btc: G0/G1 bake golden share-format fixture + parity KAT

Bake the BTC share-format baseline now that the fork pin is resolved to
p2pool-btc-jtoomim @ ece15b03fc23. Emit the golden fixture via
tools/conformance/extract_share_format.py (static extraction) and add a
gtest KAT that asserts the c2pool BTC port against it.

Bucket discipline (3-bucket rule):
 - Isolation primitives (IDENTIFIER/PREFIX/P2P_PORT/SEGWIT=33): byte-equal.
 - MINIMUM_PROTOCOL_VERSION: c2pool floor (3500) >= baseline (3301), an
   intentional forward-compatible raise, not a parity break.
 - share-versions additive-v36: boundary pinned by BTC_version_gate KAT.

Rides the existing allowlisted btc_share_test exe (no new target, no
build.yml change). btc_share_test 14/14 green; fixture re-emit MATCH 9/9.

Author: frstrtr

src/impl/btc/test/CMakeLists.txt

@@ -1,7 +1,7 @@
 if (BUILD_TESTING AND GTest_FOUND)
     # btc twin of ltc share_test — uniquely named to avoid the CMP0002 target
     # collision with src/impl/ltc/test (both subdirs build in the same tree).
-    add_executable(btc_share_test share_test.cpp f11_donation_invariance_test.cpp f10b_version_punish_removal_test.cpp)
+    add_executable(btc_share_test share_test.cpp f11_donation_invariance_test.cpp f10b_version_punish_removal_test.cpp g01_share_format_parity_test.cpp)
     target_link_libraries(btc_share_test PRIVATE
         GTest::gtest_main GTest::gtest
         core btc

src/impl/btc/test/g01_share_format_parity_test.cpp

@@ -0,0 +1,62 @@
+#include <gtest/gtest.h>
+
+#include <string>
+
+#include <impl/btc/config_pool.hpp>
+
+// G0/G1 — BTC share-format byte-parity against the BAKED p2pool baseline.
+//
+// Golden fixture: tools/conformance/fixtures/btc.g01.golden.json
+//   provenance: p2pool-btc-jtoomim @ ece15b03fc23 (the canonical BTC fork pin),
+//   emitted by tools/conformance/extract_share_format.py (static extraction).
+//
+// The fixture is the SSOT; the literals below are transcribed from it so the
+// C++ port asserts byte-identity at run time. If the fixture is re-baked (a
+// fork re-pin => a different --tree), update both in lockstep; the python
+// `compare` subcommand guards the fixture against silent baseline drift.
+//
+// Bucket discipline (operator 3-bucket rule):
+//   * ISOLATION PRIMITIVES (IDENTIFIER / PREFIX / P2P_PORT) — must be
+//     byte-identical to the live sharechain or peers reject us. EQUALITY.
+//   * Intentional / v36-native deltas — NOT asserted equal here:
+//       - MINIMUM_PROTOCOL_VERSION: c2pool raises the floor (3500) above the
+//         baseline (3301) to admit jtoomim-master/SPB and exclude forrestv-era
+//         v17/v32. A floor RAISE is forward-compatible => assert >=, not ==.
+//       - share-versions: c2pool is additive-v36 over the baseline [0..35]; the
+//         v36 activation boundary is pinned separately by
+//         BTC_version_gate.V36ActivationBoundary. Not re-asserted here.
+
+namespace {
+
+// --- transcribed from btc.g01.golden.json @ ece15b03fc23 ---------------------
+constexpr const char* GOLDEN_IDENTIFIER = "fc70035c7a81bc6f";
+constexpr const char* GOLDEN_PREFIX     = "2472ef181efcd37b";
+constexpr uint16_t    GOLDEN_P2P_PORT   = 9333;
+constexpr uint32_t    GOLDEN_SEGWIT_ACTIVATION_VERSION = 33;
+constexpr uint32_t    GOLDEN_MINIMUM_PROTOCOL_VERSION  = 3301;
+
+} // namespace
+
+// Isolation primitives: byte-identical or we are off-network.
+TEST(BTC_g01_share_format, IsolationPrimitivesMatchBaseline)
+{
+    EXPECT_EQ(btc::PoolConfig::DEFAULT_IDENTIFIER_HEX, std::string(GOLDEN_IDENTIFIER));
+    EXPECT_EQ(btc::PoolConfig::DEFAULT_PREFIX_HEX,     std::string(GOLDEN_PREFIX));
+    EXPECT_EQ(btc::PoolConfig::P2P_PORT,               GOLDEN_P2P_PORT);
+    // Testnet shares the mainnet transport identity in this phase (config_pool).
+    EXPECT_EQ(btc::PoolConfig::TESTNET_IDENTIFIER_HEX, std::string(GOLDEN_IDENTIFIER));
+    EXPECT_EQ(btc::PoolConfig::TESTNET_PREFIX_HEX,     std::string(GOLDEN_PREFIX));
+}
+
+// Segwit activation version is a consensus byte — must match the baseline.
+TEST(BTC_g01_share_format, SegwitActivationMatchesBaseline)
+{
+    EXPECT_EQ(btc::PoolConfig::SEGWIT_ACTIVATION_VERSION, GOLDEN_SEGWIT_ACTIVATION_VERSION);
+}
+
+// Protocol floor is an INTENTIONAL raise, not a parity break: forward-compatible.
+TEST(BTC_g01_share_format, ProtocolFloorIsForwardCompatibleRaise)
+{
+    EXPECT_GE(btc::PoolConfig::MINIMUM_PROTOCOL_VERSION, GOLDEN_MINIMUM_PROTOCOL_VERSION)
+        << "c2pool floor must not drop below the p2pool baseline";
+}

tools/conformance/fixtures/btc.g01.golden.json

@@ -0,0 +1,28 @@
+{
+  "coin": "bitcoin",
+  "constants": {
+    "DONATION_SCRIPT": "4104ffd03de44a6e11b9917f3a29f9443283d9871c9d743ef30d5eddcd37094b64d1b3d8090496b53256786bf5c82932ec23c3b74d9f05a6f95a8b5529352656664bac",
+    "IDENTIFIER": "fc70035c7a81bc6f",
+    "MINIMUM_PROTOCOL_VERSION": 3301,
+    "P2P_PORT": 9333,
+    "PREFIX": "2472ef181efcd37b",
+    "SEGWIT_ACTIVATION_VERSION": 33,
+    "gentx_before_refhash_expr": "pack.VarStrType().pack(DONATION_SCRIPT) + pack.IntType(64).pack(0) + pack.VarStrType().pack('\\x6a\\x28' + pack.IntType(256).pack(0) + pack.IntType(64).pack(0))[:3]",
+    "gentx_layout_sig": "5193e3e6ee1a562e23a5a36be01c7d072306a1743bd0998abaa1d7874372c62f",
+    "share_versions": [
+      0,
+      17,
+      32,
+      33,
+      34,
+      35
+    ]
+  },
+  "provenance": {
+    "data_source": "p2pool/data.py",
+    "git_rev": "ece15b03fc23",
+    "network_source": "p2pool/networks/bitcoin.py",
+    "tree": "/home/ubuntu/Github/p2pool-btc-jtoomim"
+  },
+  "schema": "c2pool.g01.share-format/v1"
+}