feat: offline mode

[reez]

This issue is about graceful offline support, not a full offline-first architecture.

Scope:

• Make sure the app still behaves reasonably when the device has no Wi-Fi/cellular access or is in a more restricted environment such as Lockdown Mode.
• Preserve access to locally persisted cards so previously scanned SATSCARDs still load.
• Keep local SATSCARD flows working where possible, including NFC + CKTap reads, setup-next-slot, and local address derivation.
• Audit network-backed paths and make sure they fail gracefully instead of feeling broken. This includes balance refresh, slot history, fee lookup, fiat price lookup, and send/broadcast-related network work.
• Show clear offline or unavailable states in the UI where network-backed data cannot be loaded.

Out of scope:

• Full offline-first sync/caching for balances, transactions, or prices.
• Broadcasting or completing send flows without network.
• Reworking the app around a separate local cache layer unless that becomes necessary.

Context from discussion:

• We already support part of this: cards persist locally, and the card read/setup path is mostly NFC + CKTap + local address derivation.
• The main risk area is network requests that currently assume connectivity.

[reez]

network request: mempool.space

[r1b2ns]

Do you mean offline mode like offline-first apps? Apps that persist all data and instantly show cached data?

[reez]

it was mostly about making sure the app still works of the device has no wifi/data or is in lockdown mode or something. I haven't tested this path yet, I know we have network request we have to watch out for.

The right scope is just “graceful offline support” I think. its sort of a desired thing, but I haven't put much work into scoping it out yet, even though I think we already support half of this with cards persisted locally and the card read/setup path is NFC + CKTap + local address derivation