refactor(sync): retire dead graph zone option and dedupe microsoft recurrence mapping

packages/sync/src/providers/microsoft/microsoft-event-reader.adapter.ts

@@ -14,7 +14,6 @@ import { microsoftGraphRequest } from "@sync/providers/microsoft/microsoft-graph
 import {
   MICROSOFT_EVENT_SELECT,
   MICROSOFT_GRAPH_BASE_URL,
-  MICROSOFT_GRAPH_OUTLOOK_TIMEZONE,
   MICROSOFT_GRAPH_PREFER_EVENT_PAGE,
 } from "@sync/providers/microsoft/microsoft-http.constants";
 import { ProviderEventError } from "@sync/providers/provider-event.port";
@@ -100,17 +99,12 @@ export class MicrosoftEventReaderAdapter implements ProviderEventReader {
     const seenProviderIds = new Set<string>();
     let skipped = 0;
     const colorLabels = input.colorLabels ?? new Map();
-    const normalizeOptions = {
-      graphPreferTimeZone: MICROSOFT_GRAPH_OUTLOOK_TIMEZONE,
-    };
     const seriesMasterIds = new Set<string>();
 
     const pushItem = (item: GraphEventDeltaItem) => {
       if (!item.id || seenProviderIds.has(item.id)) return;
       try {
-        events.push(
-          normalizeMicrosoftEvent(item, colorLabels, normalizeOptions),
-        );
+        events.push(normalizeMicrosoftEvent(item, colorLabels));
         seenProviderIds.add(item.id);
       } catch (error) {
         if (error instanceof ProviderEventError) {

packages/sync/src/providers/microsoft/microsoft-event-writer.adapter.ts

@@ -16,7 +16,6 @@ import { microsoftGraphRequest } from "@sync/providers/microsoft/microsoft-graph
 import {
   MICROSOFT_EVENT_SELECT,
   MICROSOFT_GRAPH_BASE_URL,
-  MICROSOFT_GRAPH_OUTLOOK_TIMEZONE,
   MICROSOFT_GRAPH_PREFER_OUTLOOK_TIMEZONE,
 } from "@sync/providers/microsoft/microsoft-http.constants";
 import {
@@ -204,9 +203,7 @@ export class MicrosoftEventWriter implements ProviderEventWriter {
     const api = this.#makeApi(input.accessToken);
     try {
       const event = await api.get({ eventId: input.providerEventId });
-      return normalizeMicrosoftEvent(event, undefined, {
-        graphPreferTimeZone: MICROSOFT_GRAPH_OUTLOOK_TIMEZONE,
-      });
+      return normalizeMicrosoftEvent(event);
     } catch (error) {
       if (isNotFound(error)) return null;
       throw classifyWriteError(error);
@@ -230,7 +227,6 @@ export class MicrosoftEventWriter implements ProviderEventWriter {
       if (!match) return null;
       return normalizeMicrosoftEvent(match, undefined, {
         allowOccurrence: true,
-        graphPreferTimeZone: MICROSOFT_GRAPH_OUTLOOK_TIMEZONE,
       });
     } catch (error) {
       if (isNotFound(error)) return null;

packages/sync/src/providers/microsoft/microsoft-event.normalizer.recurrence.test.ts

@@ -104,9 +104,7 @@ const toMasterRecord = (
 
 describe("normalizeMicrosoftEvent Microsoft recurring Unwind (UTC daily)", () => {
   it("keeps UTC when Graph declares UTC on the series and maps OID cancelledOccurrences to EXDATE", () => {
-    const read = normalizeMicrosoftEvent(unwindUtcDailyMaster(), undefined, {
-      graphPreferTimeZone: "UTC",
-    });
+    const read = normalizeMicrosoftEvent(unwindUtcDailyMaster());
     const master = asSeriesMaster(read);
 
     expect(read.schedule.kind).toBe("timed");
@@ -120,9 +118,7 @@ describe("normalizeMicrosoftEvent Microsoft recurring Unwind (UTC daily)", () =>
   });
 
   it("does not project occurrences on cancelled UTC dates", () => {
-    const read = normalizeMicrosoftEvent(unwindUtcDailyMaster(), undefined, {
-      graphPreferTimeZone: "UTC",
-    });
+    const read = normalizeMicrosoftEvent(unwindUtcDailyMaster());
     const master = toMasterRecord(read);
     const horizon = {
       start: new Date("2025-10-19T00:00:00.000Z"),
@@ -139,20 +135,8 @@ describe("normalizeMicrosoftEvent Microsoft recurring Unwind (UTC daily)", () =>
   });
 
