feat(batch-agent): integrate Langfuse tracing

- tracing.py: init/shutdown, trace_span, get_langfuse_callback, prompt mgmt
- main.py: init_langfuse at startup, shutdown on teardown
- redis_consumer.py: trace_span around journey_start/message/agent_trigger
- agent_runner.py: thread langfuse_handler through classify + processing LLM
- journey.py: thread langfuse_handler through _call_llm_with_tools
- llm.py: accept callbacks param, forward to LLM constructors
- requirements.txt: add langfuse>=3.0.0

services/batch-agent/app/journey.py

@@ -190,6 +190,7 @@ async def _call_llm_with_tools(
     system_prompt: str,
     history: list[dict[str, Any]],
     tools: list[Any],
+    langfuse_handler: Any | None = None,
 ) -> str:
     """Build LangChain messages from history and invoke the LLM with tools.
 
@@ -203,7 +204,8 @@ async def _call_llm_with_tools(
         else:
             messages.append(AIMessage(content=turn["content"]))
 
-    llm = get_llm(model=None, temperature=0.4)
+    callbacks = [langfuse_handler] if langfuse_handler else None
+    llm = get_llm(model=None, temperature=0.4, callbacks=callbacks)
     llm_with_tools = llm.bind_tools(tools)
     tool_map = {tool_def.name: tool_def for tool_def in tools}
 
@@ -247,6 +249,8 @@ async def _call_llm_with_tools(
 async def handle_journey_start(
     user_id: str,
     frame: dict[str, Any],
+    *,
+    langfuse_handler: Any | None = None,
 ) -> dict[str, Any]:
     """Handle a ``journey_start`` request.
 
@@ -277,6 +281,7 @@ async def handle_journey_start(
         system_prompt=system_prompt,
         history=seed_history,
         tools=list(FILESYSTEM_TOOLS),
+        langfuse_handler=langfuse_handler,
     )
 
     session.history.extend(seed_history)
@@ -313,6 +318,8 @@ async def handle_journey_start(
 async def handle_journey_message(
     user_id: str,
     frame: dict[str, Any],
+    *,
+    langfuse_handler: Any | None = None,
 ) -> dict[str, Any]:
     """Handle a ``journey_message`` request.
 
@@ -338,6 +345,7 @@ async def handle_journey_message(
         system_prompt=session.system_prompt,
         history=session.history,
         tools=list(FILESYSTEM_TOOLS),
+        langfuse_handler=langfuse_handler,
     )
 
     session.history.append({"role": "assistant", "content": ai_reply})
@@ -358,6 +366,7 @@ async def handle_journey_message(
                 system_prompt=session.system_prompt,
                 history=session.history,
                 tools=list(FILESYSTEM_TOOLS),
+                langfuse_handler=langfuse_handler,
             )
             session.history.append({"role": "assistant", "content": nudge_reply})