feat(daily): react in place when new data lands

Today gains two additive-nullable digest fields. `justIn` names the day's
newest arrival while it is still news — under three hours old, after which the
record is simply current rather than new. `reactionLine` carries a single
generated sentence about that arrival and replaces the hero's standing lead for
the rest of the local day, never appending a second paragraph, so the hero stays
one lead line tall and nothing below it shifts.

Nothing here polls. The open dashboard picks the change up on the cadence it
already runs — a state change, not a notification.

The generated sentence is bounded before it is written: the arrival spine's
unique row per kind per local day IS the throttle, the worker re-checks the
same claim before spending, and the reservation is reconciled on every exit
including each failure path. Without a provider, without consent, or against an
exhausted budget the row stays line-less and the surface falls back to the
deterministic lead — the chip and the provisional-to-final flip are unaffected.

The chip's time string is formatted client-side after mount; `justIn.at`
crosses the wire as an ISO instant so the server never renders a local
wall-clock time the browser would disagree with.

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

@@ -63,6 +63,8 @@ function digest(over: Partial<DailyDigest> = {}): DailyDigest {
     briefingLead: "Your week is trending steady.",
     line: "Your week is trending steady.",
     worthALook: [doseItem, syncItem],
+    justIn: null,
+    reactionLine: null,
     ...over,
   };
 }

src/components/daily/today-hero.tsx

@@ -37,6 +37,7 @@
 import Link from "next/link";
 import { Moon } from "lucide-react";
 
+import { useMounted } from "@/hooks/use-mounted";
 import { ScoreRing } from "@/components/insights/derived/score-ring";
 import type { ScoreBand } from "@/components/insights/derived/band-tokens";
 import { ProseBlocks } from "@/components/insights/prose-blocks";
@@ -62,8 +63,40 @@ function formatDelta(
   return t("daily.today.deltaVsBaseline", { delta: signed });
 }
 
+/**
+ * The "just in" chip's clock face.
+ *
+ * Formatted CLIENT-side, and only after mount. `justIn.at` crosses the wire as
+ * an ISO instant precisely so this stays a client concern: the server has no
+ * business rendering a local wall-clock time it would format under its OWN
+ * locale and timezone, and any such string would differ from the browser's on
+ * the hydration render — React #418, a class of bug this project has already
+ * paid for once.
+ *
+ * `undefined` locale lets the browser pick the user's own regional format
+ * (24-hour here, 12-hour there); the chip is a timestamp, not copy.
+ */
+function formatJustInTime(iso: string): string | null {
+  const at = new Date(iso);
+  if (Number.isNaN(at.getTime())) return null;
+  try {
+    return at.toLocaleTimeString(undefined, {
+      hour: "2-digit",
+      minute: "2-digit",
+    });
+  } catch {
+    return null;
+  }
+}
+
 export function TodayHero({ digest }: { digest: DailyDigest }) {
   const { t } = useTranslations();
+  // Gates ONLY the chip's time string — never the chip's presence. The hero
+  // itself is deliberately NOT mount-gated (v1.30.9: it is the LCP element and
+  // paints from the server-dehydrated digest on both the SSR and the hydration
+  // render). So the slot renders on both passes and the formatted time fills in
+  // on the first client re-render, keeping those two passes byte-identical.
+  const mounted = useMounted();
   const { keep, letGo } = useCoachCheckinAction();
   const dismissItem = usePriorityItemDismiss();
 
@@ -83,17 +116,25 @@ export function TodayHero({ digest }: { digest: DailyDigest }) {
 
   const hasScore = digest.score !== null;
   const hasItems = digest.worthALook.length > 0;
-  // The briefing lead is the warmest read; the deterministic `line` is the
-  // floor a keyless self-hoster still gets. Prefer the lead for the hero.
-  const lead = digest.briefingLead ?? digest.line;
+  // Lead precedence, warmest first: the day's reaction line REPLACES the
+  // briefing lead once something landed — it never appends as a second
+  // paragraph, so the hero stays exactly one lead line tall and nothing below
+  // it shifts. The briefing lead is the standing read; the deterministic
+  // `line` is the floor a keyless self-hoster still gets.
+  const lead = digest.reactionLine ?? digest.briefingLead ?? digest.line;
   const topSignal = digest.topSignal;
+  const justInTime = digest.justIn ? formatJustInTime(digest.justIn.at) : null;
 
   // Calm degrade (plan §3): a genuinely empty account — no score, no rail
   // items, and no cached briefing lead — surfaces nothing here. The tile
   // strip below carries its own "add your first reading" empty state, so a
   // second alarming empty card on the hero would be noise. The all-clear
   // state (score present, nothing needs attention) is handled inline below.
-  if (!hasScore && !hasItems && !digest.briefingLead) {
+  // A freshly-generated reaction line counts as content in its own right: an
+  // otherwise-bare account whose first reading just landed has something
+  // honest to say, and swallowing it here would hide the one moment this
+  // surface exists for.
+  if (!hasScore && !hasItems && !digest.briefingLead && !digest.reactionLine) {
     return null;
   }
 
@@ -184,17 +225,46 @@ export function TodayHero({ digest }: { digest: DailyDigest }) {
           </div>
         </div>
 
-        {/* Freshness note (plan §2.4) — provisional day, last night's sleep
-            not yet folded in. Muted, non-blocking, refreshes in place when
-            the morning job lands. */}
-        {digest.sleepPending ? (
-          <p
-            data-slot="today-hero-sleep-pending"
-            className="text-muted-foreground flex items-center gap-1.5 text-xs"
-          >
-            <Moon className="size-3.5 shrink-0" aria-hidden="true" />
-            {t("daily.today.sleepPending")}
-          </p>
+        {/* Meta row — the hero's quiet tier (UI-STANDARDS §text: `text-xs
+            text-muted-foreground` is the meta floor; never an accent, never an
+            opacity modifier). Holds the freshness note and the "just in" chip;
+            they can legitimately co-occur (a weight landed while last night's
+            sleep is still pending), so they share one wrapping row rather than
+            competing for the same slot. */}
+        {digest.sleepPending || digest.justIn ? (
+          <div className="text-muted-foreground flex flex-wrap items-center gap-x-3 gap-y-1 text-xs">
+            {/* Freshness note (plan §2.4) — provisional day, last night's
+                sleep not yet folded in. Muted, non-blocking, refreshes in
+                place when the morning job lands. */}
+            {digest.sleepPending ? (
+              <p
+                data-slot="today-hero-sleep-pending"
+                className="flex items-center gap-1.5"
+              >
+                <Moon className="size-3.5 shrink-0" aria-hidden="true" />
+                {t("daily.today.sleepPending")}
+              </p>
+            ) : null}
+
+            {/* The "just in" chip — a state change, not a notification. No
+                badge count, no accent, no animation: the record simply reads
+                differently on the next refresh, and this names why. It is
+                present for as long as the arrival is news (the server applies
+                the window, so the chip expires on a poll rather than on a
+                client timer) and carries the arrival's local time once the
+                client has mounted and can format it honestly. */}
+            {digest.justIn ? (
+              <p
+                data-slot="today-hero-just-in"
+                data-just-in-kind={digest.justIn.kind}
+                className="flex items-center gap-1.5"
+              >
+                {mounted && justInTime
+                  ? t("daily.today.justInAt", { time: justInTime })
+                  : t("daily.today.justIn")}
+              </p>
+            ) : null}
+          </div>
         ) : null}
 
         {/* Worth-a-look rail — S1's `PriorityCard`s, bounded 0–3. When the