refactor(cdsl_engine): executor registry + per-family executor package

Phase 3 of the decoupling refactor (behavior-preserving):
- registry.py: atomic_executor decorator, ALL_ATOMIC_IDS with
  fail-fast registration validation, execute_node dispatcher
- executors/: one module per family (extrude, revolve, surfaces,
  loft_sweep, bodies, context, primitives, parametric, holes,
  dressup, patterns) + shared helpers in executors/common
- executors/__init__: explicit aggregation + completeness check
  (registry must cover every declared atomic id at import time)
- runtime.py: slimmed to entry points (analyze_cdsl/rebuild_cdsl)
  plus full historical re-exports incl. test-referenced privates

Adding an atomic operation now touches only one executor module and
its schema contract; the shared registry never changes. Verified
against baseline: zero new failures.

backend/engine/cdsl_engine/executors/holes.py

@@ -0,0 +1,78 @@
+"""Hole executors (hole_blind / hole_countersink / hole_counterbore / hole_wizard)."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+from ..registry import atomic_executor
+from ..specs import HoleSpec, PlaneSpec, vector_scale
+from ..topology import FeaturePlanNode, FeatureResult, RuntimeDiagnostic
+from .common import _hole_starts, _host_plane
+
+if TYPE_CHECKING:  # pragma: no cover - import for type checkers only
+    from ..session import ExecutionSession
+
+
+@atomic_executor("hole_blind", "hole_countersink", "hole_counterbore")
+def _hole_executor(node: FeaturePlanNode, session: "ExecutionSession", sketch: dict[str, Any] | None) -> FeatureResult:
+    del sketch
+    return _execute_hole(node, session, wizard=False)
+
+
+@atomic_executor("hole_wizard")
+def _hole_wizard_executor(node: FeaturePlanNode, session: "ExecutionSession", sketch: dict[str, Any] | None) -> FeatureResult:
+    del sketch
+    return _execute_hole(node, session, wizard=True)
+
+
+def _execute_hole(node: FeaturePlanNode, session: "ExecutionSession", *, wizard: bool = False) -> FeatureResult:
+    # 孔特征（hole）执行入口：在指定宿主面上按孔规格生成切除工具，并从主体上减去。
+    
+    # 1. 校验：孔是切除操作，必须先有主体。
+    if session.body is None:
+        raise ValueError("hole feature has no body")
+    # 2. 确定宿主面 host_face：
+    host_selector = node.params.get("host_face")
+    if isinstance(host_selector, dict) and isinstance(host_selector.get("frame"), dict):
+        #   若直接带 frame（平面定义），则以该平面为宿主，孔位按局部坐标解释。
+        host = PlaneSpec.from_mapping(host_selector["frame"])
+        positions_are_local = True
+    else:
+        #   否则从特征选择器中取 face，解析出宿主平面，孔位按世界坐标解释。
+        selectors = list(node.selectors)
+        if isinstance(host_selector, dict):
+            selectors.append(host_selector)
+        selector = next((item for item in selectors if item.get("kind") == "face"), None)
+        if selector is None:
+            raise ValueError("hole requires host_face selector or frame")
+        host = _host_plane(session.resolve(selector))
+        positions_are_local = False
+    # 3. 解析孔规格 HoleSpec（直径、深度、类型等，wizard 模式提供额外默认值）。
+    spec = HoleSpec.from_feature(node.atomic_id, node.params, wizard=wizard)
+    # 4. A host-face normal is an outward B-rep orientation, so its inverse
+    # always enters the material.  Inferring direction from the global body
+    # centre fails for concave or multi-leg parts: for example, the top face
+    # of an L bracket can sit below the whole body's centre and the old rule
+    # drilled outward, producing a no-op feature reported as successful.
+    # The selected topology face is the local, authoritative orientation.
+    inward = vector_scale(host.normal, -1)
+    # 5. 生成孔切除工具：按孔规格、起始位置、内方向及“贯穿到主体底面”的深度构造工具实体。
+    tool = session.adapter.hole_tool(
+        spec,
+        _hole_starts(spec, host_plane=host, positions_are_local=positions_are_local),
+        inward,
+        session.adapter.body_span(session.body, inward) + 2.0,
+    )
+    # 6. 从主体上减去工具实体，登记新主体并返回结果。
+    #    thread 是装饰螺纹（无螺距、不进实体几何，SolidWorks/STEP 的螺纹孔
+    #    即光滑孔）：孔按光滑圆柱孔执行，同时记录 info 级诊断便于批量报告
+    #    追溯降级数量（issue #9，capabilities 已不再拒绝 thread）。
+    diagnostics: list[RuntimeDiagnostic] = []
+    if wizard and node.params.get("thread"):
+        diagnostics.append(RuntimeDiagnostic(
+            code="thread_decoration_ignored",
+            message="Thread decoration is not modeled; the hole falls back to a plain cylindrical bore",
+            feature_id=node.feature_id,
+        ))
+    session.register_body(node.feature_id, session.adapter.cut(session.body, tool), replay_node=node)
+    return session.result(node, diagnostics=diagnostics)