ww: preserve original environment for directory tests

docs/test-system-v2.md

@@ -305,6 +305,16 @@ the private run and install only after success. Compile-only, assembly-only,
 no-test, rejected, and build requests start no test process and therefore have
 no test-PATH state.
 
+For a directory product, the rest of the child vector is a Go-like snapshot of
+the caller environment rather than the build-tool environment: the first
+case-sensitive occurrence of every normal `key=value` survives, later normal
+duplicates and raw empty entries do not, and nonempty malformed entries remain
+in order. Only the effective `PATH` and package `PWD` are then appended.
+Caller `LC_ALL`, `TMPDIR`, empty values, case-distinct keys, and arbitrary
+variables therefore reach dependency initialization and selected tests.
+Build-plan compiler, assembler, archiver, linker, and scratch environments keep
+their existing pinned locale and request-private temporary directory.
+
 Every such product also receives an independently opened null device as fd 0.
 Caller terminal, pipe, and file bytes remain with the coordinator; serial and
 parallel products observe immediate EOF rather than consuming a shared input