Add authenticated encryption, in-flight recovery, and Lightning withdrawal

[nisfeb]

Summary

• Authenticated encryption: encrypt-then-MAC with HMAC-SHA256 — rejects tampered ciphertext before decrypting, random ephemeral keys via eny, mint URL inside encrypted payload
• In-flight token recovery: tokens held in escrow 30 min after signing, NUT-03 swapped for fresh proofs if unused — prevents permanent loss from failed pushes
• Lightning withdrawal: maintainers can withdraw received tokens to Lightning via NUT-05 melt, with per-mint wallet display in admin UI

Changes

Security (agent)

• ecash-encrypt takes eny param, derives separate enc_key and mac_key from DH shared secret
• HMAC-SHA256 over ciphertext (encrypt-then-MAC), included as ecash-mac field
• ecash-decrypt verifies MAC first, returns ~ on failure
• Token payload now {mint, tokens} JSON — mint URL protected by encryption
• In-flight map with 30-min Behn timer, NUT-03 swap on expiry via verify-keys/verify-swap flow

Withdrawal (agent + UI)

• State-8: adds pending-melts=(map @t pending-melt)
• POST /vitriol/admin/withdraw: accepts mint + BOLT11 invoice
• Iris melt handlers: quote → select proofs → execute → restore on failure
• Admin UI: per-mint balance display with proof count, invoice input, withdraw button

Types

• pending-melt: mint, step, invoice, proofs-used, quote-id, fee-reserve

Test plan

• MAC verification rejects modified ciphertext
• In-flight tokens return to wallet via NUT-03 swap after 30 min
• Per-mint balances display correctly in maintainer admin
• Withdraw to Lightning: quote + execute succeeds, proofs consumed
• Failed melt restores proofs to wallet
• State migration from 6/7 → 8 preserves existing data

🤖 Generated with Claude Code