Make the sep-compile == combined-compile output equivalence a standing
regression test — the last criterion before M4 can delete the combined.ww
embedding model.
989_c6soak_run (phase-1): Tier-A/B + same-leaf collision soak. Two real
roots (utf8: encoding.utf8 dotted-path + strings; collide: strings.contains
+ bytes.contains) built both ways with isolated cold WW_PKGCACHE; asserts
combined-run-exit == sep-run-exit on both drivers, cs==ww per-pkg .s/.wwi,
and two distinct collision labels.
994_w6c_ww (phase-2): Tier-C folded into the existing w6c byte-id oracle.
A sep-built w6c emits byte-identical .s to a combined-built w6c on all five
bootstrap targets (w6c/wwdump/w6a/w6l/ww .combined.ww); .wwi is in the
compare set. The tool binaries themselves differ by a benign constant
link-layout delta — the oracle is tool OUTPUT, not tool-binary identity.
Test-only; the five wwstage binary pins are unchanged.