9proc core becomes a backend of cloud9.fs; engine gains optional features

9proc's own fid table, walk loop and dir-read engine are replaced by
cloud9.fs.Server; the tree (static, vars, providers) is served through the
engine's Req/Reply contract with node ids that keep the old qid scheme.
Providers may answer later by returning error.Again (parked in the engine,
retried each step, Tflush -> EINTR); no new files are exposed.
Engine (backward compatible, all opt-in via Backend.features / Options):
create, remove, wstat, reference accounting for backends that count
handles, a salted fid index, name_capacity 0 (names from getattr),
Reply.ename for backend-chosen error text, Attr.path/version/atime.
Engine-level error strings and the 217-byte msize floor now apply to 9proc;
tests updated accordingly.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/README.md b/README.md
index 4c4d24c..01e35a5 100644
--- a/README.md
+++ b/README.md
@@ -98,7 +98,8 @@ lists the steps). New related programs follow the same layout.
   `web/static/`). Always built; steps `serve`, `web`, `http-test`, `e2e`.
 * [`9proc/`](9proc/README.md) — a 9P debug/introspection server as
   a library (module `9proc`, exported next to `cloud9`; freestanding
-  core, Linux debug layer) and its demo binary `9proc-demo`.
+  core that is a backend of `fs.Server`, Linux debug layer) and its demo
+  binary `9proc-demo`.
   `-D9proc=[bool]`; steps `9proc`, `9proc-test`,
   `9proc-check-freestanding`, `9proc-debug-test`,
   `9proc-debug-itest`, `9proc-adv`.