Detect and confirm page orientation during automatic splitting

Bundle the trained heatmap/image orientation model and run it after provisional
blank-page and split analysis. Confirm candidates with Gemini using low thinking;
resolve mixed A3 sheet ordering with the complete statement and medium thinking.
Keep A4 scans independent and export paired A3 scans in booklet reading order.

Reanalyse uniformly inverted source sheets, validate ordering permutations, and
preserve source provenance, corrected rotations and reading slots in manual review.
Document the experiments, rejected approaches, calibration and runtime limits.

Validation: focused splitting/orientation regression suites pass; bundled model
checksum and wheel assets verified. Full Interro07 offline run: 44.26 seconds,
eight candidates, mocked upright confirmations, source hashes and geometry intact.

copienator/page_orientation_detector.py

@@ -0,0 +1,68 @@
+"""Orientation screen for 75 dpi, full logical pages supplied as RGB arrays.
+
+Create one Detector per process and reuse it. The conservative profile is the
+recommended default. Scores are screening signals, not calibrated probabilities.
+"""
+from pathlib import Path
+import json
+import cv2
+import joblib
+import numpy as np
+import onnxruntime as ort
+
+
+def ink(image, level=100):
+    mask = 255 - cv2.inRange(image, (level,)*3, (255,)*3)
+    mask[:15] = mask[-15:] = 0
+    mask[:, :15] = mask[:, -15:] = 0
+    return mask
+
+
+def spatial(mask):
+    result = []
+    for width, height in [(8, 12), (16, 24)]:
+        grid = np.sqrt(cv2.resize(mask.astype(np.float32)/255, (width, height), interpolation=cv2.INTER_AREA))
+        result.append((grid/(np.linalg.norm(grid)+1e-6)).ravel())
+    return np.concatenate(result)
+
+
+def bounds(mask):
+    ys, xs = np.where(mask)
+    if len(xs) < 5:
+        return 0, 0, mask.shape[1], mask.shape[0]
+    x0, x1 = np.quantile(xs, [.005, .995]).astype(int)
+    y0, y1 = np.quantile(ys, [.005, .995]).astype(int)
+    return max(0,x0-12), max(0,y0-12), min(mask.shape[1],x1+13), min(mask.shape[0],y1+13)
+
+
+class Detector:
+    def __init__(self, directory=None, profile='conservative'):
+        directory = Path(directory) if directory else Path(__file__).parent/'data'/'page_orientation'
+        config = json.loads((directory/'settings.json').read_text())
+        self.threshold = config['profiles'][profile]['threshold']
+        model = joblib.load(directory/'model.joblib')
+        self.heat_model, self.fusion_model = model['heat_model'], model['model']
+        options = ort.SessionOptions()
+        options.intra_op_num_threads = options.inter_op_num_threads = 1
+        options.log_severity_level = 3
+        self.session = ort.InferenceSession(str(directory/'doc.onnx'), options, providers=['CPUExecutionProvider'])
+        self.input_name = self.session.get_inputs()[0].name
+        self.mean = np.array([.485,.456,.406], np.float32)
+        self.std = np.array([.229,.224,.225], np.float32)
+
+    def predict(self, image_rgb):
+        mask = ink(image_rgb)
+        x0, y0, x1, y1 = bounds(mask)
+        crop = image_rgb[y0:y1, x0:x1]
+        feature = np.concatenate([spatial(mask), spatial(mask[y0:y1,x0:x1]), spatial(ink(image_rgb,140))])
+        heat_score = float(self.heat_model.decision_function(feature[None])[0])
+        probabilities = []
+        for view in [image_rgb, crop]:
+            for rotate in [False, True]:
+                image = np.rot90(view,2).copy() if rotate else view
+                image = cv2.resize(image,(224,224))
+                tensor = ((image.astype(np.float32)/255-self.mean)/self.std).transpose(2,0,1)[None].copy()
+                probabilities.extend(self.session.run(None,{self.input_name:tensor})[0][0])
+        features = np.array([probabilities+[heat_score]])
+        score = float(self.fusion_model.predict_proba(features)[0,1])
+        return {'flag': score > self.threshold, 'score': score, 'threshold': self.threshold, 'heatmap_score': heat_score}