Ensure time to first token logged only once per chat response

Time to first token Log lines were shown multiple times if new chunk
bein streamed was empty for some reason.

This change makes the logic robust to empty chunks being recieved.

src/khoj/processor/conversation/anthropic/utils.py

@@ -144,6 +144,7 @@ async def anthropic_chat_completion_with_backoff(
         formatted_messages, system_prompt = format_messages_for_anthropic(messages, system_prompt)
 
         aggregated_response = ""
+        response_started = False
         final_message = None
         start_time = perf_counter()
         async with client.messages.stream(
@@ -157,7 +158,8 @@ async def anthropic_chat_completion_with_backoff(
         ) as stream:
             async for chunk in stream:
                 # Log the time taken to start response
-                if aggregated_response == "":
+                if not response_started:
+                    response_started = True
                     logger.info(f"First response took: {perf_counter() - start_time:.3f} seconds")
                 # Skip empty chunks
                 if chunk.type != "content_block_delta":

src/khoj/processor/conversation/google/utils.py

@@ -195,13 +195,15 @@ async def gemini_chat_completion_with_backoff(
 
         aggregated_response = ""
         final_chunk = None
+        response_started = False
         start_time = perf_counter()
         chat_stream: AsyncIterator[gtypes.GenerateContentResponse] = await client.aio.models.generate_content_stream(
             model=model_name, config=config, contents=formatted_messages
         )
         async for chunk in chat_stream:
             # Log the time taken to start response
-            if final_chunk is None:
+            if not response_started:
+                response_started = True
                 logger.info(f"First response took: {perf_counter() - start_time:.3f} seconds")
             # Keep track of the last chunk for usage data
             final_chunk = chunk

src/khoj/processor/conversation/openai/utils.py

@@ -226,6 +226,7 @@ async def chat_completion_with_backoff(
 
         aggregated_response = ""
         final_chunk = None
+        response_started = False
         start_time = perf_counter()
         chat_stream: openai.AsyncStream[ChatCompletionChunk] = await client.chat.completions.create(
             messages=formatted_messages,  # type: ignore
@@ -237,7 +238,8 @@ async def chat_completion_with_backoff(
         )
         async for chunk in stream_processor(chat_stream):
             # Log the time taken to start response
-            if final_chunk is None:
+            if not response_started:
+                response_started = True
                 logger.info(f"First response took: {perf_counter() - start_time:.3f} seconds")
             # Keep track of the last chunk for usage data
             final_chunk = chunk