milter, postfix, app, domain: cite the source of what they rely on (assumptions part B)

Comments only, no behaviour changed. go-milter v0.4.1 (session.go: one
session per connection, replaced after a non-continue reply; macros per
stage), Postfix 3.7.11 (milter8.c, smtpd_check.c
reject_auth_sender_login_mismatch(), mail_addr_find.c, showq_compat.c,
mail_conf_time.c, mail_params.h), Cyrus SASL 2.1.28 (saslpasswd.c,
plugins/sasldb.c: deleting a missing login is not an error), OpenDKIM
2.11.0~beta2 (opendkim-db.c, opendkim-genkey), Berkeley DB 5.3 db_dump,
rspamd 3.11.0. Comments that claimed what the source denies are corrected
(sasldb keeps the password as given, not hashed; an embedded newline is
kept, not truncated; rspamd sorts symbols by absolute weight); fixtures say
seen or composed. The sender check's From: parsing gets no citations: it is
replaced by the port of OpenDKIM's dkim_mail_parse next.

Contradictions left for their own commits: B-G5 cleanAddress, B-PS1 first
key wins, B-PQ1 the forced-expire flag, B-PQ10/PQ11 Postfix's time units.

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

internal/postfix/postfix.go

@@ -59,6 +59,9 @@ type Binding struct {
 // architecture.md § Mail path) — their logins are merged onto a single line as
 // a comma-separated list, which is how Postfix expects multiple owners of one
 // sender.
+//
+// Postfix 3.7.11, src/smtpd/smtpd_check.c, reject_auth_sender_login_mismatch():
+// the value is split into owners with mystrtok(&cp, CHARS_COMMA_SP).
 func (p *Postfix) RebuildSenderLoginMaps(bindings []Binding) error {
 	content, err := renderSenderLoginMaps(bindings)
 	if err != nil {
@@ -128,6 +131,12 @@ func appendUnique(list []string, v string) []string {
 // end it, the comma that separates values, the colon a lookup key cannot carry,
 // and the backslash. A login additionally may not carry "@" — that would make it
 // look like an address.
+//
+// Postfix 3.7.11, src/util/dict_thash.c, dict_thash_open(): the key ends at
+// the first blank outside quotes, a backslash escapes the next character;
+// src/util/readlline.c: a newline ends the line (one that starts with a blank
+// continues the one before); the owners split on comma and blank (see
+// RebuildSenderLoginMaps).
 const (
 	senderMapAddressForbidden = " \t\r\n,:\\"
 	senderMapLoginForbidden   = " \t\r\n,:@\\"
@@ -161,6 +170,15 @@ func assertMapSafe(address, login string) error {
 //
 // Arguments are fixed literals — no user input is interpolated into the command,
 // and it never goes through a shell (security.md).
+//
+// Postfix 3.7.11, conf/postfix-script, start-fg: a process that is not PID 1
+// runs "$daemon_directory/master -s" as its child, and src/master/master.c
+// puts that master in a session of its own (setsid()). "reload" sends the
+// master SIGHUP; src/master/master.c calls master_refresh(), and
+// master_conf.c, master_config(), lets the running children "commit suicide
+// whenever it is convenient" while new ones get the new configuration; a
+// texthash table is read into memory once per process
+// (README_FILES/DATABASE_README).
 func reloadViaSupervisor() error {
 	return supervisor.Start("postfix-reload")
 }