test(e2e): make vacuous feed/SSE tests assert real behavior

Several tests ran green while asserting nothing. Replace them with real
assertions, and fix the SSE helper they depend on.

sse-listener: exchange the JWT for a single-use ticket (POST /stream/ticket) and
connect via ?ticket= — the helper still used the dead ?token= scheme, so every
SSE-based assertion would have silently failed to receive events.

like-comment:
- "like is idempotent" asserted nothing (void feed; void b) → now seeds a real
  upload and pins the like contract: counted once per user, toggles off on repeat
  (guards double-count), and a second user's like is counted independently.
- "comment → SSE to B" asserted length >= 0 (always true) → B now subscribes to
  the stream, A comments, and B must receive the new-comment event for that upload
  (comment_count === 1). ~30s due to reverse-proxy SSE buffering; timeout raised.

sse-realtime: only checked a nav link was visible → now counts EventSource opens
and asserts a fresh stream connection after hidden→visible (also fixes the sim,
which set visibilityState but not document.hidden, so the close never fired).

multi-tab "SSE delivers to both": only checked nav links → now asserts each tab
opens its own stream connection (delivery isn't asserted — it hinges on the ~30s
proxy buffering; connection establishment is the reliable, honest signal).

safe-area: delete the /join probe whose only assertion was Array.isArray(x) ===
true (always true); the real sheet-level env() check already exists below it.

All verified green against the live backend.

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

e2e/specs/03-feed/sse-realtime.spec.ts

@@ -1,27 +1,51 @@
 /**
  * SSE reconnection after tab background. USER_JOURNEYS.md §17 / edge cases.
+ *
+ * The app closes the EventSource on `document.hidden` and reopens it (minting a
+ * fresh ticket + new EventSource) when the tab becomes visible again — see
+ * frontend/src/lib/sse.ts. We assert the reconnect by counting stream-open
+ * requests rather than event delivery, which keeps the test fast and independent
+ * of the reverse proxy's SSE buffering.
  */
 import { test, expect } from '../../fixtures/test';
 
+/** Count EventSource opens (GET /api/v1/stream?ticket=…), not the ticket POST. */
+function trackStreamOpens(page: import('@playwright/test').Page): () => number {
+  let n = 0;
+  page.on('request', (req) => {
+    if (req.method() === 'GET' && req.url().includes('/api/v1/stream?')) n++;
+  });
+  return () => n;
+}
+
 test.describe('Feed — SSE behavior', () => {
-  test('SSE reconnects after tab visibility goes hidden then visible', async ({ page, guest, signIn }) => {
-    const h = await guest('SseReconnect');
-    await signIn(page, h);
-    await page.goto('/feed');
+  test('backgrounding then foregrounding the tab opens a fresh SSE connection', async ({ page, guest, signIn }) => {
+    const g = await guest('SseReconnect');
+    const streamOpens = trackStreamOpens(page);
 
-    // Force-fire a visibilitychange to hidden, then back to visible. The app's
-    // sse.ts is expected to close + reopen the EventSource around this.
+    await signIn(page, g); // lands on /feed, which calls connectSse() on mount
+    // Initial connection established.
+    await expect.poll(streamOpens, { timeout: 10_000 }).toBeGreaterThanOrEqual(1);
+    const afterInitial = streamOpens();
+
+    // Background: the visibility handler reads document.hidden, so override that
+    // (not just visibilityState) before dispatching, or the close never fires.
     await page.evaluate(() => {
-      Object.defineProperty(document, 'visibilityState', { configurable: true, value: 'hidden' });
+      Object.defineProperty(document, 'hidden', { configurable: true, get: () => true });
+      Object.defineProperty(document, 'visibilityState', { configurable: true, get: () => 'hidden' });
       document.dispatchEvent(new Event('visibilitychange'));
     });
-    await page.waitForTimeout(500);
+    // Foreground again → connectSse() mints a new ticket and opens a new EventSource.
     await page.evaluate(() => {
-      Object.defineProperty(document, 'visibilityState', { configurable: true, value: 'visible' });
+      Object.defineProperty(document, 'hidden', { configurable: true, get: () => false });
+      Object.defineProperty(document, 'visibilityState', { configurable: true, get: () => 'visible' });
       document.dispatchEvent(new Event('visibilitychange'));
     });
 
-    // App should still be functional — assert the bottom nav remains visible.
+    // A reconnect means a brand-new stream GET beyond the initial one.
+    await expect.poll(streamOpens, { timeout: 10_000 }).toBeGreaterThan(afterInitial);
+
+    // And the app is still functional.
     await expect(page.getByRole('link', { name: 'Galerie' })).toBeVisible();
   });
 });