feat(tasks): add clear_list tool (v0.11.6)

Deletes all tasks in a list within a single authenticated session,
avoiding N×(login+logout) overhead — Login once, N×delete, logout once.
Supports only_open=True to keep completed tasks.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/mcp_familywall/server.py

@@ -1041,6 +1041,71 @@ def delete_task(task_id: str) -> str:
     return json.dumps({"deleted": True, "id": task_id}, ensure_ascii=False, indent=2)
 
 
+# ---------------------------------------------------------------------------
+# Tool: clear_list
+# ---------------------------------------------------------------------------
+
+
+@mcp.tool()
+def clear_list(list_id: str, only_open: bool = False) -> str:
+    """Delete all tasks in a list within a single authenticated session.
+
+    IMPORTANT: Ask the user for confirmation before calling this tool.
+
+    Significantly faster than deleting tasks one by one because all
+    delete calls share a single login/logout session.
+
+    Args:
+        list_id: List metaId from get_lists
+            (e.g. ``"taskList/16282169_29775360"``).
+        only_open: When ``True`` only incomplete tasks are deleted;
+            completed tasks are kept. Default ``False`` deletes all.
+
+    Returns:
+        JSON with ``deleted_count`` and ``list_id`` on success,
+        or an error message.
+    """
+    if not list_id.startswith("taskList/"):
+        return "Error: list_id must start with 'taskList/'"
+
+    try:
+        email, password = get_credentials()
+    except RuntimeError as exc:
+        return f"Error: {exc}"
+
+    try:
+        with FamilyWallClient() as client:
+            client.login(email, password)
+
+            data = client.call(
+                "accgetallfamily",
+                {"a01call": "taskcategorysync", "a02call": "tasksync"},
+            )
+            raw_tasks = _extract_tasks(data)
+
+            tasks_to_delete = [
+                t
+                for t in raw_tasks
+                if t.get("taskListId") == list_id
+                and (not only_open or str(t.get("complete", "false")).lower() != "true")
+            ]
+
+            for task in tasks_to_delete:
+                client.call("metadelete", {"id": task["metaId"]})
+
+            client.logout()
+    except FamilyWallError as exc:
+        return f"Error: Family Wall API error: {exc}"
+    except Exception as exc:
+        return f"Error: Connection error: {exc}"
+
+    return json.dumps(
+        {"deleted_count": len(tasks_to_delete), "list_id": list_id},
+        ensure_ascii=False,
+        indent=2,
+    )
+
+
 # ---------------------------------------------------------------------------
 # Tool: create_list
 # ---------------------------------------------------------------------------