dgb(#82): extract SSOT gentx coinbase assembler + oracle-pinned round-trip KAT

Factor the p2pool non-witness coinbase (gentx) wire layout out of
generate_share_transaction() (share_check.hpp:933, the verification SSOT)
into coin/gentx_coinbase.hpp::assemble_gentx_coinbase() so emission and
verification cannot diverge on a byte. Pure: takes already-built
scripts/amounts (no tracker/share-template dependency) so it is directly
KAT-able; this is the single builder that create_local_share() and the
won-block reconstruction body will consume in follow-up slices.

KAT vectors are GROUND-TRUTH from the canonical oracle
frstrtr/p2pool-dgb-scrypt (util/pack.py byte logic + bitcoin/data.py
tx_id_type; donation script 4104ffd0...ac), not self-generated, so a PASS
proves build -> non-witness serialize -> double-SHA256 == oracle bytes/txid,
not mere self-consistency. Covers the no-segwit and witness-commitment-first
layouts; the only DGB<->BCH divergence is the gated segwit predicate at
serialize time. dgb_gentx_coinbase_test 3/3 PASS, build EXIT=0; target wired
into ctest + BOTH build.yml --target allowlists (#143 NOT_BUILT trap avoided).

Scope: factor + KAT only. The won-block-reaches-network wiring (m_on_block_found
and submit_block_hex) is fix #82 and stays separate.

Author: frstrtr

.github/workflows/build.yml

@@ -67,7 +67,7 @@ jobs:
                     test_phase4_embedded \
                     test_mweb_builder \
                     test_address_resolution test_compute_share_target \
-                    test_utxo test_dgb_subsidy dgb_share_test \
+                    test_utxo test_dgb_subsidy dgb_share_test dgb_gentx_coinbase_test \
                     rpc_request_test softfork_check_test genesis_check_test algo_select_test digishield_walk_test header_chain_test \
                     v37_test \
             -j$(nproc)
@@ -197,7 +197,7 @@ jobs:
                     test_phase4_embedded \
                     test_mweb_builder \
                     test_address_resolution test_compute_share_target \
-                    test_utxo test_dgb_subsidy dgb_share_test \
+                    test_utxo test_dgb_subsidy dgb_share_test dgb_gentx_coinbase_test \
                     rpc_request_test softfork_check_test genesis_check_test algo_select_test digishield_walk_test header_chain_test \
                     test_coin_broadcaster test_multiaddress_pplns test_pplns_stress \
                     v37_test \

