Function legacy_baseline_dir 

pub fn legacy_baseline_dir() -> PathBuf

Directory holding the legacy-surface corpus for the pinned CLI version: the same scenarios captured with the CLI’s ambient routing on a model id it does not recognize. The CLI tailors its tool surface per model, so this corpus records the surface a proxy-backed account actually gets. That surface is neither identical to the recognized one nor a superset of it: measure both rather than assuming the older “unrecognized ids keep the full legacy surface” story still holds. Resolves to baseline_dir()’s legacy-surface/ subdirectory, which keeps the two corpora out of each other’s diffs.