feat: add Sentry error monitoring and tracing to FastAPI backend

- Install sentry-sdk[fastapi] with auto-enabled FastAPI + Anthropic
  integrations
- Init before app = FastAPI() with env-aware sample rates
  (100% dev, 20% prod)
- Filter /health endpoint from traces to reduce noise
- Add SENTRY_DSN to config settings

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/core/config.py

@@ -118,6 +118,9 @@ class Settings(BaseSettings):
         """Check if any AI provider is configured."""
         return self.ANTHROPIC_API_KEY is not None or self.GOOGLE_AI_API_KEY is not None
 
+    # Monitoring
+    SENTRY_DSN: Optional[str] = None
+
     # Deployment – auto-seed test data on PR environments
     SEED_ON_DEPLOY: bool = False
 

backend/app/main.py

@@ -8,6 +8,21 @@ from slowapi import _rate_limit_exceeded_handler
 from slowapi.errors import RateLimitExceeded
 
 from app.core.config import settings
+
+# Initialize Sentry before any other app code
+import sentry_sdk
+if settings.SENTRY_DSN:
+    sentry_sdk.init(
+        dsn=settings.SENTRY_DSN,
+        environment="development" if settings.DEBUG else "production",
+        send_default_pii=True,
+        traces_sample_rate=1.0 if settings.DEBUG else 0.2,
+        # Filter out noisy health check transactions
+        traces_sampler=lambda ctx: (
+            0.0 if ctx.get("transaction_context", {}).get("name", "").startswith("GET /health") else None
+        ),
+    )
+
 from app.core.database import init_db, async_session_maker
 from app.core.logging_config import setup_logging
 from app.core.middleware import RequestLoggingMiddleware, ErrorLoggingMiddleware

backend/requirements.txt

@@ -39,6 +39,9 @@ google-genai>=1.0.0
 pgvector>=0.3.6
 voyageai>=0.3.0
 
+# Monitoring
+sentry-sdk[fastapi]>=2.54.0
+
 # Utilities
 python-dotenv==1.0.1
 croniter>=2.0.0