volt: q132 verifier names the self-consistent empty render (9th leg)

A document rendered after the LEGS table broke is accepted as current by
the pre-fix parser with no gate column at all, so mutant-doc-drifts alone
would pass a tree that never had the column. The new leg reads that same
mutant's fresh render and requires rc 0 with a '-' cell, pinning the
failure mode the repair removes.

Measured: q132_verify.py 9 legs, 0 fault, rc 0.

wizard-work/volt/q132_verify.py

@@ -147,6 +147,12 @@ def main():
         "rc=%d gate=%r" % (rc_m, mcell))
     leg("mutant-doc-drifts", rc_c == 1 and "DRIFT" in out_c,
         "rc=%d first=%r" % (rc_c, (out_c or err_c).splitlines()[:1]))
+    # ...and a document rendered AFTER the breakage would have been current
+    # and leg-less: rc 0 from the same parser, with no gate column at all.
+    rc_s, out_s, err_s = run([sys.executable, mutant, "--repo", fx,
+                              "--check", mdoc])
+    leg("mutant-self-consistent", rc_s == 0 and gate_cell(mtext) == "-",
+        "rc=%d (a fresh empty render is 'current' to the pre-fix parser)" % rc_s)
 
     # -- 3. a LEGS that is not data is named, not rendered as `-` -----------
     fx2 = os.path.join(td, "fx2")