feat(api): Introduce workflow pause state management (#27298)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/core/workflow/runtime/graph_runtime_state_protocol.py

@@ -3,6 +3,7 @@ from typing import Any, Protocol
 
 from core.model_runtime.entities.llm_entities import LLMUsage
 from core.variables.segments import Segment
+from core.workflow.system_variable import SystemVariableReadOnlyView
 
 
 class ReadOnlyVariablePool(Protocol):
@@ -30,6 +31,9 @@ class ReadOnlyGraphRuntimeState(Protocol):
     All methods return defensive copies to ensure immutability.
     """
 
+    @property
+    def system_variable(self) -> SystemVariableReadOnlyView: ...
+
     @property
     def variable_pool(self) -> ReadOnlyVariablePool:
         """Get read-only access to the variable pool."""

api/core/workflow/runtime/read_only_wrappers.py

@@ -6,6 +6,7 @@ from typing import Any
 
 from core.model_runtime.entities.llm_entities import LLMUsage
 from core.variables.segments import Segment
+from core.workflow.system_variable import SystemVariableReadOnlyView
 
 from .graph_runtime_state import GraphRuntimeState
 from .variable_pool import VariablePool
@@ -42,6 +43,10 @@ class ReadOnlyGraphRuntimeStateWrapper:
         self._state = state
         self._variable_pool_wrapper = ReadOnlyVariablePoolWrapper(state.variable_pool)
 
+    @property
+    def system_variable(self) -> SystemVariableReadOnlyView:
+        return self._state.variable_pool.system_variables.as_view()
+
     @property
     def variable_pool(self) -> ReadOnlyVariablePoolWrapper:
         return self._variable_pool_wrapper