fix: Support UI-format edge routing with sourceHandle

Logic-Nodes evaluated correctly but activated_edges was empty because
_get_edges_by_label() only checked e.label, which is null in UI format.

UI format uses:
- sourceHandle: "true" / "false" (instead of label: "then" / "else")
- targetHandle: "in" / "path_1" / etc.

Changes:
1. Added source_handle/target_handle fields to WorkflowEdge model
   - With aliases sourceHandle/targetHandle for camelCase JSON
2. Updated _get_edges_by_label() to check both formats:
   - Legacy: e.label == "then" / "else"
   - UI: e.source_handle == "true" / "false"

Now Logic-Nodes correctly activate outgoing edges → Join-Node receives
completed paths → End-Node executes → Workflow completes!

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/workflow_executor.py

@@ -816,17 +816,31 @@ def _get_edges_by_label(node_id: str, label: str, graph: WorkflowGraph) -> List[
     """
     Findet alle ausgehenden Edges mit bestimmtem Label.
 
+    Unterstützt beide Formate:
+    - Legacy: e.label == label (z.B. "then", "else")
+    - UI: e.source_handle == label (z.B. "true", "false")
+
     Args:
         node_id: Node-ID
-        label: Edge-Label (z.B. "then", "else", "uncertainty")
+        label: Edge-Label oder sourceHandle (z.B. "then"/"true", "else"/"false")
         graph: WorkflowGraph
 
     Returns:
         Liste von Edge-IDs
     """
+    # Map label to sourceHandle equivalents
+    label_to_handle = {
+        "then": "true",
+        "else": "false"
+    }
+    handle_equivalent = label_to_handle.get(label, label)
+
     matching_edges = [
         e.id for e in graph.edges
-        if e.from_node == node_id and e.label == label
+        if e.from_node == node_id and (
+            e.label == label or  # Legacy format
+            (hasattr(e, 'source_handle') and e.source_handle == handle_equivalent)  # UI format
+        )
     ]
     return matching_edges
 

backend/workflow_models.py

@@ -230,6 +230,10 @@ class WorkflowEdge(BaseModel):
     to_node: str = Field(..., alias="to", description="Ziel-Knoten-ID")
     label: Optional[str] = Field(None, description="Label für visuelle Darstellung (z.B. 'then', 'else')")
 
+    # UI-Format fields (React Flow)
+    source_handle: Optional[str] = Field(None, alias="sourceHandle", description="Source handle ID (UI format: 'true', 'false', 'out')")
+    target_handle: Optional[str] = Field(None, alias="targetHandle", description="Target handle ID (UI format: 'in', 'path_1', etc.)")
+
 
 class WorkflowGraph(BaseModel):
     """