src/impl/dgb/coin/gentx_coinbase.hpp

@@ -0,0 +1,131 @@
+#pragma once
+// ============================================================================
+// gentx_coinbase.hpp — SSOT non-witness coinbase (gentx) assembler.
+//
+// Single source of the p2pool coinbase wire layout. Consumed by:
+//   - share_check.hpp generate_share_transaction()  (the verification SSOT)
+//   - share_check.hpp create_local_share()          (the "same format as" smell)
+//   - won-block reconstruction (as_block framing)
+// so that emission and verification can never diverge on a byte.
+//
+// Produces the NON-WITNESS serialization and its double-SHA256 txid
+// (== p2pool gentx_hash). Byte layout mirrors
+// frstrtr/p2pool-merged-v36 data.py generate_transaction():
+//
+//   version(4 LE = 1)
+//   vin_count(varint = 1)
+//   vin[0] = prev_hash(32 zero) | prev_idx(0xffffffff) | script(VarStr) | seq(0xffffffff)
+//   vout_count(varint)
+//   vouts: [segwit_commitment?] ++ payout_outputs ++ donation ++ op_return_commitment
+//          each vout = value(8 LE) | script(VarStr)
+//   lock_time(4 = 0)
+//
+// Pure: takes already-built script/amount inputs (no tracker, no share template
+// dependency) so it is directly KAT-able against a canonical oracle vector.
+// ============================================================================
+
+#include <core/pack.hpp>
+#include <core/pack_types.hpp>
+#include <core/hash.hpp>
+#include <core/uint256.hpp>
+
+#include <cstdint>
+#include <optional>
+#include <span>
+#include <utility>
+#include <vector>
+
+namespace dgb::coin
+{
+
+struct GentxCoinbase
+{
+    std::vector<unsigned char> bytes; // non-witness serialization
+    uint256 txid;                     // double-SHA256(bytes) == gentx_hash
+};
+
+// payout_outputs: (scriptPubKey, value) pairs in final consensus order.
+// segwit_commitment_script / segwit absent -> no witness-commitment vout.
+inline GentxCoinbase assemble_gentx_coinbase(
+    const std::vector<unsigned char>& coinbase_script,
+    const std::optional<std::vector<unsigned char>>& segwit_commitment_script,
+    const std::vector<std::pair<std::vector<unsigned char>, uint64_t>>& payout_outputs,
+    uint64_t donation_amount,
+    const std::vector<unsigned char>& donation_script,
+    const std::vector<unsigned char>& op_return_script)
+{
+    PackStream tx;
+
+    // tx version = 1
+    uint32_t tx_version = 1;
+    tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&tx_version), 4));
+
+    // vin count = 1
+    {
+        unsigned char one = 1;
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&one), 1));
+    }
+
+    // vin[0]: prev_output = 0...0:ffffffff, script = coinbase, sequence = 0xffffffff
+    {
+        uint256 zero_hash;
+        tx << zero_hash;
+        uint32_t prev_idx = 0xffffffff;
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&prev_idx), 4));
+        BaseScript cb; cb.m_data = coinbase_script;
+        tx << cb;
+        uint32_t seq = 0xffffffff;
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&seq), 4));
+    }
+
+    // vout count
+    size_t n_outs = payout_outputs.size() + 1 /* donation */ + 1 /* OP_RETURN */
+                  + (segwit_commitment_script.has_value() ? 1 : 0);
+    if (n_outs < 253)
+    {
+        uint8_t cnt = static_cast<uint8_t>(n_outs);
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&cnt), 1));
+    }
+    else
+    {
+        uint8_t marker = 0xfd;
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&marker), 1));
+        uint16_t cnt = static_cast<uint16_t>(n_outs);
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&cnt), 2));
+    }
+
+    auto write_txout = [&](uint64_t value, const std::vector<unsigned char>& script) {
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&value), 8));
+        BaseScript bs; bs.m_data = script;
+        tx << bs;
+    };
+
+    // segwit witness-commitment vout (value 0)
+    if (segwit_commitment_script.has_value())
+        write_txout(0, segwit_commitment_script.value());
+
+    // PPLNS payout outputs (caller supplies final sorted order)
+    for (auto& [script, amount] : payout_outputs)
+        write_txout(amount, script);
+
+    // donation output
+    write_txout(donation_amount, donation_script);
+
+    // OP_RETURN ref commitment (value 0)
+    write_txout(0, op_return_script);
+
+    // lock_time = 0
+    {
+        uint32_t locktime = 0;
+        tx.write(std::span<const std::byte>(reinterpret_cast<const std::byte*>(&locktime), 4));
+    }
+
+    GentxCoinbase out;
+    out.bytes.assign(reinterpret_cast<const unsigned char*>(tx.data()),
+                     reinterpret_cast<const unsigned char*>(tx.data()) + tx.size());
+    auto sp = std::span<const unsigned char>(out.bytes.data(), out.bytes.size());
+    out.txid = Hash(sp);
+    return out;
+}
+
+} // namespace dgb::coin

src/impl/dgb/test/CMakeLists.txt

@@ -25,6 +25,20 @@ if (BUILD_TESTING AND GTest_FOUND)
     # transport rpc.cpp wiring is deferred (Option-B scope). Each MUST appear
     # in BOTH this ctest registration AND the build.yml --target allowlist,
     # or it becomes a #143-style NOT_BUILT sentinel that reds master.
+
+    # --- #82 SSOT gentx coinbase assembler KAT ----------------------------
+    # coin/gentx_coinbase.hpp uses core primitives (PackStream/BaseScript/Hash/
+    # uint256), so it links the same proven set as dgb_share_test rather than
+    # the header-only guard foreach above. Oracle ground-truth vectors. MUST
+    # also be in the build.yml --target allowlist (#143 NOT_BUILT trap).
+    add_executable(dgb_gentx_coinbase_test gentx_coinbase_test.cpp)
+    target_link_libraries(dgb_gentx_coinbase_test PRIVATE
+        GTest::gtest_main GTest::gtest
+        core dgb
+        c2pool_payout c2pool_merged_mining c2pool_hashrate c2pool_storage
+        dgb_coin pool sharechain)
+    gtest_add_tests(dgb_gentx_coinbase_test "" AUTO)
+
     foreach(dgb_guard rpc_request_test softfork_check_test genesis_check_test algo_select_test digishield_walk_test header_chain_test)
         add_executable(${dgb_guard} ${dgb_guard}.cpp)
         target_link_libraries(${dgb_guard} PRIVATE

