A reply to a case mail becomes a note on its record

Whatever reads the mailbox publishes on portal.mail.received; portal
appends the note after checking the record exists in a bucket this
site has and the sender is the address the record itself holds. A
note never moves a case: a mailbox is the one door anyone may knock
on, so it cannot drive a state machine even if someone forges their
way past the checks. The desks show the conversation beside the case.

Tested: the address parser, every refusal (a stranger, no address to
compare, an empty reply, the same reply twice, an unknown contract),
and the whole path through a real JetStream - the note lands, the
state does not move, and no event is written.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/jetstream.rs

@@ -63,4 +63,33 @@ async fn a_submission_is_created_moved_refused_and_read_back_through_the_real_en
     let replayed = aggregates::replay(schema, "rec-1", &events).expect("replays");
     assert_eq!(replayed.state, "won");
     assert!(replayed.sequence > moved.sequence);
+
+    // A reply to the mail this record was sent becomes a note on it,
+    // through the same store the desks read - and moves nothing: the
+    // record is still where the desk left it.
+    let mut record: Answer = serde_json::from_slice(&store.get("rec-1").await.unwrap().expect("record")).unwrap();
+    let reply = portal::mail::Incoming {
+        v: portal::mail::CONTRACT,
+        id: "mail-1".into(),
+        bucket: bucket.clone(),
+        record: "rec-1".into(),
+        from: "A <A@B.example>".into(),
+        subject: "Re: your enquiry".into(),
+        text: "Thursday suits us.".into(),
+        received_ms: now + 10,
+    };
+    let note = portal::mail::note_for(&reply, &record).expect("the address matches the record");
+    record.notes.push(note);
+    store.put("rec-1", serde_json::to_vec(&record).unwrap().into()).await.expect("note stored");
+
+    let read_back: Answer = serde_json::from_slice(&store.get("rec-1").await.unwrap().expect("record")).unwrap();
+    assert_eq!(read_back.notes.len(), 1);
+    assert_eq!(read_back.notes[0].text, "Thursday suits us.");
+    assert_eq!(read_back.notes[0].from, "a@b.example");
+    assert_eq!(read_back.state, "quoted", "a reply is a note, never a decision");
+    // The same reply read twice adds nothing.
+    assert!(portal::mail::note_for(&reply, &read_back).is_err());
+    // And the event log is untouched by it.
+    let after = load_events(&js, &bucket, "rec-1").await.expect("events");
+    assert_eq!(after.len(), 3, "a note writes no event");
 }