Prefer init-provided system instruction in Nova Sonic

Add system_instruction parameter to the Nova Sonic adapter's
get_llm_invocation_params() and call _resolve_system_instruction() to
prefer init-provided over context-provided system instructions and
warn on conflicts. Previously context-provided took precedence.

Remove the service-side fallback logic, as the adapter now handles
resolution.

src/pipecat/adapters/services/aws_nova_sonic_adapter.py

@@ -72,20 +72,26 @@ class AWSNovaSonicLLMAdapter(BaseLLMAdapter[AWSNovaSonicLLMInvocationParams]):
         """Get the identifier used in LLMSpecificMessage instances for AWS Nova Sonic."""
         return "aws-nova-sonic"
 
-    def get_llm_invocation_params(self, context: LLMContext) -> AWSNovaSonicLLMInvocationParams:
+    def get_llm_invocation_params(
+        self, context: LLMContext, *, system_instruction: Optional[str] = None
+    ) -> AWSNovaSonicLLMInvocationParams:
         """Get AWS Nova Sonic-specific LLM invocation parameters from a universal LLM context.
 
-        This is a placeholder until support for universal LLMContext machinery is added for AWS Nova Sonic.
-
         Args:
             context: The LLM context containing messages, tools, etc.
+            system_instruction: Optional system instruction from service settings.
 
         Returns:
             Dictionary of parameters for invoking AWS Nova Sonic's LLM API.
         """
         messages = self._from_universal_context_messages(self.get_messages(context))
+        effective_system = self._resolve_system_instruction(
+            messages.system_instruction,
+            system_instruction,
+            discard_context_system=True,
+        )
         return {
-            "system_instruction": messages.system_instruction,
+            "system_instruction": effective_system,
             "messages": messages.messages,
             # NOTE: LLMContext's tools are guaranteed to be a ToolsSchema (or NOT_GIVEN)
             "tools": self.from_standard_tools(context.tools) or [],

src/pipecat/services/aws/nova_sonic/llm.py

@@ -629,7 +629,9 @@ class AWSNovaSonicLLMService(LLMService):
 
         # Read context
         adapter: AWSNovaSonicLLMAdapter = self.get_llm_adapter()
-        llm_connection_params = adapter.get_llm_invocation_params(self._context)
+        llm_connection_params = adapter.get_llm_invocation_params(
+            self._context, system_instruction=self._settings.system_instruction
+        )
 
         # Send prompt start event, specifying tools.
         # Tools from context take priority over self._tools.
@@ -642,12 +644,9 @@ class AWSNovaSonicLLMService(LLMService):
         await self._send_prompt_start_event(tools)
 
         # Send system instruction.
-        # Instruction from context takes priority over self._settings.system_instruction.
-        system_instruction = (
-            llm_connection_params["system_instruction"]
-            if llm_connection_params["system_instruction"]
-            else self._settings.system_instruction
-        )
+        # The adapter resolves conflicts between init-provided and
+        # context-provided system instructions (preferring init-provided).
+        system_instruction = llm_connection_params["system_instruction"]
         logger.debug(f"Using system instruction: {system_instruction}")
         if system_instruction:
             await self._send_text_event(text=system_instruction, role=Role.SYSTEM)