diff --git a/apps/api/src/routes/events.ts b/apps/api/src/routes/events.ts
index bc8ae19..3a795cc 100644
--- a/apps/api/src/routes/events.ts
+++ b/apps/api/src/routes/events.ts
@@ -308,6 +308,15 @@ eventsRouter.patch('/:uid/edit', zValidator('json', eventFieldsSchema), async (c
     // Join calendarEvents → calendars so we can read calendars.url and calendars.userId
     // in the same query. Without the join, referencing calendars.* produces invalid SQL
     // (Drizzle throws at toSQL() time) → 503. Mirrors the GET / join idiom at line 153.
+    //
+    // CR-01: calendar_events is keyed (calendarId, uid), NOT uid alone (schema.ts:121).
+    // With a shared Fastmail account (D-16) the SAME uid is cached once per member's
+    // calendar, so a uid-only lookup returns 2+ rows and an arbitrary [0] (typically the
+    // OTHER member's row). Scope the lookup to the acting member's writable set
+    // (own calendars OR shared) so the etag/objectUrl/ownership we act on belong to the
+    // right calendar. Order so the current user's OWN row ranks before a shared/other row
+    // — when both a personal and a shared copy of the uid exist, the acting member's copy
+    // is authoritative for the write target. limit(1) makes the pick deterministic.
     const [eventRow] = await db
       .select({
         uid: calendarEvents.uid,
@@ -319,13 +328,22 @@ eventsRouter.patch('/:uid/edit', zValidator('json', eventFieldsSchema), async (c
       })
       .from(calendarEvents)
       .innerJoin(calendars, eq(calendarEvents.calendarId, calendars.id))
-      .where(eq(calendarEvents.uid, uid))
+      .where(
+        and(
+          eq(calendarEvents.uid, uid),
+          or(eq(calendars.userId, currentUserId), eq(calendars.isShared, true)),
+        ),
+      )
+      .orderBy(sql`(${calendars.userId} = ${currentUserId}) desc`)
+      .limit(1)
 
     if (!eventRow) {
       return c.json({ error: 'Event not found' }, 404)
     }
 
-    // Ownership check: must be the calendar owner or shared (T-03-06)
+    // Ownership check: must be the calendar owner or shared (T-03-06).
+    // The WHERE above already restricts to the writable set, so any returned row is
+    // either the user's own calendar or a shared one — re-verify defensively.
     if (eventRow.userId !== currentUserId) {
       // Check if the calendar is shared (shared calendars are writable by all household members)
       const [calRow] = await db
@@ -408,6 +426,10 @@ eventsRouter.delete('/:uid', async (c) => {
     // Look up the event — join calendars so calendars.url / calendars.userId are accessible.
     // Same innerJoin idiom as the GET / handler (line 153). Without this join, Drizzle
     // throws at toSQL() time → 503.
+    //
+    // CR-01: scope to the acting member's writable set and pick deterministically — a
+    // shared Fastmail account (D-16) caches the same uid once per member's calendar, so a
+    // uid-only lookup would otherwise act on an arbitrary member's etag/objectUrl.
     const [eventRow] = await db
       .select({
         uid: calendarEvents.uid,
@@ -419,7 +441,14 @@ eventsRouter.delete('/:uid', async (c) => {
       })
       .from(calendarEvents)
       .innerJoin(calendars, eq(calendarEvents.calendarId, calendars.id))
-      .where(eq(calendarEvents.uid, uid))
+      .where(
+        and(
+          eq(calendarEvents.uid, uid),
+          or(eq(calendars.userId, currentUserId), eq(calendars.isShared, true)),
+        ),
+      )
+      .orderBy(sql`(${calendars.userId} = ${currentUserId}) desc`)
+      .limit(1)
 
     if (!eventRow) {
       return c.json({ error: 'Event not found' }, 404)