feat: Add Langfuse user feedback for ChatAgent

.env.example

@@ -0,0 +1,4 @@
+
+# Browser-safe (public key only, VITE_ prefix exposes to Vite client bundle)
+VITE_LANGFUSE_PUBLIC_KEY=pk-lf-...
+VITE_LANGFUSE_BASE_URL=https://langfuse.cofacts.tw

.github/workflows/deploy.yml

@@ -83,7 +83,10 @@ jobs:
           SHA: ${{ github.sha }}
         run: |
           # Build frontend
-          docker build -t asia-east1-docker.pkg.dev/$PROJECT_ID/cofacts-ai/frontend:$SHA -f Dockerfile .
+          docker build \
+            --build-arg VITE_LANGFUSE_PUBLIC_KEY=${{ secrets.LANGFUSE_PUBLIC_KEY }} \
+            --build-arg VITE_LANGFUSE_BASE_URL="https://langfuse.cofacts.tw" \
+            -t asia-east1-docker.pkg.dev/$PROJECT_ID/cofacts-ai/frontend:$SHA -f Dockerfile .
           docker push asia-east1-docker.pkg.dev/$PROJECT_ID/cofacts-ai/frontend:$SHA
 
           # Build backend

Dockerfile

@@ -9,6 +9,8 @@ RUN pnpm install --frozen-lockfile --ignore-scripts
 
 # Copy source and build
 COPY . .
+ARG VITE_LANGFUSE_PUBLIC_KEY
+ARG VITE_LANGFUSE_BASE_URL
 RUN pnpm run build
 
 # --- runtime ---

README.md

@@ -33,14 +33,20 @@ pnpm install:agent
 > source adk/.venv/bin/activate
 > ```
 
-3. Set up environment variables for the ADK agent:
+3. Set up environment variables:
 
+For the ADK backend agent:
 ```bash
 cp adk/cofacts_ai/.env.example adk/cofacts_ai/.env
 ```
-
 Edit `adk/cofacts_ai/.env` and fill in the required values (at minimum `GOOGLE_API_KEY`).
 
+For the frontend UI (Vite / TanStack Start):
+```bash
+cp .env.example .env
+```
+Edit `.env` to configure your browser-safe variables (e.g. Langfuse keys).
+
 4. Start the development server:
 
 ```bash

adk/cofacts_ai/agent.py

@@ -26,7 +26,8 @@
     submit_cofacts_reply,
     resolve_vertex_redirect
 )
-from .instrumentation import setup_instrumentation
+from google.adk.apps.app import App
+from .instrumentation import setup_instrumentation, LangfuseTracingPlugin
 
 load_dotenv()
 
@@ -545,5 +546,9 @@ async def append_grounding_sources(
     ],
 )
 
-root_agent = ai_writer
+app = App(
+    name="cofacts_ai",
+    root_agent=ai_writer,
+    plugins=[LangfuseTracingPlugin()],
+)
 

adk/cofacts_ai/instrumentation.py

@@ -2,6 +2,9 @@
 import logging
 from openinference.instrumentation.google_adk import GoogleADKInstrumentor
 from langfuse import get_client
+from google.adk.plugins.base_plugin import BasePlugin
+from google.adk.agents.invocation_context import InvocationContext
+from google.adk.events.event import Event
 
 logger = logging.getLogger(__name__)
 
@@ -20,3 +23,34 @@ def setup_instrumentation():
         logger.info("Langfuse instrumentation initialized.")
     else:
         logger.warning("Langfuse authentication failed. Skipping instrumentation.")
+
+
+class LangfuseTracingPlugin(BasePlugin):
+    """
+    ADK Plugin that stamps each emitted event with the current Langfuse
+    trace ID in custom_metadata.
+
+    We use `before_run_callback` and `run_config.custom_metadata` because:
+    1. ADK's `Runner` merges `run_config.custom_metadata` into every event
+       generated during the invocation.
+    2. This merging happens *before* the event is persisted to the session
+       store.
+    3. Using `on_event_callback` would be too late for persistence, as ADK
+       saves the event to the database before the plugin's `on_event` is called.
+    """
+
+    def __init__(self):
+        super().__init__(name="langfuse_tracing")
+
+    async def before_run_callback(
+        self, *, invocation_context: InvocationContext
+    ):
+        langfuse = get_client()
+        trace_id = langfuse.get_current_trace_id()
+        if trace_id:
+            # Set the trace ID in run_config so ADK automatically stamps all
+            # future events in this invocation before they are saved to the DB.
+            if invocation_context.run_config.custom_metadata is None:
+                invocation_context.run_config.custom_metadata = {}
+            invocation_context.run_config.custom_metadata["langfuse_trace_id"] = trace_id
+        return None

package.json

@@ -30,6 +30,7 @@
     "@tanstack/router-plugin": "^1.132.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "langfuse": "^3.38.20",
     "lucide-react": "^0.574.0",
     "nitro": "latest",
     "openapi-fetch": "^0.17.0",