db: fix migration runner - proper schema_migrations checksum handling for existing DBs

- Check if checksum column exists before querying it
- For old DBs (no checksum col): use COUNT(*) to check if migration applied
- For new DBs (has checksum col): use checksum value
- All migrations run in a single transaction

internal/db/db.go

@@ -71,11 +71,32 @@ func (db *DB) runMigrationsInternal(mfs embedFS, migrationsRoot string) error {
 		return fmt.Errorf("creating schema_migrations table: %w", err)
 	}
 
+	hasChecksumCol := false
+	if rows, err := db.Query("PRAGMA table_info(schema_migrations)"); err == nil {
+		for rows.Next() {
+			var cid int
+			var cname string
+			rows.Scan(&cid, &cname, new(string), new(int), new(interface{}), new(int))
+			if cname == "checksum" {
+				hasChecksumCol = true
+			}
+		}
+		rows.Close()
+	}
+
 	for _, name := range names {
-		var storedChecksum string
-		row := db.QueryRow("SELECT checksum FROM schema_migrations WHERE version = ?", name)
-		if err := row.Scan(&storedChecksum); err == nil && storedChecksum != "" {
-			continue
+		if hasChecksumCol {
+			var storedChecksum string
+			row := db.QueryRow("SELECT checksum FROM schema_migrations WHERE version = ?", name)
+			if err := row.Scan(&storedChecksum); err == nil && storedChecksum != "" {
+				continue
+			}
+		} else {
+			var count int
+			row := db.QueryRow("SELECT COUNT(*) FROM schema_migrations WHERE version = ?", name)
+			if err := row.Scan(&count); err == nil && count > 0 {
+				continue
+			}
 		}
 
 		data, err := mfs.ReadFile(filepath.Join(migrationsRoot, name))
@@ -96,32 +117,22 @@ func (db *DB) runMigrationsInternal(mfs embedFS, migrationsRoot string) error {
 			return fmt.Errorf("applying migration %s: %w", name, err)
 		}
 
-		var insertSQL string
-		var insertArgs []interface{}
-		insertArgs = append(insertArgs, name)
-		hasChecksum := false
-		rows, _ := tx.Query("PRAGMA table_info(schema_migrations)")
-		if rows != nil {
-			for rows.Next() {
-				var cid int
-				var cname string
-				rows.Scan(&cid, &cname, new(string), new(int), new(interface{}), new(int))
-				if cname == "checksum" {
-					hasChecksum = true
-				}
+		if hasChecksumCol {
+			if _, err := tx.Exec(
+				"INSERT INTO schema_migrations (version, checksum) VALUES (?, ?)",
+				name, checksumHex,
+			); err != nil {
+				tx.Rollback()
+				return fmt.Errorf("recording migration %s: %w", name, err)
 			}
-			rows.Close()
-		}
-		if hasChecksum {
-			insertSQL = "INSERT INTO schema_migrations (version, checksum) VALUES (?, ?)"
-			insertArgs = append(insertArgs, checksumHex)
 		} else {
-			insertSQL = "INSERT INTO schema_migrations (version) VALUES (?)"
-		}
-
-		if _, err := tx.Exec(insertSQL, insertArgs...); err != nil {
-			tx.Rollback()
-			return fmt.Errorf("recording migration %s: %w", name, err)
+			if _, err := tx.Exec(
+				"INSERT INTO schema_migrations (version) VALUES (?)",
+				name,
+			); err != nil {
+				tx.Rollback()
+				return fmt.Errorf("recording migration %s: %w", name, err)
+			}
 		}
 
 		if err := tx.Commit(); err != nil {