diff --git a/apps/pwa/src/api/client.ts b/apps/pwa/src/api/client.ts
index cd330f4..e997fda 100644
--- a/apps/pwa/src/api/client.ts
+++ b/apps/pwa/src/api/client.ts
@@ -103,3 +103,108 @@ export async function fetchEvents(
 
 // Phase 1 legacy types (CalendarEvent, EventsResponse, fetchEventsLegacy) removed in Plan 05
 // when the Phase 1 broker-proof component was retired.
+
+// ── /api/events (write — Plan 03-05) ─────────────────────────────────────────
+
+/**
+ * Recurrence presets supported by the EventForm.
+ * Maps 1:1 to the RRULE frequency values the API accepts.
+ */
+export type RecurrencePreset = 'none' | 'daily' | 'weekly' | 'monthly' | 'yearly'
+
+/**
+ * Payload for creating or updating a calendar event.
+ * Mirrors the Zod schema on POST /api/events/create and PATCH /api/events/:uid/edit.
+ */
+export interface CreateEventPayload {
+  title: string
+  allDay: boolean
+  start: string            // 'YYYY-MM-DD' for allDay; ISO 8601 for timed
+  end: string              // same format as start
+  recurrence: RecurrencePreset
+  location?: string
+  description?: string
+  calendarUrl?: string     // omit to use the member's default writable calendar (D-01)
+}
+
+/** Response from POST /api/events/create and PATCH /api/events/:uid/edit */
+export interface CreateEventResponse {
+  uid: string
+}
+
+/**
+ * A writable calendar returned by GET /api/events/writable-calendars.
+ * The server is the authoritative source of the writable set (D-03).
+ * The client never derives writability — it reads this endpoint verbatim.
+ */
+export interface WritableCalendar {
+  url: string
+  displayName: string
+  color: string
+  isShared: boolean
+}
+
+/**
+ * Create a new calendar event.
+ *
+ * POSTs to /api/events/create and returns immediately with 202 + uid.
+ * The server enqueues the write to CalDAV asynchronously (D-05/D-12).
+ */
+export async function createEvent(payload: CreateEventPayload): Promise<CreateEventResponse> {
+  const res = await fetch('/api/events/create', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    credentials: 'include',
+    body: JSON.stringify(payload),
+  })
+
+  if (!res.ok) {
+    throw new Error(`POST /api/events/create failed: ${res.status}`)
+  }
+
+  return res.json() as Promise<CreateEventResponse>
+}
+
+/**
+ * Update an existing calendar event.
+ *
+ * PATCHes /api/events/:uid/edit with the updated payload.
+ * Returns 202 + uid; the write is enqueued asynchronously (D-05).
+ */
+export async function updateEvent(
+  uid: string,
+  payload: CreateEventPayload,
+): Promise<CreateEventResponse> {
+  const res = await fetch(`/api/events/${uid}/edit`, {
+    method: 'PATCH',
+    headers: { 'Content-Type': 'application/json' },
+    credentials: 'include',
+    body: JSON.stringify(payload),
+  })
+
+  if (!res.ok) {
+    throw new Error(`PATCH /api/events/${uid}/edit failed: ${res.status}`)
+  }
+
+  return res.json() as Promise<CreateEventResponse>
+}
+
+/**
+ * Fetch the authoritative list of writable calendars for the current member.
+ *
+ * The server owns the D-03 writable set (WHERE userId=currentUser.id OR isShared=1).
+ * The client NEVER derives writability — it reads this endpoint verbatim.
+ * Drives the calendar picker visibility (D-02: hidden when only 1 writable calendar).
+ */
+export async function fetchWritableCalendars(): Promise<WritableCalendar[]> {
+  const res = await fetch('/api/events/writable-calendars', {
+    credentials: 'include',
+  })
+
+  if (!res.ok) {
+    throw new Error(`GET /api/events/writable-calendars failed: ${res.status}`)
+  }
+
+  const body = (await res.json()) as { calendars: WritableCalendar[] }
+  return body.calendars
+}
diff --git a/apps/pwa/src/store/calendarStore.ts b/apps/pwa/src/store/calendarStore.ts
index e266433..0ab50d0 100644
--- a/apps/pwa/src/store/calendarStore.ts
+++ b/apps/pwa/src/store/calendarStore.ts
@@ -35,10 +35,27 @@ export interface CalendarStore {
   openEventId: string | null
   calendarRange: { start: string; end: string }
 
+  // ── EventForm UI state (Plan 03-05) ──────────────────────────────────────
+  // Server state (events, calendars) lives in TanStack Query. These are pure
+  // UI-shape keys: whether the form is open, what mode it is in, and which
+  // event UID to pre-populate in edit mode.
+  eventFormOpen: boolean
+  eventFormMode: 'create' | 'edit'
+  eventFormUid: string | null
+
   setSelectedView: (view: string) => void
   setSelectedDate: (date: string) => void
   setOpenEventId: (id: string | null) => void
   setCalendarRange: (range: { start: string; end: string }) => void
+
+  /**
+   * Open or close the EventForm.
+   *
+   * @param open   true to open, false to close
+   * @param mode   'create' (default) or 'edit'
+   * @param uid    UID of the event to pre-populate in edit mode (null otherwise)
+   */
+  setEventForm: (open: boolean, mode?: 'create' | 'edit', uid?: string | null) => void
 }
 
 // ── Helpers ────────────────────────────────────────────────────────────────
@@ -93,6 +110,11 @@ export const useCalendarStore = create<CalendarStore>((set) => ({
   openEventId: null,
   calendarRange: initialCalendarRange(),
 
+  // EventForm UI state — closed by default, create mode, no pre-fill UID
+  eventFormOpen: false,
+  eventFormMode: 'create',
+  eventFormUid: null,
+
   setSelectedView: (view: string) => {
     set({ selectedView: view })
     // Persist to localStorage keyed by breakpoint group
@@ -110,4 +132,7 @@ export const useCalendarStore = create<CalendarStore>((set) => ({
 
   setCalendarRange: (range: { start: string; end: string }) =>
     set({ calendarRange: range }),
+
+  setEventForm: (open: boolean, mode: 'create' | 'edit' = 'create', uid: string | null = null) =>
+    set({ eventFormOpen: open, eventFormMode: mode, eventFormUid: uid }),
 }))