fix(metadata): preserve canonical PowerPC subject identity

docs/rust-binaries.md

@@ -165,3 +165,8 @@ Package and dependency counts are checked against the minimum required JSON
 representation before graph allocation or schema cloning. Oversized graphs
 report the output byte budget; the compiler-path capacity reports
 `maximum_rustc_hashes` in hashes, independently of byte limits.
+
+Reader architecture names remain verbatim in the report. Evidence subjects use
+the recognized canonical family: `386` maps to `x86`, `amd64` to `x86_64`, and
+`ppc` to `powerpc`. Unknown families such as `ppc64` remain unknown rather than
+being inferred from a related spelling.