ww test: omit marker for empty list results

docs/test-system-v2.md

@@ -219,6 +219,16 @@ every `-j` level, and `-j 1` — the default — matches the former sequential
 run loop exactly. Measured on the 31-package `lib/...` walk:
 7.0s sequential, 2.4s at `-j 4`.
 
+List mode uses that same product process and initialization boundary but starts
+no per-test child. The shared language harness emits only selected qualified
+test names, one per line in descriptor order. A valid filter selecting no tests
+therefore produces no harness list bytes, no `[no matches]` marker, and no
+accounting while the process returns success; the coordinator continues with
+the package's normal `ok` result. Ordinary non-list zero-selection execution
+retains its `[no matches]` marker and accounting. Concurrent products keep
+independent empty or nonempty captures, and persistent work never caches a test
+result.
+
 Directory test binaries are always linked under the coordinator's temporary
 product root. `-c` independently requests a caller-visible executable copy and
 suppresses execution. `-o` independently requests a copy and still runs the