feat: Implement signal_workflow method

Signed-off-by: Tim Li <ltim@uber.com>

Author: timl3136

cadence/client.py

@@ -15,6 +15,7 @@
 from grpc.aio import Channel, ClientInterceptor, secure_channel, insecure_channel
 from cadence.api.v1.service_workflow_pb2_grpc import WorkflowAPIStub
 from cadence.api.v1.service_workflow_pb2 import (
+    SignalWorkflowExecutionRequest,
     StartWorkflowExecutionRequest,
     StartWorkflowExecutionResponse,
 )
@@ -229,6 +230,51 @@ async def start_workflow(
         except Exception:
             raise
 
+    async def signal_workflow(
+        self,
+        workflow_id: str,
+        run_id: str,
+        signal_name: str,
+        signal_input: Any = None,
+    ) -> None:
+        """
+        Send a signal to a running workflow execution.
+
+        Args:
+            workflow_id: The workflow ID
+            run_id: The run ID (can be empty string to signal current run)
+            signal_name: Name of the signal
+            signal_input: Input data for the signal
+
+        Raises:
+            ValueError: If signal encoding fails
+            Exception: If the gRPC call fails
+        """
+        signal_payload = None
+        if signal_input is not None:
+            try:
+                signal_payload = await self.data_converter.to_data(signal_input)
+            except Exception as e:
+                raise ValueError(f"Failed to encode signal input: {e}")
+
+        workflow_execution = WorkflowExecution()
+        workflow_execution.workflow_id = workflow_id
+        if run_id:
+            workflow_execution.run_id = run_id
+
+        signal_request = SignalWorkflowExecutionRequest(
+            domain=self.domain,
+            workflow_execution=workflow_execution,
+            identity=self.identity,
+            request_id=str(uuid.uuid4()),
+            signal_name=signal_name,
+        )
+
+        if signal_payload:
+            signal_request.signal_input.CopyFrom(signal_payload)
+
+        await self.workflow_stub.SignalWorkflowExecution(signal_request)
+
 
 def _validate_and_copy_defaults(options: ClientOptions) -> ClientOptions:
     if "target" not in options:

tests/integration_tests/test_client.py

@@ -136,3 +136,52 @@ async def test_workflow_stub_start_and_describe(helper: CadenceHelper):
         assert task_timeout_seconds == task_timeout.total_seconds(), (
             f"task_start_to_close_timeout mismatch: expected {task_timeout.total_seconds()}s, got {task_timeout_seconds}s"
         )
+
+
+@pytest.mark.usefixtures("helper")
+async def test_signal_workflow(helper: CadenceHelper):
+    """Test signal_workflow method.
+
+    This integration test verifies:
+    1. Starting a workflow execution
+    2. Sending a signal to the running workflow
+    3. Signal is accepted (no errors thrown)
+    """
+    async with helper.client() as client:
+        workflow_type = "test-workflow-signal"
+        task_list_name = "test-task-list-signal"
+        workflow_id = "test-workflow-signal-789"
+        execution_timeout = timedelta(minutes=5)
+        signal_name = "test-signal"
+        signal_input = {"action": "update", "value": 42}
+
+        execution = await client.start_workflow(
+            workflow_type,
+            task_list=task_list_name,
+            execution_start_to_close_timeout=execution_timeout,
+            workflow_id=workflow_id,
+        )
+
+        await client.signal_workflow(
+            workflow_id=execution.workflow_id,
+            run_id=execution.run_id,
+            signal_name=signal_name,
+            signal_input=signal_input,
+        )
+
+        describe_request = DescribeWorkflowExecutionRequest(
+            domain=DOMAIN_NAME,
+            workflow_execution=WorkflowExecution(
+                workflow_id=execution.workflow_id,
+                run_id=execution.run_id,
+            ),
+        )
+
+        response = await client.workflow_stub.DescribeWorkflowExecution(
+            describe_request
+        )
+
+        assert (
+            response.workflow_execution_info.workflow_execution.workflow_id
+            == workflow_id
+        )