docs: clarify mailbox packet flow

minions/mail/README.md

@@ -42,6 +42,15 @@ Examples:
 4. gate owner records verdict if needed
 5. `PM` mirrors durable state into shared docs and same-day chat summary
 
+## ASCII Flow
+
+```text
+sender        -> opens packet -> writes request.md
+recipient     -> reads request -> writes response.md
+gate owner    -> reviews       -> writes verdict.md (if needed)
+PM            -> curates       -> updates shared docs + daily chat summary
+```
+
 ## Staged Rollout Rule
 
 - already-open legacy chat packets may remain where they are until they close