chore(glucose,berlin-day): drop unreferenced mmolToMgdl and berlinDayKey exports

The glucose UI only converts canonical mg/dL into mmol/L for display
via convertGlucose; the reverse helper had no caller outside its own
test. The Berlin-only day-key helper was already superseded by
userDayKey(date, tz) in v1.4.38 for every read path that consumed it;
its remaining presence as a tested module was dead weight.

src/app/api/analytics/route.ts

@@ -208,12 +208,9 @@ async function buildAnalyticsResponse(user: AuthedUser) {
   // cost flat across the three branches.
   const coverage = await probeRollupCoverage(user.id);
 
-  // v1.4.25 W7b — every day-bucket call inside this route now honours
-  // the user's display timezone. The legacy `berlinDayKey()` import
-  // remains for sleep-stage and correlation paths that share their
-  // helper signature with non-tz-aware code (`computeSleepStageBreakdown`
-  // is called with a userId only); the per-call sites below all pass
-  // `userTz` through `userDayKey()`.
+  // v1.4.25 W7b — every day-bucket call inside this route honours the
+  // user's display timezone via `userDayKey(date, userTz)` (the legacy
+  // `berlinDayKey()` helper was retired in v1.4.40).
   const userTz = user.timezone ?? DEFAULT_TIMEZONE;
 
   // Derived from canonical enum so a new measurement type is auto-summarised

src/lib/__tests__/glucose.test.ts

@@ -1,7 +1,6 @@
 import { describe, it, expect } from "vitest";
 import {
   mgdlToMmol,
-  mmolToMgdl,
   convertGlucose,
   resolveGlucoseUnit,
   thresholdMetricForContext,
@@ -14,18 +13,6 @@ describe("glucose conversion", () => {
     expect(mgdlToMmol(70)).toBeCloseTo(3.9, 1); // hypoglycemia threshold
   });
 
-  it("converts mmol/L to mg/dL rounded to integer", () => {
-    expect(mmolToMgdl(5.5)).toBe(99);
-    expect(mmolToMgdl(7.0)).toBe(126);
-  });
-
-  it("roundtrips within 1 mg/dL", () => {
-    for (const mgdl of [70, 99, 100, 126, 140, 200, 300]) {
-      const back = mmolToMgdl(mgdlToMmol(mgdl));
-      expect(Math.abs(back - mgdl)).toBeLessThanOrEqual(1);
-    }
-  });
-
   it("convertGlucose dispatches to the right unit", () => {
     expect(convertGlucose(100, "mg/dL")).toBe(100);
     expect(convertGlucose(100, "mmol/L")).toBe(5.5);

src/lib/analytics/__tests__/berlin-day.test.ts

@@ -1,31 +0,0 @@
-import { describe, it, expect } from "vitest";
-import { berlinDayKey } from "../berlin-day";
-
-/**
- * v1.4.22 W5 reconcile (Code-MED-3) — pin that the helper buckets a
- * 23:30-Berlin reading on Tuesday into the Tuesday key, regardless of
- * UTC offset (CET / CEST, DST).
- */
-describe("berlinDayKey", () => {
-  it("buckets a 23:30-Berlin reading on Tuesday into Tuesday's key (CEST)", () => {
-    // 2025-10-25T21:30:00Z = 2025-10-25T23:30 CEST (Saturday before DST end)
-    expect(berlinDayKey(new Date("2025-10-25T21:30:00Z"))).toBe("2025-10-25");
-  });
-
-  it("buckets a 23:30-Berlin reading after DST end into the right Berlin day", () => {
-    // 2025-10-26 is the DST end day in Europe/Berlin (CET takes over).
-    // 2025-10-26T22:30:00Z = 2025-10-26T23:30 CET — still Sunday in Berlin.
-    expect(berlinDayKey(new Date("2025-10-26T22:30:00Z"))).toBe("2025-10-26");
-  });
-
-  it("crosses the UTC-midnight boundary in Berlin's favour", () => {
-    // 2026-05-09T22:30:00Z falls on 2026-05-10T00:30 CEST — Berlin says
-    // Sunday, UTC says Saturday. The helper must follow Berlin.
-    expect(berlinDayKey(new Date("2026-05-09T22:30:00Z"))).toBe("2026-05-10");
-  });
-
-  it("returns YYYY-MM-DD format (sortable, padded)", () => {
-    expect(berlinDayKey(new Date("2026-01-09T12:00:00Z"))).toBe("2026-01-09");
-    expect(berlinDayKey(new Date("2026-12-09T12:00:00Z"))).toBe("2026-12-09");
-  });
-});

