🛡️ Sentinel: [MEDIUM] Fix swallowed exception tracebacks in global error handler

.jules/sentinel.md

@@ -35,3 +35,8 @@
 **Vulnerability:** The FastAPI application was missing the `Referrer-Policy` security header, which could leak sensitive path information or query parameters via the `Referer` header to external sites when navigating away from the application.
 **Learning:** Even when setting strict `Content-Security-Policy` and `X-Frame-Options`, `Referrer-Policy` is needed to prevent cross-origin information leakage on outbound requests.
 **Prevention:** Always include `Referrer-Policy: no-referrer` in the global security headers middleware to strictly drop referrer information on all outbound requests.
+
+## 2025-02-21 - [Prevented Swallowing of Unhandled Exception Tracebacks]
+**Vulnerability:** The global `@app.exception_handler(Exception)` in `src/tacet/serve/server.py` suppressed unhandled exceptions without logging them. This bypassed Starlette's `ServerErrorMiddleware` logging, causing silent server-side failures and hiding critical errors.
+**Learning:** Overriding the default exception handler to add security headers removes the framework's default behavior of logging unhandled exceptions.
+**Prevention:** Always explicitly log the exception (e.g., `logging.error("...", exc_info=_exc)`) when defining a generic catch-all exception handler in FastAPI.

src/tacet/serve/server.py

@@ -357,6 +357,7 @@ async def add_security_headers(request: Request, call_next):
 
     @app.exception_handler(Exception)
     async def unhandled_exception_handler(request: Request, _exc: Exception) -> Response:
+        logging.error("Unhandled server exception", exc_info=_exc)
         response = PlainTextResponse("Internal Server Error", status_code=500)
         return _apply_security_headers(response, request.url.path)