Several subtle IODriver bug fixes

test/Spec.hs

@@ -1809,16 +1809,56 @@ ioDriverTests = testGroup "IO driver tests"
           ]
       final @?= ofString "child done"
       st @?= Leaf
+
+  -- Scheduler hardening tests
+  , testCase "runIO rejects non-IO tree with sentinel error" $ do
+      result <- runIO unsafePerms (ofString "not an io program")
+      case result of
+        Left _  -> return ()
+        Right _ -> assertFailure "Expected Left for invalid sentinel"
+
+  , testCase "cyclic await returns error instead of hanging" $ do
+      (final, _) <- runIOSourceWith unsafePerms Leaf Leaf $
+        unlines
+          [ "main = io (bind (fork (await (pair \"task\" 0))) (h :"
+          , "  await h))"
+          ]
+      final @?= ioErrResult 63
+
+  , testCase "writeBytes and readFile roundtrip binary data" $
+      withSystemTempDirectory "tricu-io-bytes" $ \dir -> do
+        let path = dir ++ "/binary.bin"
+        final <- runIOSource $
+          unlines
+            [ "main = io (bind (writeBytes \"" ++ path ++ "\" [(0) (255) (128) (1)])"
+            , "  (_ : readFile \"" ++ path ++ "\"))"
+            ]
+        final @?= ioOkResult (ofBytes (BS.pack [0, 255, 128, 1]))
+
+  , testCase "stress test: many sleeping tasks complete promptly" $ do
+      let n = 100
+          build 0 = "pure \"done\""
+          build k = "bind (fork (bind (sleep 1) (_ : pure \"x\"))) (h : bind (await h) (_ : " ++ build (k - 1) ++ "))"
+      (final, _) <- runIOSourceWith unsafePerms Leaf Leaf ("main = io (" ++ build n ++ ")")
+      final @?= ofString "done"
+
+  , testCase "long fork await loop does not leak" $ do
+      let n = 200
+          build 0 = "pure \"done\""
+          build k = "bind (fork (pure \"x\")) (h : bind (await h) (_ : " ++ build (k - 1) ++ "))"
+      (final, _) <- runIOSourceWith unsafePerms Leaf Leaf ("main = io (" ++ build n ++ ")")
+      final @?= ofString "done"
   ]
 
 runIOSourceWith :: IOPermissions -> T -> T -> String -> IO (T, T)
 runIOSourceWith perms readerEnv initialState source = do
   ioEnv <- evaluateFile "./lib/io.tri"
   evalEnv <- evalTricuWithStore Nothing ioEnv (parseTricu source)
-  case checkIOSentinel (mainResult evalEnv) of
-    Right (1, action) -> runIOWith perms readerEnv initialState action
-    Right (v, _)      -> assertFailure ("Unsupported IO ABI version: " ++ show v)
-    Left err          -> assertFailure ("Expected IO sentinel: " ++ err)
+  let fullTree = mainResult evalEnv
+  result <- runIOWith perms readerEnv initialState fullTree
+  case result of
+    Left err   -> assertFailure ("IO runtime error: " ++ err)
+    Right pair -> pure pair
 
 runIOSource :: String -> IO T
 runIOSource source = fmap fst $ runIOSourceWith unsafePerms Leaf Leaf source