diff --git a/cadence/_internal/decision_state_machine.py b/cadence/_internal/decision_state_machine.py
index 245ba4e..8b721dc 100644
--- a/cadence/_internal/decision_state_machine.py
+++ b/cadence/_internal/decision_state_machine.py
@@ -2,7 +2,7 @@
 
 from dataclasses import dataclass, field
 from enum import Enum
-from typing import Dict, List, Optional, Callable
+from typing import Dict, List, Optional, Callable, TypedDict, Literal
 
 from cadence.api.v1 import (
     decision_pb2 as decision,
@@ -81,12 +81,18 @@ def __str__(self) -> str:
 @dataclass
 class StateTransition:
     """Represents a state transition with associated actions."""
-    next_state: DecisionState
+    next_state: Optional[DecisionState]
     action: Optional[Callable[['BaseDecisionStateMachine', history.HistoryEvent], None]] = None
     condition: Optional[Callable[['BaseDecisionStateMachine', history.HistoryEvent], bool]] = None
 
 
-decision_state_transition_map = {
+class TransitionInfo(TypedDict):
+    type: Literal["initiated", "started", "completion", "canceled", "cancel_initiated", "cancel_failed", "initiation_failed"]
+    decision_type: DecisionType
+    transition: StateTransition
+
+
+decision_state_transition_map: Dict[str, TransitionInfo] = {
     "activity_task_scheduled_event_attributes": {
         "type": "initiated",
         "decision_type": DecisionType.ACTIVITY,
@@ -247,6 +253,10 @@ class BaseDecisionStateMachine:
     Subclasses are responsible for mapping workflow history events into state
     transitions and producing the next set of decisions when queried.
     """
+    
+    # Common fields that subclasses may use
+    scheduled_event_id: Optional[int] = None
+    started_event_id: Optional[int] = None
 
     def get_id(self) -> str:
         raise NotImplementedError
@@ -890,12 +900,12 @@ def handle_history_event(self, event: history.HistoryEvent) -> None:
         if transition_info:
             event_type = transition_info["type"]
             # Route to all relevant machines using the new unified handle_event method
-            for m in list(self.activities.values()):
-                m.handle_event(event, event_type)
-            for m in list(self.timers.values()):
-                m.handle_event(event, event_type)
-            for m in list(self.children.values()):
-                m.handle_event(event, event_type)
+            for activity_machine in list(self.activities.values()):
+                activity_machine.handle_event(event, event_type)
+            for timer_machine in list(self.timers.values()):
+                timer_machine.handle_event(event, event_type)
+            for child_machine in list(self.children.values()):
+                child_machine.handle_event(event, event_type)
 
     # ----- Decision aggregation -----
 
@@ -907,11 +917,11 @@ def collect_pending_decisions(self) -> List[decision.Decision]:
             decisions.extend(machine.collect_pending_decisions())
 
         # Timers
-        for machine in list(self.timers.values()):
-            decisions.extend(machine.collect_pending_decisions())
+        for timer_machine in list(self.timers.values()):
+            decisions.extend(timer_machine.collect_pending_decisions())
 
         # Children
-        for machine in list(self.children.values()):
-            decisions.extend(machine.collect_pending_decisions())
+        for child_machine in list(self.children.values()):
+            decisions.extend(child_machine.collect_pending_decisions())
 
         return decisions
diff --git a/cadence/_internal/rpc/metadata.py b/cadence/_internal/rpc/metadata.py
index e4c1fe3..c46b909 100644
--- a/cadence/_internal/rpc/metadata.py
+++ b/cadence/_internal/rpc/metadata.py
@@ -1,4 +1,5 @@
 import collections
+from typing import Any, Callable
 
 from grpc.aio import Metadata
 from grpc.aio import UnaryUnaryClientInterceptor, ClientCallDetails
@@ -16,7 +17,12 @@ class MetadataInterceptor(UnaryUnaryClientInterceptor):
     def __init__(self, metadata: Metadata):
         self._metadata = metadata
 
-    async def intercept_unary_unary(self, continuation, client_call_details: ClientCallDetails, request):
+    async def intercept_unary_unary(
+        self, 
+        continuation: Callable[[ClientCallDetails, Any], Any], 
+        client_call_details: ClientCallDetails, 
+        request: Any
+    ) -> Any:
         return await continuation(self._replace_details(client_call_details), request)
 
 
diff --git a/cadence/client.py b/cadence/client.py
index 0eccd17..bfca66b 100644
--- a/cadence/client.py
+++ b/cadence/client.py
@@ -11,7 +11,7 @@ class ClientOptions(TypedDict, total=False):
     identity: str
 
 class Client:
-    def __init__(self, channel: Channel, options: ClientOptions):
+    def __init__(self, channel: Channel, options: ClientOptions) -> None:
         self._channel = channel
         self._worker_stub = WorkerAPIStub(channel)
         self._options = options
@@ -31,7 +31,7 @@ def worker_stub(self) -> WorkerAPIStub:
         return self._worker_stub
 
