feat(utxo): add RXD ForkIdRxd sighash signing path

[cdonnachie]

Summary

Adds Radiant (RXD) sighash support by introducing a ForkIdRxd variant to SignatureVersion, keeping the signing dispatch clean and self-contained in mm2_bitcoin/script.

What changed

• Added SignatureVersion::ForkIdRxd variant (serde: "fork_id_rxd") to route RXD signing through its own preimage path.
• Implemented signature_hash_fork_id_rxd on TransactionInputSigner — follows the BIP143-style ForkId preimage but inserts an additional hashOutputHashes commitment before hashOutputs.
• Added compute_hash_output_hashes_rxd which commits per-output summaries: value, double-SHA256 of scriptPubKey, push-ref count, and double-SHA256 of sorted push-refs.
• Added sorted_push_refs_rxd script parser that extracts and deduplicates OP_PUSHINPUTREF / OP_PUSHINPUTREFSINGLETON 36-byte references from output scripts, with checked_add for wasm32 safety.
• Extended Sighash::is_defined and Sighash::from_u32 to recognize ForkIdRxd alongside ForkId.
• Minor clippy doctest fix in enum_derives (cherry-picked).

Coin configuration

RXD coins specify the signing path via config — no protocol-level inference needed:

{
    "fork_id": "0x40",
    "signature_version": "fork_id_rxd"
}

Why

RXD consensus requires a distinct sighash preimage that includes output-hash summaries with push-ref commitments. Routing via SignatureVersion (where all signing dispatch already happens) avoids adding chain_variant to TransactionInputSigner and the propagation issues that would cause (e.g. From<Transaction> hardcoding Standard).

Tests

• test_rxd_forkid_sighash_vector: Verifies sighash against a real on-chain RXD transaction with signature verification.
• test_sorted_push_refs_rxd_extracts_and_sorts_push_refs: Tests push-ref opcode parsing, deduplication, and sorting with crafted scripts containing OP_PUSHINPUTREF, OP_REQUIREINPUTREF, and OP_PUSHINPUTREFSINGLETON.
• Extended existing test_sighash_forkid_is_defined with ForkIdRxd assertions.

Validation

• Successful atomic swap (RXD/KMD) completed with the ForkIdRxd signing path.
• Tested by @cipig with confirmed working swaps.
• cargo fmt and build checks passed.

Files changed

• mm2src/mm2_bitcoin/script/src/sign.rs — All RXD sighash logic and tests
• mm2src/derives/enum_derives/src/lib.rs — Clippy doctest fix

[shamardy]

can you please rebase to latest dev branch?

[cdonnachie]

can you please rebase to latest dev branch?

done

[shamardy]

Thanks for the PR, below is my first review to make sure we are on the right track before going deeper.

I think the approach of adding chain_variant to TransactionInputSigner is not the right fit here. ChainVariant is used for block header deserialization routing, not signing. All the existing helpers (is_btc(), is_qtum(), is_rvn(), is_pivx()) branch header parsing logic in the Reader. Adding it to the signer struct mixes two different concerns.

It also creates propagation issues. The From<Transaction> impl hardcodes ChainVariant::Standard, so any code path that does let signer: TransactionInputSigner = tx.into() (like sign_raw_utxo_tx or check_all_utxo_inputs_signed_by_pub) will silently use the wrong sighash for RXD.

I think a cleaner approach would be to add a ForkIdRxd variant to SignatureVersion instead. The signing algorithm is already dispatched via SignatureVersion, so this would be the natural place for it. Something like:

match sigversion {
    SignatureVersion::ForkId if sighash.fork_id => {
        self.signature_hash_fork_id(...)
    },
    SignatureVersion::ForkIdRxd if sighash.fork_id => {
        self.signature_hash_fork_id_rxd(...)
    },
    // ...
}

The mapping would happen once in utxo_conf_builder.rs::signature_version() where RXD maps to ForkIdRxd. This way there's no new field on TransactionInputSigner, no changes needed in utxo.rs or utxo_common.rs, and no propagation gaps. It would shrink the PR from 5 files to basically 2.

