Two devices editing an account in the same instant — or migrating one,
since every migrated account is stamped at the epoch — each kept its own
label and considered the matter closed. Equal timestamps are now broken
by the label, on the incoming side and in the conflict resolver alike,
the same rule the context already uses.
Cached feeds were thrown away on every ordinary launch: recomputing
statuses posts a notification, and the observer ran before the value it
compares against had been seeded. The seed now happens first.
Cache ownership is checked once at launch and compared against a
recorded owner afterwards. An unresolved identity at launch means the
owner cannot be established at all — a switch to an unseen Apple account
while offline looks exactly like that — so the caches are discarded;
mid-session it is a transient, and with iCloud Drive off it happens on
every activation, so it no longer clears anything.
Whether a Keychain item syncs is fixed when it is written, so a login
stored while sync was off stayed on this device while its account record
travelled, leaving every other device with an account whose credential
never arrives. Turning sync on rewrites them.
Reseeding a deleted zone marks the account records dirty even while the
category is off, so re-enabling it restores them instead of finding an
empty outbox.
An additional login could be created but never selected: the legacy
picker lists one entry per instance and always resolved to whichever
account signed in first. Account rows gain a "Use This Account" action,
and the subscriptions view reloads on the data context rather than on
the legacy setting — two logins on the same instance map onto the same
legacy value, so switching between them changed nothing on screen while
writes went to the other account.
Two devices migrating different legacy selections produced contexts with
identical epoch timestamps, and each refused the other's: a permanent,
silent divergence that both sides considered settled. Equal timestamps
are now broken by the selected account's ID, on the incoming side and in
the conflict resolver alike — a record that wins the upload must not be
refused on arrival.
Credential cleanup falls back to both managers whenever the backend
cannot be resolved, not only when the account is unknown here: an
instance deletion can arrive before the tombstone, and the credential
was then left in the Keychain.
Signing in wrote `usesAccountLogin`, which syncs through key-value
storage independently of the account records. A device receiving that
flag before the account synthesized a migrated account for a login that
was never legacy — and the marker arriving later deliberately retracts
nothing, so the credential-less duplicate was permanent and uploaded.
The flag is pre-revamp state that migration only reads; accounts
describe logins now. `needsCredentials` reads the account list for any
instance that has one, so the badge it drives is unaffected.
A tombstone now dominates contexts as well as accounts: an offline
device can select an account another device deleted and publish that
choice with a newer timestamp, which would have left every device
pointing at an account that is never coming back.
Cached private feeds survived an Apple-account switch two ways. A scope
this device has seen before resolves while `CredentialIdentityScope` is
still being constructed, so the change notification fires before any
observer exists — startup now compares the persisted cache owner. And a
purge asked for before the disk cache is read was undone by the load,
which now carries it.
The need to re-bootstrap after dropping records for want of a resolved
identity is persisted. The engine may already have moved its token past
those records, so a launch that lost the in-memory flag would neither
replay nor bootstrap them.
A login created after the revamp got a random account UUID that never
left the device, so its credential was keyed to an ID no other device
had and the login was unusable there. Migrated accounts were fine only
because their ID is deterministically the instance ID.
Accounts, the permanent legacy-migration markers, the permanent deletion
tombstones and the selected data context now ride the existing
CKSyncEngine as four record types, with the rules the category needs:
- Absence proves nothing. A fetch resumes from a change token and never
enumerates the zone, so deletions are records of their own and they
dominate the account wherever they are seen — including the engine's
retry-as-insert path, which is how a queued offline edit would
otherwise resurrect a deleted account.
- Fetched records are staged durably before each delegate event returns
and applied as a set, tombstones first, gated on the zone's own result
rather than didFetchChanges, which fires after failed fetches too.
- Nothing activates for an identity that has not bootstrapped: a device
left on the previous release consumed these record types as unknown
and advanced its token past them, so each identity fetches the zone
once from a nil token, outside the engine's own token.
- A disabled category defers records rather than discarding them; every
persisted artifact is namespaced by identity, and async work is
generation-checked so a fetch begun under one Apple account can never
land in another's state.
- Uploads are ordered: a marker never outruns the account it describes,
and a context naming an account is never published before that account
is server-confirmed.
