feat(edge): RingBuffer + face blur + JPEG snapshotter

edge/snapshot.py

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+from collections import deque
+
+import cv2
+
+from edge.models import BBox
+
+
+class RingBuffer:
+    def __init__(self, maxlen: int = 90):
+        self.frames: deque = deque(maxlen=maxlen)
+
+    def push(self, t: float, frame) -> None:
+        self.frames.append((t, frame))
+
+    def window(self, pre: int, post: int, index: int) -> list:
+        lo = max(0, index - pre)
+        hi = min(len(self.frames), index + post + 1)
+        return [f for (_t, f) in list(self.frames)[lo:hi]]
+
+
+class FaceBlurrer:
+    def blur(self, frame, head_boxes: list[BBox]):
+        for b in head_boxes:
+            x1, y1 = int(max(0, b.x1)), int(max(0, b.y1))
+            x2, y2 = int(min(frame.shape[1], b.x2)), int(min(frame.shape[0], b.y2))
+            if x2 > x1 and y2 > y1:
+                roi = frame[y1:y2, x1:x2]
+                frame[y1:y2, x1:x2] = cv2.GaussianBlur(roi, (0, 0), sigmaX=12)
+        return frame
+
+
+class Snapshotter:
+    def __init__(self, blurrer: FaceBlurrer, quality: int = 80):
+        self.blurrer = blurrer
+        self.quality = quality
+
+    def capture(self, frames: list, head_boxes_per_frame: list) -> list[bytes]:
+        out: list[bytes] = []
+        for frame, heads in list(zip(frames, head_boxes_per_frame))[:3]:
+            blurred = self.blurrer.blur(frame.copy(), heads)
+            ok, buf = cv2.imencode(".jpg", blurred,
+                                   [cv2.IMWRITE_JPEG_QUALITY, self.quality])
+            if ok:
+                out.append(buf.tobytes())
+        return out

tests/test_snapshot.py

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+import numpy as np
+from edge.models import BBox
+from edge.snapshot import RingBuffer, FaceBlurrer, Snapshotter
+
+def _frame(val=128):
+    return np.full((64, 64, 3), val, dtype=np.uint8)
+
+def test_ringbuffer_keeps_recent():
+    rb = RingBuffer(maxlen=3)
+    for i in range(5):
+        rb.push(float(i), _frame(i))
+    assert len(rb.frames) == 3
+    assert rb.frames[-1][0] == 4.0
+
+def test_face_blur_changes_region():
+    fb = FaceBlurrer()
+    f = _frame(0)
+    f[0:10, 0:10] = 255
+    out = fb.blur(f.copy(), [BBox(0, 0, 10, 10)])
+    assert out is not None
+    assert out.shape == f.shape
+
+def test_snapshotter_returns_jpeg_bytes():
+    snap = Snapshotter(FaceBlurrer())
+    imgs = snap.capture([_frame(100), _frame(120)], [[], []])
+    assert 1 <= len(imgs) <= 3
+    assert imgs[0][:2] == b"\xff\xd8"  # JPEG magic