One more thing, it would be good to add at least one RXD sighash test vector from a known transaction to verify correctness end-to-end. The Radiant node repo has src/test/sighash_tests.cpp that could be a source for this.

[cdonnachie]

Thanks, agreed. I’ll switch dispatch to SignatureVersion::ForkIdRxd and remove chain_variant from TransactionInputSigner to eliminate propagation gaps. I’ll also add an RXD on-chain sighash test vector.

[cdonnachie]

Hi @shamardy ,

• Implemented reviewer request to route RXD signing via SignatureVersion::ForkIdRxd instead of passing chain_variant through TransactionInputSigner.
• RXD default mapping now comes from config (protocol.chain_variant == "RXD" -> signature_version = fork_id_rxd, fork_id = 0x40).
• Removed chain_variant from signer construction paths in UTXO preimage builders.
• Added a real RXD on-chain sighash vector test in sign.rs.
• Validated locally with focused test pass (test_rxd_forkid_sighash_vector) and build checks.

If you’d like this structured differently, I can adjust. I will be out of country on vacation for 5 days starting Thursday, so my response time may be delayed.

[cdonnachie]

Just for reference, I have run this through a successful swap with the latest change (reduced json):

{
  "type": "Taker",
  "uuid": "71997f0d-9ddb-4587-a558-66fc23c6ec10",
  "pair": "RXD/KMD",
  "amounts": {
    "taker_amount": "10 RXD",
    "maker_amount": "0.04 KMD"
  },
  "sighash_type": "0x41 (ALL|FORKID)",
  "htlc": {
    "secret_hash": "c5e61f8d5102af8e88e4634d3e8f3d4f3cf06cbc",
    "secret_revealed": "e998d47a14fb649037f61a7dda3b67b15dd09da02ca4598f703f1f7f6eae0164"
  },
  "transactions": {
    "taker_fee_tx": "3684bbf882f271ff716110bcfce12123057d41da72892e8961683d297a3f1a09",
    "maker_payment_tx": "df4f861a07f9c85c3316199cf2164624a7bec30a08b9561dd513e84d2c723789",
    "taker_payment_tx": "fb77ee357a4fa2d657f4dbc2d48c132676f98c3ca585aae8986f42eab123278c",
    "taker_payment_spent_tx": "73300377eeb6fb73ff7732b0d560f232b062b004560774f52b17e7e366f4874b",
    "maker_payment_spent_tx": "8a3da3efdc5037a8491251832cf6b9763f75cce49c474734f863e00595df1463"
  },
  "status": {
    "finished": true,
    "success": true
  },
  "mm_version": "2.6.0-beta_779faf886"
}

coins:

 {
    "coin": "RXD",
    "name": "rxd",
    "fname": "Radiant",
    "rpcport": 7332,
    "pubtype": 0,
    "p2shtype": 5,
    "wiftype": 128,
    "txfee": 1000000,
    "segwit": false,
    "fork_id": "0x40",
    "signature_version": "fork_id_rxd",
    "mm2": 1,
    "sign_message_prefix": "Bitcoin Signed Message:\n",
    "required_confirmations": 2,
    "avg_blocktime": 300,
    "protocol": { "type": "UTXO", "chain_variant": "RXD" },
    "derivation_path": "m/44'/512'",
}

[shamardy]

Thanks for the fixes. I have more comments below, since you mentioned you'll be on vacation, would it be ok if I continue this PR, I can push fixes to your branch directly.

[shamardy]

There are some nits / small changes that I will fix and push.

[cdonnachie]

There are some nits / small changes that I will fix and push.

Thanks for doing this, much appreciated, my rust coding is rusty :)

[cipig]

works fine with

    "fork_id": "0x40",
    "signature_version": "fork_id_rxd",