ludicc / ludic build: --stdin-file <path> checks an unsaved buffer in place of its file (R10)

stdin is read once, whole, and read_file serves a copy of it wherever the program opens <path> -
the entry, an import through a barrel, a component's .xml / .lss, an .lres. Paths match after
normalising both ('/' separators, relative under $PWD, . / .. / // folded, case on Windows);
diagnostics keep the file's usual name, with the buffer's lines and columns. A <path> nothing
opens is one warning. On ludic build it implies --check. Reseeded; bootstrap-cfree fixpoint holds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/support/io.ludic

@@ -2,6 +2,8 @@
 # The compiler reads one .ludic file whole and emits LLVM IR text to stdout.
 
 function read_file(path: pointer) -> pointer {
+  let unsaved = stdin_file_serve(path)            # --stdin-file: the buffer stands for its file (stdin_file.ludic)
+  if unsaved != null { return unsaved }
   let f = file_open(path, "rb")
   if (f == null) { return null }
   file_seek(f, 0, 2)