pg_rewind: confused about recovery.conf/restore_command

Pg 9.6.6 on Ubuntu.

I have a master and a streamer/standby. Streamer runs wal_log_hints=on,
archive_mode=always, archive_command='send it to some repo'.

Promote streamer and make some changes to it.

Halt and run pg_rewind as per my understanding of the docs.

Rewind immediately errors out due to missing wal segments on target
system (streamer).

Same target has a recovery.conf at this point w/restore_command that
knows how to fetch wal segment from 'some repo'. ISTM rewind is
supposed to use it to fetch wals.

Success in same attempt if streamer has archive_command='' thus
retaining wals inside data directory.

Running pg_rewind with --progress --debug shows no indication that it's
trying to use restore command and in fact chmod 0 on the recovery.conf
file makes no difference either.

Am I dreaming that this should work? :-)

Thanks

--
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres(dot)consulting(at)comcast(dot)net
p: 312.241.7800