system: prototype self-hosted native builds

docs/GUIX_DIFFERENCES.md

@@ -263,6 +263,17 @@ The intent is:
 
 Compared with Guix, this is conceptually similar to keeping development-oriented state separate from the main runtime identity, but Fruix currently expresses it as a system-attached development overlay rather than through Guix's broader profile/tooling model.
 
+Fruix now also has a narrow guest self-hosted native-build prototype helper at:
+
+- `/usr/local/bin/fruix-self-hosted-native-build`
+
+That helper does **not** just reuse the whole exported development shell wholesale.  The validated prototype had to sanitize development-oriented variables such as `MAKEFLAGS`, `CPPFLAGS`, `CFLAGS`, `CXXFLAGS`, and `LDFLAGS` before `buildworld`, because those are convenient for smaller development tasks but can poison the FreeBSD world/kernel bootstrap path.
+
+The practical Fruix takeaway is:
+
+- the development overlay makes native base work possible inside the system
+- but real guest self-hosted base builds still need their own stricter build contract
+
 ## Where Fruix is intentionally trying to improve on Guix's representation
 
 Fruix is not trying to improve on Guix's core semantics. Guix already got those right.