{
  "coordinate_system": "decoded source pixels;416x240; image top-left origin",
  "source": "manual visual observation of source-key pairs, supplementing SAM edge-touch observations",
  "fixed_anchors": [
    "source top",
    "source right cap"
  ],
  "middle_bottom_crop": {
    "rendered_frames": [
      30,
      40
    ],
    "lower_contour_target_y": 248,
    "hidden_continuation_verified": false
  },
  "final_tip_return": {
    "rendered_frames": [
      48,
      52
    ],
    "lower_contour_target_y": 238.5,
    "reason": "rounded lower rim tip visibly returns inside source frame; edge-touching SAM mask overextends to viewport"
  },
  "interpolation": "linear target transition from frame40 to48; source landmark trajectories remain independently smoothed"
}