[API v1 - Conversations] Require non-empty user messages

[philipperolet]

Description

Fixes https://github.com/dust-tt/tasks/issues/2123 (see also slack thread in issue)

Reverts #10650 . Throws 400 if empty string is passed as message

Risks

We are slightly changing the API v1 contract.

Risk: pissed off clients that used to send empty messages to non-anthropic clients and don't want to send " " instead.

Also, if we ever send empty messages internally, we'll soon know (but doubt we do, there's always the mention at least)

Deploy

• warn spendesk
• warn customer success team & user runner
• deploy front

[github-actions]

	Warnings
⚠️	Files in **/api/v1/ have been modified and the PR has the documentation-ack label. Don't forget to run npm run docs and use the Deploy OpenAPI Docs Github action to update https://docs.dust.tt/reference.

Generated by 🚫 dangerJS against 0b15311

[spolu]

LGTM

[Fraggle]

@philipperolet can we update the front end to avoid allowing to send an empty message (It happens all the time to me)

[philipperolet]

in the frontend we can't send an empty message already, since we have the mention. If we did, as per the PR, this would fail yes.