diff --git a/package.json b/package.json
index 7b01ae120..04626bf0b 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "healthlog",
-  "version": "1.30.35",
+  "version": "1.31.0",
   "description": "Self-hosted personal-health-tracking PWA with Withings integration, AI insights, and doctor-report PDF export.",
   "license": "PolyForm-Noncommercial-1.0.0",
   "homepage": "https://healthlog.dev",
diff --git a/public/sw.js b/public/sw.js
index 1c48fd505..219a29024 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -36,7 +36,7 @@ try {
 // v1.4.38.4 → v1.4.42. Do not hand-edit; bump `package.json` and rebuild.
 const CACHE_VERSION =
   (typeof self !== "undefined" && self.__APP_VERSION__) ||
-  /* @sw-version-fallback */ "v1.30.35";
+  /* @sw-version-fallback */ "v1.31.0";
 const STATIC_CACHE = `healthlog-static-${CACHE_VERSION}`;
 const PAGE_CACHE = `healthlog-pages-${CACHE_VERSION}`;
 // v1.18.6 — read-only data cache for a curated allowlist of safe GET `/api/*`
diff --git a/src/lib/ai/prompts/arrival-reaction.ts b/src/lib/ai/prompts/arrival-reaction.ts
index 830a96aa9..e1f29b725 100644
--- a/src/lib/ai/prompts/arrival-reaction.ts
+++ b/src/lib/ai/prompts/arrival-reaction.ts
@@ -85,12 +85,45 @@ export interface ArrivalReactionPromptInput {
    * only to say what the block already establishes.
    */
   evidence: string;
+  /**
+   * Rotating opener-archetype hint (`openerArchetypeHint`, seeded
+   * `${userId}:reaction:${kind}:${localDate}` at the call site) — the same
+   * per-user, per-day rotation every other assessment surface uses so this
+   * line does not open on the same shape every time. This sits ALONGSIDE the
+   * fixed meaning-first instruction below, not in place of it — the rotation
+   * varies the angle, the instruction is the invariant every surface owes.
+   */
+  openerHint?: string;
 }
 
+/**
+ * The fixed, always-present meaning-first instruction, phrased exactly the
+ * way every other assessment surface's user prompt phrases it. The system
+ * prompt's `REACTION_CONTRACT` states the same rule in its own words for the
+ * model to follow; this line exists so the INSTRUCTION SHAPE itself matches
+ * the family's shared contract, in the same prompt the harness inspects for
+ * it. Two locale bodies only — fr/es/it/pl ride the English one, exactly
+ * like the system prompt's own `instructionLocale` split.
+ */
+const OPENING_INSTRUCTION_EN =
+  "Open with what just landed MEANS in plain words — the overall read, not the number — then bring the figure in right after as support.";
+const OPENING_INSTRUCTION_DE =
+  "Beginne mit dem, was gerade eingetroffen ist, in klaren Worten — nicht der Zahl — und bring sie danach als Beleg.";
+
 export function getArrivalReactionUserPrompt(
   input: ArrivalReactionPromptInput,
+  locale: Locale,
 ): string {
-  return `WHAT JUST LANDED: ${KIND_SUBJECT[input.kind]}.
+  const openingInstruction =
+    instructionLocale(locale) === "en"
+      ? OPENING_INSTRUCTION_EN
+      : OPENING_INSTRUCTION_DE;
+  const openerLine =
+    input.openerHint && input.openerHint.trim().length > 0
+      ? `\nOPENER HINT: ${input.openerHint}`
+      : "";
+
+  return `WHAT JUST LANDED: ${KIND_SUBJECT[input.kind]}. ${openingInstruction}${openerLine}
 
 EVIDENCE BLOCK — everything below is already computed from this person's own record. Use only what is here; if it does not support a verdict, say so.
 ${input.evidence}
diff --git a/src/lib/insights/eval/prompt-surfaces.ts b/src/lib/insights/eval/prompt-surfaces.ts
index 02b9e045b..df2b7e1b9 100644
--- a/src/lib/insights/eval/prompt-surfaces.ts
+++ b/src/lib/insights/eval/prompt-surfaces.ts
@@ -15,6 +15,10 @@
  */
 import type { Locale } from "@/lib/i18n/config";
 
+import {
+  getArrivalReactionSystemPrompt,
+  getArrivalReactionUserPrompt,
+} from "@/lib/ai/prompts/arrival-reaction";
 import {
   getBiomarkerSystemPrompt,
   getBiomarkerUserPrompt,
@@ -182,4 +186,17 @@ export const ASSESSMENT_SURFACES: readonly AssessmentSurface[] = [
     system: getWorkoutInsightSystemPrompt,
     user: (l) => getWorkoutInsightUserPrompt(SNAPSHOT, TODAY, l, OPENER_HINT),
   },
+  {
+    // The one-sentence Today-hero reaction to a salient arrival. Smallest
+    // surface in the registry, and the one whose own module docblock warns
+    // most explicitly against the two-locale collapse — grading it here is
+    // what makes that warning enforced rather than just written down.
+    name: "arrival-reaction",
+    system: getArrivalReactionSystemPrompt,
+    user: (l) =>
+      getArrivalReactionUserPrompt(
+        { kind: "sleep_night", evidence: SNAPSHOT, openerHint: OPENER_HINT },
+        l,
+      ),
+  },
 ];
diff --git a/src/lib/jobs/reaction-line.ts b/src/lib/jobs/reaction-line.ts
index eef7925af..72e70c9c6 100644
--- a/src/lib/jobs/reaction-line.ts
+++ b/src/lib/jobs/reaction-line.ts
@@ -49,6 +49,7 @@ import { singleUserTurn } from "@/lib/ai/types";
 import { screenCoachReply } from "@/lib/ai/coach/outbound-guard";
 import { encryptToBytes } from "@/lib/ai/coach/bytes-codec";
 import { defaultLocale, locales, type Locale } from "@/lib/i18n/config";
+import { openerArchetypeHint } from "@/lib/ai/prompts/opener-archetype";
 import { loadDailyDigest } from "@/lib/daily/load-digest";
 import {
   getArrivalReactionSystemPrompt,
@@ -231,10 +232,17 @@ export async function runReactionLine(
     const result = await chain[0].instance.generateCompletion(
       singleUserTurn({
         system: getArrivalReactionSystemPrompt(locale),
-        user: getArrivalReactionUserPrompt({
-          kind: job.kind,
-          evidence: buildEvidence(digest),
-        }),
+        user: getArrivalReactionUserPrompt(
+          {
+            kind: job.kind,
+            evidence: buildEvidence(digest),
+            openerHint: openerArchetypeHint(
+              `${job.userId}:reaction:${job.kind}:${job.localDate}`,
+              locale,
+            ),
+          },
+          locale,
+        ),
         temperature: budget.temperature,
         maxTokens,
         timeoutMs: REACTION_LINE_TIMEOUT_MS,