test: mock the unit-display hook in the crosstab, vitals, and MCP suites

The crosstab, vitals, and cycle-summary renders are static server renders with
no QueryClient; the new preferred-unit hook reads through the auth query, so
mock it to a real metric-preference implementation (identity values, canonical
symbols) that matches the render those suites assert. Register the new unit
resolver on the MCP write-tools module mock so the preview path resolves.

src/components/cycle/__tests__/cycle-insight-summary-card.test.tsx

@@ -1,6 +1,29 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { renderToStaticMarkup } from "react-dom/server";
 
+// The embedded crosstab reads the unit preference through `useUnitDisplay`,
+// which hangs off `useAuth` (a react-query hook). These are static SSR renders
+// with no QueryClient, so mock the hook to a real metric-preference impl.
+vi.mock("@/hooks/use-unit-display", async () => {
+  const dt = await import("@/lib/measurements/display-transform");
+  const forType = (t: string) => dt.getDisplayTransform(t, "metric");
+  return {
+    useUnitDisplay: () => ({
+      preference: "metric" as const,
+      transformFor: forType,
+      toDisplay: (t: string, v: number) =>
+        dt.applyDisplayTransform(v, forType(t)),
+      fromDisplay: (t: string, v: number) =>
+        dt.invertDisplayTransform(v, forType(t)),
+      toDisplayDelta: (t: string, v: number) =>
+        dt.applyDisplayTransformDelta(v, forType(t)),
+      unitFor: (t: string) => forType(t).displayUnit,
+      decimalsFor: (t: string) => forType(t).decimals,
+      isTransformed: (t: string) => dt.hasDisplayTransform(t),
+    }),
+  };
+});
+
 import { I18nProvider } from "@/lib/i18n/context";
 import type { CalendarResponse } from "../types";
 import type { CycleInsightsResponse } from "../use-cycle";

src/components/cycle/__tests__/cycle-phase-crosstab.test.tsx

@@ -1,6 +1,31 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import { renderToStaticMarkup } from "react-dom/server";
 
+// The crosstab reads the unit preference through `useUnitDisplay`, which hangs
+// off `useAuth` (a react-query hook). These are static SSR renders with no
+// QueryClient, so mock the hook to a real metric-preference implementation —
+// metric is the identity on values and yields the canonical display symbols,
+// so the assertions below (kg, °C, unchanged numbers) hold.
+vi.mock("@/hooks/use-unit-display", async () => {
+  const dt = await import("@/lib/measurements/display-transform");
+  const forType = (t: string) => dt.getDisplayTransform(t, "metric");
+  return {
+    useUnitDisplay: () => ({
+      preference: "metric" as const,
+      transformFor: forType,
+      toDisplay: (t: string, v: number) =>
+        dt.applyDisplayTransform(v, forType(t)),
+      fromDisplay: (t: string, v: number) =>
+        dt.invertDisplayTransform(v, forType(t)),
+      toDisplayDelta: (t: string, v: number) =>
+        dt.applyDisplayTransformDelta(v, forType(t)),
+      unitFor: (t: string) => forType(t).displayUnit,
+      decimalsFor: (t: string) => forType(t).decimals,
+      isTransformed: (t: string) => dt.hasDisplayTransform(t),
+    }),
+  };
+});
+
 import {
   CyclePhaseCrosstab,
   CyclePhaseHeadline,

src/components/insights/derived/__tests__/vitals-dashboard.test.tsx

@@ -1,6 +1,31 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { renderToStaticMarkup } from "react-dom/server";
 
+// The vitals tiles read the unit preference through `useUnitDisplay`, which
+// hangs off `useAuth` (a react-query hook). These are static SSR renders with
+// no QueryClient, so mock the hook to a real metric-preference implementation
+// — metric is the identity on values and yields the canonical display symbols
+// (e.g. °C), matching the pre-fix render the assertions expect.
+vi.mock("@/hooks/use-unit-display", async () => {
+  const dt = await import("@/lib/measurements/display-transform");
+  const forType = (t: string) => dt.getDisplayTransform(t, "metric");
+  return {
+    useUnitDisplay: () => ({
+      preference: "metric" as const,
+      transformFor: forType,
+      toDisplay: (t: string, v: number) =>
+        dt.applyDisplayTransform(v, forType(t)),
+      fromDisplay: (t: string, v: number) =>
+        dt.invertDisplayTransform(v, forType(t)),
+      toDisplayDelta: (t: string, v: number) =>
+        dt.applyDisplayTransformDelta(v, forType(t)),
+      unitFor: (t: string) => forType(t).displayUnit,
+      decimalsFor: (t: string) => forType(t).decimals,
+      isTransformed: (t: string) => dt.hasDisplayTransform(t),
+    }),
+  };
+});
+
 import { I18nProvider } from "@/lib/i18n/context";
 import type {
   DerivedMetricResponse,