Count system prompt tokens (#850)
* Count sysmte prompt tokens
* show error only once
* fix
* fix css
* simplify
* fix
* simplify
* Revert "simplify"
This reverts commit 61c0a2281f9795c4a4351d9ad473993a3c01c59f.
* `model.tokenizer` config & fix reactivity issues
* rm gated tokenizer
* use `truncate`
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Co-authored-by: Nathan Sarrazin <sarrazin.nathan@gmail.com>
