Bonsai: report a clean error instead of a traceback for unsupported bend profiles

FitFlowSegments calls bpy.ops.bim.mep_add_bend/transition/obstruction as
nested operator invocations. Blender re-raises any ERROR-level report from
a nested bpy.ops.X() call as a RuntimeError to the Python caller, so a
clean self.report + CANCELLED from those nested operators (e.g. "profile
class not supported for a bend") was surfacing as an uncaught exception
instead. That exception then propagated further through the S,Y hotkey,
triggering Bonsai's generic "experienced an error" popup with a full
traceback rather than the intended single-line message.

Catch the RuntimeError at both nesting points (FitFlowSegments's calls to
the mep_add_* operators, and the S,Y hotkey's call to fit_flow_segments)
and re-surface it as a single clean self.report instead of letting it
propagate uncaught.

Fixes #5450.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/bim/module/model/mep.py

@@ -159,6 +159,29 @@ class FitFlowSegments(bpy.types.Operator, tool.Ifc.Operator):
     bl_label = "Fit Flow Segments"
     bl_options = {"REGISTER", "UNDO"}
 
+    def _call_fitting_op(self, op) -> bool:
+        """Invoke a nested ``bim.mep_add_*`` operator, converting its reported
+        error into a clean ``self.report`` instead of letting it surface as a
+        raw developer traceback.
+
+        Blender raises a ``RuntimeError`` back to the Python caller whenever an
+        operator invoked via ``bpy.ops.X()`` reports an ``ERROR`` (e.g. an
+        unsupported profile class for a bend), regardless of the nested
+        operator's own clean ``self.report`` + ``CANCELLED``. Left uncaught,
+        that exception bubbles all the way up to whatever ultimately called
+        ``bim.fit_flow_segments`` (e.g. a hotkey), producing Bonsai's generic
+        "experienced an error" popup with a full traceback (see #5450) instead
+        of the single-line message the nested operator already produced.
+
+        Returns True on success, False if the nested operator reported an
+        error (already surfaced via ``self.report``)."""
+        try:
+            op()
+        except RuntimeError as e:
+            self.report({"ERROR"}, str(e).removeprefix("Error: ").strip())
+            return False
+        return True
+
     def _execute(self, context):
         # TODO: need to add ui for parameters:
         # - obstruction cap thickness
@@ -184,7 +207,8 @@ class FitFlowSegments(bpy.types.Operator, tool.Ifc.Operator):
 
         if total_selected_objs == 1:
             fitting_type = "OBSTRUCTION"
-            bpy.ops.bim.mep_add_obstruction()
+            if not self._call_fitting_op(bpy.ops.bim.mep_add_obstruction):
+                return
 
         elif total_selected_objs == 2:
             # Shorten the axis by the profile size to allow for fuzzy intersections
@@ -211,7 +235,8 @@ class FitFlowSegments(bpy.types.Operator, tool.Ifc.Operator):
                 is_on_axis2 = tool.Cad.is_point_on_edge(intersect2, axis2)
                 if not is_on_axis1 and not is_on_axis2:
                     fitting_type = "BEND"
-                    bpy.ops.bim.mep_add_bend()
+                    if not self._call_fitting_op(bpy.ops.bim.mep_add_bend):
+                        return
                 elif is_on_axis1 and is_on_axis2:
                     fitting_type = "CROSS"
                 else:
@@ -219,7 +244,8 @@ class FitFlowSegments(bpy.types.Operator, tool.Ifc.Operator):
             elif total_profiles == 2:
                 if is_parallel:
                     fitting_type = "TRANSITION"
-                    bpy.ops.bim.mep_add_transition()
+                    if not self._call_fitting_op(bpy.ops.bim.mep_add_transition):
+                        return
 
         elif total_selected_objs == 3:
             if total_profiles > 1:

src/bonsai/bonsai/bim/module/model/workspace.py

@@ -1411,7 +1411,18 @@ class Hotkey(bpy.types.Operator, tool.Ifc.Operator):
         if not bpy.context.selected_objects:
             return
         if self.active_class in ("IfcDuctSegment", "IfcPipeSegment", "IfcCableCarrierSegment", "IfcCableSegment"):
-            bpy.ops.bim.fit_flow_segments()
+            # bim.fit_flow_segments() reports a clean single-line ERROR (e.g.
+            # an unsupported profile class for a bend, see #5450) when it
+            # can't build a fitting. Blender re-raises any ERROR-level report
+            # from a nested bpy.ops.X() call as a RuntimeError to the Python
+            # caller, so without this guard that clean message would surface
+            # as an uncaught exception here, producing Bonsai's generic
+            # "experienced an error" popup with a full traceback instead of
+            # the intended one-line message.
+            try:
+                bpy.ops.bim.fit_flow_segments()
+            except RuntimeError as e:
+                self.report({"ERROR"}, str(e).removeprefix("Error: ").strip())
         elif self.active_material_usage == "PROFILE":
             bpy.ops.bim.extend_profile(join_type="V")