 
-    async def close(self):
+    async def close(self) -> None:
         await self._channel.close()
 
 
diff --git a/cadence/data_converter.py b/cadence/data_converter.py
index 819fd90..ca54712 100644
--- a/cadence/data_converter.py
+++ b/cadence/data_converter.py
@@ -17,7 +17,7 @@ async def to_data(self, values: List[Any]) -> Payload:
         raise NotImplementedError()
 
 class DefaultDataConverter(DataConverter):
-    def __init__(self):
+    def __init__(self) -> None:
         self._encoder = json.Encoder()
         self._decoder = json.Decoder()
         self._fallback_decoder = JSONDecoder(strict=False)
@@ -38,7 +38,7 @@ async def from_data(self, payload: Payload, type_hints: List[Type]) -> List[Any]
 
 
     def _decode_whitespace_delimited(self, payload: str, type_hints: List[Type]) -> List[Any]:
-        results = []
+        results: List[Any] = []
         start, end = 0, len(payload)
         while start < end and len(results) < len(type_hints):
             remaining = payload[start:end]
@@ -50,7 +50,7 @@ def _decode_whitespace_delimited(self, payload: str, type_hints: List[Type]) ->
 
     @staticmethod
     def _convert_into(values: List[Any], type_hints: List[Type]) -> List[Any]:
-        results = []
+        results: List[Any] = []
         for i, type_hint in enumerate(type_hints):
             if i < len(values):
                 value = convert(values[i], type_hint)
diff --git a/cadence/worker/_activity.py b/cadence/worker/_activity.py
index 0ae24e1..ec1ef7e 100644
--- a/cadence/worker/_activity.py
+++ b/cadence/worker/_activity.py
@@ -11,7 +11,7 @@
 
 
 class ActivityWorker:
-    def __init__(self, client: Client, task_list: str, options: WorkerOptions):
+    def __init__(self, client: Client, task_list: str, options: WorkerOptions) -> None:
         self._client = client
         self._task_list = task_list
         self._identity = options["identity"]
@@ -19,7 +19,7 @@ def __init__(self, client: Client, task_list: str, options: WorkerOptions):
         self._poller = Poller[PollForActivityTaskResponse](options["activity_task_pollers"], permits, self._poll, self._execute)
         # TODO: Local dispatch, local activities, actually running activities, etc
 
-    async def run(self):
+    async def run(self) -> None:
         await self._poller.run()
 
     async def _poll(self) -> Optional[PollForActivityTaskResponse]:
@@ -34,7 +34,7 @@ async def _poll(self) -> Optional[PollForActivityTaskResponse]:
         else:
             return None
 
-    async def _execute(self, task: PollForActivityTaskResponse):
+    async def _execute(self, task: PollForActivityTaskResponse) -> None:
         await self._client.worker_stub.RespondActivityTaskFailed(RespondActivityTaskFailedRequest(
             task_token=task.task_token,
             identity=self._identity,
diff --git a/cadence/worker/_decision.py b/cadence/worker/_decision.py
index 0510f61..47e0817 100644
--- a/cadence/worker/_decision.py
+++ b/cadence/worker/_decision.py
@@ -12,7 +12,7 @@
 
 
 class DecisionWorker:
-    def __init__(self, client: Client, task_list: str, options: WorkerOptions):
+    def __init__(self, client: Client, task_list: str, options: WorkerOptions) -> None:
         self._client = client
         self._task_list = task_list
         self._identity = options["identity"]
@@ -20,7 +20,7 @@ def __init__(self, client: Client, task_list: str, options: WorkerOptions):
         self._poller = Poller[PollForDecisionTaskResponse](options["decision_task_pollers"], permits, self._poll, self._execute)
         # TODO: Sticky poller, actually running workflows, etc.
 
