test(daily): pin the just-in window, the degrade floor, and the hydration edge

Three properties, each with a mutation-verified guard:

The chip and the line run on DIFFERENT clocks and must keep doing so. The chip
expires after three hours; the line stands for the rest of the local day.
Collapsing them onto one clock reads like a simplification and silently deletes
the day's read at lunchtime.

Degradation is the headline. For every reason a line can fail to exist — no
provider, no consent, an exhausted budget, a dead provider, an unusable output
— the row stays line-less, the reservation is reconciled, and the chip and the
provisional-to-final flip still work. The degraded digest is built through the
real composer rather than a hand-shaped fixture, so the assertions cannot agree
with themselves.

The server pass carries no wall-clock time. The hero paints on the SSR pass
because it is the LCP element, so a locale-formatted time inside it would differ
from the browser's — React #418. The tests render through the server snapshot,
which is exactly the pass that must stay clock-free.

The seeded end-to-end spec lands a sleep batch through the real ingest route,
writes the arrival marker, and asserts the chip and the phase flip in place on
a refetch trigger the digest hook already declares — no reload, no new cadence.

src/components/daily/__tests__/today-hero-just-in.test.tsx

@@ -0,0 +1,202 @@
+/**
+ * The Today hero's "just in" chip and the reaction line's lead replacement.
+ *
+ * Two invariants, both of which have a specific failure this project has
+ * already paid for:
+ *
+ * 1. HYDRATION. The hero is deliberately NOT mount-gated — it paints from the
+ *    server-dehydrated digest on the SSR pass because it is the LCP element
+ *    (v1.30.9). So anything inside it that differs between the server and the
+ *    browser is a React #418 mismatch. A wall-clock time is exactly that: the
+ *    server's locale and timezone are not the reader's. The chip therefore
+ *    renders its SLOT on both passes and fills the time in only after mount.
+ *    These tests render through `renderToStaticMarkup`, which takes the SERVER
+ *    snapshot of `useSyncExternalStore` — i.e. precisely the pass that must
+ *    carry no formatted time.
+ *
+ * 2. NO LAYOUT SHIFT. The reaction line REPLACES the lead; it is never a second
+ *    paragraph. The hero stays one lead line tall, so nothing below it moves
+ *    when the line arrives on a poll.
+ */
+import { describe, it, expect } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+import { I18nProvider } from "@/lib/i18n/context";
+import { TodayHero } from "../today-hero";
+import type { DailyDigest } from "@/lib/daily/digest";
+
+function render(node: React.ReactNode, locale: "en" | "de" = "en") {
+  const client = new QueryClient();
+  return renderToStaticMarkup(
+    <QueryClientProvider client={client}>
+      <I18nProvider initialLocale={locale}>{node}</I18nProvider>
+    </QueryClientProvider>,
+  );
+}
+
+const ARRIVED_AT = "2026-07-16T05:41:00.000Z";
+
+function digest(over: Partial<DailyDigest> = {}): DailyDigest {
+  return {
+    generatedAt: "2026-07-16T06:00:00.000Z",
+    phase: "final",
+    sleepPending: false,
+    score: { value: 82, band: "green", delta: 3 },
+    topSignal: null,
+    briefingLead: "Your week is trending steady.",
+    line: "Your week is trending steady.",
+    worthALook: [],
+    justIn: null,
+    reactionLine: null,
+    ...over,
+  };
+}
+
+/** Any hh:mm clock face — the thing the server must never emit. */
+const CLOCK_FACE = /\d{1,2}:\d{2}/;
+
+describe("TodayHero — the just-in chip", () => {
+  it("renders no chip when nothing landed", () => {
+    const html = render(<TodayHero digest={digest()} />);
+    expect(html).not.toContain('data-slot="today-hero-just-in"');
+  });
+
+  it("renders the chip slot on the server pass, carrying the kind", () => {
+    const html = render(
+      <TodayHero
+        digest={digest({ justIn: { kind: "sleep_night", at: ARRIVED_AT } })}
+      />,
+    );
+
+    // The slot is present on the SSR pass, so the hydration render — which
