fix: derive worker sdk_version from installed package metadata

Removes the hard-coded "durable-workflow-python/0.1.0" default in
Client.register_worker() so workers advertise the version of the SDK
they were actually built against. The default now uses
importlib.metadata so it tracks the next published bump
automatically. Also exports __version__ on the package for callers
that need to inspect it directly.

Closes TD-P011.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: durable-workflow-ops

src/durable_workflow/__init__.py

@@ -1,3 +1,11 @@
+from importlib.metadata import PackageNotFoundError
+from importlib.metadata import version as _pkg_version
+
+try:
+    __version__ = _pkg_version("durable-workflow")
+except PackageNotFoundError:  # source checkout without installed metadata
+    __version__ = "0.0.0+unknown"
+
 from . import activity, sync, workflow
 from .activity import ActivityContext, ActivityInfo
 from .client import (
@@ -36,6 +44,7 @@
 from .workflow import ContinueAsNew, StartChildWorkflow
 
 __all__ = [
+    "__version__",
     "ActivityCancelled",
     "ActivityContext",
     "ActivityInfo",

src/durable_workflow/client.py

@@ -2,6 +2,8 @@
 
 import asyncio
 from dataclasses import dataclass
+from importlib.metadata import PackageNotFoundError
+from importlib.metadata import version as _pkg_version
 from typing import Any
 
 import httpx
@@ -19,6 +21,16 @@
 CONTROL_PLANE_VERSION = "2"
 
 
+def _default_sdk_version() -> str:
+    try:
+        return f"durable-workflow-python/{_pkg_version('durable-workflow')}"
+    except PackageNotFoundError:
+        return "durable-workflow-python/0.0.0+unknown"
+
+
+DEFAULT_SDK_VERSION = _default_sdk_version()
+
+
 @dataclass
 class WorkflowExecution:
     workflow_id: str
@@ -703,8 +715,10 @@ async def register_worker(
         supported_workflow_types: list[str] | None = None,
         supported_activity_types: list[str] | None = None,
         runtime: str = "python",
-        sdk_version: str = "durable-workflow-python/0.1.0",
+        sdk_version: str | None = None,
     ) -> Any:
+        if sdk_version is None:
+            sdk_version = DEFAULT_SDK_VERSION
         body: dict[str, Any] = {
             "worker_id": worker_id,
             "task_queue": task_queue,

tests/test_client.py

@@ -348,3 +348,28 @@ async def test_register(self, client: Client) -> None:
             assert result["registered"] is True
             body = mock.call_args.kwargs.get("json") or mock.call_args[1].get("json")
             assert body["runtime"] == "python"
+
+    @pytest.mark.asyncio
+    async def test_register_advertises_installed_package_version(self, client: Client) -> None:
+        from importlib.metadata import version as _pkg_version
+
+        import durable_workflow
+
+        installed = _pkg_version("durable-workflow")
+        assert durable_workflow.__version__ == installed
+
+        resp = _mock_response(201, {"worker_id": "w1", "registered": True})
+        with patch.object(client._http, "request", new_callable=AsyncMock, return_value=resp) as mock:
+            await client.register_worker(worker_id="w1", task_queue="q1")
+            body = mock.call_args.kwargs.get("json") or mock.call_args[1].get("json")
+            assert body["sdk_version"] == f"durable-workflow-python/{installed}"
+
+    @pytest.mark.asyncio
+    async def test_register_honors_explicit_sdk_version_override(self, client: Client) -> None:
+        resp = _mock_response(201, {"worker_id": "w1", "registered": True})
+        with patch.object(client._http, "request", new_callable=AsyncMock, return_value=resp) as mock:
+            await client.register_worker(
+                worker_id="w1", task_queue="q1", sdk_version="custom-runtime/9.9.9"
+            )
+            body = mock.call_args.kwargs.get("json") or mock.call_args[1].get("json")
+            assert body["sdk_version"] == "custom-runtime/9.9.9"