`SyncConnectionState` was a one-variant enum (`SignedOut`), so the
Sync page rendered "Local-only · sign-in coming soon" even after the
bearer token landed on disk and the upload thread completed. The
state machine now mirrors the actual lifecycle.
What lands:
- `SyncConnectionState` gains `SignedIn`, `AwaitingDeviceApproval`,
`SyncReady { last_synced_at_secs }`, `SyncError { message }`.
`SyncObjectState::Synced` joins the per-object enum so individual
rows can advertise "Synced" once a successful upload lands.
- `BrowserCore` stores the current `SyncConnectionState` and exposes
`set_sync_connection_state`. `sync_status` now propagates the live
state into the snapshot the UI reads.
- `ElyShell::probe_initial_sync_state` inspects
`<profile_data>/sync/bearer.token` synchronously at construction
so the first render of the sync page is honest about whether the
user is signed in.
- A `std::sync::mpsc` channel ferries upload outcomes from the
off-thread worker back to the shell; the existing 8 ms tick
drains it and stamps `core.set_sync_connection_state` with the
freshest result. The UI now shows "Signed in · awaiting first
sync", "Synced · last upload Xm ago", "Sync error · …", and the
worker-special "Signed in · waiting for device approval" when the
server returns `device_not_approved`.
ZacharyZhang-NY
467dcb1f87