feat(frontend): Progressive Web App (PWA) with offline invoice management and background sync

[samjay8]

Description

Convert the InvoFi frontend into a Progressive Web App (PWA) that works offline, caches critical data, and syncs invoice changes when connectivity returns. This enables business users in low-connectivity environments (common in emerging markets where invoice financing is most needed) to draft invoices, review offers, and prepare repayments offline.

Current state

The app is a standard Next.js SPA with no offline capability. Losing connectivity means losing access to all invoice data and functionality.

Proposed implementation

Service Worker

• Workbox-based service worker for asset caching
• Cache-first strategy for static assets (fonts, icons, CSS)
• Network-first strategy for API calls with offline fallback
• Background sync for deferred invoice submissions

Offline Storage

• IndexedDB via idb-keyval for invoice drafts and cached responses
• Conflict resolution for concurrent edits
• Storage quota management with LRU eviction

PWA Manifest

• Web app manifest with app icons, theme color, display mode
• Install prompt handling with custom UI
• Splash screen and loading states

Background Sync

• Queue invoice submissions when offline
• Auto-sync when connectivity returns
• Retry logic with exponential backoff
• User notification when sync completes/fails

Data Layer

• SWR/React Query cache configuration for offline-first
• Optimistic updates with rollback on sync failure
• Cache invalidation strategy for real-time data

Acceptance criteria

• App installable on mobile and desktop (PWA install prompt)
• Service worker caches all static assets
• Invoice list viewable offline from cache
• Invoice drafts saved to IndexedDB when offline
• Background sync submits queued invoices when online
• Conflict resolution for concurrent edits
• Storage quota indicator in settings
• Lighthouse PWA score >= 90
• Works in airplane mode for read operations

Dependencies

• Benefits from IndexedDB cache layer (PR feat(sdk): add IndexedDB offline cache with stale-while-revalidate #236)
• Should integrate with existing Zustand stores

Complexity

High — Service worker lifecycle, IndexedDB schema design, background sync, conflict resolution, and cross-platform PWA compatibility.

[samjay8]

This core issue is available to work on during the GrantFox Third Campaign.

[p3ris0n]

hi maintainer, can i work on this? ETA 24hrs

Phase 1: Common Trait & Version Function Definition (common/)
Compile-Time Version Exposure:

Define a contract_version view function in the common crate (or shared trait) that returns a String or Symbol constructed at compile-time using env!("CARGO_PKG_VERSION").

Zero On-Chain Storage Cost:

Return the baked-in version directly as a static value without reading or writing to contract instance or persistent storage.

Phase 2: Contract Suite Export & Cargo Alignment
Universal Crate Exposure:

Implement/export contract_version() across all 5 contract crates via the shared common module.

Cargo as Source of Truth:

Rely entirely on each crate's Cargo.toml version key during build time—avoiding auto-increments or hardcoded state variables.

Phase 3: Testing & Verification
Unit Test Suite:

Add unit tests across all 5 contract crates invoking contract_version() and asserting the returned string matches env!("CARGO_PKG_VERSION").

WASM Invocation Verification:

Verify that invoking contract_version against compiled contract WASM binaries via the Soroban SDK/CLI returns the exact Cargo version string.

[grantfox-oss]

🦊 GrantFox — @p3ris0n has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #256)
2. Your PR will be reviewed by the Stellar-VaultLink maintainers

Good luck! Track your progress on GrantFox.