_model_sort_key treated YYYYMMDD snapshot stamps (e.g.
claude-opus-4-20250514) as version components, so 20250514 > 8
and resolve_alias("opus", "anthropic") returned the wrong model.
Fix: split components ≥ 19_000_101 (smallest plausible date stamp)
out of the version tuple, keeping them as a trailing tiebreaker so
bare IDs sort before their dated snapshots and newer snapshots
before older ones. Shorter numeric components (mistral-large-2411,
gpt-4-0613) keep their current behavior. No models.dev dependency
in the sort path.