feat: implement turn-based conversation modalities (addresses #1103)

[jacyanthis]

This adds feature #1103

This is a turn-based mode where each agent sends one message in a cycle. The moderator speaks first, then a random order of participants, then the moderator and a new random order... Participants see their text entry disabled and a "Waiting" banner then a "It's your turn" banner.

There is a checkbox in Conversation Settings for the Group Chat stage.

This PR was heavily assisted with an LLM agent, and it's my first time contributing, so thank you for the review! (maybe @rasmi for API regression? @jimbojw ?) I hope to add a few other related features.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[jimbojw]

Hi @jacyanthis, I'm working on running this locally to check it out. In the mean time, it looks like the schemas need to be updated (there's a failing check to this effect).

[jimbojw]

@jacyanthis What are the steps to test this out manually? Do you start as an Experimenter and make an experiment from scratch? Thanks in advance for step-by-step instructions.

[jacyanthis]

@jimbojw thanks! Schemas are updated. Yes, this is a checkbox in Conversation Settings for the Group Chat stage when editing an experiment.

1. Run ./run_locally.sh.
2. Visit localhost:4201.
3. Click Build experiment from scratch (or use one of your existing experiments).
4. Create a Group Chat stage or use one.
5. In the settings menu that appears, click the new Turn-based checkbox (see screenshot).
6. Launch the experiment as usual. The Group Chat stage should operate in a turn-based manner.

[jimbojw]

@jacyanthis OK thanks, I was able to test locally using simulated human participants.

There seems to be a bug at the end of the first turn of conversation.

To reproduce:

1. Create a new experiment with a Group Chat stage enforcing the turn-based conversation (feature under test).
2. Create a new cohort with at least two "human" participants.
3. For each simulated participant, select the participant and click the "Click to begin experiment button".
4. With the experiment started, iterate through the participants as prompted, entering a chat message.

Expected: After the last participant has entered a message, the first participant should be prompted to continue.

Actual: The last participant is prompted a second time. After they enter a second comment, then the conversation rotates back to the first participant.

In the following screenshot, you can see that the third active participant, camel-red-7804, was prompted for both the third conversation turn (C, correct) but also the fourth (D).

[jimbojw]

Note: In my test example, I included only simulated "human" participants, with no mediators. That may be relevant to the bug.