Log HTTPSD handler failures when debug is enabled

ober

cf7cd17a94e675f970f35009f8b9f08f031ee23f

diff --git a/lib/std/net/httpsd.ss b/lib/std/net/httpsd.ss
index ab74042..eeab5b7 100644
--- a/lib/std/net/httpsd.ss
+++ b/lib/std/net/httpsd.ss
@@ -37,6 +37,11 @@
         (newline err)
         (flush-output-port err))))
 
+  (def (httpsd-exception-string e)
+    (if (message-condition? e)
+      (condition-message e)
+      (format "~a" e)))
+
   (def (debug-byte-preview bv len)
     (let* ([n (min len 200)]
            [copy (make-bytevector n)])
@@ -181,11 +186,15 @@
                 [req
                  (let ([resp (try (normalize-response (handler req))
                                   (catch (e)
+                                    (httpsd-debug "handler exception: "
+                                      (httpsd-exception-string e))
                                     (th:respond-text 500 "Internal Server Error\n")))])
                    (write-response conn (apply-security-headers server resp)))]
                 [status (write-error-response server conn status)]
                 [else (void)]))
             (catch (e)
+              (httpsd-debug "client response exception: "
+                (httpsd-exception-string e))
               (try (write-error-response server conn 500)
                    (catch (write-e) (void)))))
           (try (rustls-close conn)