test: cover server version compatibility check in worker._register

- Add 7 unit tests verifying the compatibility branch introduced in
  18f1825: accepts major 0 and 2, rejects 1 and 3, tolerates unparseable
  versions, and falls through when /cluster/info itself errors.
- Narrow Client.get_cluster_info return type with an isinstance assert
  (matches the pattern used by Client.health) so mypy infers dict[str, Any]
  cleanly.

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

Author: durable-workflow-ops

src/durable_workflow/client.py

@@ -301,7 +301,9 @@ async def _do_request() -> httpx.Response:
 
     async def get_cluster_info(self) -> dict[str, Any]:
         """Fetch server version and capabilities from /api/cluster/info."""
-        return await self._request("GET", "/cluster/info", worker=False, context="get_cluster_info")
+        result = await self._request("GET", "/cluster/info", worker=False, context="get_cluster_info")
+        assert isinstance(result, dict)
+        return result
 
     def get_workflow_handle(
         self, workflow_id: str, *, run_id: str | None = None, workflow_type: str = ""

tests/test_worker.py

@@ -38,6 +38,7 @@ def mock_client() -> AsyncMock:
     client.complete_activity_task = AsyncMock(return_value={"outcome": "completed"})
     client.fail_workflow_task = AsyncMock(return_value={"outcome": "failed"})
     client.fail_activity_task = AsyncMock(return_value={"outcome": "failed"})
+    client.get_cluster_info = AsyncMock(return_value={"version": "2.0.0"})
     return client
 
 
@@ -58,6 +59,56 @@ async def test_register(self, mock_client: AsyncMock) -> None:
         assert "test-wf" in call_kwargs["supported_workflow_types"]
         assert "test-act" in call_kwargs["supported_activity_types"]
 
+    @pytest.mark.asyncio
+    async def test_register_calls_cluster_info(self, mock_client: AsyncMock) -> None:
+        worker = Worker(mock_client, task_queue="q1", workflows=[TestWorkflow], activities=[])
+        await worker._register()
+        mock_client.get_cluster_info.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    async def test_register_accepts_server_major_0(self, mock_client: AsyncMock) -> None:
+        mock_client.get_cluster_info = AsyncMock(return_value={"version": "0.1.9"})
+        worker = Worker(mock_client, task_queue="q1", workflows=[TestWorkflow], activities=[])
+        await worker._register()
+        mock_client.register_worker.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    async def test_register_accepts_server_major_2(self, mock_client: AsyncMock) -> None:
+        mock_client.get_cluster_info = AsyncMock(return_value={"version": "2.3.4"})
+        worker = Worker(mock_client, task_queue="q1", workflows=[TestWorkflow], activities=[])
+        await worker._register()
+        mock_client.register_worker.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    async def test_register_rejects_incompatible_major_1(self, mock_client: AsyncMock) -> None:
+        mock_client.get_cluster_info = AsyncMock(return_value={"version": "1.4.0"})
+        worker = Worker(mock_client, task_queue="q1", workflows=[TestWorkflow], activities=[])
+        with pytest.raises(RuntimeError, match="incompatible"):
+            await worker._register()
+        mock_client.register_worker.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_register_rejects_incompatible_major_3(self, mock_client: AsyncMock) -> None:
+        mock_client.get_cluster_info = AsyncMock(return_value={"version": "3.0.0"})
+        worker = Worker(mock_client, task_queue="q1", workflows=[TestWorkflow], activities=[])
+        with pytest.raises(RuntimeError, match="incompatible"):
+            await worker._register()
+        mock_client.register_worker.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_register_skips_check_on_unparseable_version(self, mock_client: AsyncMock) -> None:
+        mock_client.get_cluster_info = AsyncMock(return_value={"version": "unknown"})
+        worker = Worker(mock_client, task_queue="q1", workflows=[TestWorkflow], activities=[])
+        await worker._register()
+        mock_client.register_worker.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    async def test_register_continues_when_cluster_info_fails(self, mock_client: AsyncMock) -> None:
+        mock_client.get_cluster_info = AsyncMock(side_effect=RuntimeError("network down"))
+        worker = Worker(mock_client, task_queue="q1", workflows=[TestWorkflow], activities=[])
+        await worker._register()
+        mock_client.register_worker.assert_awaited_once()
+
 
 class TestWorkflowTaskExecution:
     @pytest.mark.asyncio