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/api/src/broker/poller.ts

@@ -16,7 +16,7 @@
  */
 
 import { schedule } from 'node-cron'
-import { eq } from 'drizzle-orm'
+import { and, eq } from 'drizzle-orm'
 import { db } from '../db/client.js'
 import { memberCredentials, calendars } from '../db/schema.js'
 import { decryptPassword } from './crypto.js'
@@ -44,11 +44,15 @@ export async function runPoll(): Promise<void> {
       const davCalendars = await client.fetchCalendars()
 
       for (const davCal of davCalendars) {
-        // Look up the stored calendar row to get the known ctag (D-13)
+        // Look up the stored calendar row to get the known ctag (D-13).
+        // BUG B: scope by (userId, url). The two members share one Fastmail account
+        // (D-16), so the same collection URL exists for both. A url-only predicate
+        // matched the OTHER member's row → wrong ctag compared, and syncCalendar
+        // wrote events under the wrong calendar. Match on this member's row only.
         const [stored] = await db
           .select()
           .from(calendars)
-          .where(eq(calendars.url, davCal.url))
+          .where(and(eq(calendars.userId, cred.userId), eq(calendars.url, davCal.url)))
           .limit(1)
 
         // ctag/syncToken: defensive null handling (Pitfall #6)

apps/api/src/broker/sync.ts

@@ -18,7 +18,7 @@
 import type { DAVCalendar } from 'tsdav'
 import type { FastmailClient } from './client.js'
 import ICAL from 'ical.js'
-import { eq } from 'drizzle-orm'
+import { and, eq } from 'drizzle-orm'
 import { db } from '../db/client.js'
 import { calendars, calendarEvents } from '../db/schema.js'
 
@@ -56,10 +56,17 @@ export async function syncCalendar(
     })
 
   // 2. Select the calendar row to get its DB id (insertId is unreliable on ON DUPLICATE KEY UPDATE).
-  const [cal] = await db.select().from(calendars).where(eq(calendars.url, davCal.url)).limit(1)
+  //    BUG B: scope by (userId, url) — the same collection URL exists for both members
+  //    (shared Fastmail account, D-16). A url-only lookup returned the OTHER member's
+  //    row (lowest id), so events were cached under the wrong calendarId.
+  const [cal] = await db
+    .select()
+    .from(calendars)
+    .where(and(eq(calendars.userId, userId), eq(calendars.url, davCal.url)))
+    .limit(1)
   if (!cal) {
     // Should never happen — we just upserted it
-    throw new Error(`syncCalendar: could not find calendar row for url=${davCal.url}`)
+    throw new Error(`syncCalendar: could not find calendar row for userId=${userId} url=${davCal.url}`)
   }
 
   // 3. Fetch all calendar objects (REPORT calendar-query).

apps/api/src/db/migrations/0001_calendars_user_url_unique.sql

@@ -0,0 +1,41 @@
+-- BUG B — calendars: add composite unique key (user_id, url).
+--
+-- Context (D-16): the two household members share ONE Fastmail account, so the
+-- SAME collection URL is polled by both credentials. The calendar upsert keyed on
+-- url alone never triggered onDuplicateKeyUpdate (no unique key on url), so every
+-- poll inserted a fresh calendar row; the url-only lookup then resolved to the
+-- other member's row, caching events under the wrong calendarId.
+--
+-- This migration is hand-written (not drizzle-kit generated) because drizzle-kit
+-- push is unsafe on populated MariaDB (false destructive diffs) and there is no
+-- migrations baseline. Apply it directly to the live DB before/with the image
+-- rebuild that ships the schema + broker fixes.
+--
+-- Order matters: duplicate (user_id, url) rows must be collapsed BEFORE the unique
+-- key is added, or ADD UNIQUE fails. We keep the LOWEST id per (user_id, url),
+-- repoint any cached events from the loser rows onto the keeper, then delete losers.
+
+-- 1. Repoint calendar_events from duplicate calendar rows onto the keeper
+--    (lowest id) for each (user_id, url) group.
+UPDATE calendar_events ce
+JOIN calendars dup       ON dup.id = ce.calendar_id
+JOIN (
+  SELECT user_id, url, MIN(id) AS keep_id
+  FROM calendars
+  GROUP BY user_id, url
+) keeper ON keeper.user_id = dup.user_id AND keeper.url = dup.url
+SET ce.calendar_id = keeper.keep_id
+WHERE ce.calendar_id <> keeper.keep_id;
+
+-- 2. Delete the duplicate (loser) calendar rows, keeping the lowest id per group.
+DELETE c FROM calendars c
+JOIN (
+  SELECT user_id, url, MIN(id) AS keep_id
+  FROM calendars
+  GROUP BY user_id, url
+) keeper ON keeper.user_id = c.user_id AND keeper.url = c.url
+WHERE c.id <> keeper.keep_id;
+
+-- 3. Add the composite unique key that makes the upsert idempotent per (user_id, url).
+ALTER TABLE calendars
+  ADD CONSTRAINT uniq_calendar_user_url UNIQUE (user_id, url);

apps/api/src/db/schema.ts

@@ -73,7 +73,16 @@ export const calendars = mysqlTable(
     lastSyncedAt: timestamp('last_synced_at'),
     isShared: boolean('is_shared').default(false).notNull(),
   },
-  (t) => [index('idx_calendars_user_id').on(t.userId)],
+  (t) => [
+    index('idx_calendars_user_id').on(t.userId),
+    // BUG B: calendar identity is (userId, url), not url alone. The two household
+    // members share one Fastmail account (D-16), so the SAME collection URL is
+    // polled by both credentials. Without this unique key the calendar upsert's
+    // onDuplicateKeyUpdate never fired → a new row per poll, and the url-only
+    // lookup resolved to the other member's row → events cached under the wrong
+    // calendarId. Keying on (userId, url) makes the upsert idempotent per member.
+    unique('uniq_calendar_user_url').on(t.userId, t.url),
+  ],
 )
 
 /**

apps/api/tests/broker/poller.test.ts

@@ -194,6 +194,44 @@ describe('broker poller — runPoll', () => {
     expect(mockSyncCalendar).not.toHaveBeenCalled()
   })
 
+  it('BUG B: scopes the stored-calendar lookup to (userId, url), not url alone', async () => {
+    // Capture the predicate passed to db.select().from(calendars).where(...).
+    // The buggy code passed eq(url) only; the fix passes and(eq(userId), eq(url)).
+    // We serialize the predicate and assert it references the member's user_id column.
+    const capturedWhere: unknown[] = []
+    mockSelectWhere.mockImplementation((pred: unknown) => {
+      capturedWhere.push(pred)
+      return { limit: mockSelectLimit }
+    })
+
+    const { runPoll } = await import('../../src/broker/poller.js')
+
+    mockCredentialsSelectResult.push({
+      id: 7,
+      userId: 42,
+      fastmailEmail: 'lucas@fastmail.com',
+      encryptedPassword: 'enc',
+    })
+
+    mockFetchCalendars.mockResolvedValue([
+      { url: 'https://caldav.fastmail.com/cal/', displayName: 'Calendar', ctag: 'c', syncToken: null },
+    ])
+
+    await runPoll()
+
+    expect(capturedWhere.length).toBeGreaterThan(0)
+    // A composite and(...) predicate exposes multiple queryChunks; a single eq does not
+    // contain a nested SQL referencing the user_id column. Serialize and inspect.
+    const pred = capturedWhere[0] as { queryChunks?: unknown[] }
+    const serialized = JSON.stringify(pred, (_k, v) =>
+      typeof v === 'object' && v !== null && 'name' in (v as Record<string, unknown>)
+        ? (v as { name?: unknown }).name
+        : v,
+    )
+    expect(serialized).toContain('user_id')
+    expect(serialized).toContain('url')
+  })
+
   it('processes all member credentials in a poll cycle', async () => {
     const { runPoll } = await import('../../src/broker/poller.js')
 

apps/api/tests/broker/sync.test.ts

@@ -247,6 +247,52 @@ describe('syncCalendar', () => {
     expect(eventUpdateArg.set).toHaveProperty('hasRrule', true)
   })
 
+  it('BUG B: scopes the calendar-row select to (userId, url), not url alone', async () => {
+    // Capture the predicate passed to db.select().from(calendars).where(...).limit(1).
+    const capturedWhere: unknown[] = []
+    mockWhere.mockImplementation((pred: unknown) => {
+      capturedWhere.push(pred)
+      return { limit: mockLimit }
+    })
+
+    const { syncCalendar } = await import('../../src/broker/sync.js')
+    const mockClient = { fetchCalendarObjects: vi.fn().mockResolvedValue([]) }
+    const mockDavCal = {
+      url: 'https://caldav.fastmail.com/dav/calendars/user/test@fm.com/Default/',
+      displayName: 'Test',
+      ctag: 'v1',
+      syncToken: null,
+    }
+
+    await syncCalendar(mockClient as never, mockDavCal as never, 99)
+
+    expect(capturedWhere.length).toBeGreaterThan(0)
+    const serialized = JSON.stringify(capturedWhere[0], (_k, v) =>
+      typeof v === 'object' && v !== null && 'name' in (v as Record<string, unknown>)
+        ? (v as { name?: unknown }).name
+        : v,
+    )
+    expect(serialized).toContain('user_id')
+    expect(serialized).toContain('url')
+  })
+
+  it('BUG B: calendar upsert is idempotent — onDuplicateKeyUpdate fires for the calendar row', async () => {
+    const { syncCalendar } = await import('../../src/broker/sync.js')
+    const mockClient = { fetchCalendarObjects: vi.fn().mockResolvedValue([]) }
+    const mockDavCal = {
+      url: 'https://caldav.fastmail.com/dav/calendars/user/test@fm.com/Default/',
+      displayName: 'Test',
+      ctag: 'v1',
+      syncToken: null,
+    }
+    await syncCalendar(mockClient as never, mockDavCal as never, 1)
+    // The calendar insert (call 0) must use onDuplicateKeyUpdate so the (userId,url)
+    // unique key makes re-polls update-in-place instead of inserting duplicate rows.
+    expect(mockOnDuplicateKeyUpdate).toHaveBeenCalled()
+    const calUpdateArg = mockOnDuplicateKeyUpdate.mock.calls[0][0]
+    expect(calUpdateArg.set).toHaveProperty('ctag')
+  })
+
   it('updates the calendar ctag/syncToken after a successful sync', async () => {
     const { syncCalendar } = await import('../../src/broker/sync.js')