haskell: Phase 9 — hk-run-io catches errors and appends to io-lines

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

lib/haskell/tests/io-input.sx

@@ -64,12 +64,11 @@
 
 (hk-test
   "readFile error on missing file"
-  (guard
-    (e (true (>= (index-of e "file not found") 0)))
-    (begin
-      (set! hk-vfs (dict))
-      (hk-run-io "main = readFile \"no.txt\" >>= putStrLn")
-      false))
+  (begin
+    (set! hk-vfs (dict))
+    (let
+      ((lines (hk-run-io "main = readFile \"no.txt\" >>= putStrLn")))
+      (>= (index-of (str lines) "file not found") 0)))
   true)
 
 (hk-test