docs: clarify imported nwlog simple backend layout

REDESIGN.md

@@ -1447,26 +1447,59 @@ Protocol handlers, providers, `nwconn`, `nwserv`, `nwbind`, future `nwqueue`,
 not include zlog headers or call zlog macros directly.
 
 That facade can initially keep using the existing mars-nwe logging functions,
-`stderr`, or `syslog`.  Later it may use an advanced backend.
+`stderr`, or a small vendored backend.  Later it may grow simple and advanced
+backends behind the same API.
 
-`zlog` is a good candidate for that advanced backend because it is a C logging
-library with category, format, and rule based configuration.  That model fits
-mars-nwe well: code can emit category-specific events such as `ncp`, `handoff`,
-`queue`, `directory`, `auth`, or `transport`, while the administrator decides in
-the logging configuration whether those categories go to a file, stdout/stderr,
-syslog-style output, a pipe, or an external log-forwarder path.  The zlog
-project documentation describes these three core concepts as categories, formats,
-and rules, where rules bind a category/level to an output and format.  Before
-choosing it, packaging, license compatibility, portability, and maintenance state
-still need to be verified for the target distributions.
+There are two useful backend classes:
+
+1. **Simple built-in backend.**  A tiny C backend derived from `rxi/log.c` can be
+   imported into the source tree for simple builds.  It should be treated as
+   vendored implementation code, renamed and namespaced for mars-nwe.  The base
+   upstream code only provides local-style logging primitives such as stderr,
+   file output, and callback hooks; it is not an out-of-the-box syslog, GELF, or
+   remote routing solution.  That is fine for the built-in backend, but mars-nwe
+   must adapt it for the project requirements: redaction hooks, category mapping,
+   context/correlation fields, optional file output, and any future syslog-like
+   bridge should live behind `nwlog`, not in endpoint code.
+
+   The project layout should make the imported code clearly internal, for
+   example:
+
+   ```text
+   include/nwlog_simple.h   internal/simple backend declarations, if needed
+   src/nwlog_simple.c       imported/adapted rxi/log.c-style backend
+   ```
+
+   If the backend later grows real syslog support, that can either stay in the
+   simple backend or split into `src/nwlog_syslog.c`.  Until then, avoid naming
+   the vendored `rxi/log.c` adaptation as if it already were a full syslog
+   backend.  Imported symbols such as `log_info`, `log_error`, or `log_add_fp`
+   must be renamed, hidden, or made `static` so they do not leak into the global
+   mars-nwe namespace.  Public entry points should look like
+   `nwlog_simple_init()` and `nwlog_simple_emit()`.
+2. **Advanced routing backend.**  `zlog` remains the preferred candidate for
+   administrator-controlled routing because it is a C logging library with
+   category, format, and rule based configuration.  That model fits mars-nwe
+   well: code can emit category-specific events such as `ncp`, `handoff`,
+   `queue`, `directory`, `auth`, or `transport`, while the administrator decides
+   in the logging configuration whether those categories go to a file,
+   stdout/stderr, syslog-style output, a pipe, or an external log-forwarder path.
+   The zlog project documentation describes these three core concepts as
+   categories, formats, and rules, where rules bind a category/level to an output
+   and format.
+
+Before choosing any backend, packaging, license compatibility, portability, and
+maintenance state still need to be verified for the target distributions.  The
+architecture must not depend on one backend being available.
 
 The preferred dependency shape is therefore:
 
 ```text
 mars-nwe code
   -> nwlog facade
-       -> simple built-in backend: stderr/file/syslog
-       -> optional advanced backend: zlog
+       -> builtin/simple backend: src/nwlog_simple.c from imported/adapted rxi/log.c-style code
+       -> optional syslog bridge: src/nwlog_syslog.c, if implemented later
+       -> optional advanced backend: src/nwlog_zlog.c using zlog
             -> admin-configured zlog rules/formats/outputs
 ```
 
@@ -1491,7 +1524,7 @@ to edit C-style backend internals directly:
 
 ```ini
 [logging]
-backend = zlog          ; builtin, syslog, file, zlog
+backend = zlog          ; builtin, simple, syslog, file, zlog
 level = info
 redact_secrets = yes
 config = /etc/mars-nwe/zlog.conf