fix: surface the real reason a contract email fails

backend/app/routers/applications.py

@@ -190,9 +190,11 @@ def send_contract(index: int, request: SendContractRequest):
             candidate_name=application.name,
         )
     except email_service.EmailNotConfiguredError as exc:
-        raise HTTPException(status_code=503, detail=str(exc)) from exc
+        raise HTTPException(status_code=409, detail=str(exc)) from exc
     except email_service.EmailSendError as exc:
-        raise HTTPException(status_code=502, detail=str(exc)) from exc
+        # 424 (not 502): a CDN in front of the API rewrites upstream 5xx into its
+        # own error page, which would hide the reason from the coordinator.
+        raise HTTPException(status_code=424, detail=str(exc)) from exc
 
     application.contract_sent_to = request.to
     application.contract_sent_at = datetime.now(timezone.utc).isoformat()

backend/app/services/email_service.py

@@ -73,10 +73,16 @@ def send_signed_contract(
         )
         response.raise_for_status()
     except httpx.HTTPStatusError as exc:
-        raise EmailSendError(
+        message = (
             f"n8n webhook returned {exc.response.status_code}: {exc.response.text[:200]}"
-        ) from exc
+        )
+        logger.error("Contract email failed — %s", message)
+        raise EmailSendError(message) from exc
     except httpx.HTTPError as exc:
-        raise EmailSendError(f"Could not reach the n8n webhook: {exc}") from exc
+        # Log the exception type too: a bare message like "" is common for
+        # connect/DNS errors and tells the operator nothing on its own.
+        message = f"Could not reach the n8n webhook ({type(exc).__name__}): {exc}"
+        logger.error("Contract email failed — %s", message)
+        raise EmailSendError(message) from exc
 
     logger.info("Signed contract emailed via n8n to %s", to)