proto, memoryd: no line of an entry may start with §, and headers are exact

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/memoryd/tests/notes.rs

@@ -59,3 +59,21 @@ fn a_time_is_shown_to_the_minute() {
         "2026-09-24T20:14Z"
     );
 }
+
+#[test]
+fn a_noted_header_with_an_unknown_last_part_is_not_a_header() {
+    let text = "§ noted 2026-09-24T20:14Z in session mm-s1 · private · untrusted\nfirst\n§ noted 2026-09-24T20:15Z in session mm-s2 · private · trusted\nsecond\n";
+    let notes = parse(text);
+    assert_eq!(notes.len(), 1);
+    assert_eq!(
+        notes[0].kind,
+        Kind::Noted {
+            class: DataClass::Private,
+            untrusted: true,
+        }
+    );
+    assert_eq!(
+        notes[0].text,
+        "first\n§ noted 2026-09-24T20:15Z in session mm-s2 · private · trusted\nsecond"
+    );
+}