InsertId not returned on upsert into table with a trigger

Description

When upserting (on duplicate key update) into a table without a trigger, the insertId is always returned. When there is a trigger on the table, the insertId is not returned if the upsert results in no change to the row.

Steps to reproduce

SQL

create table t1 (
  id bigint(20) not null auto_increment,
  description1 varchar(45) default null,
  description2 varchar(45) default null,
  primary key (id),
  unique key idx_description_uq (description1)
) engine=InnoDB;

create table t2 (
  id bigint(20) not null,
  description1 varchar(45) default null,
  description2 varchar(45) default null
) engine=InnoDB;

create trigger trig after update on t1
	for each row
		insert into t2 (id, description1, description2) values (OLD.id, OLD.description1, OLD.description2);

Node

const mysql = require('mysql2/promise');
let connection;

makeCalls();

async function makeCalls() {
    connection = await mysql.createConnection({
    host: "localhost",
    port: 3306,
    user: "user",
    password: "password",
    database: "database"
  });

  await makeCall(1, 'test1');
  await makeCall(2, 'test1');
  await makeCall(3, 'test2');
}  

async function makeCall(run, description2) {    
  const [rows1] = await connection.execute(
    `insert into t1
        (description1, description2)
        values
        ('test1','${description2}') on duplicate key update id = last_insert_id(id), description1 = 'test1', description2 = '${description2}';`
    );
  console.log(`run ${run}: affectedRows ${rows1.affectedRows}, insertId ${rows1.insertId}`);
}

Output without trigger

run 1: affectedRows 1, insertId 1 <-initial insert
run 2: affectedRows 1, insertId 1 <-update, with the same data
run 3: affectedRows 2, insertId 1 <-update, with a change in data

Output with trigger

run 1: affectedRows 1, insertId 1 <-initial insert
run 2: affectedRows 1, insertId 0 <-update, with the same data
run 3: affectedRows 2, insertId 1 <-update, with a change in data

Environment

MySQL v5.7
mysql2 v2.3.3 and v3.1.2
node v14, v16 and v18.

Start by reproducing the behavior with the provided MySQL schema, trigger, and Node mysql2/promise execute example. Trace how the result metadata exposes affectedRows and insertId for an unchanged upsert, then add regression coverage showing that insertId is returned consistently with and without the trigger.