fix(insights): plot the trends row and log fevers in the reader's units

Two more surfaces carried a fixed unit. The insights trends row labelled
weight in kg and body temperature in °C for every reader, and plotted
walking distance as raw metres under a km label; its trend caption
said the same. A single transformed series there now takes unit, scale
and offset from the preference, and the caption describes the converted
series against a converted noise floor.

The illness day sheet and timeline showed and took a fever in °C. The
fever is now seeded, typed and shown in the reader's temperature unit
and stored in °C as before.

Refs #1067

src/components/insights/__tests__/trends-row.test.tsx

@@ -21,14 +21,40 @@ import { I18nProvider } from "@/lib/i18n/context";
 
 vi.mock("next/dynamic", () => ({
   default: () => {
-    const Stub = ({ title }: { title?: string }) => (
-      <div data-slot="trends-row-chart-stub">{title ?? "chart"}</div>
+    const Stub = ({
+      title,
+      unit,
+      valueScale,
+      valueOffset,
+    }: {
+      title?: string;
+      unit?: string;
+      valueScale?: number;
+      valueOffset?: number;
+    }) => (
+      <div
+        data-slot="trends-row-chart-stub"
+        data-unit={unit}
+        data-scale={valueScale}
+        data-offset={valueOffset}
+      >
+        {title ?? "chart"}
+      </div>
     );
     Stub.displayName = "TrendsRowChartStub";
     return Stub;
   },
 }));
 
+const account = vi.hoisted(() => ({
+  user: null as Record<string, unknown> | null,
+}));
+vi.mock("@/hooks/use-auth", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("@/hooks/use-auth")>()),
+  useAuth: () => ({ user: account.user, isAuthenticated: true }),
+  useAccountOnceMounted: () => account.user,
+}));
+
 import { TrendsRow } from "../trends-row";
 import type { DailyBriefing } from "@/lib/ai/schema";
 
@@ -306,4 +332,27 @@ describe("<TrendsRow>", () => {
     expect(html).toMatch(/data-metric="steps"/);
     expect(html).toContain('href="/insights/steps"');
   });
+
+  it("plots a transformed slot in the reader's unit, scale and offset included", () => {
+    account.user = { unitPreference: "imperial", glucoseUnit: null };
+    try {
+      const html = render(
+        <TrendsRow briefing={briefing(["weight", "distance", "body_temp"])} />,
+      );
+      expect(html).toContain('data-unit="lb"');
+      expect(html).toContain('data-unit="mi"');
+      expect(html).toContain('data-unit="°F"');
+      expect(html).toContain('data-offset="32"');
+      expect(html).not.toContain('data-unit="kg"');
+      expect(html).not.toContain('data-unit="km"');
+    } finally {
+      account.user = null;
+    }
+  });
+
+  it("plots distance in kilometres, scaled from metres, for a metric reader", () => {
+    const html = render(<TrendsRow briefing={briefing(["distance"])} />);
+    expect(html).toContain('data-unit="km"');
+    expect(html).toContain('data-scale="0.001"');
+  });
 });

src/components/insights/trend-annotation.tsx

@@ -20,6 +20,7 @@ import {
 import { cn } from "@/lib/utils";
 import { CONFIDENCE_BADGE_CLASS } from "./confidence-badge";
 import { apiGet } from "@/lib/api/api-fetch";
+import { useUnitDisplay } from "@/hooks/use-unit-display";
 
 /**
  * v1.4.20 phase B3 — single-sentence AI annotation rendered directly
@@ -264,6 +265,7 @@ export function TrendDescriptorCaption({
 }) {
   const { t } = useTranslations();
   const { isAuthenticated } = useAuth();
+  const { toDisplay, transformFor, unitFor } = useUnitDisplay();
 
   const isMood = kind === "mood";
   const primaryType = types[0] ?? "";
@@ -323,18 +325,28 @@ export function TrendDescriptorCaption({
     }
     // The numeric series is already server-bounded to the trailing
     // 30-day window by the fetch, so every returned row is in-window.
+    // Described in the reader's unit, the same one the chart above plots.
     return (numericQuery.data ?? []).map((row) => ({
       timestamp: new Date(row.measuredAt).getTime(),
-      value: row.value,
+      value: toDisplay(primaryType, row.value),
     }));
-  }, [isMood, moodQuery.data, numericQuery.data]);
+  }, [isMood, moodQuery.data, numericQuery.data, toDisplay, primaryType]);
 
   const descriptor = useMemo(() => {
+    const meta = TREND_SLOT_DESCRIPTOR_META[metric];
+    // A slot that converts its series converts its noise floor with it (a
+    // floor is a difference: factor only).
     const config = isMood
       ? MOOD_DESCRIPTOR_CONFIG
-      : TREND_SLOT_DESCRIPTOR_META[metric]?.config;
+      : meta?.unitType
+        ? {
+            ...meta.config,
+            absoluteFloor:
+              meta.config.absoluteFloor * transformFor(meta.unitType).factor,
+          }
+        : meta?.config;
     return computeTrendDescriptor(points, config);
-  }, [points, isMood, metric]);
+  }, [points, isMood, metric, transformFor]);
 
   // Tier 4 — genuinely too few points (also covers the in-flight window
   // before the small series lands). Surface the real empty hint so the
@@ -361,7 +373,7 @@ export function TrendDescriptorCaption({
   // copy defensively (should not happen for the legacy triple).
   const copy = isMood
     ? moodDescriptorCopy(descriptor)
-    : (numericDescriptorCopy(metric, descriptor) ??
+    : (numericDescriptorCopy(metric, descriptor, unitFor) ??
       moodDescriptorCopy(descriptor));
 
   return (

src/components/insights/trends-row.tsx

@@ -22,6 +22,7 @@ import {
   type TrendAnnotationConfidenceBand,
   type TrendAnnotationStatus,
 } from "./trend-annotation";
+import { useUnitDisplay } from "@/hooks/use-unit-display";
 
 /**
  * Trends row — a small chart per metric above a one-sentence
@@ -116,17 +117,29 @@ function MetricChart({
   title: string;
 }) {
   const { user } = useAuth();
+  const { transformFor, isTransformed } = useUnitDisplay();
   const userTimezone = user?.timezone;
   if (config.kind === "mood") {
     return <MoodChart title={title} mini />;
   }
+  // A single transformed series (weight, distance, temperature) plots in
+  // the reader's unit: the chart folds scale and offset in at its read
+  // boundary, exactly as the metric's own insights page does. Distance
+  // used to plot raw metres under a "km" label for every reader.
+  const primary = config.types[0] ?? "";
+  const transform =
+    config.types.length === 1 && isTransformed(primary)
+      ? transformFor(primary)
+      : null;
   return (
     <HealthChartDynamicMini
       types={config.types}
       title={title}
       colors={config.colors}
-      unit={config.unit}
-      yAxisUnit={config.yAxisUnit}
+      unit={transform ? transform.displayUnit : config.unit}
+      yAxisUnit={transform ? undefined : config.yAxisUnit}
+      valueScale={transform?.factor}
+      valueOffset={transform?.offset}
       mini
       userTimezone={userTimezone}
     />