Function scrub_credentials_value 

pub fn scrub_credentials_value(value: Value) -> Value

Structured-aware credential scrub for a JSON value bound for a human-facing surface. Object entries whose key names a credential have their entire value replaced with a marker, preserving the key. Every other string leaf still runs through the text scrub_credentials so inline token=... patterns inside unrelated fields are caught too. Serialize-then-scrub would corrupt key names that merely contain a sensitive word (e.g. access_token), so this walks the value instead. Same rendering-boundary contract as scrub_credentials.