docs: REPORT — confirm inline CID image renders in Gmail (Resend preview unreliable)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

REPORT.md

@@ -82,6 +82,16 @@ Test count: **+~17** controller test functions (mailrelay 9, stacks/mailenv 8);
   additionally exercise that app's own SMTP client (already spike-proven) — recommended as the final manual
   smoke once the catalog sync has the new templates.
 
+- **Inline CID image — confirmed rendering in the real client (Gmail):** a well-formed
+  `multipart/related; type="text/html"` message with a CID-referenced inline PNG, sent through the same
+  pipeline, **renders inline in the Gmail inbox** (Resend "Delivered", From `vaultwarden@felhom.eu`,
+  signed-by `felhom.eu`, TLS). NOTE: Resend's dashboard *preview pane* unreliably shows CID images as a broken
+  `attachment-0` even when the delivered mail renders correctly — validate against a real inbox, not the Resend
+  preview (as the spike did). An earlier synthetic test that used Python's `MIMEMultipart("related")` (which
+  omits the `type="text/html"` container param) was filed by Resend's parser as a loose attachment and broke —
+  that was a malformed *test message*, not a pipeline defect; real app mailers (e.g. Vaultwarden) emit a
+  well-formed related part and render correctly. No code change resulted.
+
 > **Demo box state:** global app-email left **ON** on guest 9201 (the validated working state). No customer apps
 > have the per-app toggle on, so nothing else changed.