test: prove package-source test execution cwd

docs/test-system-v2.md

@@ -225,10 +225,32 @@ including a combined internal/external directory:
 the coordinator rejects a multi-package fan-out ("cannot use -o with
 multiple packages", Go's `go test -o` rule), and `-o` without `-c` is
 rejected at the driver ("needs -c for a package target") because a plain
-run always executes from the temp root. Without `-c`, it removes the
+run leaves no caller-owned artifact for `-o` to name. Without `-c`, it removes the
 temporary binary and scratch with its workspace. The language runtime
 owns individual `@test` functions.
 
+Every actually executed directory product gives its single generated binary
+the product's canonical absolute physical source directory as child cwd. A
+fresh per-run environment removes inherited exact uppercase `PWD` entries and
+appends one `PWD` with that same directory, matching Go 1.26.5's observable
+`AppendPWD` plus last-value-wins `os/exec` behavior. The coordinator's cwd and
+environment do not change, and overlapping `-j N` children share no writable
+environment vector. Relative ordinary data, `testdata`, and writes resolve in
+the tested directory. Production and test-only dependency initializers run in
+that product process and see its directory; separately testing the dependency
+creates a separate process using the dependency directory. Equivalent direct,
+recursive, redundant, absolute, and root-symlink spellings converge before
+this runtime field is assigned.
+
+The physical directory remains distinct from exact dotted package identity and
+from production, internal, external, recompiled, support, and generated-main
+action identity. Only product execution uses it. Compiler, assembler, archiver,
+linker, support, and generated-main commands retain their build-plan cwd and
+environment. `ww build`, `ww test -c`, `-c -o`, and no-selected-test products
+start no test child. A published test binary run directly and the raw
+single-file compatibility path inherit the user's cwd/environment and contain
+no forced package-directory behavior.
+
 Before package grouping, both directory drivers and the shared recursive
 coordinator apply Go 1.26.5's filename OS/architecture rule for WW's fixed
 `linux/amd64` target. The basename stem ends at its first dot; a final `_test`
@@ -291,6 +313,23 @@ exact-argv, command, and persistent-workdir observers, the package suite proves
 archive-only link argv and exact warm/rejection-state behavior without
 duplicating those broader mechanisms in this observer.
 
+The same package owner contains the focused
+`directory_test_execution_working_directory` observer. It constructs
+independent temporary directories from an unrelated caller cwd and compares
+Cstage/WWstage output for production/internal/external/combined and every
+test-only shape; production and test-only dependency initialization;
+recompiled external self-import; duplicate inherited `PWD`; ordinary data,
+`testdata`, and relative writes; direct/recursive/redundant/absolute/symlink
+roots; reversed request and creation order; serial and parallel products;
+filters, list, and no-match execution; failure and timeout; build/no-test and
+compile-only paths; direct published binaries and raw single-file execution;
+build-tool cwd/argv/environment; persistent data-only reuse and artifact bytes;
+and deterministic post-build child-`chdir` failure isolated from a successful
+sibling. It pads the inherited environment beyond former fixed observer sizes,
+requires one appended product `PWD`, and sweeps the persistent workdir for
+staged residue. Command-global bounded-memory failure remains independently
+owned by `allocation_failure_is_command_global`.
+
 The same package owner contains the focused
 `platform_filename_source_selection` observer. It independently generates the
 suffix matrix, production/internal/external sources, wrong-target import and
@@ -387,6 +426,14 @@ real directory test products always run, while no-selected-test directories do
 not create a process. The byte-identity and bootstrap gates keep building on
 fresh scratch. `make clean` reclaims every workdir under `out/`.
 
+Directory-product cwd and `PWD` are request-time child-process metadata, not
+persisted action inputs or results. A runtime directory-entry failure therefore
+does not erase a successfully committed compilation generation. Changing only
+ordinary fixture data causes no unit/export/assembly/object/archive/main/binary
+change and no producer work beyond the same established warm final relink,
+while the next always-run product observes the new bytes. Build workdir format
+remains 18, test workdir format remains 19, and semantic storage remains 3.
+
 Fold keys and first-spelling tables are request-only loader state and are never
 stored in a workdir. They do not alter successful unit bytes, action/storage
 keys, or tool records, so build format 18, test format 19, and semantic storage