Local counter in loop as side effect

The code below doesn't work correctly, most likely it breaks the side effect system, but based on the documentation, this behavior is not obvious. I managed to fix it by wrapping counter in external:counter = await conv.external(counter - 1).

async function counter(conv: Conversation, ctx: Context) {
    await ctx.reply('Please send me a message');
    let counter = 0;
    while (true) {
      conv.log(`Loop begin: Counter: ${counter}`);
      const text = await conv.form.text();
      conv.log(`After wait: Counter: ${counter}`);

      const idx = conv.session.tags.indexOf(text);
      if (idx !== -1) {
        conv.log(`Remove "${text}" at ${idx} index`);
        conv.session.tags.splice(idx, 1);
        counter--;
      } else {
        conv.log(`Add "${text}"`);
        conv.session.tags.push(text);
        counter++;
      }
      await ctx.reply(`Counter: ${counter}`);

      if (counter === 3) {
        await ctx.reply('Done');
        return;
      }

      conv.log(`Loop end: Counter: ${counter}`);
    }
  }

Logs:

Loop begin: Counter: 0
After wait: Counter: 0
Add "1"
Loop end: Counter: 1

Loop begin: Counter: 1
After wait: Counter: 1
Remove "1" at 0 index
Loop end: Counter: 0

Loop begin: Counter: 0
After wait: Counter: -2 <--- Unexpected after wait
Add "1"
Loop end: Counter: -1

Loop begin: Counter: -1
[Stuck, no more interactions work]

grammyjs / conversations

Local counter in loop as side effect #67