T-Junction Phase 2 + Layer-Smart-Join: Backbone-Drill bis Stahl-Layer-Far-Face

Phase-2-Fixes:
- Backbone-Ext berechnet bis MATCHING-Layer (Stahl) far-face, nicht bis
  Body-far-face. Beton drillt durch Stahl-Band, nicht durch Daemm/Putz.
- Case A/B detection via dot(out_dir, RhinoPerp). Rhino Curve.Offset
  benutzt (tan × +z) = (b_tan.Y, -b_tan.X), nicht (-b_tan.Y, b_tan.X).
- Backbone-axis-ext separat von _my_axis_ext: nur Backbone-Column
  extended, non-backbone columns stoppen am Snap.
- Through-only Mats (z.B. Daemm wo T-stem keinen hat) werden auch
  durchlaufen damit hoehere-prio backbone diese carven kann.
- Post-Carve Union: gleiche-Material-Pieces mergen (Backbone-Beton-Col
  + Through-Stahl-Band → T-Shape).
- BBox-overlap strict-Filter vor BoolDiff: touching coplanar faces
  ueberspringen, vermeidet Rhino BoolDiff "punch-through" Artefakte.
- _has_my_cols guard: KeyError beim consume von T-stem-Layern fuer
  through-only mats verhindert.

Layer-Smart-Join (smart_join.py):
- Neue _layer_join_attempt: 2 selektierte wand_volume Breps gleicher
  Material via BoolUnion mergen. Manueller Override fuer Edge-Cases
  wo auto Phase 2 nicht reicht.

Cluster-Volume Select-Handler (elemente.py):
- Alt-Click bypassed Cluster-Swap → User kann einzelne Layer-Breps
  direkt anwaehlen (= fuer Layer-Smart-Join).

rhino/aliases/cmd/smart_join.py

@@ -296,12 +296,80 @@ def _l_join_attempt(doc, sel):
         doc.EndUndoRecord(ur)
 
 
+def _layer_join_attempt(doc, wand_volumes):
+    """Layer-Level Join: Versuch BoolUnion zwischen 2 wand_volume Breps.
+    Wenn beide gleiches Material haben + sich beruehren oder ueberlappen
+    → mergen zu einem Brep. Behaelt UserStrings (= wand_id, material,
+    layer_idx) vom ersten Brep."""
+    if len(wand_volumes) != 2: return False
+    br0 = wand_volumes[0].Geometry
+    br1 = wand_volumes[1].Geometry
+    if not isinstance(br0, rg.Brep) or not isinstance(br1, rg.Brep):
+        return False
+    # Material-Check via UserStrings (= dossier_element_material)
+    mat0 = wand_volumes[0].Attributes.GetUserString(
+        "dossier_layer_material") or ""
+    mat1 = wand_volumes[1].Attributes.GetUserString(
+        "dossier_layer_material") or ""
+    if mat0 and mat1 and mat0 != mat1:
+        print("[SMART-JOIN] Layer-Join: Materialien unterschiedlich "
+              "({} vs {}), skip.".format(mat0, mat1))
+        return False
+    try:
+        union = rg.Brep.CreateBooleanUnion([br0, br1], 0.01)
+    except Exception as ex:
+        print("[SMART-JOIN] Layer-Join BoolUnion exc:", ex)
+        return False
+    if not union or len(union) == 0:
+        print("[SMART-JOIN] Layer-Join: Breps overlappen nicht "
+              "(BoolUnion returned None/empty)")
+        return False
+    if len(union) > 1:
+        print("[SMART-JOIN] Layer-Join: Breps overlappen nicht (BoolUnion"
+              " returned {} pieces, brauche 1)".format(len(union)))
+        return False
+    # 1 merged Brep
+    merged = union[0]
+    if not merged.IsValid:
+        print("[SMART-JOIN] Layer-Join: merged Brep invalid")
+        return False
+    try: merged.MergeCoplanarFaces(0.01)
+    except Exception: pass
+    ur = doc.BeginUndoRecord("DOSSIER Layer-Join")
+    try:
+        ok = doc.Objects.Replace(wand_volumes[0].Id, merged)
+        if ok:
+            doc.Objects.Delete(wand_volumes[1].Id, True)
+            return True
+        return False
+    finally:
+        doc.EndUndoRecord(ur)
+
+
 def _run():
     doc = Rhino.RhinoDoc.ActiveDoc
     if doc is None: return
     sel = list(doc.Objects.GetSelectedObjects(False, False))
     if not sel:
         Rhino.RhinoApp.RunScript("_Join", False); return
+    # Layer-Level Join: wenn GENAU 2 wand_volume Breps selektiert + keine
+    # wand_axis → versuche Layer-Join (= BoolUnion der zwei Layer-Breps).
+    _wand_vols = [o for o in sel
+                   if (o.Attributes.GetUserString("dossier_element_type")
+                        or "") == "wand_volume"]
+    _wand_axes = [o for o in sel
+                   if (o.Attributes.GetUserString("dossier_element_type")
+                        or "") == "wand_axis"]
+    if (len(_wand_vols) == 2 and len(_wand_axes) == 0
+            and len(sel) == 2):
+        print("[SMART-JOIN] Layer-Join attempt: 2 wand_volume Breps")
+        try:
+            if _layer_join_attempt(doc, _wand_vols):
+                doc.Views.Redraw()
+                print("[SMART-JOIN] Layer-Join: Breps zu einem gemerged")
+                return
+        except Exception as ex:
+            print("[SMART-JOIN] Layer-Join exc:", ex)
     # Info-Hint (T-Join unterstuetzt 1-Wand-Modus, L-Join braucht 2)
     n_wand_axes = sum(1 for o in sel
                        if (o.Attributes.GetUserString("dossier_element_type")