MAS-WP-0005-T12: gateway reads trusted A-R verdict; ticket service replies only on DMARC pass

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

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 252470@bnt-lap001
Assistant-Session: ad628c8f-4be2-4979-94c9-76c7ed6f8241

workplans/MAS-WP-0005-spec-errata-v0-1-1.md

@@ -393,7 +393,7 @@ never reject on DMARC failure. Milter failure means accept
 
 ```task
 id: MAS-WP-0005-T12
-status: todo
+status: done
 priority: medium
 ```
 
@@ -404,6 +404,23 @@ header_from}` into the event. The ticket service gets
 sends auto-replies (intake confirmation, closed notice) only when
 `dmarc == pass`. Unit tests cover forged A-R headers from other ids.
 
+- 2026-10-18 done:
+  - `mas_gateway.core.authentication_from_headers` reads only A-R headers
+    with the trusted authserv-id **above the first Received header**
+    (RFC 8601 §5). Forged copies below our hop are ignored even if the
+    MTA did not strip them. Several DKIM results count as pass if any one
+    passes.
+  - The event gets `message.authentication = {dmarc, spf, dkim,
+    header_from}` or null. `--trusted-authserv-id` works on both pipe and
+    webhook; a JSON webhook passes the provider's verdict through.
+  - Ticket service `--require-dmarc-pass`: tickets are still created and
+    mail attached, but replies go out only on `dmarc == pass`.
+  - Entrypoint: gateway `--trusted-authserv-id $DOMAIN`, ticket service
+    `--require-dmarc-pass`.
+  - Tests: own header read; forged (below Received) and foreign ids
+    ignored; no trusted id gives no verdict; reply gated off without a
+    verdict and sent on pass. 183 tests pass.
+
 ## Live check: authenticated vs forged sender
 
 ```task