Can A* algorithm be applied to

Yeah it can be done, you can subclass the embedding class and change the way it currently performs similarity search.

For instance llamaindex uses by default cosine, but you can change it to the given attached SS modes

https://github.com/run-llama/llama_index/blob/df7890c56bb69b496b985df9ad28121c7f620c45/llama-index-core/llama_index/core/base/embeddings/base.py#L52

Ok thanks

I don't think A* makes sense for vector seach.

Levenshtein is also very basic, and doesn't involve vectors (just edit distance)