add tap-to-pay support for both android and ios via HCE and VAS

[pedrouid]

Add NFC tap-to-pay functionality to the POS app, enabling customers to receive payment URLs by tapping their phone on the merchant device.

• Android: HCE (Host Card Emulation) for NDEF tag emulation
• iOS: VAS (Value Added Services) via Tap to Pay on iPhone

Includes NFC toggle in settings, status indicator on scan screen, and QR code fallback when NFC is unavailable.

[vercel]

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[ignaciosantise]

@pedrouid can you remove this file?

[ignaciosantise]

@claude review

[claude]

Claude encountered an error —— View job

Command failed: git fetch origin --depth=20 pedrouid-nfc-research

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I'll analyze this and get back to you.

[ignaciosantise]

PR #345 Review Summary

Verdict: COMMENT

This PR adds NFC tap-to-pay functionality to the POS app using HCE (Android) and VAS (iOS). The implementation is well-structured with platform-specific abstractions and graceful fallbacks.

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What's Good

• Clean architecture: Separation of concerns with useNfcCapabilities (detection) and useNfcPayment (transmission) hooks
• Graceful degradation: Falls back gracefully when native modules aren't available or NFC is unsupported
• User control: Settings toggle allows users to enable/disable NFC, with proper validation
• State management: Store migration is properly versioned (v6 → v7) with backwards compatibility
• Clear UI feedback: NFC status indicator shows HCE/VAS mode when active
• Good documentation: Comprehensive roadmap.md explaining the three-tier fallback strategy

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Concerns

1. No tests for new hooks - The new useNfcCapabilities and useNfcPayment hooks have no test coverage. These contain complex platform-specific logic and state management that would benefit from unit tests.

2. Potential stale closure in onNfcReady callback (scan.tsx:48-56) - The nfcMode used inside onNfcReady may be stale when the callback fires:

   onNfcReady: () => {
     const modeLabel = nfcMode === "hce" ? "HCE" : nfcMode === "vas" ? "VAS" : "NFC";
     // nfcMode comes from hook destructuring, may be stale
   }

   Consider passing the mode through the callback parameter or using a ref.

3. Effect cleanup race condition (use-nfc-payment.ts:639-641) - The cleanup function calls stopNfc() but this is also called conditionally in the main effect body. This could lead to double-stopping.

4. Missing native module implementations - The hooks reference HceModule and VasModule from NativeModules, but the PR doesn't include the actual native Android/iOS implementations. Are these expected to exist already or be added in a follow-up PR?

5. Hardcoded color (scan.tsx:95) - The NFC indicator uses a hardcoded green color #4CAF50 instead of using the theme system.

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Suggestions (non-blocking)

• Consider adding a brief loading state or animation when NFC is initializing
• The showNfcToggle variable in settings.tsx is always true for iOS/Android - the check Platform.OS === "android" || Platform.OS === "ios" is redundant in a React Native context
• Consider debouncing the updateUrl calls in use-nfc-payment.ts to avoid rapid re-broadcasts if URL changes quickly

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Risk Assessment: LOW-MEDIUM

• Low risk to existing functionality (NFC is additive, QR code remains primary)
• Medium risk of runtime errors if native modules aren't properly linked
• The lack of tests makes regression risk higher for future changes

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