feat(payment): track pending transfers after expiry

[Alike001]

Summary

• detect exact transparent invoice outputs in the Zcash mempool using getrawmempool and getrawtransaction
• persist pre-expiry candidates by transaction ID, output index, integer zatoshi value, mempool entry time, and transaction expiry height
• continue polling as Payment pending after the invoice timer ends, without generating a receipt or claiming settlement
• accept a previously proven candidate if it is mined after invoice expiry, and expire it only after its Zcash expiry height passes unmined
• add desktop/mobile checkout messaging that warns customers not to resend while the transaction is unresolved
• document the sixth RPC method and the updated demo flow

Database

Adds migration 0002_track_pending_payments.sql. The existing vercel-build command applies it before the Next.js build.

Verification

• npm run format:check
• npm run lint
• npm run typecheck
• npm test -- --maxWorkers=2 --reporter=dot — 147 passed, 1 skipped
• npm run secret:check
• npm run build
• rendered Chrome QA at 1440×1000 and 390×844; pending warning, RPC evidence, TxID copy control, and mobile wrapping verified

Safety notes

• mempool evidence remains pending and cannot create a receipt
• late-mined outputs are accepted only when the same output was proven in the mempool during the invoice lifetime
• provider failures remain unavailable state, never proof of payment or non-payment
• QuickNode and database credentials remain server-side

Closes #29

[vercel]

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Project	Deployment	Actions	Updated (UTC)
zecceipt	Ready	Preview	Aug 30, 2026 11:00am

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