src/lib/analytics/berlin-day.ts

@@ -1,35 +0,0 @@
-/**
- * v1.4.22 W5 reconcile (Code-MED-1) — shared Berlin-day-key helper.
- *
- * The CLAUDE.md timezone convention is "Europe/Berlin for display,
- * UTC in database". The dashboard analytics route used a private
- * `berlinDayKey()` (defined in `src/app/api/analytics/route.ts:330`)
- * to bucket measurements by Berlin calendar day. The targets route's
- * `sparklinePoints()` was bucketing by UTC `YYYY-MM-DD` — a 23:30
- * Berlin reading on Tuesday landed in Wednesday's bucket, drifting
- * the sparkline 1 day on cross-DST boundaries.
- *
- * Lift the helper into `src/lib/analytics/` so every display surface
- * shares the same bucket contract.
- */
-
-const BERLIN_DATE_PARTS = new Intl.DateTimeFormat("en-CA", {
-  timeZone: "Europe/Berlin",
-  year: "numeric",
-  month: "2-digit",
-  day: "2-digit",
-});
-
-/**
- * Format a `Date` as a `YYYY-MM-DD` string anchored to Europe/Berlin
- * calendar day. Used as a stable key for daily aggregation so a
- * 23:30-Berlin reading on Tuesday lands in Tuesday's bucket
- * regardless of UTC offset (CET / CEST, DST).
- */
-export function berlinDayKey(d: Date): string {
-  const parts = BERLIN_DATE_PARTS.formatToParts(d);
-  const y = parts.find((p) => p.type === "year")?.value ?? "1970";
-  const m = parts.find((p) => p.type === "month")?.value ?? "01";
-  const day = parts.find((p) => p.type === "day")?.value ?? "01";
-  return `${y}-${m}-${day}`;
-}

src/lib/glucose.ts

@@ -15,10 +15,6 @@ export function mgdlToMmol(mgdl: number): number {
   return Math.round((mgdl / MGDL_PER_MMOL) * 10) / 10;
 }
 
-export function mmolToMgdl(mmol: number): number {
-  return Math.round(mmol * MGDL_PER_MMOL);
-}
-
 export function convertGlucose(value: number, to: GlucoseUnit): number {
   return to === "mmol/L" ? mgdlToMmol(value) : Math.round(value);
 }

src/lib/tz/format.ts

@@ -121,7 +121,7 @@ export type FormatInUserTzShape =
  *     `DISPLAY_TIMEZONE`.
  *
  *   - "date" — `2026-05-11` (ISO date in the user's zone). Used as a
- *     day-bucket key parallel to the legacy `berlinDayKey()`.
+ *     stable day-bucket key for per-user aggregation.
  */
 export function formatInUserTz(
   date: Date,
@@ -151,11 +151,11 @@ export function formatInUserTz(
 }
 
 /**
- * Day-bucket key in the user's timezone. Mirrors `berlinDayKey()` but
- * parameterised. Used as a stable Map key for daily aggregation so a
- * 23:30-local reading lands on today's bucket regardless of UTC
- * offset. The legacy `berlinDayKey()` stays for surfaces that are
- * not yet user-scoped (admin tables, audit log viewer).
+ * Day-bucket key in the user's timezone. Used as a stable Map key for
+ * daily aggregation so a 23:30-local reading lands on today's bucket
+ * regardless of UTC offset. Every display surface in v1.4.40 anchors
+ * here — the legacy Berlin-only `berlinDayKey()` was retired in that
+ * release.
  */
 export function userDayKey(date: Date, tz: string): string {
   return formatInUserTz(date, tz, "date");