Break unnecessary Temporal dependency in Workflow and Executor (#405)

* Break Temporal runtime dependency in Workflow and Executor

* Fix errorneous import

Author: saqadri

src/mcp_agent/executor/temporal/workflow_signal.py

@@ -1,11 +1,15 @@
 from contextvars import ContextVar
-from dataclasses import dataclass
 from datetime import timedelta
-from typing import Any, Callable, Dict, Generic, Optional, TYPE_CHECKING
+from typing import Any, Callable, Optional, TYPE_CHECKING
 
 from temporalio import exceptions, workflow
 
-from mcp_agent.executor.workflow_signal import BaseSignalHandler, Signal, SignalValueT
+from mcp_agent.executor.workflow_signal import (
+    BaseSignalHandler,
+    Signal,
+    SignalValueT,
+    SignalMailbox,
+)
 from mcp_agent.logging.logger import get_logger
 
 if TYPE_CHECKING:
@@ -15,62 +19,6 @@
 logger = get_logger(__name__)
 
 
-@dataclass(slots=True)
-class _Record(Generic[SignalValueT]):
-    """Record for tracking signal values with versioning for broadcast semantics"""
-
-    value: Optional[SignalValueT] = None
-    version: int = 0  # monotonic counter
-
-
-class SignalMailbox(Generic[SignalValueT]):
-    """
-    Deterministic broadcast mailbox that stores signal values with versioning.
-    Each workflow run has its own mailbox instance.
-    """
-
-    def __init__(self) -> None:
-        self._store: Dict[str, _Record[SignalValueT]] = {}
-
-    def push(self, name: str, value: SignalValueT) -> None:
-        """
-        Store a signal value and increment its version counter.
-        This enables broadcast semantics where all waiters see the same value.
-        """
-        rec = self._store.setdefault(name, _Record())
-        rec.value = value
-        rec.version += 1
-
-        logger.debug(
-            f"SignalMailbox.push: name={name}, value={value}, version={rec.version}"
-        )
-
-    def version(self, name: str) -> int:
-        """Get the current version counter for a signal name"""
-        return self._store.get(name, _Record()).version
-
-    def value(self, name: str) -> SignalValueT:
-        """
-        Get the current value for a signal name
-
-        Returns:
-            The signal value
-
-        Raises:
-            ValueError: If no value exists for the signal
-        """
-        value = self._store.get(name, _Record()).value
-
-        if value is None:
-            raise ValueError(f"No value for signal {name}")
-
-        logger.debug(
-            f"SignalMailbox.value: name={name}, value={value}, version={self._store.get(name, _Record()).version}"
-        )
-
-        return value
-
-
 class TemporalSignalHandler(BaseSignalHandler[SignalValueT]):
     """
     Temporal-based signal handling using workflow signals.

src/mcp_agent/executor/workflow.py

@@ -16,17 +16,13 @@
 
 from pydantic import BaseModel, ConfigDict, Field
 from mcp_agent.core.context_dependent import ContextDependent
-from mcp_agent.executor.temporal import TemporalExecutor
-from mcp_agent.executor.temporal.workflow_signal import (
-    SignalMailbox,
-    TemporalSignalHandler,
-)
-from mcp_agent.executor.workflow_signal import Signal
+from mcp_agent.executor.workflow_signal import Signal, SignalMailbox
 from mcp_agent.logging.logger import get_logger
 
 if TYPE_CHECKING:
     from temporalio.client import WorkflowHandle
     from mcp_agent.core.context import Context
+    from mcp_agent.executor.temporal import TemporalExecutor
 
 T = TypeVar("T")
 
