Address review feedback on SEP-2663 tasks

- Client task support is opt-in via importing fastmcp_tasks (drop the core
  auto-load of companion packages); a plain Client never advertises tasks.
- A worker restores the submitting caller's auth token and headers from the
  task snapshot into the standard ambient context, so get_access_token() /
  get_http_headers() work in a distributed worker with no new core hooks.
- worker_cli validates the loaded extension's resolved backend, not env defaults,
  so a constructor-configured Redis worker starts.
- Thread the per-call read timeout through task polling; bound ToolTask.wait by
  its deadline; set_elicitation_callback rebuilds internal extensions so a
  later-set handler answers in-task input.
- README imports TaskConfig from fastmcp.utilities.tasks.

Co-Authored-By: Claude <noreply@anthropic.com>

tests/cli/test_tasks.py

@@ -1,27 +1,48 @@
 """Tests for the fastmcp tasks CLI."""
 
 import pytest
-from fastmcp_tasks.settings import docket_settings
-from fastmcp_tasks.worker_cli import check_distributed_backend, tasks_app
+from fastmcp_tasks.settings import DocketSettings
+from fastmcp_tasks.worker_cli import (
+    check_distributed_backend,
+    resolve_docket_settings,
+    tasks_app,
+)
+
+from fastmcp import FastMCP
+from fastmcp_tasks import TasksExtension
+
+
+class TestResolveDocketSettings:
+    """`resolve_docket_settings` reads the server's *registered* extension."""
+
+    def test_reads_the_registered_extensions_settings(self):
+        """The constructor-configured URL is visible without any env var."""
+        mcp = FastMCP("t")
+        mcp.add_extension(TasksExtension(url="redis://example:6379/0"))
+        settings = resolve_docket_settings(mcp)
+        assert settings.url == "redis://example:6379/0"
+
+    def test_exits_when_no_tasks_extension_registered(self):
+        """A server with no TasksExtension has nothing for the CLI to serve."""
+        mcp = FastMCP("t")
+        with pytest.raises(SystemExit) as exc_info:
+            resolve_docket_settings(mcp)
+        assert exc_info.value.code == 1
 
 
 class TestCheckDistributedBackend:
     """Test the distributed backend checker function."""
 
-    def test_succeeds_with_redis_url(self, monkeypatch: pytest.MonkeyPatch):
+    def test_succeeds_with_redis_url(self):
         """Test that it succeeds with Redis URL."""
-        # Docket settings moved to `fastmcp_tasks.settings.DocketSettings`
-        # (env prefix `FASTMCP_DOCKET_`), so patch the settings object directly.
-        monkeypatch.setattr(docket_settings, "url", "redis://localhost:6379/0")
-        check_distributed_backend()
+        settings = DocketSettings(url="redis://localhost:6379/0")
+        check_distributed_backend(settings)
 
-    def test_exits_with_helpful_error_for_memory_url(
-        self, monkeypatch: pytest.MonkeyPatch
-    ):
+    def test_exits_with_helpful_error_for_memory_url(self):
         """Test that it exits with helpful error for memory:// URLs."""
-        monkeypatch.setattr(docket_settings, "url", "memory://test-123")
+        settings = DocketSettings(url="memory://test-123")
         with pytest.raises(SystemExit) as exc_info:
-            check_distributed_backend()
+            check_distributed_backend(settings)
 
         assert isinstance(exc_info.value, SystemExit)
         assert exc_info.value.code == 1