diff --git a/backend/engine/cdsl_engine/capabilities.py b/backend/engine/cdsl_engine/capabilities.py
index 150184d1..6ad669aa 100644
--- a/backend/engine/cdsl_engine/capabilities.py
+++ b/backend/engine/cdsl_engine/capabilities.py
@@ -18,6 +18,9 @@ from .operation_contracts import materialized_feature_contracts
 
 _SELECTOR_REQUIRED = frozenset({"fillet", "chamfer"})
 _SKETCH_ATOM_PREFIXES = ("extrude_", "revolve_")
+# 开放轮廓（closed=false / role=open）只有"刀具截面补槽口边闭合后作切除"的
+# 物理意义：仅 extrude 直切类原子支持；add/回转对开放轮廓会造出无意义的封块。
+_OPEN_PROFILE_ATOMICS = frozenset({"extrude_cut_blind", "extrude_cut_through"})
 _PRIMARY_ATOMICS = frozenset({
     "extrude_add_blind", "extrude_add_two_sided", "extrude_cut_blind", "extrude_cut_two_sided",
     "extrude_cut_through",
@@ -299,6 +302,17 @@ class CapabilityAnalyzer:
                                 "The resolved sketch contains no closed profile region",
                                 sketch_id=node.sketch_id,
                             ))
+                        elif (
+                            not resolution_error
+                            and sketches[node.sketch_id].get("_open_contour")
+                            and node.atomic_id not in _OPEN_PROFILE_ATOMICS
+                        ):
+                            blockers.append(self._blocker(
+                                node.feature_id, "unsupported_open_profile",
+                                "Open profiles are only supported for straight extruded cut features",
+                                sketch_id=node.sketch_id,
+                                atomic_id=node.atomic_id,
+                            ))
                 if node.atomic_id == "loft_add":
                     profile_ids = params.get("profile_sketch_ids")
                     if not isinstance(profile_ids, list) or len(profile_ids) < 2:
diff --git a/backend/engine/cdsl_engine/sketch_solver.py b/backend/engine/cdsl_engine/sketch_solver.py
index b211bf49..b9429afc 100644
--- a/backend/engine/cdsl_engine/sketch_solver.py
+++ b/backend/engine/cdsl_engine/sketch_solver.py
@@ -128,7 +128,9 @@ def _reverse(edge: _Ctx) -> _Ctx:
     return output
 
 
-def _join(edges: list[_Ctx]) -> list[_Ctx]:
+def _join(edges: list[_Ctx], *, allow_open: bool = False) -> list[_Ctx]:
+    # 将边排序成一条连通链。allow_open=False（默认）要求首尾相接成闭合环；
+    # allow_open=True 时允许链首尾不接（供开放轮廓先拼链、后补闭合边）。
     if not edges:
         return []
     remaining = [deepcopy(edge) for edge in edges]
@@ -144,11 +146,22 @@ def _join(edges: list[_Ctx]) -> list[_Ctx]:
                 break
         else:
             raise ValueError("analytic_contours: segments do not form a connected contour")
-    if _distance(ordered[0]["start_mm"], ordered[-1]["end_mm"]) > _TOLERANCE_MM:
+    if not allow_open and _distance(ordered[0]["start_mm"], ordered[-1]["end_mm"]) > _TOLERANCE_MM:
         raise ValueError("analytic_contours: closed contour endpoints do not meet")
     return ordered
 