   it("renders edited Oct 17 occurrence at 8:15 PM Denver without duplicating the series slot", () => {
-    const masterRead = normalizeMicrosoftEvent(
-      unwindUtcDailyMaster(),
-      undefined,
-      {
-        graphPreferTimeZone: "UTC",
-      },
-    );
-    const exceptionRead = normalizeMicrosoftEvent(
-      oct17DenverException(),
-      undefined,
-      {
-        graphPreferTimeZone: "UTC",
-      },
-    );
+    const masterRead = normalizeMicrosoftEvent(unwindUtcDailyMaster());
+    const exceptionRead = normalizeMicrosoftEvent(oct17DenverException());
     expect(exceptionRead.kind).toBe("event");
     if (exceptionRead.kind !== "event") return;
     expect(exceptionRead.schedule.kind).toBe("timed");
@@ -213,17 +197,13 @@ describe("normalizeMicrosoftEvent Microsoft recurring Unwind (UTC daily)", () =>
         id: "series-a",
         cancelledOccurrences: [OID("2025-10-26")],
       }),
-      undefined,
-      { graphPreferTimeZone: "UTC" },
     );
     const second = normalizeMicrosoftEvent(
       unwindUtcDailyMaster({
         id: "series-b",
         iCalUId: "other-ical-uid",
         cancelledOccurrences: [OID("2025-10-25")],
       }),
-      undefined,
-      { graphPreferTimeZone: "UTC" },
     );
     const eventA = toMasterRecord(first);
     const eventB = toMasterRecord(second);

packages/sync/src/providers/microsoft/microsoft-event.normalizer.timezone.test.ts

@@ -133,13 +133,7 @@ describe("normalizeMicrosoftEvent Microsoft time zones", () => {
   it.each(zoneFixtures)(
     "maps Unwind ($label) to Denver wall time and weekly BYDAY",
     (fixture) => {
-      const read = normalizeMicrosoftEvent(
-        unwindGraphEvent(fixture),
-        undefined,
-        {
-          graphPreferTimeZone: "UTC",
-        },
-      );
+      const read = normalizeMicrosoftEvent(unwindGraphEvent(fixture));
       const schedule = asTimedSchedule(read);
       const recurrence = asSeriesMaster(read);
 
@@ -157,8 +151,6 @@ describe("normalizeMicrosoftEvent Microsoft time zones", () => {
         startEndTimeZone: "UTC",
         recurrenceTimeZone: "Mountain Standard Time",
       }),
-      undefined,
-      { graphPreferTimeZone: "UTC" },
     );
     const event = toEventRecord(read.schedule, asSeriesMaster(read).rules);
     const slots = projectedLocalSlots(
@@ -181,8 +173,6 @@ describe("normalizeMicrosoftEvent Microsoft time zones", () => {
         startEndTimeZone: "UTC",
         originalStartTimeZone: "Mountain Standard Time",
       }),
-      undefined,
-      { graphPreferTimeZone: "UTC" },
     );
     const event = toEventRecord(read.schedule, asSeriesMaster(read).rules);
     const slots = projectedLocalSlots(
@@ -207,8 +197,6 @@ describe("normalizeMicrosoftEvent Microsoft time zones", () => {
     try {
       const read = normalizeMicrosoftEvent(
         unwindGraphEvent({ startEndTimeZone: "Mountain Standard Time" }),
-        undefined,
-        { graphPreferTimeZone: "UTC" },
       );
       const event = toEventRecord(read.schedule, asSeriesMaster(read).rules);
       const slots = projectedLocalSlots(

packages/sync/src/providers/microsoft/microsoft-event.normalizer.ts

@@ -10,7 +10,6 @@ import { SyncEventContentSchema } from "@core/types/sync/event.contracts";
 import dayjs from "@core/util/date/dayjs";
 import { cancelledOccurrencesToExdateRules } from "@sync/providers/microsoft/microsoft-cancelled-occurrences";
 import { outlookCategoryNameToSlot } from "@sync/providers/microsoft/microsoft-event-category.map";
-import { MICROSOFT_GRAPH_OUTLOOK_TIMEZONE } from "@sync/providers/microsoft/microsoft-http.constants";
 import { toRRule } from "@sync/providers/microsoft/microsoft-recurrence";
 import { UnsupportedRecurrenceError } from "@sync/providers/microsoft/microsoft-recurrence.error";
 import { type GraphPatternedRecurrence } from "@sync/providers/microsoft/microsoft-recurrence.types";
@@ -35,8 +34,6 @@ const MEETING_PROVIDER_LABELS: Readonly<Record<string, string>> = {
 
 export interface NormalizeMicrosoftEventOptions {
   readonly allowOccurrence?: boolean;
-  /** Matches Prefer outlook.timezone on Graph reads (see event reader adapter). */
-  readonly graphPreferTimeZone?: string;
 }
 
 export interface GraphDateTimeTimeZone {
@@ -126,7 +123,7 @@ export function normalizeMicrosoftEvent(
   }
 
   const providerVersion = requireVersion(item);
-  const schedule = mapSchedule(item, options);
+  const schedule = mapSchedule(item);
 
   return {
     kind: "event",
@@ -270,10 +267,7 @@ export function mapConference(item: GraphEvent): Conference | null {
   return parsed.success ? parsed.data : null;
 }
 
