diff --git a/apps/calendar-web/src/auth/providers/authorization/useStartProviderAuthorization.impl.ts b/apps/calendar-web/src/auth/providers/authorization/useStartProviderAuthorization.impl.ts
index 864b8f2fa..13e6cf790 100644
--- a/apps/calendar-web/src/auth/providers/authorization/useStartProviderAuthorization.impl.ts
+++ b/apps/calendar-web/src/auth/providers/authorization/useStartProviderAuthorization.impl.ts
@@ -3,7 +3,7 @@ import {
   useGoogleLogin as useGoogleLoginBase,
 } from "@react-oauth/google";
 import { useCallback, useMemo, useState } from "react";
-import { buildOAuthStateForClient } from "@core/desktop/desktop-oauth-state.util";
+import { buildSignInOAuthState } from "@core/auth/signin-oauth-state.util";
 import { GOOGLE_SCOPES } from "@core/providers/google.scopes";
 import { MICROSOFT_SCOPES } from "@core/providers/microsoft.scopes";
 import { type ProviderKind } from "@core/types/sync/identity.contracts";
@@ -191,7 +191,7 @@ const useGoogleProviderAuthorizationStrategy: ProviderAuthorizationStrategy = ({
   const { state, redirectUri } = useAuthorizationSession(
     "google",
     (_redirectUri, posthogDistinctId) =>
-      buildOAuthStateForClient(false, posthogDistinctId),
+      buildSignInOAuthState({ isDesktopClient: false, posthogDistinctId }),
   );
 
   const loginOptions = useMemo<
@@ -235,7 +235,7 @@ const useMicrosoftProviderAuthorizationStrategy =
     getClientId: () => getMicrosoftSignInClientId(),
     notConfiguredMessage: "Microsoft sign-in is not configured",
     createState: (_redirectUri, posthogDistinctId) =>
-      buildOAuthStateForClient(false, posthogDistinctId),
+      buildSignInOAuthState({ isDesktopClient: false, posthogDistinctId }),
     buildAuthorizationUrl: ({ clientId, redirectUri, state, prompt }) =>
       buildMicrosoftAuthorizationUrl({
         clientId,
diff --git a/apps/calendar-web/src/views/Forms/EventForm/DateControlsSection/DateTimeSection/DatePickers/DatePickers.tsx b/apps/calendar-web/src/views/Forms/EventForm/DateControlsSection/DateTimeSection/DatePickers/DatePickers.tsx
index 4d50cb4e3..003847420 100644
--- a/apps/calendar-web/src/views/Forms/EventForm/DateControlsSection/DateTimeSection/DatePickers/DatePickers.tsx
+++ b/apps/calendar-web/src/views/Forms/EventForm/DateControlsSection/DateTimeSection/DatePickers/DatePickers.tsx
@@ -49,19 +49,13 @@ export const DatePickers: FC<Props> = ({
         end: selectedEndDate,
       });
 
-    if (shouldAdjustEnd) {
-      onScheduleChange({
-        kind: "allDay",
-        start: toAllDayDate(start),
-        end: toAllDayDate(compliment),
-      });
-    } else {
-      onScheduleChange({
-        kind: "allDay",
-        start: toAllDayDate(start),
-        end: currentAllDayBounds().end,
-      });
-    }
+    onScheduleChange({
+      kind: "allDay",
+      start: toAllDayDate(start),
+      end: shouldAdjustEnd
+        ? toAllDayDate(compliment)
+        : currentAllDayBounds().end,
+    });
   };
 
   const onSelectEndDate = (end: Date) => {
diff --git a/packages/core/src/auth/signin-oauth-state.util.ts b/packages/core/src/auth/signin-oauth-state.util.ts
index 8f73d476a..6502b4981 100644
--- a/packages/core/src/auth/signin-oauth-state.util.ts
+++ b/packages/core/src/auth/signin-oauth-state.util.ts
@@ -109,25 +109,21 @@ export function parseSignInOAuthState(
   };
 }
 