-    async def run(self):
+    async def run(self) -> None:
         await self._poller.run()
 
     async def _poll(self) -> Optional[PollForDecisionTaskResponse]:
@@ -36,7 +36,7 @@ async def _poll(self) -> Optional[PollForDecisionTaskResponse]:
             return None
 
 
-    async def _execute(self, task: PollForDecisionTaskResponse):
+    async def _execute(self, task: PollForDecisionTaskResponse) -> None:
         await self._client.worker_stub.RespondDecisionTaskFailed(RespondDecisionTaskFailedRequest(
             task_token=task.task_token,
             cause=DecisionTaskFailedCause.DECISION_TASK_FAILED_CAUSE_UNHANDLED_DECISION,
diff --git a/cadence/worker/_poller.py b/cadence/worker/_poller.py
index 3b2889b..a185d27 100644
--- a/cadence/worker/_poller.py
+++ b/cadence/worker/_poller.py
@@ -7,24 +7,23 @@
 T = TypeVar('T')
 
 class Poller(Generic[T]):
-    def __init__(self, num_tasks: int, permits: asyncio.Semaphore, poll: Callable[[], Awaitable[Optional[T]]], callback: Callable[[T], Awaitable[None]]):
+    def __init__(self, num_tasks: int, permits: asyncio.Semaphore, poll: Callable[[], Awaitable[Optional[T]]], callback: Callable[[T], Awaitable[None]]) -> None:
         self._num_tasks = num_tasks
         self._permits = permits
         self._poll = poll
         self._callback = callback
         self._background_tasks: set[asyncio.Task[None]] = set()
-        pass
 
-    async def run(self):
+    async def run(self) -> None:
         try:
             async with asyncio.TaskGroup() as tg:
                 for i in range(self._num_tasks):
                     tg.create_task(self._poll_loop())
         except asyncio.CancelledError:
-            pass
+           pass 
 
 
-    async def _poll_loop(self):
+    async def _poll_loop(self) -> None:
         while True:
             try:
                 await self._poll_and_dispatch()
@@ -34,7 +33,7 @@ async def _poll_loop(self):
                 logger.exception('Exception while polling')
 
 
-    async def _poll_and_dispatch(self):
+    async def _poll_and_dispatch(self) -> None:
         await self._permits.acquire()
         try:
             task = await self._poll()
@@ -51,7 +50,7 @@ async def _poll_and_dispatch(self):
         self._background_tasks.add(scheduled)
         scheduled.add_done_callback(self._background_tasks.remove)
 
-    async def _execute_callback(self, task: T):
+    async def _execute_callback(self, task: T) -> None:
         try:
             await self._callback(task)
         except Exception:
diff --git a/cadence/worker/_registry.py b/cadence/worker/_registry.py
index 6822351..4ba0972 100644
--- a/cadence/worker/_registry.py
+++ b/cadence/worker/_registry.py
@@ -33,7 +33,7 @@ class Registry:
     workflows and activities in a Cadence application.
     """
     
-    def __init__(self):
+    def __init__(self) -> None:
         """Initialize the registry."""
         self._workflows: Dict[str, Callable] = {}
         self._activities: Dict[str, Callable] = {}
diff --git a/cadence/worker/_worker.py b/cadence/worker/_worker.py
index bb3ccc3..8d8932a 100644
--- a/cadence/worker/_worker.py
+++ b/cadence/worker/_worker.py
@@ -1,6 +1,6 @@
 import asyncio
 import uuid
-from typing import Unpack
+from typing import Unpack, cast
 
 from cadence.client import Client
 from cadence.worker._activity import ActivityWorker
@@ -10,7 +10,7 @@
 
 class Worker:
 
-    def __init__(self, client: Client, task_list: str, **kwargs: Unpack[WorkerOptions]):
+    def __init__(self, client: Client, task_list: str, **kwargs: Unpack[WorkerOptions]) -> None:
         self._client = client
         self._task_list = task_list
 
@@ -21,7 +21,7 @@ def __init__(self, client: Client, task_list: str, **kwargs: Unpack[WorkerOption
         self._decision_worker = DecisionWorker(client, task_list, options)
 
 
-    async def run(self):
+    async def run(self) -> None:
         async with asyncio.TaskGroup() as tg:
             if not self._options["disable_workflow_worker"]:
                 tg.create_task(self._decision_worker.run())
@@ -30,13 +30,13 @@ async def run(self):
 
 
 
-def _validate_and_copy_defaults(client: Client, task_list: str, options: WorkerOptions):
+def _validate_and_copy_defaults(client: Client, task_list: str, options: WorkerOptions) -> None:
     if "identity" not in options:
         options["identity"] = f"{client.identity}@{task_list}@{uuid.uuid4()}"
 
     # TODO: More validation
 
-    for (key, value) in _DEFAULT_WORKER_OPTIONS.items():
+    # Set default values for missing options
+    for key, value in _DEFAULT_WORKER_OPTIONS.items():
         if key not in options:
-            # noinspection PyTypedDict
-            options[key] = value
+            cast(dict, options)[key] = value
diff --git a/pyproject.toml b/pyproject.toml
index 7eb7aed..c154d3e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -113,17 +113,15 @@ warn_no_return = true
 warn_unreachable = true
 strict_equality = true
 explicit_package_bases = true
-disable_error_code = [
-    "var-annotated",
-    "arg-type",
-    "attr-defined",
-    "assignment",
-    "literal-required",
-]
 exclude = [
-    "cadence/api/*",  # Exclude entire api directory with generated proto files
+    "cadence/api",
+    "cadence/api/.*",
+    "cadence/sample",
 ]
 
