fix: fix docstrings related to CallContextBuilder args in constructors and make ServerCallContext mandatory in compat folder (#907)

# Changes
- change docstrings related to `CallContextBuilder` args in constructors
from innaccurate "If None, no ServerCallContext is passed." to accurate
"If None the DefaultCallContextBuilder is used."
- make `ServerCallContext` mandatory in
[‎src/a2a/compat/v0_3/rest_adapter.py](https://github.com/a2aproject/a2a-python/pull/907/changes#diff-308e6baa6b4fcc3040166435af1735c54e3aa717ad2d39479fd588afd5e180d9)

Author: sokoliva

src/a2a/compat/v0_3/rest_adapter.py

@@ -109,7 +109,7 @@ async def event_generator(
         )
 
     async def handle_get_agent_card(
-        self, request: Request, call_context: ServerCallContext | None = None
+        self, request: Request, call_context: ServerCallContext
     ) -> dict[str, Any]:
         """Handles GET requests for the agent card endpoint."""
         card_to_serve = self.agent_card
@@ -119,7 +119,7 @@ async def handle_get_agent_card(
         return v03_card.model_dump(mode='json', exclude_none=True)
 
     async def handle_authenticated_agent_card(
-        self, request: Request, call_context: ServerCallContext | None = None
+        self, request: Request, call_context: ServerCallContext
     ) -> dict[str, Any]:
         """Hook for per credential agent card response."""
         if not self.agent_card.capabilities.extended_agent_card:
@@ -132,9 +132,8 @@ async def handle_authenticated_agent_card(
             card_to_serve = self.agent_card
 
         if self.extended_card_modifier:
-            context = self._context_builder.build(request)
             card_to_serve = await maybe_await(
-                self.extended_card_modifier(card_to_serve, context)
+                self.extended_card_modifier(card_to_serve, call_context)
             )
         elif self.card_modifier:
             card_to_serve = await maybe_await(self.card_modifier(card_to_serve))

src/a2a/server/routes/jsonrpc_dispatcher.py

@@ -215,8 +215,8 @@ def __init__(  # noqa: PLR0913
             extended_agent_card: An optional, distinct AgentCard to be served
               at the authenticated extended card endpoint.
             context_builder: The CallContextBuilder used to construct the
-              ServerCallContext passed to the request_handler. If None, no
-              ServerCallContext is passed.
+              ServerCallContext passed to the request_handler. If None the
+              DefaultCallContextBuilder is used.
             card_modifier: An optional callback to dynamically modify the public
               agent card before it is served.
             extended_card_modifier: An optional callback to dynamically modify

src/a2a/server/routes/jsonrpc_routes.py

@@ -54,8 +54,8 @@ def create_jsonrpc_routes(  # noqa: PLR0913
         extended_agent_card: An optional, distinct AgentCard to be served
           at the authenticated extended card endpoint.
         context_builder: The CallContextBuilder used to construct the
-          ServerCallContext passed to the request_handler. If None, no
-          ServerCallContext is passed.
+          ServerCallContext passed to the request_handler. If None the
+          DefaultCallContextBuilder is used.
         card_modifier: An optional callback to dynamically modify the public
           agent card before it is served.
         extended_card_modifier: An optional callback to dynamically modify

src/a2a/server/routes/rest_routes.py

@@ -76,8 +76,8 @@ def create_rest_routes(  # noqa: PLR0913
         extended_agent_card: An optional, distinct AgentCard to be served
           at the authenticated extended card endpoint.
         context_builder: The CallContextBuilder used to construct the
-          ServerCallContext passed to the request_handler. If None, no
-          ServerCallContext is passed.
+          ServerCallContext passed to the request_handler. If None the
+          DefaultCallContextBuilder is used.
         card_modifier: An optional callback to dynamically modify the public
           agent card before it is served.
         extended_card_modifier: An optional callback to dynamically modify
@@ -176,7 +176,7 @@ async def event_generator() -> AsyncIterator[str]:
         return EventSourceResponse(event_generator())
 
     async def _handle_authenticated_agent_card(
-        request: 'Request', call_context: ServerCallContext | None = None
+        request: 'Request', call_context: ServerCallContext
     ) -> dict[str, Any]:
         if not agent_card.capabilities.extended_agent_card:
             raise ExtendedAgentCardNotConfiguredError(
@@ -185,10 +185,8 @@ async def _handle_authenticated_agent_card(
         card_to_serve = extended_agent_card or agent_card
 
         if extended_card_modifier:
-            # Re-generate context if none passed to replicate RESTAdapter exact logic
-            context = call_context or _build_call_context(request)
             card_to_serve = await maybe_await(
-                extended_card_modifier(card_to_serve, context)
+                extended_card_modifier(card_to_serve, call_context)
             )
         elif card_modifier:
             card_to_serve = await maybe_await(card_modifier(card_to_serve))