feat: Sprint 1 — IPA hardening, regression framework, ground-truth review

Track A (Backend):
- Compound word IPA decomposition (schoolbag→school+bag)
- Trailing garbled IPA fragment removal after brackets (R21 fix)
- Regression runner with DB persistence, history endpoints
- Page crop determinism verified with tests

Track B (Frontend):
- OCR Regression dashboard (/ai/ocr-regression)
- Ground Truth Review workflow (/ai/ocr-ground-truth)
  with split-view, confidence highlighting, inline edit,
  batch mark, progress tracking

Track C (Docs):
- OCR-Pipeline.md v5.0 (Steps 5e-5h)
- Regression testing guide
- mkdocs.yml nav update

Track D (Infra):
- TrOCR baseline benchmark script
- run-regression.sh shell script
- Migration 008: regression_runs table

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

klausur-service/backend/tests/test_page_crop.py

@@ -415,3 +415,53 @@ class TestDetectAndCropPage:
             assert 0 <= pct["y"] <= 100
             assert 0 < pct["width"] <= 100
             assert 0 < pct["height"] <= 100
+
+
+class TestCropDeterminism:
+    """A3: Verify that page crop produces identical results across N runs."""
+
+    @pytest.mark.parametrize("image_factory,desc", [
+        (
+            lambda: _make_image_with_content(800, 600, (100, 700, 80, 520)),
+            "standard content",
+        ),
+        (
+            lambda: _make_book_scan(1000, 800),
+            "book scan with spine shadow",
+        ),
+    ])
+    def test_determinism_10_runs(self, image_factory, desc):
+        """Same image must produce identical crops in 10 consecutive runs."""
+        img = image_factory()
+        results = []
+        for _ in range(10):
+            cropped, result = detect_and_crop_page(img.copy())
+            results.append({
+                "crop_applied": result["crop_applied"],
+                "cropped_size": result["cropped_size"],
+                "border_fractions": result["border_fractions"],
+                "shape": cropped.shape,
+            })
+
+        first = results[0]
+        for i, r in enumerate(results[1:], 1):
+            assert r["crop_applied"] == first["crop_applied"], (
+                f"Run {i} crop_applied differs from run 0 ({desc})"
+            )
+            assert r["cropped_size"] == first["cropped_size"], (
+                f"Run {i} cropped_size differs from run 0 ({desc})"
+            )
+            assert r["shape"] == first["shape"], (
+                f"Run {i} output shape differs from run 0 ({desc})"
+            )
+
+    def test_determinism_pixel_identical(self):
+        """Crop output pixels must be identical across runs."""
+        img = _make_image_with_content(800, 600, (100, 700, 80, 520))
+        ref_crop, _ = detect_and_crop_page(img.copy())
+
+        for i in range(5):
+            crop, _ = detect_and_crop_page(img.copy())
+            assert np.array_equal(ref_crop, crop), (
+                f"Run {i} produced different pixel output"
+            )