Found on the iPad: after signing a second login into an instance, its
migrated account could no longer retire the unscoped legacy item when it
was deleted, and the instance was left still claiming a pre-revamp login.
Storing a credential retires the adoption marker, but it matched on
service, instance and identity only. An instance holds several logins, so
a sibling sign-in silently withdrew the migrated account's claim on a
secret it had nothing to do with. After that the legacy item outlived the
account that adopted it, and could be adopted a second time.
Erring that way costs nothing — an item that is not deleted is an item
nobody is logged out of — but the marker already carries the account it
was written for, and deletion authority already checks it. Retiring it
now matches on the same thing.
Review of the silent migration found two paths that defeat the point of
writing the adopted copy device-local.
The marker is written after the copy it describes, so a launch that ends
in between leaves an adopted credential nothing claims — and adoption
never retries, because the key is no longer empty. Enabling iCloud sync
then rewrites it as synchronizable. The resync now also recognizes the
value: a scoped credential identical to the unscoped item it could only
have come from is an adopted copy whether or not a marker says so.
The opposite failure is a marker that outlives what it described.
Signing in again replaces the credential with one the user proved they
hold, but the marker stayed, so enabling sync afterwards skipped the
account and left every other device showing a login it never receives.
Storing a credential now retires the marker.
Also corrects four comments that still describe adoption as something
the user is asked about, and states plainly what the legacy-deletion
conditions do and do not prove now that no one is asked.
The pre-revamp release reads its unscoped Keychain item with
kSecAttrSynchronizableAny and no identity in the key, so a credential
retained across an Apple Account change is already served to whoever
holds the device. Asking before reusing it prevents nothing that is not
already happening, and it cost every upgrading user a trip into the
instance editor to find a button they had no reason to look for.
What silent adoption could genuinely add is re-filing that secret as
synchronizable under the identity signed in now, which uploads a login
of unproven provenance into that person's iCloud Keychain and spreads it
to their devices. So the copy is written device-local instead, and the
migration runs where the status is computed. The real owner loses
nothing: the item it was copied from syncs, so each of their devices
finds it and adopts its own copy, and adoption still never deletes it.
Two things keep that closed. Turning iCloud sync on rewrites stored
credentials to follow the setting, which would undo the whole point, so
adopted ones are left out of it. And only the account the instance's
legacy login became may inherit the secret — the old item is keyed by
instance, so a second login the user added themselves would otherwise
match it.
Local data is always a valid context. The legacy validator predates
that: it treats local as unavailable without a Yattee Server, which is a
feed concern the feed reports itself — and since the correction now
moves the data context with it, that would have quietly put users on
somebody's backend account, overwriting a local choice made on another
device.
Stale feed responses no longer touch anything. Rejecting only the videos
still let a request from a login the cache had moved off overwrite the
new one's loading state, error state and pagination — replacement
requests are allowed to overlap, so both were in flight.
The unreachable retry timers are cancelled when the namespace reloads. A
migrated account reuses its instance's UUID, so the same ID can exist
under the next Apple account, and an old timer would declare that
account reachable on the strength of a verdict about someone else's.
Rewriting a credential's sync flag is skipped when it already matches
and restores the original if the re-add fails. Changing that flag means
delete-then-add, and the delete propagates to every device — turning
sync on should never be able to log the user out.
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.
A deletion can reach a device before the account it deletes does — the
tombstone and the account are separate records, and iCloud Keychain runs
on its own timeline — and the credential cleanup was skipped whenever
the account was unknown here. The scoped key needs only the account ID,
so both credential managers are now asked to drop it; the unscoped
legacy item still needs the instance and is left alone.
Cached data is invalidated on the data context rather than on the legacy
selection it maps to. Two logins on the same instance collapse onto the
same legacy value, so switching between them cleared nothing and the
subscriptions feed kept showing the previous account's videos. Home
feeds are keyed by instance alone and had the same hole across accounts
and across Apple accounts; they are dropped with it.
The third source-deletion path now cascades to accounts like the other
two, and the Invidious private-playlist lookup resolves its session
through the account — a login created after the revamp writes only an
account-scoped credential, so the instance-keyed lookup missed it and
fell through to the public endpoint.
Fifth review pass, which prompted measuring whether SecItemDelete can be
conditioned on a value. It cannot: a delete issued with a deliberately
wrong kSecValueData still returns 0 and removes the item, so there is no
compare-and-delete and every check-then-delete is a race by construction.
That measurement decides both fixes here.
Adoption no longer rolls back its own write when the verification read
comes back empty. The rollback could only ever be a blind delete of
whatever occupied the key by then - including a credential synced from
another device in the gap - and it would propagate. Nothing is deleted; no
marker is written, so the account stays signed out and an ordinary sign-in
recovers it.
Legacy deletion re-reads immediately before deleting and aborts if the
value moved, shrinking the window to a single call gap and catching a
replacement that landed while the fingerprint was being computed. A
residual race remains and is documented at the call site: closing it is not
possible with these APIs, and never deleting would leave a credential the
user explicitly removed sitting in their iCloud Keychain.
The debug provenance report repeated the same nil-token ambiguity the scope
logic was fixed for, reporting "no Apple account signed in" when iCloud
Drive is merely off. It now reports the token as unavailable and shows
CloudKit's account status separately, so a re-run cannot draw a false
conclusion from it.