src/impl/dgb/test/gentx_coinbase_test.cpp

@@ -0,0 +1,104 @@
+// DGB #82 — SSOT non-witness coinbase (gentx) assembler KAT.
+//
+// Locks dgb::coin::assemble_gentx_coinbase() (coin/gentx_coinbase.hpp) — the
+// single coinbase wire-layout extracted from generate_share_transaction()
+// (share_check.hpp:933, the verification SSOT) — against GROUND-TRUTH vectors
+// derived from the canonical oracle frstrtr/p2pool-dgb-scrypt
+// (util/pack.py byte logic + bitcoin/data.py tx_id_type; donation script
+// 4104ffd0...ac). The vectors are NOT self-generated from this builder: they
+// are the oracle serializer's output, so a PASS proves emission==oracle, not
+// merely self-consistency.
+//
+// Asserts, for both the no-segwit and witness-commitment-first layouts:
+//   build -> non-witness serialize == oracle BYTES
+//   double-SHA256(bytes) (GetHex display) == oracle TXID
+// Per-coin isolation: the only DGB<->BCH divergence is the segwit predicate at
+// serialize time (witness vout present-or-absent), exercised by both cases.
+
+#include <gtest/gtest.h>
+#include <impl/dgb/coin/gentx_coinbase.hpp>
+
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace {
+
+std::vector<unsigned char> unhex(const std::string& h) {
+    std::vector<unsigned char> v; v.reserve(h.size() / 2);
+    auto nyb = [](char c) -> int { return (c <= '9') ? c - '0' : (c | 0x20) - 'a' + 10; };
+    for (size_t i = 0; i + 1 < h.size(); i += 2)
+        v.push_back(static_cast<unsigned char>((nyb(h[i]) << 4) | nyb(h[i + 1])));
+    return v;
+}
+std::string tohex(const std::vector<unsigned char>& v) {
+    static const char* H = "0123456789abcdef";
+    std::string s; s.reserve(v.size() * 2);
+    for (unsigned char b : v) { s.push_back(H[b >> 4]); s.push_back(H[b & 0xf]); }
+    return s;
+}
+
+// --- fixed inputs shared verbatim with the oracle generator ----------------
+const std::vector<unsigned char> CB    = unhex("03a1b2c3041122334455667788");
+const std::vector<unsigned char> P1    = unhex(std::string("76a914") + std::string(40, '1') + "88ac");
+const std::vector<unsigned char> P2    = unhex(std::string("76a914") + std::string(40, '2') + "88ac");
+const std::vector<unsigned char> DON   = unhex("4104ffd03de44a6e11b9917f3a29f9443283d9871c9d743ef30d5eddcd37094b64d1b3d8090496b53256786bf5c82932ec23c3b74d9f05a6f95a8b5529352656664bac");
+
+const std::vector<std::pair<std::vector<unsigned char>, uint64_t>> PAYOUTS = {
+    {P1, 5000000000ull},
+    {P2, 2500000000ull},
+};
+
+// Ground truth from the oracle serializer (see file header).
+const std::string NOSEG_BYTES =
+    "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";
+const std::string NOSEG_TXID =
+    "c5734775c1521b216e0e1bca506e4d15755cf55125caf56b7e0728a6d54a9b59";
+const std::string SEG_BYTES =
+    "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";
+const std::string SEG_TXID =
+    "4b66aabff52ca1336b52688815cece123075856880aaf6e77cb44f0d477b6162";
+
+} // namespace
+
+// op_return / wc literals: build them explicitly to avoid std::string surprises.
+static std::vector<unsigned char> make_opret() {
+    auto v = unhex("6a28");
+    for (int i = 0; i < 32; ++i) v.push_back(0xab);
+    const unsigned char nonce[8] = {0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01};
+    for (unsigned char b : nonce) v.push_back(b);
+    return v;
+}
+static std::vector<unsigned char> make_wc() {
+    auto v = unhex("6a24aa21a9ed");
+    for (int i = 0; i < 32; ++i) v.push_back(0xcd);
+    return v;
+}
+
+TEST(DGB_gentx_coinbase, NoSegwitOracleVector) {
+    auto opret = make_opret();
+    auto g = dgb::coin::assemble_gentx_coinbase(
+        CB, std::nullopt, PAYOUTS, /*donation_amount=*/1, DON, opret);
+    EXPECT_EQ(tohex(g.bytes), NOSEG_BYTES);
+    EXPECT_EQ(g.txid.GetHex(), NOSEG_TXID);
+}
+
+TEST(DGB_gentx_coinbase, SegwitCommitmentFirstOracleVector) {
+    auto opret = make_opret();
+    auto wc = make_wc();
+    auto g = dgb::coin::assemble_gentx_coinbase(
+        CB, std::optional<std::vector<unsigned char>>(wc), PAYOUTS,
+        /*donation_amount=*/1, DON, opret);
+    EXPECT_EQ(tohex(g.bytes), SEG_BYTES);
+    EXPECT_EQ(g.txid.GetHex(), SEG_TXID);
+}
+
+// Guard the per-coin isolation invariant: toggling only the segwit predicate
+// changes vout-count + prepends exactly one 0-value commitment vout, nothing
+// else — the divergence is gated, not a forked framer.
+TEST(DGB_gentx_coinbase, SegwitPredicateIsTheOnlyDivergence) {
+    EXPECT_NE(NOSEG_BYTES, SEG_BYTES);
+    // both share the identical coinbase-script vin prefix and donation/op_return tail
+    EXPECT_EQ(NOSEG_BYTES.substr(0, 90), SEG_BYTES.substr(0, 90));
+}