Whole row var issue

I had Claude code look for bugs in new Postgres 19 features. It
authored the test case added by the attached patch. The test fails for
me on master (but not on 18) as follows:

# SELECT x.m0, x::text FROM t_missing_wholerow x ORDER BY 1;
# - m0 | x
# -----+------------
# - 40 | (5,,40,41)
# - 40 | (6,,40,41)
# + m0 | x
# +----+----------
# + 40 | (5,,,41)
# + 40 | (6,,,41)
# (2 rows)

As you can see, when run on master the query shows m0 with the value
40 when it is read as a column (which is correct). However, the same
query also incorrectly shows that m0 contains NULL values in each
whole row value. Obviously, m0 should have the same value within each
row (in this case 40, which comes from "ADD COLUMN m0 int NOT NULL
DEFAULT 40"), regardless of how it is queried or how the underlying
value is represented on disk.

CC'ing David Rowley, because git bisect indicates this test case
starts failing at commit c456e3911.

--
Peter Geoghegan