Keep progress bars aligned

The server now sends each fresh position on every poll that has one, and
sends positions advanced to send time; clients count only the time since
they received it. Bars realign every poll and no longer drift by however
far the viewer's clock is off.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/api/test/progress.test.ts

@@ -3,7 +3,7 @@ import { afterEach, describe, expect, it } from 'vitest';
 import { db, schema } from '../src/db';
 import { createRedis, nowPlayingChannel } from '../src/lib/redis';
 import { reportedPosition } from '../src/routes/devices';
-import { applyPollResult } from '../src/services/nowPlaying';
+import { applyPollResult, getNowPlaying } from '../src/services/nowPlaying';
 import { nextPollDelay } from '../src/services/scheduler';
 import { createUser, useTestApp } from './helpers';
 
@@ -54,27 +54,44 @@ describe('phone-reported positions', () => {
   });
 });
 
-describe('seeking', () => {
-  it('tells watchers when the position jumps, but not as it ticks along', async () => {
+describe('realigning progress bars', () => {
+  it('sends the fresh position on every poll that has one, advanced to send time', async () => {
     const { user } = await createUser(app(), 'alice');
     await applyPollResult(user.id, 'plex', playing(0));
-    // Pretend the last poll was 10 seconds ago.
-    await db
-      .update(schema.nowPlaying)
-      .set({ updatedAt: new Date(Date.now() - 10_000) })
-      .where(eq(schema.nowPlaying.userId, user.id));
-
     const messages: string[] = [];
     await sub.subscribe(nowPlayingChannel(user.id));
     sub.on('message', (_channel, msg) => messages.push(msg));
 
-    await applyPollResult(user.id, 'plex', playing(10_500)); // right where it should be
-    await new Promise((r) => setTimeout(r, 150));
-    expect(messages).toHaveLength(0);
-
+    await applyPollResult(user.id, 'plex', playing(10_500));
+    await db
+      .update(schema.nowPlaying)
+      .set({ updatedAt: new Date(Date.now() - 3_000) }) // as if that poll was 3s ago
+      .where(eq(schema.nowPlaying.userId, user.id));
     await applyPollResult(user.id, 'plex', playing(120_000)); // skipped ahead
     await new Promise((r) => setTimeout(r, 150));
-    expect(messages).toHaveLength(1);
-    expect(JSON.parse(messages[0]!)).toMatchObject({ progressMs: 120_000 });
+    const sent = messages.map((m) => JSON.parse(m).progressMs as number);
+    expect(sent).toHaveLength(2);
+    expect(sent[0]).toBeGreaterThanOrEqual(10_500);
+    expect(sent[0]).toBeLessThan(11_500);
+    expect(sent[1]).toBeGreaterThanOrEqual(120_000);
+    expect(sent[1]).toBeLessThan(121_000);
+
+    // Fetched later, the position has moved on by the time since the poll.
+    const [np] = await getNowPlaying([user.id]);
+    await db.update(schema.nowPlaying).set({ updatedAt: new Date(Date.now() - 4_000) }).where(eq(schema.nowPlaying.userId, user.id));
+    const [later] = await getNowPlaying([user.id]);
+    expect(np!.progressMs).toBeGreaterThanOrEqual(120_000);
+    expect(later!.progressMs).toBeGreaterThanOrEqual(124_000);
+  });
+
+  it("doesn't send anything extra for sources without a position", async () => {
+    const { user } = await createUser(app(), 'alice');
+    await applyPollResult(user.id, 'lastfm', playing(null));
+    const messages: string[] = [];
+    await sub.subscribe(nowPlayingChannel(user.id));
+    sub.on('message', (_channel, msg) => messages.push(msg));
+    await applyPollResult(user.id, 'lastfm', playing(null));
+    await new Promise((r) => setTimeout(r, 150));
+    expect(messages).toHaveLength(0);
   });
 });