-function mapSchedule(
-  item: GraphEvent,
-  options: NormalizeMicrosoftEventOptions,
-) {
+function mapSchedule(item: GraphEvent) {
   const { start, end } = item;
   if (!start || !end) {
     throw new ProviderEventError(
@@ -299,20 +293,14 @@ function mapSchedule(
   }
 
   if (start.dateTime && end.dateTime) {
-    const graphPreferTimeZone =
-      options.graphPreferTimeZone ?? MICROSOFT_GRAPH_OUTLOOK_TIMEZONE;
     const startFieldZone = toIanaTimeZone(
       start.timeZone ?? end.timeZone ?? "UTC",
     );
-    const timeZone = resolveTimedEventTimeZone(
-      item,
-      startFieldZone,
-      graphPreferTimeZone,
-    );
+    const timeZone = resolveTimedEventTimeZone(item, startFieldZone);
     return parseSchedule({
       kind: "timed",
-      start: toOffsetIso(start, timeZone, graphPreferTimeZone),
-      end: toOffsetIso(end, timeZone, graphPreferTimeZone),
+      start: toOffsetIso(start, timeZone),
+      end: toOffsetIso(end, timeZone),
       timeZone,
     });
   }
@@ -330,28 +318,27 @@ function extractDatePart(value: GraphDateTimeTimeZone): string | null {
   return parsed.format(DATE_ONLY);
 }
 
+/**
+ * Reads come back under `Prefer: outlook.timezone="UTC"`, so a UTC start field
+ * carries no zone of its own: fall back to the series' recurrence zone, then to
+ * the original start zone. Any other start-field zone is the event's real one.
+ */
 function resolveTimedEventTimeZone(
   item: GraphEvent,
   startFieldZone: string,
-  graphPreferTimeZone: string,
 ): string {
+  if (startFieldZone !== "UTC") return startFieldZone;
   const recurrenceZone = item.recurrence?.range?.recurrenceTimeZone
     ? toIanaTimeZone(item.recurrence.range.recurrenceTimeZone)
     : null;
+  if (recurrenceZone && recurrenceZone !== "UTC") return recurrenceZone;
   const originalStartZone = item.originalStartTimeZone
     ? toIanaTimeZone(item.originalStartTimeZone)
     : null;
-  if (
-    graphPreferTimeZone === MICROSOFT_GRAPH_OUTLOOK_TIMEZONE &&
-    startFieldZone === "UTC"
-  ) {
-    if (recurrenceZone && recurrenceZone !== "UTC") return recurrenceZone;
-    if (originalStartZone && originalStartZone !== "UTC") {
-      return originalStartZone;
-    }
+  if (originalStartZone && originalStartZone !== "UTC") {
+    return originalStartZone;
   }
-  if (startFieldZone !== "UTC") return startFieldZone;
-  return recurrenceZone ?? originalStartZone ?? startFieldZone;
+  return "UTC";
 }
 
 function parseSchedule(candidate: unknown) {
@@ -410,21 +397,14 @@ function stripGraphDateTimeFraction(dateTime: string): string {
   return dateTime.replace(/\.\d+$/, "");
 }
 
-function toOffsetIso(
-  value: GraphDateTimeTimeZone,
-  timeZone: string,
-  graphPreferTimeZone: string,
-): string {
+/** Graph wall clocks arrive in UTC (see the Prefer header), then shift to `timeZone`. */
+function toOffsetIso(value: GraphDateTimeTimeZone, timeZone: string): string {
   if (!value.dateTime) {
     throw new ProviderEventError(
       "unmappableSchedule",
       "Event date-time had no dateTime",
     );
   }
   const raw = stripGraphDateTimeFraction(value.dateTime);
-  const anchored =
-    graphPreferTimeZone === MICROSOFT_GRAPH_OUTLOOK_TIMEZONE
-      ? dayjs.utc(raw).tz(timeZone)
-      : dayjs.tz(raw, timeZone);
-  return anchored.format(RFC3339_OFFSET);
+  return dayjs.utc(raw).tz(timeZone).format(RFC3339_OFFSET);
 }

packages/sync/src/providers/microsoft/microsoft-http.constants.ts

@@ -8,8 +8,8 @@ export const MICROSOFT_CALENDAR_LIST_SELECT =
   "id,name,color,hexColor,canEdit,canShare,isDefaultCalendar,owner,isRemovable";
 const MICROSOFT_EVENT_PAGE_SIZE = 200;
 
-// Graph Prefer header: wall clocks in UTC so readers and writers share one
-// zone contract with the normalizer's graphPreferTimeZone default.
+// Graph Prefer header: wall clocks in UTC, which is the zone contract the
+// normalizer assumes when it resolves a timed event's real time zone.
 export const MICROSOFT_GRAPH_OUTLOOK_TIMEZONE = "UTC";
 export const MICROSOFT_GRAPH_PREFER_OUTLOOK_TIMEZONE = `outlook.timezone="${MICROSOFT_GRAPH_OUTLOOK_TIMEZONE}"`;
 export const MICROSOFT_GRAPH_PREFER_EVENT_PAGE = `odata.maxpagesize=${MICROSOFT_EVENT_PAGE_SIZE}, ${MICROSOFT_GRAPH_PREFER_OUTLOOK_TIMEZONE}`;