feat(insights): fold a confidence-gated derived signal into the daily briefing

When a derived wellness score (readiness or recovery) crosses a notability gate
— outside the green band AND confidence at least medium — the insights
generator now appends a SYSTEM CONTEXT block so the briefing can narrate the
shift observationally. Mirrors the GLP-1 plateau detector's append mechanism:
reads the one derived contract, returns null (the common case) at zero token
cost, and instructs the model to frame the signal as an observed pattern, never
a diagnosis or a dose recommendation. Add the readiness/recovery sourceMetric
enum values plus their briefing href + icon + trend-chart mappings.

src/app/api/insights/generate/route.ts

@@ -11,6 +11,11 @@ import {
   detectGlp1Plateau,
   buildGlp1PlateauPrompt,
 } from "@/lib/insights/glp1-plateau";
+import {
+  detectDerivedBriefingSignals,
+  buildDerivedBriefingPrompt,
+} from "@/lib/insights/derived-briefing";
+import { getAgeFromDateOfBirth } from "@/lib/analytics/pulse-targets";
 import {
   buildUserPrompt,
   type ComparisonSnapshot,
@@ -199,6 +204,10 @@ export const POST = apiHandler(async (request: NextRequest) => {
       // LLM never sees the excluded blocks.
       insightsExcludeMetrics: true,
       locale: true,
+      // v1.10.0 — profile for the derived-signal briefing detector.
+      dateOfBirth: true,
+      gender: true,
+      heightCm: true,
     },
   });
 
@@ -397,6 +406,21 @@ export const POST = apiHandler(async (request: NextRequest) => {
   if (plateauContext) {
     userPrompt += buildGlp1PlateauPrompt(plateauContext, locale);
   }
+  // v1.10.0 — fold a notable derived wellness signal (readiness / recovery
+  // shift, confidence-gated) into the briefing as a SYSTEM CONTEXT block.
+  // Reads the one derived contract; null (the common case) costs nothing.
+  const derivedSex =
+    dbUser?.gender === "MALE" || dbUser?.gender === "FEMALE"
+      ? (dbUser.gender as "MALE" | "FEMALE")
+      : null;
+  const derivedBriefing = await detectDerivedBriefingSignals(userId, {
+    ageYears: getAgeFromDateOfBirth(dbUser?.dateOfBirth ?? null),
+    sex: derivedSex,
+    heightCm: dbUser?.heightCm ?? null,
+  });
+  if (derivedBriefing) {
+    userPrompt += buildDerivedBriefingPrompt(derivedBriefing, locale);
+  }
 
   let result;
   let workingProviderType: string;