test(e2e): lock the channel content-filter inherit + no-leak (bug 2)

Add feed-content-<key> testids to the toolbar's content pills and two channel
specs: the channel view inherits the feed's Live/Upcoming both ways, and a
content toggle made in the channel view does not leak back into the feed.

frontend/e2e/channel.spec.ts

@@ -56,6 +56,51 @@ test.describe("channel view", () => {
       .toBeGreaterThan(saved - 500);
   });
 
+  // Bug 2 (Platform S5): opening a channel no longer FORCES Live/Upcoming on — the channel view
+  // seeds its content-type prefs (normal / shorts / live) from the global feed. Locked both ways so
+  // a future refactor can't silently re-hardcode it.
+  test("the channel view inherits the feed's content filters (no forced Live/Upcoming)", async ({ page }) => {
+    await openApp(page);
+    await expect(page.getByTestId("video-card").first()).toBeVisible();
+    const feedLive = page.getByTestId("feed-content-includeLive");
+    await expect(feedLive).toHaveAttribute("aria-pressed", "false");
+
+    // Inherit OFF: the channel toolbar's Live/Upcoming stays off, not forced on.
+    await page.getByTestId("video-card-channel").first().click();
+    await expect(page.getByTestId("channel-title")).toBeVisible();
+    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute("aria-pressed", "false");
+    await page.getByTestId("channel-back").click();
+    await expect(page.getByTestId("channel-title")).toHaveCount(0);
+
+    // Inherit ON: flip the feed's Live/Upcoming on, reopen the channel → it inherits the on state.
+    await feedLive.click();
+    await expect(feedLive).toHaveAttribute("aria-pressed", "true");
+    await expect(page.getByTestId("video-card").first()).toBeVisible();
+    await page.getByTestId("video-card-channel").first().click();
+    await expect(page.getByTestId("channel-title")).toBeVisible();
+    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute("aria-pressed", "true");
+  });
+
+  // Bug 2 (Platform S5): the channel view is its OWN filter scope — a content toggle made there
+  // must NOT leak back into the global feed. (FeedFiltersProvider owns the feed's filters; the
+  // channel page keeps a separate local cell.)
+  test("a channel's content toggle does not leak into the feed", async ({ page }) => {
+    await openApp(page);
+    await expect(page.getByTestId("video-card").first()).toBeVisible();
+    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute("aria-pressed", "false");
+
+    // Turn Live/Upcoming ON inside the channel view.
+    await page.getByTestId("video-card-channel").first().click();
+    await expect(page.getByTestId("channel-title")).toBeVisible();
+    await page.getByTestId("feed-content-includeLive").click();
+    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute("aria-pressed", "true");
+
+    // Back on the feed, its Live/Upcoming is still off — the channel's change stayed local.
+    await page.getByTestId("channel-back").click();
+    await expect(page.getByTestId("channel-title")).toHaveCount(0);
+    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute("aria-pressed", "false");
+  });
+
   // Platform S4b: the whole channel chrome (banner, identity, tabs, toolbar) is fixed — it stays
   // put while only the video grid scrolls.
   test("the channel chrome stays fixed while the video grid scrolls", async ({ page }) => {

frontend/src/components/Feed.tsx

@@ -544,6 +544,7 @@ export default function Feed({
           return (
             <button
               key={c.key}
+              data-testid={`feed-content-${c.key}`}
               onClick={() => setFilters({ ...filters, [c.key]: !on })}
               aria-pressed={on}
               className={`text-xs px-3 py-1.5 rounded-full border transition ${