fix(api): Disable SSE events truncation for service api (#27484)

Disable SSE events truncation for service api invocations to ensure backward compatibility.

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

api/services/variable_truncator.py

@@ -1,4 +1,5 @@
 import dataclasses
+from abc import ABC, abstractmethod
 from collections.abc import Mapping
 from typing import Any, Generic, TypeAlias, TypeVar, overload
 
@@ -66,7 +67,17 @@ class TruncationResult:
     truncated: bool
 
 
-class VariableTruncator:
+class BaseTruncator(ABC):
+    @abstractmethod
+    def truncate(self, segment: Segment) -> TruncationResult:
+        pass
+
+    @abstractmethod
+    def truncate_variable_mapping(self, v: Mapping[str, Any]) -> tuple[Mapping[str, Any], bool]:
+        pass
+
+
+class VariableTruncator(BaseTruncator):
     """
     Handles variable truncation with structure-preserving strategies.
 
@@ -418,3 +429,38 @@ class VariableTruncator:
             return _PartResult(val, self.calculate_json_size(val), False)
         else:
             raise AssertionError("this statement should be unreachable.")
+
+
+class DummyVariableTruncator(BaseTruncator):
+    """
+    A no-op variable truncator that doesn't truncate any data.
+
+    This is used for Service API calls where truncation should be disabled
+    to maintain backward compatibility and provide complete data.
+    """
+
+    def truncate_variable_mapping(self, v: Mapping[str, Any]) -> tuple[Mapping[str, Any], bool]:
+        """
+        Return original mapping without truncation.
+
+        Args:
+            v: The variable mapping to process
+
+        Returns:
+            Tuple of (original_mapping, False) where False indicates no truncation occurred
+        """
+        return v, False
+
+    def truncate(self, segment: Segment) -> TruncationResult:
+        """
+        Return original segment without truncation.
+
+        Args:
+            segment: The segment to process
+
+        Returns:
+            The original segment unchanged
+        """
+        # For Service API, we want to preserve the original segment
+        # without any truncation, so just return it as-is
+        return TruncationResult(result=segment, truncated=False)