Playground feedback: paste character limit, copy button, and cross-session chat history

[karagozemin]

Feedback from a developer testing the Raven web playground (https://raven.stellar.org/playground):

1. Character limit on pasted text — copying/pasting a long prompt hits a hard cap (currently the composer and server clamp user messages at 4,000 chars). It would be much better to have no limit, or at least a substantially higher one.
2. Copy button for responses — generated answers have no one-click "Copy" action; manually selecting long markdown (tables, code blocks) is awkward. A copy button on each assistant response would help a lot.
3. Chat history across sessions — signing into the same account again shows no previous chats. It would be great if chat history were saved and accessible across sessions (ideally a list of past conversations).

All three apply to the web playground specifically.

[kalepail]

Thanks for the feedback!

I'll have to think more about 1 and 3 and if I actually want to add those to what is really supposed to just be a "try me" experience not a full on work box.

For 2. I've just shipped it!

[kalepail]

I will keep the 8000-character input limit for this demonstration.
The current source and server checks use 8000, rather than the original 4000.

The copy button shipped, as recorded in the August 27 comment.
All 51 local tests for copying, input limits, chat validation, budgets, and page wiring passed today.

I will not add persistent chat history to the demonstration.

I will keep this issue open for one remaining acceptance check.
The production page requires sign-in, so this check did not verify copying in an authenticated browser session.
No paid chat request ran.