ww: preserve original environment for directory tests

docs/spec.md

@@ -770,6 +770,17 @@ compatibility route. It does not apply to build tools, `ww build`, `ww run`,
 compile-only or assembly-only test requests, no-test products, or later direct
 execution of a retained binary.
 
+An executed directory product otherwise receives the caller's original Unix
+environment, not the build plan's tool environment. The snapshot keeps the
+first occurrence of each normal case-sensitive `key=value`, omits later normal
+duplicates and raw empty entries, and retains every nonempty malformed entry in
+order. It then applies only the effective `PATH` above and the package `PWD`.
+Consequently caller `LC_ALL`, `TMPDIR`, empty-valued variables, case-distinct
+keys, and arbitrary variables remain visible to production or test-only
+initialization and test bodies. The compiler, assembler, archiver, linker, and
+coordinator scratch continue to use their separate build-plan locale and
+temporary directory.
+
 The same coordinator-executed product reads standard input from the null
 device. Its first read observes EOF regardless of the terminal, pipe, or file
 connected to the invoking command. Each parallel product owns a separate null