+# Reduce recursive module checking
+follow_imports = "silent"
+
 [[tool.mypy.overrides]]
 module = [
     "grpcio.*",
@@ -133,6 +131,7 @@ module = [
     "google.protobuf.*",
     "uber.cadence.*",
     "msgspec.*",
+    "cadence.api.*",
 ]
 ignore_missing_imports = true
 
diff --git a/tests/cadence/data_converter_test.py b/tests/cadence/data_converter_test.py
index 2f55395..88aecd3 100644
--- a/tests/cadence/data_converter_test.py
+++ b/tests/cadence/data_converter_test.py
@@ -1,5 +1,5 @@
 import dataclasses
-from typing import Any, Type
+from typing import Any, Type, Optional
 
 import pytest
 
@@ -8,10 +8,10 @@
 from msgspec import json
 
 @dataclasses.dataclass
-class TestDataClass:
+class _TestDataClass:
     foo: str = "foo"
     bar: int = -1
-    baz: 'TestDataClass' = None
+    baz: Optional['_TestDataClass'] = None
 
 @pytest.mark.parametrize(
     "json,types,expected",
@@ -35,7 +35,7 @@ class TestDataClass:
             "[true]", [bool, bool], [True, False], id="bools"
         ),
         pytest.param(
-            '[{"foo": "hello world", "bar": 42, "baz": {"bar": 43}}]', [TestDataClass, TestDataClass], [TestDataClass("hello world", 42, TestDataClass(bar=43)), None], id="data classes"
+            '[{"foo": "hello world", "bar": 42, "baz": {"bar": 43}}]', [_TestDataClass, _TestDataClass], [_TestDataClass("hello world", 42, _TestDataClass(bar=43)), None], id="data classes"
         ),
         pytest.param(
             '[{"foo": "hello world"}]', [dict, dict], [{"foo": "hello world"}, None], id="dicts"
@@ -53,17 +53,17 @@ class TestDataClass:
             '["hello", "world"]', [list[str]], [["hello", "world"]], id="list"
         ),
         pytest.param(
-            '{"foo": "bar"} {"bar": 100} ["hello"] "world"', [TestDataClass, TestDataClass, list[str], str],
-            [TestDataClass(foo="bar"), TestDataClass(bar=100), ["hello"], "world"], id="space delimited mix"
+            '{"foo": "bar"} {"bar": 100} ["hello"] "world"', [_TestDataClass, _TestDataClass, list[str], str],
+            [_TestDataClass(foo="bar"), _TestDataClass(bar=100), ["hello"], "world"], id="space delimited mix"
         ),
         pytest.param(
-            '[{"foo": "bar"},{"bar": 100},["hello"],"world"]', [TestDataClass, TestDataClass, list[str], str],
-            [TestDataClass(foo="bar"), TestDataClass(bar=100), ["hello"], "world"], id="json array mix"
+            '[{"foo": "bar"},{"bar": 100},["hello"],"world"]', [_TestDataClass, _TestDataClass, list[str], str],
+            [_TestDataClass(foo="bar"), _TestDataClass(bar=100), ["hello"], "world"], id="json array mix"
         ),
     ]
 )
 @pytest.mark.asyncio
-async def test_data_converter_from_data(json: str, types: list[Type], expected: list[Any]):
+async def test_data_converter_from_data(json: str, types: list[Type], expected: list[Any]) -> None:
     converter = DefaultDataConverter()
     actual = await converter.from_data(Payload(data=json.encode()), types)
     assert expected == actual
@@ -78,12 +78,12 @@ async def test_data_converter_from_data(json: str, types: list[Type], expected:
             ["hello", "world"], '["hello", "world"]', id="multiple values"
         ),
         pytest.param(
-            [TestDataClass()], '{"foo": "foo", "bar": -1, "baz": null}', id="data classes"
+            [_TestDataClass()], '{"foo": "foo", "bar": -1, "baz": null}', id="data classes"
         ),
     ]
 )
 @pytest.mark.asyncio
-async def test_data_converter_to_data(values: list[Any], expected: str):
+async def test_data_converter_to_data(values: list[Any], expected: str) -> None:
     converter = DefaultDataConverter()
     actual = await converter.to_data(values)
     # Parse both rather than trying to compare strings