Improve async error handling

[callebtc]

Summary

• adds defensive try/catch blocks to wallet init/rebuild so failures are surfaced via a new WalletErrorListener
• ModernPOSActivity subscribes to wallet errors and surfaces them in-app
• MintsSettingsActivity gets consistent async error handling (load, refresh, add mint, stale refresh) with new localized strings
• RestoreWalletActivity now handles Nostr backup fetch and wallet restore errors with localized messages and logging
• LightningMintHandler surfaces WebSocket/polling failures via status updates and guards mint() with try/catch
• BalanceCheckActivity already provided user-facing errors; error handling remains intact

Testing

• ./gradlew assembleDebug

[callebtc]

maybe ACK

[callebtc]

Review (goose)

Effectiveness: 6/10

• Good start surfacing errors from wallet init/restore and guarding some Lightning flows
• Missing coverage for existing wallet instances created before the listener is attached
• Mint list still swallows balance/load errors – new strings are never used

Code Style: 5/10

• Listener is registered inside onResume so concurrent screens would clobber each other; needs lifecycle-safe owner
• No multi-listener support; setErrorListener replaces previous observers silently
• Error strings added but not wired up; several try/catch blocks only log but don’t surface messages

Safety & Robustness: 4/10

• CashuWalletManager can emit errors before ModernPOSActivity registers the listener → user never sees them
• setErrorListener is global/static and not thread-safe; other activities can null it unexpectedly
• LightningMintHandler status updates are hard-coded English strings, bypassing localization & UX patterns

Suggestions:

1. Move wallet error reporting to Application scope (e.g., shared Flow/LiveData) so multiple screens can observe without stomping each other, and register before init runs.
2. Actually surface the new strings when loading mints/balances fails (currently they’re never shown) and keep the UI responsive.
3. Localize Lightning status messages and avoid spamming toasts; consider in-view status chips like the rest of the POS UI.
4. Consider wrapping async calls (mint balances, mint info fetch) in a helper that consolidates logging + user-facing errors with retry affordances.

Given the remaining edge cases and race conditions, I’d hold merging until these issues are addressed.