateBlob, updates, nil
+}
+
+// AppendDocumentCRDTUpdate appends a new CRDT update delta for a document.
+func (s *Store) AppendDocumentCRDTUpdate(docID string, update []byte, userID string) error {
+	now := domain.NowISO()
+	_, err := s.db.Exec(`
+		INSERT INTO document_crdt_updates (doc_id, update_blob, created_at, created_by)
+		VALUES (?, ?, ?, ?)
+	`, docID, update, now, userID)
+	return err
+}
+
+// SaveDocumentCRDTState saves a compacted snapshot of the document CRDT state and prunes older incremental updates.
+func (s *Store) SaveDocumentCRDTState(docID string, stateBlob []byte, userID string) error {
+	now := domain.NowISO()
+	_, err := s.db.Exec(`
+		INSERT INTO document_crdt_state (doc_id, state_blob, updated_at, updated_by)
+		VALUES (?, ?, ?, ?)
+		ON CONFLICT(doc_id) DO UPDATE SET
+			state_blob = excluded.state_blob,
+			updated_at = excluded.updated_at,
+			updated_by = excluded.updated_by
+	`, docID, stateBlob, now, userID)
+	if err != nil {
+		return err
+	}
+	// Prune incremental updates older than the snapshot
+	_, _ = s.db.Exec(`DELETE FROM document_crdt_updates WHERE doc_id = ?`, docID)
+	return nil
+}
+
 // GetAuthorizedDocUsers returns all user IDs who have read/write/owner access to docID.
 func (s *Store) GetAuthorizedDocUsers(docID string) ([]string, error) {
 	userSet := make(map[string]bool)