certbot: certs/ links into /etc/letsencrypt, mounted at the same path; the backup follows them

C-A1, C-Q4, D-guide:258, :291, :722. certbot's live/<host>/*.pem are
relative links into ../../archive/<host>/ (eff-certbot docs, "Where are
my certificates?": point a server at them "or create symlinks"). The
guide had `ln -s /etc/letsencrypt/live/<host> certs` and the nginx
fragment mounted live/<host> alone: inside the container the links led
into a directory it did not have - postfix-config.sh's [ -f ] false, no
copy, Postfix without a certificate - and the panel's backup, reading
certs/ through /selfpost-deploy, skipped links silently.

Now certs/fullchain.pem and certs/privkey.pem are links to
/etc/letsencrypt/live/<host>/, and /etc/letsencrypt is mounted read-only
at the same path: a commented line in deploy/docker-compose.yml for the
Apache scenario, mounted in the nginx fragment (./nginx/certbot-etc). The
guide's steps add certbot's own commands for a server that is not root -
chmod 0755 live archive, chgrp 998 + chmod 0640 the key, which certbot
keeps on renewal - so the panel reads them (Health, backup). Postfix's
side follows links already ([ -f ], cp, cmp, openssl). The vhost comment
says the same. The backup table: links are followed by the panel's
backup; a stopped tar stores them as links unless -h (GNU tar).

internal/backup: addTree follows, for certs/ only, a link to a regular
file and archives that file under the link's name; a link to nothing
reachable is an error naming it and the mount.

Tests: TestCertsLinksAreFollowed (certs/ -> live/ -> archive/, the
archive holds the files; the tree gone, Check names the dangling link;
Linux). Stand (2026-10-15, make e2e, exit 0): the stand mounts
./letsencrypt at /etc/letsencrypt; new certbot_layout_followed puts a new
pair into letsencrypt/archive/, relative links in live/, absolute links
in certs/, recreates the container: 465 serves the new serial, Health
names no renewal waiting, and the full backup holds certs/*.pem as
regular files with the archive's bytes. go vet and go test ./... pass on
the server (24 packages); the Linux-only tests of this session run there
and pass.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/apache/selfpost-vhost.conf

@@ -7,11 +7,13 @@
 # add the SSLCertificateFile/SSLCertificateKeyFile directives and a :80 -> :443
 # redirect vhost, and renews in the background via its own timer. The resulting
 # PEM files land at
-# /etc/letsencrypt/live/mail.example.com/{fullchain,privkey}.pem on the host —
-# bind-mount that directory read-only into the SelfPost container (see
-# ../docker-compose.yml, the `./certs:/etc/postfix/tls:ro` volume) so Postfix
-# can present the very same certificate on 465/587. One certificate, two
-# consumers — no separate cert just for the panel.
+# /etc/letsencrypt/live/mail.example.com/{fullchain,privkey}.pem on the host,
+# as links into ../../archive/. Link certs/fullchain.pem and certs/privkey.pem
+# to them and mount /etc/letsencrypt read-only at the same path (see
+# ../docker-compose.yml and docs/guide.md, "Reverse proxy") so Postfix can
+# present the very same certificate on 465/587. Mounting live/mail.example.com
+# alone gives the container links into a directory it does not have. One
+# certificate, two consumers — no separate cert just for the panel.
 
 <VirtualHost *:443>
 	ServerName mail.example.com