feat: expand mailbox evidence scanner

docs/email-evidence-canon.md

@@ -46,3 +46,19 @@ coordination runtime decides whether those facts satisfy a coordination case.
 - Human reply does not prove legal acceptance.
 - Unknown return messages remain visible.
 - Scanner and proxy interactions must stay below identity-bound interaction.
+
+## Endpoint Quality Hints
+
+Endpoint quality rows are diagnostic state, not verdicts:
+
+| Evidence | Quality hint |
+| --- | --- |
+| Hard bounce or final failure | `reachability = unreachable`, `last_failure_at` |
+| Soft bounce or delayed delivery | `reachability = degraded`, `last_failure_at` |
+| Complaint | `suppression_state = suppressed` |
+| Unsubscribe | `suppression_state = opted_out` |
+| Human reply | `last_success_at` |
+| Out-of-office | `reachability = uncertain`, `last_auto_reply_at` |
+
+These hints can guide future suppression and review workflows, but they do not
+prove human awareness, authority, payload access, or coordination success.