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>

test/e2e/smtp_client.go

@@ -161,7 +161,8 @@ func attemptSend(a sendAttempt) sendResult {
 // waited for the panel could still race a not-yet-listening smtpd. A bare TCP
 // connect is not enough: Docker's port proxy accepts on the host side before
 // anything listens in the container and then resets the connection, which is
-// how the level-1 rate-limit case once took a reset for its limit.
+// how the level-1 rate-limit case once took a reset for its limit (seen on the
+// stand, date not recorded; Docker's documentation does not describe it).
 func waitForSMTPSReady(timeout time.Duration) error {
 	return waitFor("smtps port to greet", timeout, 300*time.Millisecond, func() (bool, error) {
 		conn, err := tls.DialWithDialer(&net.Dialer{Timeout: 2 * time.Second}, "tcp", smtpsAddr, &tls.Config{
@@ -232,8 +233,12 @@ func mailTwiceOnOneConnection(login, password, from string) [2]error {
 // the panel has just created is written into the sender map and Postfix is
 // reloaded, and an smtpd that was idle from before the reload can still take
 // a connection in the second that follows and answer 553 "not owned by user"
-// (seen on the stand; two seconds after the save it no longer happened, at 0,
-// 10, 40 or 110 s of waiting). It goes as far as RCPT and then RSET, so no
+// (seen on the stand, date not recorded; two seconds after the save it no
+// longer happened, at 0, 10, 40 or 110 s of waiting). Postfix 3.7.11: an smtpd
+// reads the texthash map once, when it starts (html/DATABASE_README.html,
+// "texthash"), and one from before the reload exits only when it next sees
+// master's status pipe closed (src/master/multi_server.c,
+// multi_server_abort()). It goes as far as RCPT and then RSET, so no
 // message is sent and no row is written. Only that 553 is waited out, for 15
 // s at most; any other answer fails at once.
 func waitForSenderMap(login, password, from string) error {