The push subscription got the contact and calendar types whenever the
account had device sync on, without asking whether its server has
contacts or calendars. Sync can be on for such an account: the settings
list every signed-in account, and a server can drop a capability later.
A server that refuses unknown types then refused the update and the
replacement, and push setup failed: a new account got no mail push, an
existing one lost it when its subscription expired.
The types are now added only for a capability the account's session
advertises, and a write the server refuses while it carries device
sync's types is retried with EmailDelivery alone, so mail push never
depends on device sync.
Checked with the push setup tests against a fake server that refuses
unknown types: a new subscription is created mail-only, an existing
one is kept and refreshed, and another account's subscription is left
alone when its server lacks the capability.
Linus Rath
11b897177d