ww test: omit marker for empty list results

docs/spec.md

@@ -803,6 +803,17 @@ linker, and other build failures retain their diagnostic standard-error
 channel; build-action stdout and stderr remain separate. Parallel products own
 independent captures and are still emitted in canonical product order.
 
+List mode starts the same directory-owned product and therefore performs its
+ordinary package initialization, but it does not start any selected test child.
+The harness emits exactly one newline-terminated qualified name for each test
+selected by the command's filters, in descriptor order. If the selected set is
+empty, the harness emits no list payload, no `[no matches]` sentinel, and no
+accounting, and returns success; the coordinator still emits the ordinary
+successful package result. This does not alter non-list execution: a valid
+filter selecting no tests continues to emit `[no matches]` and the
+discovered/selected/started/completed accounting. A retained binary invoked
+directly has no coordinator package result.
+
 After those ordered results, an ordinary explicit `ww test` request that records
 an attributable setup, build, or execution failure emits exactly one standalone
 `FAIL\n` on standard output. The line is command-owned: it follows even a later