Fire Mode: Disable chat sync

[0nko]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1207418217763355/task/1215462571225879?focus=true

Description

Duck.ai chats may sync in Regular mode but must never sync in Fire mode.

A shared rule — BrowserMode.isSyncable gates the two places sync can start:

• FE — DuckChatJSHelper reports supportsAIChatSync as false in Fire mode. The Duck.ai FE reads this capability and doesn't offer or attempt sync (no "Turn On Sync & Backup"). browserMode is supplied per-surface by the calling tab / contextual sheet / standalone screen.
• Native sync — RealDuckChatSyncRepository's write methods (recordDuckAiChatsDeleted / recordSingleChatDeletion / recordSingleChatUpdate) no-op in a non-syncable mode, so Fire chat IDs never enter the pending sync queues. DuckChatSyncDataManager reads the @RegularMode store, so a background sync that fires during a Fire session still syncs Regular chats without touching Fire data.

Steps to test this PR

Prerequisites:

• A device signed in to Sync with Duck.ai chat sync working in Regular mode (ideally a second synced device to confirm propagation)
• fireTabs FF enabled in dev settings (needs a restart)

Regular mode still syncs (no regression)

• In Regular mode with Sync enabled, create / edit / delete a Duck.ai chat
• Verify it still propagates to the second device as before

Fire mode never syncs

• Switch to Fire mode and open Duck.ai
• Create / edit / delete Duck.ai chats in Fire mode
• Verify nothing propagates to the second device

FE doesn't show sync options in Fire mode

• Switch to Fire mode and open Duck.ai
• Tap on the Chats icon
• Tap on the Settings & More link
• Select Duck.ai Settings
• Verify Duck.ai does not show Sync & Backup option

UI Changes

Regular	Fire

---

Note

Medium Risk
Touches sync metadata writes and JS capability flags for privacy-sensitive Fire mode; scope is narrow and aligned with existing Regular-mode sync paths.

Overview
Prevents Duck.ai chats from syncing when the user is in Fire mode, while keeping sync behavior in Regular mode unchanged.

A shared BrowserMode.isSyncable rule (Fire → false, Regular → true) gates both entry points: DuckChatJSHelper now takes browserMode from each Duck.ai surface and only reports supportsAIChatSync when sync is enabled and the mode is syncable, so the web UI does not offer sync in Fire. RealDuckChatSyncRepository uses the same rule on deletion/update queue writers instead of a Fire-only check, so Fire chat activity never enters pending sync metadata.

Call sites (BrowserTabViewModel, contextual fragment, standalone web view) pass browserMode into JS processing; tests cover Fire config and the updated mocks.

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[0nko]

• Fire Mode: Escape hatch #8917
• Fire Mode: Prepare fire dialog #8902
• Fire Mode: Disable chat sync  #8792 👈 (View in Graphite)
• Fire Mode: Separate Duck chat data #8791
• Fire Mode: Empty state pages #8748
• Fire Mode: Launch NTP in different modes #8742
• Fire Mode: Duck.ai and input widget theme overlay #8725
• Fire Mode: Themes and styles #8714
• develop

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[CDRussell]

@0nko , what's the plan for the duck chat UI re setting up sync. I can see it in the settings for instance, where it offers to Turn On Sync & Backup which will never work in a fire tab. Is there already a plan for the frontend UI to update around this (otherwise it's a confusing UX) ?

[CDRussell]

@0nko Perhaps we're missing a tech design for how the FE should be handling fire tabs and syncing? I feel like this PR is rather reactive to discovering that fire tabs will need special considerations re sync and returning failures to all the API messages a bit of a blunt instrument.

What you've done in this PR is maybe only part of the story but not sufficient and we require other parts in place like the FE updating too.

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[0nko]

@CDRussell Thanks for the review!

Perhaps we're missing a tech design for how the FE should be handling fire tabs and syncing? I feel like this PR is rather reactive to discovering that fire tabs will need special considerations re sync and returning failures to all the API messages a bit of a blunt instrument.

Yeah, I agree the API responses everywhere might not have been the ideal solution.. I was trying to patch up all the places where I expected that Fire mode might be doing something with sync, so I was going overboard just to make sure nothing leaked. However, after going over the code again I realized that the only guards needed were actually a the write sites where chat IDs are added to the sync queue.

I can see it in the settings for instance, where it offers to Turn On Sync & Backup which will never work in a fire tab. Is there already a plan for the frontend UI to update around this (otherwise it's a confusing UX) ?

Good catch. I completely missed the fact that sync can be accessed outside the native settings. There's a parameter that tells the FE if the sync is available (already used by the sync FF), so now it's disabled in Fire mode.

Ready for another round.