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/traefik/docker-compose.traefik.yml

@@ -6,7 +6,9 @@
 #
 # 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 ./traefik/...):
+# FIRST -f file, i.e. deploy/, which is why paths below are ./traefik/... -
+# 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 traefik/docker-compose.traefik.yml up -d
 
@@ -25,7 +27,10 @@ services:
       # Traefik only proxies the panel; it never sees the mail ports.
       # These live on the selfpost service (not traefik's) because the
       # docker provider reads routing labels off the container being routed
-      # to, not off traefik itself.
+      # to, not off traefik itself. (doc.traefik.io/traefik/v3.1/providers/
+      # docker/, "Routing Configuration": "Traefik uses container labels";
+      # with exposedByDefault=false only containers labelled
+      # traefik.enable=true.)
       - traefik.enable=true
       - traefik.http.routers.selfpost.rule=Host(`mail.example.com`)
       - traefik.http.routers.selfpost.entrypoints=websecure

deploy/traefik/extract-cert.sh

@@ -6,6 +6,13 @@
 # by SelfPost/Postfix.
 #
 # Requires jq. Usage: ./extract-cert.sh <acme.json path> <domain> <output dir>
+#
+# The layout is not documented (doc.traefik.io/traefik/v3.1/https/acme/ says
+# only "JSON file"); read in Traefik v3.1.0: pkg/provider/acme/local_store.go
+# keeps map[resolver name]*StoredData, store.go StoredData{Account,
+# Certificates}, provider.go Certificate{domain, certificate, key} with the PEM
+# as []byte - base64 in JSON (Go encoding/json). "le" is the resolver
+# docker-compose.traefik.yml names.
 set -eu
 
 ACME_JSON="${1:?path to acme.json}"