@@ -230,7 +226,7 @@ async def run_async(self, *args, **kwargs) -> "WorkflowExecution":
                 self._run_id = str(self.executor.uuid())
         elif self.context.config.execution_engine == "temporal":
             # For Temporal workflows, we'll start the workflow immediately
-            executor: TemporalExecutor = self.executor
+            executor: "TemporalExecutor" = self.executor
             handle = await executor.start_workflow(
                 self.name,
                 *args,
@@ -720,12 +716,22 @@ async def initialize(self):
         self._logger.debug(f"Initializing workflow {self.name}")
 
         if self.context.config.execution_engine == "temporal":
-            if isinstance(self.executor.signal_bus, TemporalSignalHandler):
-                # Attach the signal handler to the workflow
-                self.executor.signal_bus.attach_to_workflow(self)
-            else:
+            # Lazy import to avoid requiring Temporal unless engine is set to temporal
+            try:
+                from mcp_agent.executor.temporal.workflow_signal import (
+                    TemporalSignalHandler,
+                )
+
+                if isinstance(self.executor.signal_bus, TemporalSignalHandler):
+                    # Attach the signal handler to the workflow
+                    self.executor.signal_bus.attach_to_workflow(self)
+                else:
+                    self._logger.warning(
+                        "Signal handler not attached: executor.signal_bus is not a TemporalSignalHandler"
+                    )
+            except Exception:
                 self._logger.warning(
-                    "Signal handler not attached: executor.signal_bus is not a TemporalSignalHandler"
+                    "Signal handler not attached: Temporal support unavailable"
                 )
 
         self._initialized = True

src/mcp_agent/executor/workflow_signal.py

@@ -1,13 +1,15 @@
 import asyncio
 import uuid
 from abc import abstractmethod, ABC
-from typing import Any, Callable, Dict, Generic, List, Protocol, TypeVar
+from dataclasses import dataclass
+from typing import Any, Callable, Dict, Generic, List, Optional, Protocol, TypeVar
 
 from pydantic import BaseModel, ConfigDict
+from mcp_agent.logging.logger import get_logger
 
 SignalValueT = TypeVar("SignalValueT")
 
-# TODO: saqadri - handle signals properly that works with other execution backends like Temporal as well
+logger = get_logger(__name__)
 
 
 class Signal(BaseModel, Generic[SignalValueT]):
@@ -95,6 +97,62 @@ class PendingSignal(BaseModel):
     model_config = ConfigDict(arbitrary_types_allowed=True)
 
 
+@dataclass(slots=True)
+class _Record(Generic[SignalValueT]):
+    """Record for tracking signal values with versioning for broadcast semantics"""
+
+    value: Optional[SignalValueT] = None
+    version: int = 0  # monotonic counter
+
+
+class SignalMailbox(Generic[SignalValueT]):
+    """
+    Deterministic broadcast mailbox that stores signal values with versioning.
+    Each workflow run has its own mailbox instance.
+    """
+
+    def __init__(self) -> None:
+        self._store: Dict[str, _Record[SignalValueT]] = {}
+
+    def push(self, name: str, value: SignalValueT) -> None:
+        """
+        Store a signal value and increment its version counter.
+        This enables broadcast semantics where all waiters see the same value.
+        """
+        rec = self._store.setdefault(name, _Record())
+        rec.value = value
+        rec.version += 1
+
+        logger.debug(
+            f"SignalMailbox.push: name={name}, value={value}, version={rec.version}"
+        )
+
+    def version(self, name: str) -> int:
+        """Get the current version counter for a signal name"""
+        return self._store.get(name, _Record()).version
+
+    def value(self, name: str) -> SignalValueT:
+        """
+        Get the current value for a signal name
+
+        Returns:
+            The signal value
+
+        Raises:
+            ValueError: If no value exists for the signal
+        """
+        value = self._store.get(name, _Record()).value
+
+        if value is None:
+            raise ValueError(f"No value for signal {name}")
+
+        logger.debug(
+            f"SignalMailbox.value: name={name}, value={value}, version={self._store.get(name, _Record()).version}"
+        )
+
+        return value
+
+
 class BaseSignalHandler(ABC, Generic[SignalValueT]):
     """Base class implementing common signal handling functionality."""
 

tests/executor/temporal/test_signal_handler.py

@@ -1,10 +1,7 @@
 import pytest
 from unittest.mock import AsyncMock, MagicMock, patch
-from mcp_agent.executor.temporal.workflow_signal import (
-    TemporalSignalHandler,
-    SignalMailbox,
-)
-from mcp_agent.executor.workflow_signal import Signal
+from mcp_agent.executor.temporal.workflow_signal import TemporalSignalHandler
+from mcp_agent.executor.workflow_signal import Signal, SignalMailbox
 
 
 @pytest.fixture