chore(toolbox-core): deprecate add_headers feature

packages/toolbox-core/README.md

@@ -300,24 +300,15 @@ that fresh credentials or header values can be used.
 
 ### Configuration
 
-You can configure these dynamic headers in two ways:
+You can configure these dynamic headers as seen below:
 
-1. **During Client Initialization**
-
-    ```python
-    from toolbox_core import ToolboxClient
-
-    async with ToolboxClient("toolbox-url", client_headers={"header1": header1_getter, "header2": header2_getter, ...}) as client:
-    ```
-
-1. **After Client Initialization**
-
-    ```python
-    from toolbox_core import ToolboxClient
+```python
+from toolbox_core import ToolboxClient
 
-    async with ToolboxClient("toolbox-url") as client:
-        client.add_headers({"header1": header1_getter, "header2": header2_getter, ...})
-    ```
+async with ToolboxClient("toolbox-url", client_headers={"header1": header1_getter, "header2": header2_getter, ...}) as client:
+    # Use client
+    pass
+```
 
 ### Authenticating with Google Cloud Servers
 

packages/toolbox-core/pyproject.toml

@@ -12,6 +12,7 @@ authors = [
 dependencies = [
     "pydantic>=2.7.0,<3.0.0",
     "aiohttp>=3.8.6,<4.0.0",
+    "deprecated>=1.2.15,<2.0.0",
 ]
 
 classifiers = [

packages/toolbox-core/requirements.txt

@@ -1,2 +1,3 @@
 aiohttp==3.12.12
 pydantic==2.11.5
+deprecated==1.2.15

packages/toolbox-core/src/toolbox_core/client.py

@@ -17,6 +17,7 @@
 from typing import Any, Awaitable, Callable, Mapping, Optional, Union
 
 from aiohttp import ClientSession
+from deprecated import deprecated
 
 from .protocol import ManifestSchema, ToolSchema
 from .tool import ToolboxTool
@@ -340,16 +341,17 @@ async def load_toolset(
 
         return tools
 
+    @deprecated(
+        "Use the `client_headers` parameter in the ToolboxClient constructor instead."
+    )
     def add_headers(
         self,
         headers: Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]]]],
     ) -> None:
         """
         Add headers to be included in each request sent through this client.
-
         Args:
             headers: Headers to include in each request sent through this client.
-
         Raises:
             ValueError: If any of the headers are already registered in the client.
         """

packages/toolbox-core/src/toolbox_core/sync_client.py

@@ -17,6 +17,8 @@
 from threading import Thread
 from typing import Any, Awaitable, Callable, Mapping, Optional, Union
 
+from deprecated import deprecated
+
 from .client import ToolboxClient
 from .sync_tool import ToolboxSyncTool
 
@@ -153,6 +155,9 @@ def load_toolset(
             for async_tool in async_tools
         ]
 
+    @deprecated(
+        "Use the `client_headers` parameter in the ToolboxClient constructor instead."
+    )
     def add_headers(
         self,
         headers: Mapping[