pub fn expand_env_placeholders_strict(input: &str) -> Result<String>Expand description
Expand ${VAR} and ${VAR:-default} placeholders, failing when a
placeholder resolves to nothing.
A value that cannot be expanded is a configuration error, not a literal:
letting ${UAR_MEMORY_MCP_URL:-http://…} reach a URL parser verbatim turns
a missing setting into a confusing downstream parse failure.
§Errors
Returns an error naming every placeholder that had neither a non-empty
environment variable nor a :- default.
§Examples
// Unset and no default — a startup error rather than a literal.
assert!(expand_env_placeholders_strict("${UAR_DOC_UNSET_VAR}").is_err());