lib: refresh I/O architecture guidance

lib/CLAUDE.md

@@ -59,12 +59,12 @@ Modules with intentional divergence:
   import-free time leaf. This is what lets `errors` import `os` (for
   `os.errno` / `os.strerror`) without a cycle, mirroring Hare's
   `sys ← errors`, `sys ← io`.
-- `lib/io` keeps the ww-specific `stream` struct (vtable of fn
-  pointers, no closures, no methods). The Hare `io::handle` family
-  needs language features we don't have yet.
-- `lib/bufio` and `lib/sort` will be redesigned to Hare's
-  `scanner` / `cmpfunc` shapes; the present minimal forms are
-  placeholders until then.
+- `lib/io` keeps the ww-specific intrusive vtable stream (function
+  pointers, no closures or methods) and collapses Hare's extra stream
+  pointer layer. Its `handle` is the shipped `(file | stream)` sum.
+- `lib/bufio` ships Hare-shaped buffered-stream and scanner subsets;
+  the exact supported operations and ownership rules are documented in
+  its source header. `lib/sort` still awaits its Hare `cmpfunc` shape.
 - `lib/time` and `lib/math` ship only what callers need today;
   they're not aiming for parity yet.