Native ZSLP NFTs: mint, view, shield, sell (non-consensus overlay)

README.md

@@ -158,6 +158,83 @@ Interact with the running daemon via JSON-RPC:
 
 ---
 
+## NFTs / Collectibles (ZSLP) — dev/testnet stage
+
+ZClassic can carry **NFTs and tokens** as a **non-consensus overlay** called ZSLP (an SLP Token Type 1 message in a single `OP_RETURN`). An NFT is a 1-of-1 token: a baton-less GENESIS with `decimals=0`, `quantity=1`. The token id is the genesis transaction id. The file itself never goes on-chain — only a 32-byte fingerprint (`document_hash`, a SHA-256 of the file) is recorded, so anyone can verify that a given file matches what was minted.
+
+**Security model, in one paragraph.** ZClassic consensus does not know NFTs exist — it never changes for this feature. Instead, every node that runs the indexer re-derives the same token ledger as a deterministic function of the confirmed chain: it reads each `OP_RETURN`, debits the spent token inputs, credits the outputs, and enforces conservation (a transfer is valid only if tokens-in ≥ tokens-out). The consequence, stated honestly: a forged token message **can be mined, but it credits nobody** and every honest node agrees it is invalid. Security here is *agreement*, not chain rejection — so treat ZSLP as **dev/testnet-stage**, not mainnet-ready.
+
+**The index is ON by default.** The `zslp_*` RPCs need the read-only ZSLP index, which defaults **on** (`-zslpindex`, default `1`). It does a one-time catch-up scan in the background. Opt out with `-zslpindex=0`.
+
+### CLI walkthrough (mint → inspect → transfer → list)
+
+All arguments are **positional**. (`zslp_genesis` takes one JSON object; the rest take plain positional args.)
+
+```bash
+# 1. Compute the file fingerprint (32-byte SHA-256, lowercase hex)
+HASH=$(sha256sum my-art.png | cut -d' ' -f1)
+
+# 2. Mint a 1-of-1 NFT (nft:true forces decimals 0, quantity 1, no re-issue baton)
+./src/zclassic-cli zslp_genesis "{\"nft\":true,\"name\":\"My Photo #1\",\"document_url\":\"\",\"document_hash\":\"$HASH\"}"
+#   -> { "txid": "<hex>", "tokenid": "<hex>" }     (tokenid == txid == the NFT's identity)
+
+# 3. Inspect the token you just minted
+./src/zclassic-cli zslp_gettoken "<tokenid>"
+#   -> name, document_hash, decimals 0, totalMinted 1, hasMintBaton false  (a real 1-of-1)
+
+# 4. Transfer / gift it to someone (positional: tokenid, recipient, amount[, change_addr])
+./src/zclassic-cli zslp_send "<tokenid>" "t1RecipientAddress..." 1
+#   -> { "txid": "<hex>" }
+
+# 5. List the NFTs/tokens this wallet holds
+./src/zclassic-cli zslp_listmytokens
+```
+
+> **Honest limits.** A transfer is public and irreversible (a send to the wrong address cannot be undone). The name and image are **not** unique — anyone can mint another token reusing them; only the token id (genesis txid) is one of a kind. The fingerprint proves *which bytes* were minted, never that a creator is "genuine" or "official." ZSLP is a non-consensus overlay (dev/testnet-stage).
+
+### Private files / private NFTs (shielded data channel) — dev/testnet, default-OFF
+
+You can also send a **private file or message** over the shielded pool: the bytes are encrypted, framed into Sapling memos, and carried in one shielded transaction. This is **default-OFF** and experimental — start `zclassicd` with `-experimentalfeatures -datachannel` to enable it (the RPCs return `-32601` when off).
+
+```bash
+# SENDER (both addresses must be Sapling z-addrs in your wallet; acknowledge_permanent is REQUIRED)
+./src/zclassic-cli z_senddatafile '{"fromaddress":"zs1...","toaddress":"zs1...","filepath":"/path/to/secret.png","acknowledge_permanent":true}'
+#   -> { "operationid", "transfer_id", "fingerprint", "frames", "key" }
+#      "fingerprint" is the 32-byte ciphertext anchor (= an NFT's document_hash); "key" is yours to disclose selectively.
+
+# List the transfers this node knows about (sent this session)
+./src/zclassic-cli z_listdatatransfers
+
+# RECIPIENT: reassemble + verify-before-decrypt, then decrypt
+./src/zclassic-cli z_getdatatransfer '{"transfer_id":"<16hex>"}'
+#   -> { "verified", "complete", "frames_received", "hexdata", "filename", "content_type", ... }
+```
+
+> **What this protects / does not.** Hidden: who it's from, who it's to, the amount, the contents. Visible: *that* a private transfer happened, roughly *when*, and roughly *how big*. It is **permanent** on every full node forever and **not deletable** — private ≠ undetectable. Keep files small (per-file cap ~40000 bytes). The recipient verifies the on-chain ciphertext fingerprint **before** decrypting; selectively disclose by handing over the returned `key`, or `z_exportviewingkey` for the receiving z-addr (read/prove only, never spend).
+
+### Sell an NFT for ZCL (atomic swap) — dev/testnet
+
+You can sell a transparent NFT for transparent ZCL in a single `ALL|ANYONECANPAY` atomic swap.
+
+```bash
+# SELLER: build a signed offer for the NFT
+OFFER=$(./src/zclassic-cli nft_makeoffer '{"tokenId":"<txid>","priceZat":"100000000","buyerNftAddr":"t1Buyer...","payoutAddr":"t1Seller..."}')
+#   -> { "offerBlob": "znftoffer:..." }   (hand this blob to the buyer)
+
+# BUYER (mandatory): verify the offer BEFORE taking it
+./src/zclassic-cli nft_verifyoffer '{"offerBlob":"znftoffer:..."}'
+#   -> { "ok": true, "priceZat": ..., ... }
+
+# BUYER: take the offer (appends funding, broadcasts the single atomic tx)
+./src/zclassic-cli nft_takeoffer '{"offerBlob":"znftoffer:..."}'
+```
+
+> **Honest limit.** The single-tx swap makes the **coin** legs consensus-atomic, but token attribution is an indexer convention — so this is **trust-minimized, not trustless**. Always run `nft_verifyoffer` before `nft_takeoffer`. No shielded leg can be atomic. (Other SELL RPCs: `nft_listoffers`, `nft_canceloffer`, `nft_requestbuy`.)
+
+For the full design — mint/transfer write path, anti-burn protection, content addressing, the private data channel, and the NFT→ZCL sell design — see [doc/nft/README.md](doc/nft/README.md) (start with `NATIVE_NFT_GUIDE.md`). Runnable end-to-end proofs live in `qa/zslp/` (`zslp-nft-regtest.sh`, `nft-sell-regtest.sh`; see `qa/zslp/README.md`).
+
+---
+
 ## Advanced: Bootstrap Snapshots
 
 See [doc/bootstrap-snapshots.md](doc/bootstrap-snapshots.md) for: