fix(03): correct event-write timezone + per-user calendar identity (Gate 2 Part D)

BUG A — timed events written 4h off: EventForm sent a naive local wall-clock
string with no offset; the UTC API container parsed it via new Date() as UTC, so
09:00 America/Toronto serialized to DTSTART:...090000Z. Fix: new
apps/pwa/src/lib/eventDateTime.ts serializes timed events to an unambiguous UTC
instant in the browser (where the operator's zone is known); all-day stays a DATE
string. No backend change.

BUG B — created events attached to the wrong user's calendar + duplicate calendar
rows per poll: calendars had no unique key on url, and poller/sync matched
calendars by url alone — so under the shared single Fastmail account (D-16) one
member's collection resolved to the other member's row. Fix: composite
unique(user_id, url); scope poller lookup + sync select to (userId, url); hand
migration 0001 (dedup + add key), applied to the live DB.

Regression tests fail against the buggy url-only predicate. API 98/98, PWA 140/140,
tsc clean both packages.

apps/pwa/src/components/EventForm.tsx

@@ -40,6 +40,7 @@ import {
   type RecurrencePreset,
 } from '../api/client.js'
 import type { CalendarOccurrence } from '../api/client.js'
+import { serializeEventDateTime } from '../lib/eventDateTime.js'
 
 // ── Constants ─────────────────────────────────────────────────────────────────
 
@@ -262,11 +263,23 @@ export function EventForm() {
   const handleSubmit = () => {
     if (!validate()) return
 
+    // BUG A fix: serialize timed events to an unambiguous UTC instant here in
+    // the browser (operator's zone is known) instead of sending a naive local
+    // wall-clock string. The API container is UTC; a naive string was being read
+    // as UTC, shifting 09:00 local to 09:00Z (4h off). See lib/eventDateTime.ts.
+    const { start: serializedStart, end: serializedEnd } = serializeEventDateTime(
+      allDay,
+      startDate,
+      startTime,
+      endDate,
+      endTime,
+    )
+
     const payload: CreateEventPayload = {
       title: title.trim(),
       allDay,
-      start: allDay ? startDate : `${startDate}T${startTime}:00`,
-      end: allDay ? endDate : `${endDate}T${endTime}:00`,
+      start: serializedStart,
+      end: serializedEnd,
       recurrence,
       ...(location.trim() ? { location: location.trim() } : {}),
       ...(description.trim() ? { description: description.trim() } : {}),

apps/pwa/src/lib/eventDateTime.test.ts

@@ -0,0 +1,53 @@
+/**
+ * BUG A regression — write-path timezone serialization.
+ *
+ * Verifies that timed events are serialized to an unambiguous UTC instant
+ * (so the operator's wall-clock time round-trips correctly regardless of the
+ * API container's timezone), while all-day events keep their DATE strings.
+ *
+ * The PWA vitest harness runs with TZ=UTC, so the assertions are computed
+ * relative to the local zone (whatever it is) rather than hard-coding an offset.
+ * The core guarantee under test: the serialized timed value is a UTC instant
+ * (ends in 'Z') derived from the LOCAL wall clock — never the naive wall-clock
+ * string passed through verbatim, and never an instant that loses the local hour.
+ */
+
+import { describe, it, expect } from 'vitest'
+import { serializeEventDateTime, localWallClockToUtcIso } from './eventDateTime.js'
+
+describe('serializeEventDateTime (BUG A — write-path TZ)', () => {
+  it('serializes a timed start to a UTC instant (ends in Z)', () => {
+    const { start } = serializeEventDateTime(false, '2026-06-07', '09:00', '2026-06-07', '10:00')
+    expect(start.endsWith('Z')).toBe(true)
+    // It must NOT be the naive wall-clock string (the original bug shape).
+    expect(start).not.toBe('2026-06-07T09:00:00')
+  })
+
+  it('the serialized instant round-trips back to the SAME local wall clock', () => {
+    // This is the heart of BUG A: 09:00 in → 09:00 back out in the operator's zone.
+    const { start, end } = serializeEventDateTime(false, '2026-06-07', '09:00', '2026-06-07', '10:30')
+    const startBack = new Date(start)
+    expect(startBack.getHours()).toBe(9)
+    expect(startBack.getMinutes()).toBe(0)
+    const endBack = new Date(end)
+    expect(endBack.getHours()).toBe(10)
+    expect(endBack.getMinutes()).toBe(30)
+  })
+
+  it('equals the instant new Date(local parts) produces — not a passthrough', () => {
+    const { start } = serializeEventDateTime(false, '2026-06-07', '09:00', '2026-06-07', '10:00')
+    expect(start).toBe(new Date('2026-06-07T09:00:00').toISOString())
+  })
+
+  it('leaves all-day events as DATE strings (no time, no Z) — D-13 contract', () => {
+    const { start, end } = serializeEventDateTime(true, '2026-06-07', '09:00', '2026-06-09', '10:00')
+    expect(start).toBe('2026-06-07')
+    expect(end).toBe('2026-06-09')
+  })
+
+  it('localWallClockToUtcIso round-trips a local wall clock to a UTC instant', () => {
+    const iso = localWallClockToUtcIso('2026-06-07', '09:00')
+    expect(iso.endsWith('Z')).toBe(true)
+    expect(new Date(iso).getHours()).toBe(9)
+  })
+})

