langchain - 💡(How to fix) Fix _to_protocol_usage drops input_token_details in v3 streaming path, causing cache token counts to always be 0

# _compat_bridge.py line ~485
def _to_protocol_usage(usage: dict[str, Any] | None) -> UsageInfo | None:
    result: dict[str, Any] = {}
    for key in ("input_tokens", "output_tokens", "total_tokens", "cached_tokens"):
        if key in usage:
            result[key] = usage[key]
    # input_token_details and output_token_details are never forwarded
    return cast("UsageInfo", result) if result else None

---

def _to_protocol_usage(usage: dict[str, Any] | None) -> UsageInfo | None:
    if usage is None:
        return None
    result: dict[str, Any] = {}
    for key in ("input_tokens", "output_tokens", "total_tokens", "cached_tokens",
                "input_token_details", "output_token_details"):
        if key in usage:
            result[key] = usage[key]
    return cast("UsageInfo", result) if result else None

---

from langchain_core.language_models import _compat_bridge as _lcb
_orig = _lcb._to_protocol_usage
def _patched(usage):
    if not usage:
        return None
    result = {k: usage[k] for k in ("input_tokens", "output_tokens", "total_tokens",
              "cached_tokens", "input_token_details", "output_token_details") if k in usage}
    return result or None
_lcb._to_protocol_usage = _patched