first version

sam2-backend/adapters/base.py

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+from dataclasses import dataclass
+from typing import Protocol
+
+import numpy as np
+
+
+@dataclass
+class PredictResult:
+    """Result of one bbox-prompted segmentation.
+
+    `polygon` is a list of (x, y) pixel coordinates describing the outer
+    contour of the largest mask blob. `score` is the model's confidence for
+    the selected mask (in [0, 1]).
+    """
+    polygon: list[tuple[float, float]]
+    score: float
+
+
+class BaseAdapter(Protocol):
+    """Minimal adapter contract. Each model family implements this."""
+
+    def load(self, config: str, checkpoint: str, device: str) -> None:
+        """Load weights into memory. Called once, lazily on first predict."""
+        ...
+
+    def predict_bbox(
+        self, image_rgb: np.ndarray, bbox_xyxy: tuple[int, int, int, int]
+    ) -> PredictResult:
+        """Run segmentation with a bbox prompt, return the best polygon."""
+        ...
+
+    def unload(self) -> None:
+        """Free GPU memory. Called when the registry evicts this model."""
+        ...