Description:
I found a server-side assertion failure while testing MySQL prepared statements through the classic MySQL protocol.
The reproducer creates a deterministic stored function with normal SQL. It then sends raw prepared-statement protocol packets directly to the authenticated socket:
1. Raw `COM_STMT_PREPARE`
2. Raw `COM_STMT_EXECUTE` using `CLIENT_QUERY_ATTRIBUTES` semantics
I expected the server either to execute the prepared statement or to reject the supplied parameter data with a normal error response. Instead, the server aborted with an assertion failure.
The saved server error log starts with:
```text
mysqld: /home/fhb/mysql-server/sql/sql_prepare.cc:552: bool set_parameter_value(...): Assertion `len == 0 || len == 4 || len == 7 || len == 11 || len == 13' failed.
```
Backtrace excerpt:
```text
#10 set_parameter_value at /home/fhb/mysql-server/sql/sql_prepare.cc:552
#11 Prepared_statement::insert_parameters at /home/fhb/mysql-server/sql/sql_prepare.cc:714
#12 Prepared_statement::set_parameters at /home/fhb/mysql-server/sql/sql_prepare.cc:2806
#13 Prepared_statement::set_parameters at /home/fhb/mysql-server/sql/sql_prepare.cc:2796
#14 mysqld_stmt_execute at /home/fhb/mysql-server/sql/sql_prepare.cc:1900
```
How to repeat:
1. Start a debug/ASan MySQL server build.
2. Install Python dependencies:
```bash
pip install pymysql mysql-connector-python
```
3. Run the attached reproducer against the test server:
```bash
python3 bug_reproduce_2.py -h <host> -P <port> -u <user> -p <password> -d bug2_repro
```
4. The script creates the stored function, prepares the statement through a raw packet, and sends the raw `COM_STMT_EXECUTE` packet directly through the socket.
Observed output:
```text
Raw send packet_2_stmt39.bin: COM_STMT_EXECUTE payload_len=27
Connection lost while waiting for packet_2_stmt39.bin: server closed the connection
BUG CONFIRMED: server appears to be down
```
