feat(bun): pathExists, a total existence check for the Bun host profile

lib/codegen_deno.ml

@@ -1326,6 +1326,11 @@ let () =
     (fun a -> Printf.sprintf "__as_fs().statSync(%s).isFile()" (arg 0 a));
   b "statIsDirectory"
     (fun a -> Printf.sprintf "__as_fs().statSync(%s).isDirectory()" (arg 0 a));
+  (* Total existence test: false for a missing path, never a throw. The stat
+     predicates above keep their ENOENT contract (host_profile pins it); this
+     is the check to make before them (added for kyX). *)
+  b "pathExists"
+    (fun a -> Printf.sprintf "__as_fs().existsSync(%s)" (arg 0 a));
   b "args" (fun _ -> "(globalThis.process?.argv?.slice(2) ?? [])");
   b "exit"
     (fun a -> Printf.sprintf "__as_process().exit(%s)" (arg 0 a));

stdlib/Deno.affine

@@ -78,6 +78,10 @@ pub extern fn statIsFile(path: String) -> Bool;
 /// Throws on a missing path (pair with `isNotFound` for the absent case).
 pub extern fn statIsDirectory(path: String) -> Bool;
 
+/// True if `path` exists (file, directory or other), false if it does not.
+/// Never throws: the total check to make before the stat predicates above.
+pub extern fn pathExists(path: String) -> Bool;
+
 /// Recursive walk under `root` — every file path beneath it, depth-first.
 /// Mirrors `std/fs/walk` for the common case (no glob filter; callers
 /// filter by extension). Throws on a missing root via `Deno.readDirSync`.

tests/codegen-bun/host_profile.affine

@@ -13,6 +13,7 @@ extern fn mkdirRecursive(path: String) -> Int;
 extern fn statSize(path: String) -> Int;
 extern fn statIsFile(path: String) -> Bool;
 extern fn statIsDirectory(path: String) -> Bool;
+extern fn pathExists(path: String) -> Bool;
 extern fn bytesLength(value: Bytes) -> Int;
 extern fn bytesByteAt(value: Bytes, offset: Int) -> Int;
 extern fn args() -> [String];
@@ -27,6 +28,7 @@ pub fn make_directory(path: String) -> Int { mkdirRecursive(path) }
 pub fn file_size(path: String) -> Int { statSize(path) }
 pub fn is_file(path: String) -> Bool { statIsFile(path) }
 pub fn is_directory(path: String) -> Bool { statIsDirectory(path) }
+pub fn exists(path: String) -> Bool { pathExists(path) }
 pub fn argument_count() -> Int { len(args()) }
 
 pub fn environment_value(name: String) -> String {

tests/codegen-bun/host_profile.harness.mjs

@@ -46,6 +46,9 @@ try {
     missingPathThrew = true;
   }
   if (!missingPathThrew) throw new Error("remove did not make path absent");
+  // pathExists is the total check: false for the removed file, never a throw.
+  if (subject.exists(file) !== false) throw new Error("pathExists on a missing path is not false");
+  if (subject.exists(nested) !== true) throw new Error("pathExists on a directory is not true");
 } finally {
   rmSync(root, { recursive: true, force: true });
 }