Library Variables - String validation

[BoundedNutshell]

Variable Library string values can contain invisible/non‑printable characters. When used in pipelines (e.g. Workspace or Dataflow references), this can cause opaque runtime failures surfaced as generic 500 “token access” errors.

Suggestion: warn or block non‑printable characters (especially leading/trailing), or surface a clear validation error instead of InternalServerError.