refactor: Proper type-safe condition handling with Union types

Previous fix used Any type, breaking type safety and only handling
simple cases. This is the correct implementation:

Changes:
1. LogicExpression.operands: List[Any] → List['LogicExpression']
   - Enables recursive/nested expressions
   - Proper type checking for all operator combinations

2. WorkflowNode.condition: Any → Union[LogicExpression, Condition]
   - Type-safe deserialization
   - Supports both UI format (direct LogicExpression) and legacy (Condition wrapper)
   - Pydantic automatically tries LogicExpression first, then Condition

3. Executor: Simplified with isinstance() checks
   - Clean type detection without dict manipulation
   - Fallback for edge cases

This now correctly handles:
- Simple conditions: {operator: "eq", ref: "...", value: "..."}
- Combined: {operator: "and", operands: [...]}
- Nested: {operator: "or", operands: [{operator: "and", ...}, ...]}
- All operators: eq, neq, in, not_in, gt, lt, gte, lte, contains, and, or, not
- Legacy format: {expression: {...}, then_path: "...", else_path: "..."}

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

backend/workflow_executor.py

@@ -409,37 +409,28 @@ def execute_logic_node(
                 completed_at=datetime.utcnow().isoformat()
             )
 
-        # Handle both serialization formats:
-        # UI format: condition = {operands: [...], operator: "and"}  (dict or LogicExpression)
-        # Legacy format: condition = {expression: {operands: [...], operator: "and"}}  (Condition object)
+        # Handle both formats (thanks to Union[LogicExpression, Condition] type):
+        # 1. Direct LogicExpression (UI format): node.condition is LogicExpression
+        # 2. Wrapped in Condition (legacy): node.condition is Condition with .expression
+        from workflow_models import LogicExpression, Condition
+
         expression = None
 
-        # Convert to dict if it's a Pydantic model
-        condition_dict = node.condition
-        if hasattr(node.condition, 'model_dump'):
-            condition_dict = node.condition.model_dump()
-        elif hasattr(node.condition, 'dict'):
-            condition_dict = node.condition.dict()
-
-        # Check if it's a dict
-        if isinstance(condition_dict, dict):
+        if isinstance(node.condition, LogicExpression):
             # UI format: direct LogicExpression
-            if 'operator' in condition_dict and 'operands' in condition_dict:
-                from workflow_models import LogicExpression
-                expression = LogicExpression(**condition_dict)
+            expression = node.condition
+        elif isinstance(node.condition, Condition):
             # Legacy format: wrapped in Condition
-            elif 'expression' in condition_dict and condition_dict['expression'] is not None:
-                from workflow_models import LogicExpression
-                expression = LogicExpression(**condition_dict['expression'])
-        # Pydantic object
+            expression = node.condition.expression
         else:
+            # Fallback: try to detect format manually
             if hasattr(node.condition, 'operator') and hasattr(node.condition, 'operands'):
-                expression = node.condition
-            elif hasattr(node.condition, 'expression') and node.condition.expression is not None:
-                expression = node.condition.expression
+                expression = node.condition  # Looks like LogicExpression
+            elif hasattr(node.condition, 'expression'):
+                expression = node.condition.expression  # Looks like Condition
 
         if expression is None:
-            error_msg = f"Logic node {node.id} has invalid or empty condition (operator/operands/expression is None or missing)"
+            error_msg = f"Logic node {node.id} has no valid condition/expression defined"
             logger.error(error_msg)
             return NodeExecutionState(
                 node_id=node.id,

backend/workflow_models.py

@@ -6,7 +6,7 @@ Data validation schemas for Workflow-Graph, Knoten, Kanten, Bedingungen.
 Konzept-Basis: konzept_workflow_engine_konsolidated.md
 Anforderungsanalyse: anforderungsanalyse_umsetzungsplan.md
 """
-from typing import Optional, List, Dict, Any
+from typing import Optional, List, Dict, Any, Union
 from pydantic import BaseModel, Field
 from enum import Enum
 
@@ -148,11 +148,14 @@ class LogicExpression(BaseModel):
     }
     """
     operator: LogicOperator = Field(..., description="Logischer Operator (and, or, not) oder Vergleichsoperator")
-    operands: Optional[List[Any]] = Field(None, description="Liste von Operanden (LogicOperand oder verschachtelte LogicExpression)")
+    operands: Optional[List['LogicExpression']] = Field(None, description="Liste von Operanden (LogicOperand oder verschachtelte LogicExpression)")
     # Bei einfachem Vergleich:
     ref: Optional[str] = Field(None, description="Signal-Referenz (nur bei Vergleichsoperatoren)")
     value: Optional[Any] = Field(None, description="Vergleichswert (nur bei Vergleichsoperatoren)")
 
+# Enable forward reference resolution for recursive model
+LogicExpression.model_rebuild()
+
 
 class Condition(BaseModel):
     """
@@ -196,7 +199,7 @@ class WorkflowNode(BaseModel):
 
     # LOGIC-Knoten
     # Support both formats: direct LogicExpression (UI) or wrapped in Condition (legacy)
-    condition: Optional[Any] = Field(None, description="Bedingung für Pfad-Routing (LogicExpression or Condition)")
+    condition: Optional[Union[LogicExpression, Condition]] = Field(None, description="Bedingung für Pfad-Routing")
     fallback: Optional[FallbackConfig] = Field(None, description="Fallback-Konfiguration")
 
     # JOIN-Knoten (Phase 4)