Add versioning, update tool, and soft-delete

Schema: public_id + version columns with UNIQUE constraint,
delete_timestamp for soft-delete.

Tools: store_flashcard accepts optional public_id, update_flashcard
creates a new version preserving history, delete_flashcard inserts
a tombstone row and removes the Qdrant point.

Qdrant: point ID is public_id (only latest version indexed).

sqlite.go

@@ -42,14 +42,14 @@ func newSqliteStore(path string) (*sqliteStore, error) {
 	return &sqliteStore{db: db}, nil
 }
 
-func (s *sqliteStore) save(ctx context.Context, note, host, user, context_ string, repos, tags []string) (int64, error) {
+func (s *sqliteStore) save(ctx context.Context, note, host, user, context_ string, repos, tags []string, publicID int64) (int64, error) {
 	reposJSON := marshalStringSlice(repos)
 	tagsJSON := marshalStringSlice(tags)
 
 	result, err := s.db.ExecContext(ctx,
-		`INSERT INTO knowledge (note, repos, host, tags, "user", context)
-		 VALUES (?, ?, ?, ?, ?, ?)`,
-		note, reposJSON, host, tagsJSON, user, context_,
+		`INSERT INTO flashcard (public_id, version, note, repos, host, tags, "user", context)
+		 VALUES (?, 1, ?, ?, ?, ?, ?, ?)`,
+		publicID, note, reposJSON, host, tagsJSON, user, context_,
 	)
 	if err != nil {
 		return 0, fmt.Errorf("insert: %w", err)
@@ -60,20 +60,27 @@ func (s *sqliteStore) save(ctx context.Context, note, host, user, context_ strin
 		return 0, fmt.Errorf("last insert id: %w", err)
 	}
 
+	if publicID == 0 {
+		_, err = s.db.ExecContext(ctx, `UPDATE flashcard SET public_id = ? WHERE _id = ?`, id, id)
+		if err != nil {
+			return 0, fmt.Errorf("set public_id: %w", err)
+		}
+	}
+
 	return id, nil
 }
 
 func (s *sqliteStore) getByID(ctx context.Context, id int64) (*entry, error) {
 	row := s.db.QueryRowContext(ctx,
-		`SELECT id, note, repos, host, tags, "user", context, created
-		 FROM knowledge WHERE id = ?`, id,
+		`SELECT _id, public_id, version, note, repos, host, tags, "user", context, delete_timestamp, created
+		 FROM flashcard WHERE _id = ?`, id,
 	)
 
 	var e entry
 	var reposJSON, tagsJSON sql.NullString
-	var host, user, context_ sql.NullString
+	var host, user, context_, deleteTimestamp sql.NullString
 
-	err := row.Scan(&e.ID, &e.Note, &reposJSON, &host, &tagsJSON, &user, &context_, &e.Created)
+	err := row.Scan(&e.ID, &e.PublicID, &e.Version, &e.Note, &reposJSON, &host, &tagsJSON, &user, &context_, &deleteTimestamp, &e.Created)
 	if err == sql.ErrNoRows {
 		return nil, nil
 	}
@@ -96,10 +103,71 @@ func (s *sqliteStore) getByID(ctx context.Context, id int64) (*entry, error) {
 	if context_.Valid {
 		e.Context = context_.String
 	}
+	if deleteTimestamp.Valid {
+		e.DeleteTimestamp = deleteTimestamp.String
+	}
 
 	return &e, nil
 }
 
+func (s *sqliteStore) getLatestByPublicID(ctx context.Context, publicID int64) (*entry, error) {
+	row := s.db.QueryRowContext(ctx,
+		`SELECT _id, public_id, version, note, repos, host, tags, "user", context, delete_timestamp, created
+		 FROM flashcard WHERE public_id = ? ORDER BY version DESC LIMIT 1`, publicID,
+	)
+
+	var e entry
+	var reposJSON, tagsJSON sql.NullString
+	var host, user, context_, deleteTimestamp sql.NullString
+
+	err := row.Scan(&e.ID, &e.PublicID, &e.Version, &e.Note, &reposJSON, &host, &tagsJSON, &user, &context_, &deleteTimestamp, &e.Created)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("query: %w", err)
+	}
+
+	if reposJSON.Valid {
+		e.Repos = unmarshalStringSlice(reposJSON.String)
+	}
+	if tagsJSON.Valid {
+		e.Tags = unmarshalStringSlice(tagsJSON.String)
+	}
+	if host.Valid {
+		e.Host = host.String
+	}
+	if user.Valid {
+		e.User = user.String
+	}
+	if context_.Valid {
+		e.Context = context_.String
+	}
+	if deleteTimestamp.Valid {
+		e.DeleteTimestamp = deleteTimestamp.String
+	}
+
+	return &e, nil
+}
+
+func (s *sqliteStore) tombstone(ctx context.Context, publicID int64, version int) (int64, error) {
+	result, err := s.db.ExecContext(ctx,
+		`INSERT INTO flashcard (public_id, version, note, delete_timestamp)
+		 VALUES (?, ?, '', datetime('now'))`,
+		publicID, version,
+	)
+	if err != nil {
+		return 0, fmt.Errorf("tombstone: %w", err)
+	}
+
+	id, err := result.LastInsertId()
+	if err != nil {
+		return 0, fmt.Errorf("last insert id: %w", err)
+	}
+
+	return id, nil
+}
+
 func (s *sqliteStore) close() error {
 	return s.db.Close()
 }
@@ -146,3 +214,18 @@ func parseOptionalString(raw any) string {
 	}
 	return ""
 }
+
+func parseInt64(raw any) int64 {
+	if raw == nil {
+		return 0
+	}
+	switch v := raw.(type) {
+	case float64:
+		return int64(v)
+	case int64:
+		return v
+	case int:
+		return int64(v)
+	}
+	return 0
+}