Audit YAML parsing code path

The YAML parser we're using are not robust to untrust input, it should only be used to parse local file. We should add some basic limitation in the code base to prevent it happening.

Start by tracing the YAML parser code path and identifying where input enters the parser. Review how local files and potentially untrusted input are distinguished; done means basic limitations prevent unsafe use with untrusted input while preserving the intended local-file behavior.

Written by the indexing model from the issue text.