NIP-15: Extend event schema (payment_options, bond event, pickup_code, deprecate fiat fields)

[NOVMBILL]

Summary

This pull request introduces several extensions and refinements to the NIP-15 event schema to enable expanded payment support, add bond mechanics, simplify privacy, and deprecate fiat-specific and plaintext address fields. All changes are implemented to optimize for sovereign payment flows and increase marketplace trust.

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Changes Introduced

1. Add payment_options array (ln, cashu, silent_payment) to stall and product event content

   • Replaces the previous payment_methods string array with a structured array of supported payment types.
   • Enables future extension for additional payment protocols.
   • Payment types now explicitly support:
     • ln (Lightning Network)
     • cashu (ecash/Chaumian tokens)
     • silent_payment (Bitcoin silent payment addresses)
   • Example:

     "payment_options": [
       {"type": "ln"},
       {"type": "cashu"},
       {"type": "silent_payment"}
     ]

2. Introduce bond event kind 30330

   • New event kind to represent merchant/stall bonds for increased trust.
   • Event content format:

     {
       "bond_txid": "...",
       "amount": ...
     }

   • Event tags must include the merchant public key:

     ["p", "<merchant_pubkey>"]

   • Products or stalls referencing a bond event must include:

     ["e", "<bond_event_id>", "bond"]

3. Update product, stall, and order event schemas

   • Embed new payment_options array in product and stall metadata.
   • All fiat-specific fields are removed or marked as optional (for backward compatibility, only Lightning/Bitcoin-native payments are required going forward).
   • Plaintext address field is removed. Instead, include privacy-preserving pickup fields:

     {
       "pickup_code": "...",
       "pickup_radius": "..."
     }

   • Order events (checkout flow) now use pickup_code and pickup_radius instead of plaintext address for customer privacy.

4. Clarify event tags and UI badge logic

   • Document required e tags referencing bond events in product/stall listings.
   • Specify that client UIs should render a “bond badge” or visual trust marker when this tag is present.
   • See inline doc for format and logic.

5. Spec text updated for all changes above

   • All relevant code blocks, tables, and field descriptions are updated to reflect the new event schema, with clear deprecation notes for removed fields and expanded examples for new types.

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Implementation / Compatibility

• This PR is self-contained and does not modify other NIPs.
• No breaking changes for existing Lightning/Bitcoin workflows; changes are additive and privacy-preserving.
• Companion PR to reference client implementation (NostrMarket) will ensure UI compatibility with new schema and badge logic.

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Motivation

• Expand NIP-15 payment interoperability (Cashu, silent payments).
• Enable trust primitives via on-chain bonds.
• Remove fiat/payment and address leakage.
• Clarify event tag structure for UI integration.

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Example Data

Bond Event (kind 30330)

{
  "kind": 30330,
  "pubkey": "merchant_pubkey_here",
  "content": "{\"bond_txid\":\"deadbeef...\",\"amount\":1234}",
  "tags": [
    ["p", "merchant_pubkey_here"]
  ]
}

Product Event referencing Bond

{
  "kind": 30315,
  "pubkey": "merchant_pubkey_here",
  "content": "{\"title\":\"Coffee\",\"payment_options\":[{\"type\":\"cashu\"}]}",
  "tags": [
    ["e", "<bond_event_id>", "bond"]
  ]
}

Order Event (with privacy fields)

{
  "pickup_code": "FJ7U29",
  "pickup_radius": "200m"
}

";
}