+/**
+ * Apple relays `state` back as its own base64 JSON blob rather than the
+ * version-prefixed payload above. base64UrlDecode reads both alphabets (it
+ * only rewrites `-`/`_` and re-pads), so one pass covers plain base64 too.
+ */
 function posthogDistinctIdFromAppleOAuthState(
   state: string,
 ): string | undefined {
   try {
-    const decoded = base64UrlDecode(state);
-    const parsed = JSON.parse(decoded) as { ph?: unknown };
+    const parsed = JSON.parse(base64UrlDecode(state)) as { ph?: unknown };
     return typeof parsed.ph === "string" && parsed.ph.length > 0
       ? parsed.ph
       : undefined;
   } catch {
-    try {
-      const decoded = atob(state);
-      const parsed = JSON.parse(decoded) as { ph?: unknown };
-      return typeof parsed.ph === "string" && parsed.ph.length > 0
-        ? parsed.ph
-        : undefined;
-    } catch {
-      return undefined;
-    }
+    return undefined;
   }
 }
 
diff --git a/packages/core/src/desktop/desktop-oauth-state.util.test.ts b/packages/core/src/desktop/desktop-oauth-state.util.test.ts
index 44912d138..4a7fed373 100644
--- a/packages/core/src/desktop/desktop-oauth-state.util.test.ts
+++ b/packages/core/src/desktop/desktop-oauth-state.util.test.ts
@@ -1,7 +1,6 @@
 import {
   buildDesktopConnectRelayUrl,
   buildDesktopOAuthRelayUrl,
-  buildOAuthStateForClient,
   DESKTOP_OAUTH_STATE_PREFIX,
   hasDesktopOAuthStateMarker,
   parseDesktopAuthDeepLink,
@@ -12,16 +11,16 @@ import {
 import { describe, expect, it } from "bun:test";
 
 describe("desktop oauth state", () => {
-  it("prefixes state when the client is desktop", () => {
-    const state = buildOAuthStateForClient(true);
-    expect(state.startsWith(DESKTOP_OAUTH_STATE_PREFIX)).toBe(true);
-    expect(hasDesktopOAuthStateMarker(state)).toBe(true);
+  // buildSignInOAuthState owns which states carry the marker, and its own
+  // test covers that; this is the marker reader on its own.
+  it("recognizes the desktop marker", () => {
+    expect(
+      hasDesktopOAuthStateMarker(`${DESKTOP_OAUTH_STATE_PREFIX}v1.payload`),
+    ).toBe(true);
   });
 
-  it("leaves browser state unprefixed", () => {
-    const state = buildOAuthStateForClient(false);
-    expect(state.startsWith(DESKTOP_OAUTH_STATE_PREFIX)).toBe(false);
-    expect(hasDesktopOAuthStateMarker(state)).toBe(false);
+  it("leaves browser state unmarked", () => {
+    expect(hasDesktopOAuthStateMarker("v1.payload")).toBe(false);
   });
 });
 
diff --git a/packages/core/src/desktop/desktop-oauth-state.util.ts b/packages/core/src/desktop/desktop-oauth-state.util.ts
index dd094f581..948ffd0bf 100644
--- a/packages/core/src/desktop/desktop-oauth-state.util.ts
+++ b/packages/core/src/desktop/desktop-oauth-state.util.ts
@@ -1,4 +1,3 @@
-import { buildSignInOAuthState } from "@core/auth/signin-oauth-state.util";
 import {
   type ProviderKind,
   ProviderKindSchema,
@@ -30,13 +29,6 @@ const DESKTOP_EVENT_LINK_PREFIX = `${DESKTOP_DEEP_LINK_SCHEME}event/`;
 const DESKTOP_DAY_LINK_PATTERN =
   /^compass:\/\/day\/(?<date>\d{4}-\d{2}-\d{2})\/?$/;
 
-export function buildOAuthStateForClient(
-  isDesktopClient: boolean,
-  posthogDistinctId?: string,
-): string {
-  return buildSignInOAuthState({ isDesktopClient, posthogDistinctId });
-}
-
 export function hasDesktopOAuthStateMarker(state: string): boolean {
   return state.startsWith(DESKTOP_OAUTH_STATE_PREFIX);
 }