fix: re-derive conversation authorship from history

Rooms that Reddit returns without timeline events in /sync fell back to
isFromUs=false, so an unanswered opener of ours was projected as inbound
and surfaced in the dashboard's "Needs reply" queue. loadDetails already
paginates the authoritative history for lastMessageSnippet/Time, so take
isFromUs from the same newest message.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/services/chat/service.ts

@@ -1135,8 +1135,14 @@ export class ChatService {
       return;
     }
 
-    chat.lastMessageSnippet = chat.messages[chat.messages.length - 1].text;
+    const newest = chat.messages[chat.messages.length - 1];
-    chat.lastMessageTime = chat.messages[chat.messages.length - 1].timestamp;
+    chat.lastMessageSnippet = newest.text;
+    chat.lastMessageTime = newest.timestamp;
+    // Re-derive authorship from the authoritative history. Room summaries built
+    // from /sync default `isFromUs` to false when the room carries no timeline
+    // events (Reddit omits them for idle rooms), which would otherwise leave an
+    // unanswered opener of ours sitting in the operator's "Needs reply" queue.
+    chat.isFromUs = newest.isSelf;
 
     const firstSelf = chat.messages.find((m) => m.isSelf);
     if (firstSelf) chat.originMessage = firstSelf.text;

tests/chat-service-progressive-backfill.test.ts

@@ -214,6 +214,56 @@ describe('ChatService progressive full backfill', () => {
     }
   });
 
+  it('derives isFromUs from history when /sync returns no timeline for the room', async () => {
+    const logger = createMockLogger();
+    const tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), 'chat-authorship-backfill-'));
+    try {
+      const matrix = new MatrixClient(credentials, logger, { minRequestIntervalMs: 0 });
+      // Reddit omits timeline events for idle rooms, so the seeded summary
+      // carries no authorship signal at all.
+      matrix.sync = vi.fn(async () => ({ next_batch: 's1', rooms: { join: {} } })) as typeof matrix.sync;
+      matrix.getJoinedRooms = vi.fn(async () => ['!unanswered:reddit.com', '!answered:reddit.com']);
+      matrix.getRoomMessages = vi.fn(async (roomId: string) => ({
+        start: 'start',
+        chunk: roomId === '!unanswered:reddit.com'
+          ? [{
+              event_id: '$opener',
+              type: 'm.room.message',
+              sender: '@me:reddit.com',
+              origin_server_ts: 1_000,
+              content: { body: 'Hello there' },
+            }]
+          : [{
+              event_id: '$reply',
+              type: 'm.room.message',
+              sender: '@t2_bob:reddit.com',
+              origin_server_ts: 2_000,
+              content: { body: 'Hi back' },
+            }, {
+              event_id: '$opener',
+              type: 'm.room.message',
+              sender: '@me:reddit.com',
+              origin_server_ts: 1_000,
+              content: { body: 'Hello there' },
+            }],
+      }));
+
+      const service = new ChatService(
+        matrix, logger, undefined, undefined, undefined, undefined,
+        new ChatCache(logger, path.join(tmpDir, 'chat-cache.json')),
+        undefined, undefined, authenticatedAccountAuth,
+      );
+
+      const chats = await service.fetchAllMessages({ requireComplete: true });
+      const unanswered = chats.find((c) => c.roomId === '!unanswered:reddit.com');
+      const answered = chats.find((c) => c.roomId === '!answered:reddit.com');
+      expect(unanswered?.isFromUs).toBe(true);
+      expect(answered?.isFromUs).toBe(false);
+    } finally {
+      await fs.rm(tmpDir, { recursive: true, force: true });
+    }
+  });
+
   it('paginates beyond the former 50-page history ceiling', async () => {
     const logger = createMockLogger();
     const tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), 'chat-long-backfill-'));