"""Label-free lesion subspace interface (IMPLEMENTATION_SPEC §4).

A LesionSubspace is fit ONLY on a label-free CT token bank. It exposes:
  - fit(token_bank): build L(x) without any labels/masks,
  - project(Z): P_L Z,
  - membership_score(Z): per-token lesion-membership score (for Gate 1).

Every concrete fit() runs inside subspace_construction_guard() so any accidental label/mask
read raises LabelLeakError (tests/test_label_leak.py enforces this).
"""
from __future__ import annotations

from typing import Protocol, runtime_checkable

import torch


@runtime_checkable
class LesionSubspace(Protocol):
    def fit(self, token_bank: torch.Tensor) -> "LesionSubspace": ...   # label-free ONLY
    def project(self, Z: torch.Tensor) -> torch.Tensor: ...            # P_L Z
    def membership_score(self, Z: torch.Tensor) -> torch.Tensor: ...   # per-token, Gate 1