fix: keep unfolded messages readable when the conversation is read again after a send

lib/__tests__/held-send.test.ts

@@ -61,4 +61,13 @@ describe('echoes of sent replies', () => {
     expect(mergeEchoes([...server, { id: 'c' } as Email], [...server, echo]).map((e) => (e.sentEcho ? 'echo' : e.id))).toEqual(['a', 'b', 'c']);
     expect(mergeEchoes(server, [...server, echo]).map((e) => (e.sentEcho ? 'echo' : e.id))).toEqual(['a', 'b', 'echo']);
   });
+
+  it('keeps the body of a message already unfolded', () => {
+    const loaded = { id: 'a', keywords: {}, mailboxIds: { inbox: true }, bodyValues: { 1: { value: 'Hi' } } } as unknown as Email;
+    const listed = { id: 'a', keywords: { $seen: true }, mailboxIds: { archive: true } } as unknown as Email;
+    const [merged] = mergeEchoes([listed], [loaded]);
+    expect(merged.bodyValues).toEqual(loaded.bodyValues);
+    expect(merged.keywords).toEqual({ $seen: true });
+    expect(merged.mailboxIds).toEqual({ archive: true });
+  });
 });

lib/held-send.ts

@@ -97,6 +97,15 @@ export function addEcho(conversation: Email[], echo: Email): Email[] {
  */
 export function mergeEchoes(server: Email[], shown: Email[]): Email[] {
   const ids = new Set(server.map((e) => e.id));
+  const byId = new Map(shown.map((e) => [e.id, e]));
+  // The thread read carries list properties only: a message already unfolded
+  // keeps the body it loaded, with the server's flags and folders.
+  const merged = server.map((e) => {
+    const had = byId.get(e.id);
+    return had?.bodyValues && !e.bodyValues && !had.sentEcho
+      ? { ...had, keywords: e.keywords, mailboxIds: e.mailboxIds }
+      : e;
+  });
   const echoes = shown.filter((e) => e.sentEcho && !ids.has(e.id));
-  return echoes.length ? [...server, ...echoes] : server;
+  return echoes.length ? [...merged, ...echoes] : merged;
 }