From ecbd218c346ef58bd2b96fd2ce21dcd283d7d138 Mon Sep 17 00:00:00 2001
From: Linus Rath <139418639+rathlinus@users.noreply.github.com>
Date: Sun, 27 Sep 2026 07:47:17 +0200
Subject: [PATCH] fix: sync only the primary account's collections by default
 #34

The settings chooser and the reminder filter treat only the capability's
primary account as the user's own, while the engine also counted any
account the server marks as personal. On a server that lists a second
such account, its address books and calendars synced although the
chooser showed them off. The engine now uses the same rule as the app.
---
 src/device-sync/__tests__/engine/internals.test.ts | 13 +++++++++++++
 src/device-sync/jmap/session.ts                    |  8 ++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/device-sync/__tests__/engine/internals.test.ts b/src/device-sync/__tests__/engine/internals.test.ts
index 4fee104b..07ec9348 100644
--- a/src/device-sync/__tests__/engine/internals.test.ts
+++ b/src/device-sync/__tests__/engine/internals.test.ts
@@ -297,6 +297,19 @@ describe('JMAP side', () => {
     expect(accountsWithCapability(session, JMAP_CALENDARS).map((a) => a.id)).toEqual(['a']);
   });
 
+  it("counts only the capability's primary account as personal, like the app's chooser", () => {
+    const server = new FakeJmapServer();
+    server.addAccount('a', { name: 'alice@example.com' });
+    // Another account the server calls personal (a second mailbox of the same login, say).
+    server.addAccount('home', { name: 'alice-home@example.com', isPersonal: true });
+    const session = server.port().session();
+
+    expect(accountsWithCapability(session, JMAP_CONTACTS).map((a) => [a.id, a.primary, a.personal])).toEqual([
+      ['a', true, true],
+      ['home', false, false],
+    ]);
+  });
+
   it('takes the login as the owner address and survives a server without identities', async () => {
     const server = new FakeJmapServer();
     server.addAccount('a', { name: 'Alice@Example.com' });
diff --git a/src/device-sync/jmap/session.ts b/src/device-sync/jmap/session.ts
index caf93550..b6d6743b 100644
--- a/src/device-sync/jmap/session.ts
+++ b/src/device-sync/jmap/session.ts
@@ -12,7 +12,11 @@ export interface CapabilityAccount {
   name: string;
   /** The capability's primary account (the user's own). */
   primary: boolean;
-  /** Collections of personal accounts are selected by default, shared ones are not. */
+  /**
+   * Collections of the personal account are selected by default, those of the others are not. It is the
+   * capability's primary account only, whatever `isPersonal` says: one rule with the app's chooser and
+   * reminder filter, which know only the primary account per authority.
+   */
   personal: boolean;
   readOnly: boolean;
 }
@@ -31,7 +35,7 @@ export function accountsWithCapability(session: JmapSessionView, capability: str
       id,
       name: account.name || id,
       primary: isPrimary,
-      personal: isPrimary || account.isPersonal,
+      personal: isPrimary,
       readOnly: !!account.isReadOnly,
     });
   };