Third review pass.
adoptCurrentIdentity() treated a nil ubiquityIdentityToken as sign-out and
scoped credentials to "local". But Foundation also returns nil when iCloud
Drive is unavailable or switched off, and Yattee declares only the CloudKit
service with no ubiquity container, so the token tracks iCloud Drive state
rather than the account. In that configuration two different signed-in
Apple accounts both resolved to "local" and shared one credential
namespace - since Keychain items survive an account switch, account B could
then read account A's retained credential. That is the precise failure this
whole change exists to prevent.
A nil token now means unresolved, and CloudKit's account status settles it
during resolution: noAccount scopes to local, available proceeds to the
user-record lookup, anything else stays unresolved and retries. A scope
resolved without a token is not cached, because there is no key that could
be trusted to mean this account.
Adoption markers are now namespaced by Keychain service. Both credential
managers share one marker store and an instance UUID can outlive a change
of backend, so adopting an Invidious credential could suppress the Piped
offer for the same instance and point deletion at the wrong secret.
Writing the account-status branch also surfaced a Swift trap: an
unqualified `break` inside the switch left only the switch and fell through
to the user-record lookup, resolving a scope on an undetermined account
status. The loop is labelled now, and the test that caught it is included.
Two more issues from a second review pass.
Adoption verified its write by reading the key back and deleted it on any
mismatch. But a mismatch can also mean iCloud Keychain delivered a real
credential for that key between the add and the read - and since the delete
spans both synchronizable forms, it would propagate and revoke that
credential on every device. A readable value that is not ours is now left
strictly alone; only an unreadable key (the add reported success but
produced nothing usable) is rolled back so the offer can be retried.
An identity switch arriving while a resolution was in flight was dropped:
the observer's resolve() returned early on the isResolving guard, and the
in-flight one then bailed on its fingerprint check without starting a
lookup for the new identity, leaving credentials disabled until a
foreground transition or relaunch. Requests that arrive mid-resolution are
now replayed once the running one finishes.
Adds a fingerprint provider and an injectable backoff so identity
resolution is testable without a real Apple account or real seconds, plus
tests for retry, foreground recovery, mid-flight switching, signed-out
scoping and the cached-scope fast path.
Four issues from an external review of the previous commit.
The scope was resolved once at startup, so signing out or switching Apple
account while the app kept running left it pinned to the old identity -
reads and writes would then reach the previous account's retained
credentials, which is the exact leak scoping exists to prevent.
CredentialIdentityScope now observes NSUbiquityIdentityDidChange and
re-resolves.
Legacy deletion authority checked only the instance and the identity, not
the account. On an instance with several accounts, deleting any of them
satisfied the marker lookup and could retire the legacy item another
account had adopted, logging out devices still on the previous release.
The marker's accountID is now required to match.
A first-time resolution that failed (launched offline, CloudKit
unreachable) was never retried, disabling credentials for the rest of the
process. resolve() now retries with backoff, and resolveIfNeeded() runs on
foreground activation.
Adoption re-checked nothing at execution time, so a scoped credential
delivered by iCloud Keychain between rendering the offer and tapping it
would be overwritten with the older legacy secret. Adoption now re-verifies
eligibility and writes with a non-replacing add, leaving a duplicate
strictly alone.
Adds regression tests for the sibling-account deletion and the adoption
race.
Yattee 2 keys credentials by instance UUID with no notion of which Apple
account they belong to, and reads them back with SynchronizableAny. Apple
documents that Keychain data may stay on device when a user signs out and
chooses to keep it, so whoever signs in next would be served the previous
user's credential - guaranteed for migrated accounts, since local instances
survive the switch and the migrated account UUID is deterministically the
instance UUID.
Credentials are now keyed "<identityScope>|<accountID>", where the scope is
the CloudKit user record (identical across a user's devices, so iCloud
Keychain sync still works). Usernames get the same scope and live beside the
credential, keeping login identifiers out of synced metadata.
The legacy unscoped item is never adopted automatically. A strict
kSecAttrSynchronizable == true query was the candidate discriminator for
"this secret belongs to the current Apple account", but measured on iPadOS
27.0 a retained item keeps the attribute and still matches that query with
no Apple account signed in at all - the flag records what was once requested,
not live iCloud Keychain membership. Reads therefore never fall back to the
legacy key; adoption is an explicit user action that copies the item,
verifies the scoped read-back, then records a marker bound to the identity
and a salted fingerprint of the secret. The legacy item is retained, because
deleting a synchronizable item propagates and would log out devices still on
the previous release mid-rollout. Deleting it later needs all three of: a
marker on this device, matching identity, and the item still holding the
adopted secret.
The instance-keyed path is untouched, so no shipping call site changes
behavior. BasicAuthCredentialsManager stays instance-keyed - proxy auth
belongs to the instance, not to a user account.
While the scope is unresolved (first launch under a new Apple account,
CloudKit unreachable) reads report "can't tell yet" via isScopeResolved
rather than "signed out", and writes are refused rather than guessing a
scope. Login state is cached per scope so one identity's cache can never
answer for another.
Also adds the debug-only harness the measurement was taken with, under
Advanced > Developer > Experiments.