+    // takes the same server snapshot — produces identical HTML.
+    expect(html).toContain('data-slot="today-hero-just-in"');
+    expect(html).toContain('data-just-in-kind="sleep_night"');
+    expect(html).toContain("Just in");
+  });
+
+  it("emits NO formatted time and no raw ISO instant on the server pass", () => {
+    const html = render(
+      <TodayHero
+        digest={digest({ justIn: { kind: "weight", at: ARRIVED_AT } })}
+      />,
+    );
+
+    const chip = html.slice(html.indexOf('data-slot="today-hero-just-in"'));
+    // The mismatch itself: a wall clock the browser would render differently.
+    expect(chip).not.toMatch(CLOCK_FACE);
+    // And the raw instant must not leak either — it is machine data, not copy.
+    expect(html).not.toContain(ARRIVED_AT);
+  });
+
+  it("keeps the chip muted meta — never an accent, never an opacity modifier", () => {
+    const html = render(
+      <TodayHero
+        digest={digest({ justIn: { kind: "workout", at: ARRIVED_AT } })}
+      />,
+    );
+
+    const row = html.slice(
+      0,
+      html.indexOf('data-slot="today-hero-just-in"') + 400,
+    );
+    expect(row).toContain("text-muted-foreground");
+    expect(row).toContain("text-xs");
+    // UI-STANDARDS §text: alpha on muted text drops below AA contrast.
+    expect(html).not.toContain("text-muted-foreground/");
+    expect(html).not.toContain("text-primary");
+  });
+
+  it("shows the chip alongside a still-pending night", () => {
+    // Legitimately co-occurring: a weight landed this morning while last
+    // night's sleep has not arrived yet.
+    const html = render(
+      <TodayHero
+        digest={digest({
+          phase: "provisional",
+          sleepPending: true,
+          justIn: { kind: "weight", at: ARRIVED_AT },
+        })}
+      />,
+    );
+
+    expect(html).toContain('data-slot="today-hero-sleep-pending"');
+    expect(html).toContain('data-slot="today-hero-just-in"');
+  });
+
+  it("localises the chip", () => {
+    const html = render(
+      <TodayHero
+        digest={digest({ justIn: { kind: "sleep_night", at: ARRIVED_AT } })}
+      />,
+      "de",
+    );
+    expect(html).toContain("Gerade eingetroffen");
+    expect(html).not.toContain("Just in");
+  });
+});
+
+describe("TodayHero — the reaction line replaces the lead", () => {
+  const REACTION = "A solid night, deeper than your recent stretch.";
+
+  it("renders the reaction line instead of the briefing lead", () => {
+    const html = render(
+      <TodayHero
+        digest={digest({
+          reactionLine: REACTION,
+          briefingLead: "Your week is trending steady.",
+        })}
+      />,
+    );
+
+    expect(html).toContain(REACTION);
+    // The lead it replaced must be GONE, not pushed down into a second block.
+    expect(html).not.toContain("Your week is trending steady.");
+  });
+
+  it("stays exactly one lead line tall — no second paragraph, no shift", () => {
+    const html = render(
+      <TodayHero
+        digest={digest({
+          reactionLine: REACTION,
+          briefingLead: "Your week is trending steady.",
+        })}
+      />,
+    );
+
+    const leadSlots = html.split('data-slot="today-hero-lead"').length - 1;
+    expect(leadSlots).toBe(1);
+  });
+
+  it("falls back to the briefing lead when no line was generated", () => {
+    const html = render(
+      <TodayHero
+        digest={digest({
+          reactionLine: null,
+          briefingLead: "Your week is trending steady.",
+        })}
+      />,
+    );
+    expect(html).toContain("Your week is trending steady.");
+  });
+
+  it("still renders for an otherwise-bare account when a line exists", () => {
+    // The one moment this surface exists for must not be swallowed by the
+    // empty-account degrade.
+    const html = render(
+      <TodayHero
+        digest={digest({
+          score: null,
+          briefingLead: null,
+          worthALook: [],
+          reactionLine: REACTION,
+          justIn: { kind: "weight", at: ARRIVED_AT },
+        })}
+      />,
+    );
+
+    expect(html).toContain('data-slot="today-hero"');
+    expect(html).toContain(REACTION);
+  });
+});