`Suggest questions...` isn't working over the conversation API

[stephendonner]

Description

Suggest questions... isn't working over the conversation API

Found while testing https://github.com/brave/brave-browser/issues/37575

Steps to Reproduce

1. install 1.68.19
2. launch using --enable-logging=stderr --v=2 --enable-features=AIChat:conversation_api\/true --env-leo=staging --env-ai-chat.bsg=dev --env-ai-chat-premium.bsg=dev
3. switch to Claude 3 Haiku (since it'll replace Claude Instant)
4. load https://en.wikipedia.org/wiki/CHiPs
5. click on Leo in the sidebar
6. click on Suggest questions...
7. wait

Actual result:

The Suggestion questions... button shows the AJAX-loading spinner, but quickly resolves/stops, without producing a set of suggested questions

Expected result:

Reproduces how often:

100%

Brave version (brave://version info)

Brave | 1.68.19 Chromium: 125.0.6422.41 (Official Build) nightly (x86_64)
-- | --
Revision | 27e9c4655eb07c8e606bdd56add4e4b13c2c3fb6
OS | macOS Version 11.7.10 (Build 20G1427)

Version/Channel Information:

• Can you reproduce this issue with the current release? No
• Can you reproduce this issue with the beta channel? Yes, only with the command-line option
• Can you reproduce this issue with the nightly channel? Yes, only with the command-line option

cc @bbondy @mattmcalister @LorenzoMinto @petemill @evq @brave/qa-team

[stephendonner]

@petemill here's what it looks like over Mixtral: