Add syncing with another device logic and navigation

[MiSikora]

Task/Issue URL: https://app.asana.com/1/137249556945/project/72649045549333/task/1216422585541215?focus=true
Tech Design URL (if applicable): https://app.asana.com/1/137249556945/project/72649045549333/task/1216509582049467?focus=true
API Proposals URL(s) (if applicable): N/A

Description

Implements the pairing logic behind the connecting screen in the simplified sync flow. It also introduces a shared pairing result that travels back through the navigation tree to Sync Settings, which decides what to show when the flow finishes.

Connecting screen:

• The code captured on the scan screen is routed on the connecting screen, which distinguishes pairng code version.
• For V2 codes, a "Sync New Device?" dialog asks the user to confirm the pairing with "Sync Now" or "Cancel".
• After confirming, a "Confirm on your other device…" dialog is shown. Tapping "Got It" plays the lock animation.
• Once the pairing completes, the screen waits for the animation to finish, reports the result, and closes.
• For legacy codes, the animation plays immediately while the code is processed. Legacy exchange codes are not handled yet.

Pairing result and navigation:

• A new SyncPairingResult carries the outcome (the connected device, the elected role, and whether the code was scanned or displayed) from the leaf screens, ExchangeSyncCodeActivity and DisplayQrCodeActivity, up through the scan screen and SyncThisDeviceActivity back to SyncActivity.
• When the setup succeeds by scanning a code, Sync Settings refreshes the device list and opens the recovery code screen.
• When the setup succeeds through the displayed QR code, Sync Settings only refreshes the device list.
• When the flow reports a failure, Sync Settings treats the setup as cancelled and resets the sync toggle.
• If the connected device cannot be retrieved after a successful login, a failure is reported instead.

Steps to test this PR

Pair two devices by scanning a code

• On both devices, open Sync Dev Settings.
• On both devices, tap "Launch Sync Settings V2".
• On both devices, tap "Sync With Another Device".
• On the second device, tap "Show QR Code".
• On the first device, scan the displayed code.
• Verify the connecting screen opens on the first device.
• Tap "Sync Now" on the device that shows the "Sync New Device?" dialog.
• Verify the same device shows a "Confirm on your other device…" dialog.
• If the other device shows a "Sync New Device?" dialog, tap "Sync Now" there as well.
• Tap "Got It".
• Verify the lock animation plays to the end on the first device.
• Verify the recovery code screen opens on the first device.
• Verify the recovery code screen does not open on the second device.
• Verify both devices show each other in the synced devices list.

Add another device while sync is already enabled

• On a device with sync enabled, open Sync Settings V2.
• Tap "Sync With Another Device".
• Complete the device authentication prompt.
• Scan a sync code displayed on another device.
• Complete the pairing confirmations.
• Verify the flow returns to Sync Settings.
• Verify the recovery code screen does not open.
• Verify the new device appears in the synced devices list.

Start from Sync This Device

• On a device without sync enabled, open Sync Settings V2.
• Tap "Sync This Device".
• Tap "Sync With Another Device".
• Verify the scan screen opens on top of the Sync This Device screen.
• Complete the pairing with another device.
• Verify the recovery code screen opens.
• Verify Sync Settings shows the connected device afterwards.

Already paired error

• With both devices already synced together, tap "Sync With Another Device" on one of them.
• Complete the device authentication prompt.
• Scan a code displayed by the other device.
• Verify an error dialog is shown saying the devices are already synced.
• Dismiss the dialog.
• Verify the connecting screen closes back to Sync Settings.

UI changes

N/A

---

Note

Medium Risk
Changes sync account pairing, login outcomes, and multi-activity result handling in security-sensitive sync setup; scope is large but mostly UI/navigation with existing dispatcher/repository APIs.

Overview
Introduces SyncPairingResult so scan/display pairing screens return a structured outcome (device, host/joiner role, scanned vs displayed code) instead of coarse success/failure result codes. ExchangeSyncCodeActivity is wired to a new ExchangeSyncCodeViewModel that routes V1/V2 codes, shows simplified pairing dialogs, runs the lock animation after confirmation, and finishes with that result.

Activity result contracts (DisplayQrCode, ExchangeSyncCode, ReadSyncCode, SyncThisDevice) now parse SyncCompleted / Dismissed and bubble SyncPairingResult up the stack. SyncActivity handles pairing completion: refresh devices, show recovery code only when the user scanned a code, reset setup on failure, and launch authenticated add another device via scan. SyncThisDeviceActivity opens the read-code flow instead of finishing with a redirect result.

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[MiSikora]

• Clean up sync code before integrating pixels #9386
• Avoid signing out of a device when renaming it #9374
• Handle simplified sync deep linking #9373
• Handle restore on reinstall sync scenario #9368
• Simplified sync UI updates #9363
• Handle v1 exchange sync codes #9362
• Handle sync recovery basic scenario #9356
• Add syncing with another device logic and navigation #9343 👈 (View in Graphite)
• Add generic handling of v1 sync errors #9337
• Add sync with another device UI #9334
• Detect scanned QR sync codes #9333
• Handle sync code pasting #9332
• Refactor simplified sync class names #9329
• Handle sync logic on the displayed QR code page #9328
• Display sync QR code in simplified sync #9321
• Make remove device dialog destructive #9317
• Mitigate sync settings UI race condtions #9316
• develop

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[CDRussell]

Verify the recovery code screen does not open on the second device.

@MiSikora in this case you don't get to choose Restore on App Reinstall on one of the devices, but do on the other. While I can understand not wanting to show recovery code on both perhaps, skipping the restore prompt on one device seems odd.

[MiSikora]

@CDRussell

skipping the restore prompt on one device seems odd.

I don't really have a strong opinion about that. Both scenarios makes sense to me. If you have a preference either way I'm ok going with it.

Perhaps it should be shown only if the device that shows QR code wasn't synced before?

[CDRussell]

@MiSikora we'll pair on this as discussed soon, for posterity i think this can probably be auto-progressed instead of leaving it showing and requiring the user to tap it

[MiSikora]

@CDRussell
I added the ack dialog auto-dismiss to this PR in 9002b85.

I added the recovery code final confirmation logic to #9356; it's in cbe610b. It was easier to resolve the git conflicts this way.

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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[MiSikora]

Merge activity

• Aug 4, 12:40 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Aug 4, 1:10 PM UTC: Graphite rebased this pull request as part of a merge.
• Aug 4, 1:39 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Aug 4, 1:39 PM UTC: @MiSikora merged this pull request with Graphite.