fix(transfer): preserve longtext/mediumtext/longblob/mediumblob types for MySQL target

Previously map_column_type mapped all text types (longtext, mediumtext) to
TEXT (64KB max) and all blob types (longblob, mediumblob) to BLOB (64KB
max). This caused "Data too long" errors when transferring large data from
MariaDB to MySQL.

Also improved INSERT error messages to include the table name and absolute
row number (offset + MySQL row) instead of just chunk index.

Fixes #796

crates/dbx-core/src/transfer.rs

@@ -713,7 +713,15 @@ pub fn map_column_type(source_type: &str, _source_db: &DatabaseType, target_db:
                 "CHAR(1)".into()
             }
         }
-        "text" | "longtext" | "mediumtext" | "tinytext" | "clob" | "ntext" => "TEXT".into(),
+        "longtext" => match target_db {
+            DatabaseType::Mysql => "LONGTEXT".into(),
+            _ => "TEXT".into(),
+        },
+        "mediumtext" => match target_db {
+            DatabaseType::Mysql => "MEDIUMTEXT".into(),
+            _ => "TEXT".into(),
+        },
+        "text" | "tinytext" | "clob" | "ntext" => "TEXT".into(),
         "bool" | "boolean" => match target_db {
             DatabaseType::Mysql => "TINYINT(1)".into(),
             DatabaseType::SqlServer => "BIT".into(),
@@ -730,7 +738,19 @@ pub fn map_column_type(source_type: &str, _source_db: &DatabaseType, target_db:
             DatabaseType::SqlServer => "DATETIME2".into(),
             _ => "TIMESTAMP".into(),
         },
-        "blob" | "longblob" | "mediumblob" | "tinyblob" | "binary" | "varbinary" | "image" => match target_db {
+        "longblob" => match target_db {
+            DatabaseType::Mysql => "LONGBLOB".into(),
+            DatabaseType::Postgres => "BYTEA".into(),
+            DatabaseType::SqlServer => "VARBINARY(MAX)".into(),
+            _ => "BLOB".into(),
+        },
+        "mediumblob" => match target_db {
+            DatabaseType::Mysql => "MEDIUMBLOB".into(),
+            DatabaseType::Postgres => "BYTEA".into(),
+            DatabaseType::SqlServer => "VARBINARY(MAX)".into(),
+            _ => "BLOB".into(),
+        },
+        "blob" | "tinyblob" | "binary" | "varbinary" | "image" => match target_db {
             DatabaseType::Postgres => "BYTEA".into(),
             DatabaseType::Mysql => "BLOB".into(),
             DatabaseType::SqlServer => "VARBINARY(MAX)".into(),
@@ -766,6 +786,12 @@ fn mysql_type_needs_key_prefix(mapped_type: &str) -> bool {
     )
 }
 
+fn parse_mysql_row_error(error: &str) -> Option<u64> {
+    let error = error.trim();
+    let at_row = error.rsplit("at row ").next()?;
+    at_row.trim().parse::<u64>().ok()
+}
+
 pub fn generate_create_table_ddl(
     columns: &[db::ColumnInfo],
     table: &str,
@@ -2245,11 +2271,19 @@ where
         );
         for (statement_index, batch_sql) in write_statements.iter().enumerate() {
             execute_on_pool(state, target_pool_key, batch_sql).await.map_err(|e| {
-                format!(
-                    "Insert failed at offset {offset}, chunk {} of {}: {e}",
-                    statement_index + 1,
-                    write_statements.len()
-                )
+                let absolute_row = parse_mysql_row_error(&e).map(|row| offset + row);
+                match absolute_row {
+                    Some(row) => format!(
+                        "Insert failed for table '{table}' at row {row} (chunk {} of {}): {e}",
+                        statement_index + 1,
+                        write_statements.len()
+                    ),
+                    None => format!(
+                        "Insert failed for table '{table}' at offset {offset}, chunk {} of {}: {e}",
+                        statement_index + 1,
+                        write_statements.len()
+                    ),
+                }
             })?;
         }
 
@@ -3205,4 +3239,45 @@ mod tests {
         assert_eq!(database_from_pool_key("conn:analytics:session:editor-1"), Some("analytics"));
         assert_eq!(database_from_pool_key("conn"), None);
     }
+
+    #[test]
+    fn map_column_type_preserves_longtext_for_mysql_target() {
+        assert_eq!(map_column_type("longtext", &DatabaseType::Mysql, &DatabaseType::Mysql), "LONGTEXT");
+    }
+
+    #[test]
+    fn map_column_type_preserves_mediumtext_for_mysql_target() {
+        assert_eq!(map_column_type("mediumtext", &DatabaseType::Mysql, &DatabaseType::Mysql), "MEDIUMTEXT");
+    }
+
+    #[test]
+    fn map_column_type_preserves_longblob_for_mysql_target() {
+        assert_eq!(map_column_type("longblob", &DatabaseType::Mysql, &DatabaseType::Mysql), "LONGBLOB");
+    }
+
+    #[test]
+    fn map_column_type_preserves_mediumblob_for_mysql_target() {
+        assert_eq!(map_column_type("mediumblob", &DatabaseType::Mysql, &DatabaseType::Mysql), "MEDIUMBLOB");
+    }
+
+    #[test]
+    fn map_column_type_longtext_falls_back_to_text_for_non_mysql_target() {
+        assert_eq!(map_column_type("longtext", &DatabaseType::Mysql, &DatabaseType::Postgres), "TEXT");
+    }
+
+    #[test]
+    fn map_column_type_longblob_falls_back_for_non_mysql_target() {
+        assert_eq!(map_column_type("longblob", &DatabaseType::Mysql, &DatabaseType::Postgres), "BYTEA");
+    }
+
+    #[test]
+    fn parse_mysql_row_error_extracts_row_number() {
+        let err = "ERROR 22001 (1406): Data too long column 'content' at row 8";
+        assert_eq!(parse_mysql_row_error(err), Some(8));
+    }
+
+    #[test]
+    fn parse_mysql_row_error_returns_none_for_non_mysql_error() {
+        assert_eq!(parse_mysql_row_error("some other error"), None);
+    }
 }