ww package: reject non-function main declarations

docs/test-system-v2.md

@@ -268,6 +268,21 @@ check rather than part of `ww build`. Assembly-only `-S` still selects command
 actions and rejects a no-command directory request, but it performs no
 install-only destination validation or output-directory creation.
 
+Package declaration checking also precedes test execution. In a package whose
+declared name is `main`, `let main`, `const main`, `def main`, and `type main`
+are rejected by both compiler stages as `cannot declare main - must be func`
+and are not installed into package scope. The generated directory-test main is
+an independent tool-owned action and cannot mask the malformed production or
+same-package declaration: the product emits no test body output, accounting,
+or `ok` result. This condition keys only on the source-declared package name;
+a package with another declared name may export `main` even when its dotted
+path or physical leaf is `main`, and WW's supported argument/result-bearing
+function entries remain valid. The native
+`nonfunction_main_declarations_reject` observer covers all four declaration
+kinds, direct compiler ownership, build/test diagnostics, command-import
+precedence, declared-name/import identity, valid artifact bytes, cold cleanup,
+and warm work/output rollback and reuse across both stages.
+
 The retained executable is byte-identical to the temporary runnable and has
 executable mode `0777` filtered by the caller's umask, but it is never the path
 executed by the coordinator. Compile-only publication participates in the