[tyler-dane]

What and why

Technical-debt sweep over the merged changes from the last seven days. The Microsoft Graph provider was by far the hottest churn in that window (microsoft-event.normalizer.ts touched six times, microsoft-recurrence.ts four), and two kinds of debt had accumulated there: a configuration option that was never actually configurable, and four-way copy-paste in the recurrence mapper. Two commits, one per debt item, no behavior change in either.

1. simplify(sync): drop the always-UTC graphPreferTimeZone option. NormalizeMicrosoftEventOptions.graphPreferTimeZone looked like a seam but had exactly one value. Every production caller (reader delta pages, writer fetchEvent, writer fetchInstanceAt) passed MICROSOFT_GRAPH_OUTLOOK_TIMEZONE; every test passed the same literal "UTC"; omitting it defaulted to that same constant. Both guards that read it compared it against that constant, so graphPreferTimeZone === MICROSOFT_GRAPH_OUTLOOK_TIMEZONE was a tautology and the dayjs.tz(raw, timeZone) branch in toOffsetIso was unreachable from any caller. Removing the option lets mapSchedule drop the options bag entirely and lets resolveTimedEventTimeZone read as the rule it always implemented: a non-UTC start field is the event's real zone, and a UTC one falls back to the recurrence zone, then the original start zone. The Prefer header itself is untouched, and the zone each event resolves to is identical.

2. refactor(sync): dedupe the recurrence weekday tables and field guards. RRULE_TO_GRAPH_DAY restated GRAPH_TO_RRULE_DAY backwards, so a weekday correction meant editing two tables with nothing checking them against each other; it is now derived by inverting the forward table. requireDayOfMonth/requireMonth/requireCount/requireEndDate were the same eight lines four times, differing only in the interpolated field name, and collapse into one requireField (the numbered-range message now names the Graph field, numberOfOccurrences, instead of the local variable). The "Multiple BYDAY ordinals" rule was thrown verbatim from both splitRelativeByDay and byweekdayToTokens, and both now call one assertSingleOrdinal.

GRAPH_DAY_ORDER and RRULE_WEEKDAY_TOKENS deliberately stay as they are. They are not restatements of the token map: the first carries Graph's Sunday-first ordering, the second rrule's Monday-based weekday indexes.

Net effect across both commits: 7 files, +70 / -154, with the existing suites covering the behavior unchanged.

Verify

bun run verify --strict

Selected packages: sync
Checks run: test:sync:fast, type-check, lint, knip
Checks skipped: (none)

✓ All checks passed
VERDICT: PASS

bun test packages/sync/src/providers/microsoft/microsoft-recurrence.test.ts: 60 pass, 0 fail.

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https://claude.ai/code/session_018gVNGW5WLSrqPjZaT1ReM4

[tyler-dane]

Technical-debt sweep summary for the 2026-10-19 → 2026-10-26 window (49 merged commits reviewed).

Debt addressed in this PR

Item	Smell	Where
graphPreferTimeZone normalizer option	Speculative generality: one value in every caller, tautological guard, unreachable branch	microsoft-event.normalizer.ts, reader/writer adapters
RRULE_TO_GRAPH_DAY	Duplicated inverse table, drift risk	microsoft-recurrence.ts
requireDayOfMonth / requireMonth / requireCount / requireEndDate	Four-way copy-paste differing only in a field name	microsoft-recurrence.ts
"Multiple BYDAY ordinals" throw	Duplicated rule in two readers	microsoft-recurrence.ts

Reviewed and deliberately left alone

• apps/calendar-macos keyboard router and root model (the hottest churn in the window, and NativeGridKeyboardRouter.swift is 1075 lines with a UITestLaunchPolicy test seam worth questioning). No Swift toolchain in this sandbox, so a refactor there could not be compiled or tested before pushing. Flagging rather than guessing.
• useEventMutations.ts (1198 lines, touched three times in the window). A real splitting candidate, but the file's behavior is load-bearing and heavily commented; it wants its own scoped change, not a drive-by.
• pointer-hint.teach-policy.ts / pointer-intent.teach-policy.ts, the billing trial utils, activeTimedDraftDeckLayout.ts, timezone-mismatch.ts, booking-operation.record.ts — all read clean; refactor: share hidden-draft strip, pointer gates, and outlook prefer headers #4835, refactor: dedupe microsoft zone resolution and the email dispatch send tail #4827, simplify: share truncateSeriesRulesBefore for local recurring splits #4813–refactor(sync): dedupe live provider smoke setup-and-create block #4817 already took the duplication out of these.
• listMicrosoftEventLabels sends Prefer: outlook.timezone="UTC" to /me/outlook/masterCategories, an endpoint with no date-times on it. Harmless, from the refactor: share hidden-draft strip, pointer gates, and outlook prefer headers #4835 shared-header pass, not worth a code change.

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