Hot-swap Chat Profile within an active conversation

[Thomas-Fernandes]

Is your feature request related to a problem? Please describe.
Currently, changing Chat Profile creates a new conversation and loses the chat history. This prevents several use cases where keeping the conversation context while changing the model/prompt would be valuable.

Describe the solution you'd like
Allow switching Chat Profile mid-conversation. The chat history (messages, user/assistant exchanges) is preserved, but subsequent user messages are routed to the new profile's configuration (model, system prompt, settings).

Use cases

• A/B testing — required prerequisite for A/B testing — side-by-side model/prompt comparison in chat #2895 (side-by-side model/prompt comparison)
• Model escalation — start with a fast model (Haiku) and switch to a more capable one (Sonnet/Opus) when the conversation needs it
• Prompt iteration — test a new prompt template on an existing conversation without starting over

[FosanzDev]

@Thomas-Fernandes thanks! Doing a pull request for this soon

[FosanzDev]

Working on a first approach (https://github.com/FosanzDev/chainlit/tree/Chainlit%232899). This does work, but I need to change and add new e2e tests for this case, since there are some things that fundamentally change.