apps/pwa/src/lib/eventDateTime.ts

@@ -0,0 +1,61 @@
+/**
+ * Event date/time serialization for the write path (BUG A fix).
+ *
+ * The bug: EventForm previously sent a NAIVE local wall-clock string
+ * (`${date}T${time}:00`, e.g. "2026-06-07T09:00:00") with NO timezone offset.
+ * The API outbox worker then did `new Date(thatString)`, which Node parses in
+ * the SERVER container's local timezone (UTC in Docker). So "09:00" Toronto
+ * became 09:00 UTC, and buildVeventString serialized it as `090000Z`, which
+ * displays back as 05:00 EDT — a 4-hour error.
+ *
+ * The fix: serialize timed events to an UNAMBIGUOUS instant here in the browser,
+ * where the operator's timezone IS known. `new Date(date + 'T' + time)` is parsed
+ * in the browser's local zone (the operator's wall clock), and `.toISOString()`
+ * converts that instant to a correct UTC `...Z` string. The worker's `new Date()`
+ * then parses an unambiguous UTC instant regardless of container timezone, and
+ * the round-trip preserves the operator's wall-clock time.
+ *
+ * All-day events carry no time component and remain `YYYY-MM-DD` DATE strings
+ * (D-13) — they are timezone-independent by contract and must NOT be converted.
+ */
+
+/**
+ * Serialize the start/end of an event for the create/update payload.
+ *
+ * @param allDay    when true, returns the date strings unchanged (DATE contract, D-13)
+ * @param startDate 'YYYY-MM-DD'
+ * @param startTime 'HH:MM' (ignored when allDay)
+ * @param endDate   'YYYY-MM-DD'
+ * @param endTime   'HH:MM' (ignored when allDay)
+ * @returns { start, end } — for timed events, ISO-8601 UTC instants ('...Z');
+ *          for all-day events, the raw 'YYYY-MM-DD' date strings.
+ */
+export function serializeEventDateTime(
+  allDay: boolean,
+  startDate: string,
+  startTime: string,
+  endDate: string,
+  endTime: string,
+): { start: string; end: string } {
+  if (allDay) {
+    // DATE contract (D-13): no time component, timezone-independent.
+    return { start: startDate, end: endDate }
+  }
+
+  // Timed: build the instant from local wall-clock parts (browser is in the
+  // operator's zone) and serialize to a UTC instant so the wire value is
+  // unambiguous and container-timezone-independent.
+  return {
+    start: localWallClockToUtcIso(startDate, startTime),
+    end: localWallClockToUtcIso(endDate, endTime),
+  }
+}
+
+/**
+ * Convert a local wall-clock date+time to a UTC ISO-8601 instant.
+ * `new Date('YYYY-MM-DDTHH:MM:00')` (no offset) is parsed in the browser's
+ * local timezone per ECMAScript, giving the correct instant for the operator.
+ */
+export function localWallClockToUtcIso(date: string, time: string): string {
+  return new Date(`${date}T${time}:00`).toISOString()
+}