email: group messages into conversations (Gmail-style threading)

Hybrid grouping via a new thread_id column: new mail threads exactly on
References/In-Reply-To (id is sha1(Message-Id), so a referenced id hashes to
the ancestor's own id); already-synced mail is backfilled with a
normalized-subject + counterpart key. Folder views collapse to one row per
thread with a count badge; the reader shows the thread as a collapsible stack.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/api/email/email.ts

@@ -173,10 +173,24 @@ emailRouter.get('/messages', async (ctx) => {
 
   const db = openEmailDb(email);
   try {
+    // One row per conversation: the latest message in each thread within this folder, plus the
+    // thread's message count and how many are unread. COALESCE guards any un-backfilled rows.
     const rows = db
-      .query(`SELECT * FROM emails WHERE ${folderWhere} ORDER BY date DESC LIMIT ? OFFSET ?`)
+      .query(
+        `SELECT * FROM (
+           SELECT e.*,
+             COUNT(*) OVER (PARTITION BY COALESCE(thread_id, id)) AS thread_count,
+             SUM(CASE WHEN read = 0 THEN 1 ELSE 0 END) OVER (PARTITION BY COALESCE(thread_id, id)) AS thread_unread,
+             ROW_NUMBER() OVER (PARTITION BY COALESCE(thread_id, id) ORDER BY date DESC, id DESC) AS rn
+           FROM emails e
+           WHERE ${folderWhere}
+         ) WHERE rn = 1
+         ORDER BY date DESC LIMIT ? OFFSET ?`,
+      )
       .all(limit, offset) as Record<string, unknown>[];
-    const countRow = db.query(`SELECT COUNT(*) as total FROM emails WHERE ${folderWhere}`).get() as { total: number };
+    const countRow = db
+      .query(`SELECT COUNT(DISTINCT COALESCE(thread_id, id)) as total FROM emails WHERE ${folderWhere}`)
+      .get() as { total: number };
     const messages = rows.map(rowToSummary);
     return ctx.json({ messages, total: countRow.total });
   } finally {
@@ -184,6 +198,32 @@ emailRouter.get('/messages', async (ctx) => {
   }
 });
 
+function buildMessage(db: ReturnType<typeof openEmailDb>, row: Record<string, unknown>): EmailMessage {
+  const attachmentRows = db.query('SELECT * FROM attachments WHERE email_id = ? ORDER BY idx').all(row.id as string) as Array<
+    Record<string, unknown>
+  >;
+  const from = row.from_name ? `${row.from_name} <${row.from_address}>` : (row.from_address as string);
+  return {
+    id: row.id as string,
+    from,
+    to: row.to_address as string,
+    cc: (row.cc as string) ?? undefined,
+    subject: row.subject as string,
+    date: row.date as string,
+    snippet: row.snippet as string,
+    html: (row.html as string) ?? undefined,
+    text: (row.text_body as string) ?? undefined,
+    attachments: attachmentRows.map((a) => ({
+      filename: a.filename as string,
+      size: a.size as number,
+      contentType: a.content_type as string,
+    })),
+    ...(row.attachment_count ? { attachmentCount: row.attachment_count as number } : {}),
+    ...(row.read ? { read: true } : {}),
+    ...(row.labels ? { labels: (row.labels as string).split(',') } : {}),
+  };
+}
+
 emailRouter.get('/messages/:id', async (ctx) => {
   const email = ctx.get('user').email;
   const id = ctx.req.param('id');
@@ -192,34 +232,47 @@ emailRouter.get('/messages/:id', async (ctx) => {
   try {
     const row = db.query('SELECT * FROM emails WHERE id = ? AND deleted = 0').get(id) as Record<string, unknown> | null;
     if (!row) return ctx.text('Not found', 404);
+    return ctx.json(buildMessage(db, row));
+  } finally {
+    db.close();
+  }
+});
 
-    const attachmentRows = db.query('SELECT * FROM attachments WHERE email_id = ? ORDER BY idx').all(id) as Array<
-      Record<string, unknown>
-    >;
+// GET /thread/:id — the full conversation containing message :id, oldest message first.
+emailRouter.get('/thread/:id', (ctx) => {
+  const email = ctx.get('user').email;
+  const id = ctx.req.param('id');
 
-    const from = row.from_name ? `${row.from_name} <${row.from_address}>` : (row.from_address as string);
+  const db = openEmailDb(email);
+  try {
+    const head = db.query('SELECT thread_id, subject FROM emails WHERE id = ? AND deleted = 0').get(id) as
+      | { thread_id: string | null; subject: string }
+      | null;
+    if (!head) return ctx.text('Not found', 404);
 
-    const message: EmailMessage = {
-      id: row.id as string,
-      from,
-      to: row.to_address as string,
-      cc: (row.cc as string) ?? undefined,
-      subject: row.subject as string,
-      date: row.date as string,
-      snippet: row.snippet as string,
-      html: (row.html as string) ?? undefined,
-      text: (row.text_body as string) ?? undefined,
-      attachments: attachmentRows.map((a) => ({
-        filename: a.filename as string,
-        size: a.size as number,
-        contentType: a.content_type as string,
-      })),
-      ...(row.attachment_count ? { attachmentCount: row.attachment_count as number } : {}),
-      ...(row.read ? { read: true } : {}),
-      ...(row.labels ? { labels: (row.labels as string).split(',') } : {}),
-    };
+    const threadKey = head.thread_id ?? id;
+    const rows = db
+      .query('SELECT * FROM emails WHERE COALESCE(thread_id, id) = ? AND deleted = 0 ORDER BY date ASC')
+      .all(threadKey) as Record<string, unknown>[];
+    const messages = rows.map((row) => buildMessage(db, row));
+    return ctx.json({ id, subject: head.subject, messages });
+  } finally {
+    db.close();
+  }
+});
 
-    return ctx.json(message);
+// PATCH /thread/:id/read — mark every message in the conversation as read.
+emailRouter.patch('/thread/:id/read', (ctx) => {
+  const email = ctx.get('user').email;
+  const id = ctx.req.param('id');
+
+  const db = openEmailDb(email);
+  try {
+    const head = db.query('SELECT thread_id FROM emails WHERE id = ?').get(id) as { thread_id: string | null } | null;
+    if (!head) return ctx.text('Not found', 404);
+    const threadKey = head.thread_id ?? id;
+    db.run('UPDATE emails SET read = 1 WHERE COALESCE(thread_id, id) = ? AND read = 0', [threadKey]);
+    return ctx.json({ ok: true });
   } finally {
     db.close();
   }