fix: post-hoc soma detection acyclicity

Author: huangziwei

notebooks/example.post.ipynb

@@ -1015,7 +1015,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 33,
+   "execution_count": 32,
    "id": "8e2e1f76",
    "metadata": {},
    "outputs": [
@@ -1035,7 +1035,7 @@
        "  'C': <Axes: label='C', xlabel='z (μm)'>})"
       ]
      },
-     "execution_count": 33,
+     "execution_count": 32,
      "metadata": {},
      "output_type": "execute_result"
     },
@@ -1068,22 +1068,22 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 33,
    "id": "567c6668",
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Last updated: 2025-07-18 12:01:51CEST\n",
+      "Last updated: 2025-07-18 12:16:14CEST\n",
       "\n",
       "Python implementation: CPython\n",
       "Python version       : 3.11.11\n",
       "IPython version      : 9.2.0\n",
       "\n",
-      "numpy   : 2.3.1\n",
       "skeliner: 0.1.9\n",
+      "numpy   : 2.3.1\n",
       "\n",
       "Watermark: 2.5.0\n",
       "\n"

skeliner/post.py

@@ -315,10 +315,8 @@ def _find_soma(
     )
     return soma_est, soma_idx, has_soma
 
-# ----------------------------------------------------------------------------- 
-#  PUBLIC: detect_soma
-# -----------------------------------------------------------------------------
-def detect_soma(               # noqa: C901  (a bit long but self-contained)
+
+def detect_soma(          
     skel,
     *,
     radius_key: str = "median",
@@ -356,7 +354,7 @@ def detect_soma(               # noqa: C901  (a bit long but self-contained)
         *Either* the original instance (no change was necessary) *or* a new
         skeleton whose node 0 is the freshly detected soma centroid.
     """
-    from .core import Skeleton, Soma
+    from .core import Skeleton, Soma, _build_mst
     if radius_key not in skel.radii:
         raise KeyError(
             f"radius_key '{radius_key}' not found in skel.radii "
@@ -523,7 +521,7 @@ def detect_soma(               # noqa: C901  (a bit long but self-contained)
         soma=soma_new,
         nodes=nodes,
         radii=radii,
-        edges=edges,
+        edges=_build_mst(nodes, edges),
         ntype=ntype,
         node2verts=node2verts,
         vert2node=vert2node,