 
+def _close_open_contour(edges: list[_Ctx]) -> tuple[list[_Ctx], bool]:
+    # 开放链补闭合边：若首尾未相接，则沿两点连线补一条直线边形成闭合环。
+    # 返回 (edges, opened)；opened=False 表示首尾已天然相接（无需补边）。
+    if len(edges) < 2:
+        raise ValueError("analytic_contours: open contour needs at least 2 connected segments")
+    if _distance(edges[0]["start_mm"], edges[-1]["end_mm"]) <= _TOLERANCE_MM:
+        return edges, False
+    closing = _contour_line(edges[-1]["end_mm"][:2], edges[0]["start_mm"][:2])
+    return [*edges, closing], True
+
+
 def _circle_edges(segment: _Ctx) -> list[_Ctx]:
     center = segment.get("center") or [0.0, 0.0]
     radius = float(segment.get("radius_mm") or 0.0)
@@ -258,22 +271,35 @@ def _gen_analytic_contours(profile: _Ctx, meta: _Ctx) -> tuple[list[_Ctx], list[
     loops: list[_Ctx] = []
     entities: list[_Ctx] = []
     for index, contour in enumerate(profile.get("contours") or []):
-        if not contour.get("closed"):
-            raise ValueError(f"analytic_contours: contour {index} is open")
+        # 开放轮廓（closed=false / role=open）：先按开放链拼装，再在首尾间补一条
+        # 闭合边成闭合 region —— V 槽/开放型腔切除的刀具截面本就靠这条"槽口边"
+        # 闭合，故 B-rep 层可完全复用闭合链路。
+        contour_open = not bool(contour.get("closed", False))
+        if contour_open and contour.get("role") == "inner":
+            raise ValueError(f"analytic_contours: inner contour {index} cannot be open")
         raw_edges: list[_Ctx] = []
         for segment in contour.get("segments") or []:
             if segment.get("type") == "line":
                 entities.append(_line(segment["start"], segment["end"]))
             elif segment.get("type") == "circle":
+                if contour_open:
+                    raise ValueError(f"analytic_contours: open contour {index} cannot contain a full circle segment")
                 entities.append(_circle(segment.get("center") or [0.0, 0.0], float(segment.get("radius_mm") or 0.0)))
             raw_edges.extend(_segment_edges(segment))
         if raw_edges:
-            edges = _join(raw_edges)
+            edges = _join(raw_edges, allow_open=contour_open)
+            contour_opened = False
+            if contour_open:
+                if _distance(edges[0]["start_mm"], edges[-1]["end_mm"]) <= _TOLERANCE_MM:
+                    raise ValueError(f"analytic_contours: contour {index} is geometrically closed; use closed=true")
+                edges, contour_opened = _close_open_contour(edges)
+                meta["_has_open_contour"] = True
             _normalize_quarter_rounding_direction(edges)
             sample = _sample_loop(edges)
             if _area(sample) <= _TOLERANCE_MM * _TOLERANCE_MM:
                 raise ValueError(f"analytic_contours: contour {index} is degenerate")
-            loops.append({"edges": edges, "points": sample, "area": _area(sample)})
+            loops.append({"edges": edges, "points": sample, "area": _area(sample),
+                          "open": contour_open and contour_opened})
     for segment in profile.get("construction") or []:
         if segment.get("type") == "line":
             entities.append(_line(segment["start"], segment["end"], construction=True))
@@ -284,11 +310,13 @@ def _gen_analytic_contours(profile: _Ctx, meta: _Ctx) -> tuple[list[_Ctx], list[
     for loop in loops:
         loop["role"] = "inner" if sum(_contains(loop["points"][0], other["points"]) for other in loops if other is not loop) % 2 else "outer"
     outers = [loop for loop in loops if loop["role"] == "outer"]
-    regions = [{"outer": outer["edges"], "holes": []} for outer in outers]
+    regions = [{"outer": outer["edges"], "holes": [], "open": bool(outer.get("open"))} for outer in outers]
     for inner in (loop for loop in loops if loop["role"] == "inner"):
         containing = [outer for outer in outers if _contains(inner["points"][0], outer["points"])]
         if not containing:
             raise ValueError("analytic_contours: inner contour has no containing outer contour")
+        if any(outer.get("open") for outer in containing):
+            raise ValueError("analytic_contours: an open outer contour cannot contain nested holes")
         selected = min(containing, key=lambda outer: outer["area"])
         regions[outers.index(selected)]["holes"].append(inner["edges"])
     meta["_regions"] = regions
@@ -319,7 +347,7 @@ def resolve_profile(sketch: _Ctx) -> _Ctx:
     generator = SHAPE_GENERATORS.get(profile.get("type"))
     if generator is None:
         raise ValueError(f"sketch {sketch.get('id')}: unsupported profile type {profile.get('type')!r}")
-    meta: _Ctx = {"id": sketch.get("id"), "_entities": sketch.get("entities"), "_regions": []}
+    meta: _Ctx = {"id": sketch.get("id"), "_entities": sketch.get("entities"), "_regions": [], "_has_open_contour": False}
     entities, contour = generator(profile, meta)
     output = deepcopy(sketch)
     original_circles = [entity for entity in sketch.get("entities") or [] if entity.get("type") == "circle" and not entity.get("construction")]
@@ -329,9 +357,13 @@ def resolve_profile(sketch: _Ctx) -> _Ctx:
         output["contour_edges_mm"] = _transform_contours(contour, workplane) if workplane else contour
     if meta["_regions"]:
         output["contour_regions_mm"] = [
-            {"outer": _transform_contours(region["outer"], workplane) if workplane else region["outer"], "holes": [_transform_contours(hole, workplane) if workplane else hole for hole in region.get("holes") or []]}
+            {"outer": _transform_contours(region["outer"], workplane) if workplane else region["outer"],
+             "holes": [_transform_contours(hole, workplane) if workplane else hole for hole in region.get("holes") or []],
+             "open": bool(region.get("open"))}
             for region in meta["_regions"]
         ]
+    if meta["_has_open_contour"]:
+        output["_open_contour"] = True
     return output
 
 
diff --git a/json_to_cdsl/output/corpus-manifest.json b/json_to_cdsl/output/corpus-manifest.json
index 8db24cc1..27917825 100644
--- a/json_to_cdsl/output/corpus-manifest.json
+++ b/json_to_cdsl/output/corpus-manifest.json
@@ -5,16 +5,16 @@
   "document_stems_sha256": "ba5b905191817cd0f7b9ad07d4002ad27730e200a395f71f9c4e31ebb1867cd6",
   "phase_pools": {
     "p3": {
-      "selector_count": 770,
-      "selectors_sha256": "7b0e2142effc71bf2e3011654f020062665103cad5a6e219a323d1ee17887c89"
+      "selector_count": 771,
+      "selectors_sha256": "72093701357cd1858f2dbcc0f1ab9e6c7baea7db26357154e0586e5e1be6f801"
     },
     "p4": {
-      "selector_count": 825,
-      "selectors_sha256": "fa9bce14dc72170bd92ea8cb274490e1df733a85a8647de5f13cc39d8b1e945d"
+      "selector_count": 826,
+      "selectors_sha256": "ab9ea6edd8532ce7a0110d0725b5303c63a53617a0af502101b12f657285d371"
     },
     "p6": {
-      "selector_count": 892,
-      "selectors_sha256": "4f925d00636f471f517ccfbd1c030bc6fda8fa172332399964d80618f698ce89"
+      "selector_count": 893,
+      "selectors_sha256": "ac9f91b690bc533b1fdd1772d65ee77b248d108f39a429615d909b78332d9a08"
     }
   }
 }