Environment variable replacement is needed so that users don't have to
hardcode their secrets in configuring `tools.yaml`.
Both formats `$ENV_NAME` and `${ENV_NAME}` are standard ways to declare
an environment variable.
However, some database statement placeholders that are already using the
`$ENV_NAME` format.
Therefore, we only support env var declaration using `${ENV_NAME}` to
disambiguate it from other usages.
Fixes issue: https://github.com/googleapis/genai-toolbox/issues/431
Add the bash command to `pip install` the package directly in the README
for a quicker start.
Also add “SDK” after “Toolbox LangChain” to clearly show that “Toolbox
LangChain” is an SDK.
> [!NOTE]
> We had released the PyPI package for Toolbox LangChain SDK as
`toolbox-langchain` and not `toolbox-langchain-sdk` but it still makes
sense to call it “Toolbox LangChain SDK” in natural language.
