fix: update AttachmentOffset during angled datum editing (#66)

on_param_changed() now recomputes AttachmentOffset.Rotation for angled
datums and recalculates Placement for tangent_cylinder datums when the
angle spinner changes. Previously only ZTools_Params was updated,
leaving the visual representation unchanged until a manual recompute.

Add _resolve_source_refs() helper to parse ZTools_SourceRefs and
resolve stored object/subname pairs to actual shapes for the rotation
and placement math.

ztools/ztools/commands/datum_viewprovider.py

@@ -2,6 +2,7 @@
 # Custom ViewProvider for ZTools datum objects
 
 import json
+import math
 
 import FreeCAD as App
 import FreeCADGui as Gui
@@ -141,6 +142,23 @@ class ZToolsDatumViewProvider:
         return None
 
 
+def _resolve_source_refs(datum_obj):
+    """Parse ZTools_SourceRefs and resolve to (object, subname, shape) tuples."""
+    refs_json = getattr(datum_obj, "ZTools_SourceRefs", "[]")
+    try:
+        refs = json.loads(refs_json)
+    except json.JSONDecodeError:
+        return []
+    doc = datum_obj.Document
+    resolved = []
+    for ref in refs:
+        obj = doc.getObject(ref.get("object", ""))
+        sub = ref.get("subname", "")
+        shape = obj.getSubObject(sub) if obj and sub else None
+        resolved.append((obj, sub, shape))
+    return resolved
+
+
 class DatumEditTaskPanel:
     """
     Task panel for editing existing ZTools datum objects.
@@ -364,8 +382,45 @@ class DatumEditTaskPanel:
                 self.datum_obj.AttachmentOffset = new_offset
             self._update_params({"distance": distance})
 
-        elif ztools_type in ("angled", "tangent_cylinder"):
-            self._update_params({"angle": self.angle_spin.value()})
+        elif ztools_type == "angled":
+            angle = self.angle_spin.value()
+            if self._has_attachment():
+                refs = _resolve_source_refs(self.datum_obj)
+                if len(refs) >= 2 and refs[0][2] and refs[1][2]:
+                    face_normal = refs[0][2].normalAt(0, 0)
+                    edge_shape = refs[1][2]
+                    edge_dir = (
+                        edge_shape.Vertexes[-1].Point - edge_shape.Vertexes[0].Point
+                    ).normalize()
+                    face_rot = App.Rotation(App.Vector(0, 0, 1), face_normal)
+                    local_edge_dir = face_rot.inverted().multVec(edge_dir)
+                    angle_rot = App.Rotation(local_edge_dir, angle)
+                    self.datum_obj.AttachmentOffset = App.Placement(
+                        App.Vector(0, 0, 0), angle_rot
+                    )
+            self._update_params({"angle": angle})
+
+        elif ztools_type == "tangent_cylinder":
+            angle = self.angle_spin.value()
+            refs = _resolve_source_refs(self.datum_obj)
+            if refs and refs[0][2]:
+                face = refs[0][2]
+                if isinstance(face.Surface, Part.Cylinder):
+                    cyl = face.Surface
+                    axis = cyl.Axis
+                    center = cyl.Center
+                    radius = cyl.Radius
+                    rad = math.radians(angle)
+                    if abs(axis.dot(App.Vector(1, 0, 0))) < 0.99:
+                        local_x = axis.cross(App.Vector(1, 0, 0)).normalize()
+                    else:
+                        local_x = axis.cross(App.Vector(0, 1, 0)).normalize()
+                    local_y = axis.cross(local_x)
+                    radial = local_x * math.cos(rad) + local_y * math.sin(rad)
+                    tangent_point = center + radial * radius
+                    rot = App.Rotation(App.Vector(0, 0, 1), radial)
+                    self.datum_obj.Placement = App.Placement(tangent_point, rot)
+            self._update_params({"angle": angle})
 
         elif ztools_type in ("normal_to_edge", "on_edge"):
             parameter = self.param_spin.value()