test(e2e): un-fixme the single-target Label-as test

The blocker is gone: _thread_content renders the label menu with the
thread as its target. The test opens a conversation, attaches the seeded
label from the reading pane's menu and asserts the POST, the chip on the
list row and the tick. Not run here (no Playwright on this box).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/e2e/mail.spec.ts

@@ -867,22 +867,50 @@ test.describe("mail UI actions", () => {
         expect(composeRequests, "the click itself must still fetch one").toBe(1);
     });
 
-    // ── Still pending: needs more than wiring ────────────────────────────────
+    /**
+     * The Label-as menu inside a conversation — the single-target instance.
+     *
+     * The list toolbar's bulk menu is covered in label.spec.ts. This one is
+     * rendered by _thread_content with the thread as its target and the
+     * thread's labels pre-ticked, so it posts for this conversation alone and
+     * needs no selection in the list. It was a fixme while no template rendered
+     * the menu with a target; _thread_content does now.
+     *
+     * Asserted on the row in the list, which the returned stream replaces:
+     * that is where the chip shows, and it proves the POST reached the
+     * conversation that is open rather than whatever the list had selected.
+     */
+    test("labels a conversation via the Label-as menu", async ({ page }) => {
+        // After seed-mail (beforeEach): the label is bound to the seeded account.
+        seed("seed-label");
 
-    // Blocked: "Label as" never fires the POST from the UI. The only rendered
-    // menu is the list-toolbar bulk instance, whose _resolveTargets() reads
-    // `[data-thread-select]:checked` — but the row checkbox has no
-    // `data-thread-select`/`value`, so it finds zero targets. And no template
-    // renders _label_menu with a targetId (single-target mode). Minimal fix:
-    // add `data-thread-select value="{{ rowId }}"` to the row checkbox (unblocks
-    // bulk), or render _label_menu with targetId in _thread_content.html.twig
-    // (unblocks single-target). This one also needs a seeded custom label to
-    // click, so it stays fixme until both land.
-    test.fixme("labels a conversation via the Label-as menu", async ({
-                                                                         page,
-                                                                     }) => {
         await page.goto("/mail/inbox");
-        // TODO(app): wire a working label-menu target, then seed a custom label.
+        await mailRow(page, INBOX_SUBJECTS.read).click();
+
+        // Scoped to the reading pane — the list toolbar has its own Label-as
+        // button, and that one is the bulk instance.
+        const pane = page.locator('[data-mail--mail-pane-target="reading"]');
+        const button = pane.getByRole("button", { name: "Label as" }).first();
+        await expect(button).toBeVisible();
+        await button.click();
+
+        const panel = pane.locator('[data-mail--label-menu-target="panel"]:not(.hidden)').first();
+        await expect(panel).toBeVisible();
+
+        const entry = panel.locator("[data-label-id]", { hasText: "E2E Label" }).first();
+        await expect(entry).toHaveAttribute("data-attached", "false");
+
+        const posted = page.waitForResponse(
+            (r) => /\/status\/thread\/\d+\/label$/.test(r.url()) && r.request().method() === "POST",
+        );
+        await entry.click();
+        expect((await posted).ok(), "the label POST failed").toBe(true);
+
+        await expect(mailRow(page, INBOX_SUBJECTS.read)).toContainText("E2E Label");
+
+        // The tick follows, because the next click decides attach-or-detach
+        // from it: an unticked attached label would be attached again.
+        await expect(entry).toHaveAttribute("data-attached", "true");
     });
 
     /**