build, deploy, inbound, dmarc, backup, e2e: cite the source of what they rely on (assumptions part C)

Comments only, no behaviour changed. Each main.cf/master.cf parameter the
build sets, the wrapper's and the reload hook's reliance on Postfix 3.7.11
(postfix-script, master.5, postconf.5, cleanup_init.c, smtpd_peer.c,
README_FILES), supervisor 4.2.5 (process.py, options.py, events.rst),
logrotate 3.21.0, OpenDKIM's config, Cyrus SASL's sasldb, rspamd 3.11.1
(milter_headers.lua, multimap, the map watcher), Docker Compose, CoreDNS
and certbot now say where that is written. Measurements already there stay
measurements ("date not recorded" where none was); hand-composed fixtures
say so.

Contradictions left for their own commits: C-P31 cleanup's size limit,
C-P42 master outside supervisor's signal, C-V5/V6 startsecs, C-V10,
C-S3/Q3 sasldb written in place, C-Q4/A1 certbot's symlinks, C-R7 rspamd
skips local clients but the signature routine does not, C-P8, C-R4, C-R12,
C-M7, C-E2, C-K8/K9, C-D1.

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

deploy/caddy/docker-compose.caddy.yml

@@ -11,10 +11,18 @@
 # storage detail, not a documented public API — VERIFY the exact path against
 # the Caddy version you deploy (`docker compose exec caddy find /data/caddy/certificates -name '*.crt'`)
 # before wiring it into the volume mount below.
+# Read in the source (caddyserver/certmagic, storage.go, KeyBuilder.SiteCert():
+# certificates/<issuer key>/<domain>/<domain>.crt; acmeissuer.go, issuerKey():
+# the CA URL's host and path, "acme-v02.api.letsencrypt.org-directory" for Let's
+# Encrypt). caddy/modules/caddytls/automation.go, DefaultIssuers(): ZeroSSL is a
+# second issuer only when an email is configured, and the Caddyfile below sets
+# none. Read at the projects' master of 2026-10-14: `caddy:2` is a moving tag.
 #
 # Merge with the base file — run this from the deploy/ directory (Compose
 # resolves every relative path in both files against the directory of the
-# FIRST -f file, i.e. deploy/, which is why paths below are ./caddy/...):
+# FIRST -f file, i.e. deploy/, which is why paths below are ./caddy/... -
+# docs.docker.com/compose/how-tos/multiple-compose-files/merge/: "Paths are
+# evaluated relative to the base file"):
 #
 #   docker compose -f docker-compose.yml -f caddy/docker-compose.caddy.yml up -d