test: prove package-source test execution cwd

docs/spec.md

@@ -645,6 +645,27 @@ mixed directories are accepted from their selected test files. A directory
 with no selected test file validates ordinary production but creates no test
 support, generated main, link, binary, result, or process.
 
+When `ww test` executes a directory-owned product, the child process working
+directory is that product's canonical absolute physical package source
+directory. Its per-run environment has exactly one effective uppercase `PWD`,
+with that same value. The physical source directory is execution context, not
+canonical package identity: it does not enter dotted identity, import binding,
+action identity, mangled symbols, `.wwi`, artifacts, or persistence keys.
+Production, internal-test, external-test, recompiled-for-test, support, and
+generated-main actions in the product share the one process context while
+remaining separate actions. Reachable dependency initialization consequently
+observes the tested product's directory; a dependency tested as its own product
+observes its own directory.
+
+The coordinator does not change its own cwd or environment. Parallel products
+receive independent child environments and each uses its own source directory.
+Relative ordinary files, `testdata`, and writes resolve there for every
+executing filter or list path. `ww build`, directory `ww test -c` (including
+`-c -o`), and a no-selected-test directory execute no test child and receive no
+execution-directory effect. A published test binary invoked directly, and the
+raw single-file compatibility route, inherit the user's invocation cwd and
+environment; no package directory is embedded or forced by the binary.
+
 ---
 
 ## 11. Concurrency (reserved)