"""Loaders — the contract seam. Built in Phase 1.

The ONLY code permitted to touch raw JSONL. Produces Event[] + Turn[] per
TRACE-CONTRACT §4 behind a clean `load(path) -> {events, turns}` signature so an
hf-loader can drop in later. The engine consumes only the normalized shapes and
knows nothing about JSONL or HF layout (Non-negotiable #3).
"""