audit: stage 2c - the sender check reads From: as OpenDKIM does (owner's decision)

Owner, 2026-10-14, after reading OpenDKIM's source together
(dkim_mail_parse, called in mlfi_eoh on the first From:; SenderHeaders is
unset in build/opendkim.conf): "Да" to porting the parser so that the check
decides by the address OpenDKIM will take. The scan of the display name and
comments for another sender of the server - a guard against two parsers
parting ways, and the reason L8 is half closed - then goes.

New stage 2c (three lines) after 2.5.1 and before stage 3: the port from
the version the image runs, checked against OpenDKIM on the stand with
generated lines, then docs and wording. Stages 3 and 4 move to 2.5.3 and
2.5.4 (development.md's planned cuts). Plan 65 lines, roadmap 30/65.

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

docs/roadmap.md

@@ -42,7 +42,7 @@ in `git log` and [CHANGELOG.md](../CHANGELOG.md).
 | from-header-binding | Hold a message's `From:` header against the application that sends it | shipped `2.4.0` | 9/9 | [plans/from-header-binding.md](plans/from-header-binding.md) |
 | panel-redesign | Panel redesign (accepted mockups, design contract) | shipped `2.0.0` | 27/27 | [plans/panel-redesign.md](plans/panel-redesign.md) |
 | schema-squash | Squash SQLite migrations into a 2.x baseline | built in panel-redesign (stage 1) | — | [plans/panel-redesign.md](plans/panel-redesign.md) |
-| audit-2026-10-12 | Follow-ups of the 2026-10-12 full-tree code audit, seven stages | in progress (stage 0 shipped `2.4.2`, stages 1+2 `2.5.0`; next stage 2b → `2.5.1`) | 30/62 | [audit-2026-10-12.md](audit-2026-10-12.md) |
+| audit-2026-10-12 | Follow-ups of the 2026-10-12 full-tree code audit, seven stages | in progress (stage 0 shipped `2.4.2`, stages 1+2 `2.5.0`; next stage 2b → `2.5.1`) | 30/65 | [audit-2026-10-12.md](audit-2026-10-12.md) |
 
 **Recommended order** (not binding; owner, 2026-10-09: feature order follows
 development convenience): **panel-redesign** shipped as `2.0.0` (2026-10-11) and