dgb(coin): concrete ICoinNode + minimal rpc layer for family-1 WorkView seam

Path A minimal-stub surface for the c2pool-dgb family-1 bind, mirroring
the btc coin layer (2-arg no-MWEB submit shape):

- rpc_data.hpp: rpc::WorkData (m_data/m_hashes/m_latency; m_txs deferred
  until the DGB transaction port lands with M3)
- rpc.hpp: NodeRPC stub -- getwork() throws (ICoinNode no-template
  contract), submit_block_hex(str, bool) returns false; real transport
  is an M3 body-only swap
- node_interface.hpp: dgb::interfaces::Node shared-state surface (work
  variable + new_block event)
- node.hpp: per-coin Node owner (NodeRPC only; P2P deferred to M3)
- coin_node.{hpp,cpp}: concrete dgb::coin::CoinNode : core::coin::ICoinNode;
  full WorkData retained coin-side, agnostic WorkView slice crosses the seam
- template_builder.hpp: CoinNodeInterface trimmed mirror (submit_block
  deferred with the block.hpp port)
- coin/CMakeLists.txt: dgb_coin lib staged; NOT registered -- top-level
  wiring follows the OBJECT-lib convention, so this commit is build-inert

V36 scope: DGB validates Scrypt only; other algos accept-by-continuity or
ignored. Touches src/impl/dgb/ only; zero lines of the #69 adapter/seam
surface.

Author: frstrtr

src/impl/dgb/coin/CMakeLists.txt

@@ -0,0 +1,22 @@
+# dgb_coin -- DGB coin-layer library (Path A minimal-stub surface).
+# Mirrors src/impl/btc/coin/CMakeLists.txt, listing only the files that exist
+# at this milestone. NOT yet referenced by any add_subdirectory(): top-level
+# registration of src/impl/dgb follows the ci-steward OBJECT-lib convention
+# (see ../CMakeLists.txt); staged here so that wiring is a one-line flip.
+
+set(dgb_coin_impl
+    rpc_data.hpp
+    rpc.hpp
+    node.hpp
+    coin_node.hpp coin_node.cpp
+)
+
+set(dgb_coin_interface
+    node_interface.hpp
+    header_chain.hpp
+    template_builder.hpp
+)
+
+add_library(dgb_coin ${dgb_coin_interface} ${dgb_coin_impl})
+
+target_link_libraries(dgb_coin core nlohmann_json::nlohmann_json)

src/impl/dgb/coin/coin_node.cpp

@@ -0,0 +1,51 @@
+#include "coin_node.hpp"
+
+#include <stdexcept>
+#include <utility>
+
+namespace dgb
+{
+
+namespace coin
+{
+
+core::coin::WorkView CoinNode::get_work_view()
+{
+    // No work source configured at all -> empty view (1:1 with the btc/ltc
+    // reference).
+    if (!m_embedded && !m_rpc)
+        return {};
+
+    // Embedded preferred, external RPC fallback. getwork() throws
+    // std::runtime_error when no template can be produced -- propagated to the
+    // caller (web_server), matching the ICoinNode contract. On DGB Path A both
+    // sources are stubs, so this path always throws until M3 lands a real one.
+    rpc::WorkData wd = m_embedded ? m_embedded->getwork() : m_rpc->getwork();
+
+    // Retain the FULL WorkData coin-side. Variable::set takes its argument BY
+    // VALUE, so this copies wd; sequenced BEFORE the std::move()s below so the
+    // copy completes first -- never move out of wd beforehand.
+    work.set(wd);
+
+    core::coin::WorkView v;
+    v.m_data    = std::move(wd.m_data);
+    v.m_hashes  = std::move(wd.m_hashes);
+    v.m_latency = wd.m_latency;
+    return v;
+}
+
+bool CoinNode::submit_block_hex(const std::string& block_hex, bool ignore_failure)
+{
+    // Guard sits ahead of the submit: in embedded-preferred mode m_rpc can be
+    // null. Returning false is the correct "no RPC sink" result.
+    if (!m_rpc)
+        return false;
+
+    // DGB's NodeRPC::submit_block_hex is already the agnostic 2-arg/no-mweb
+    // form (MWEB is LTC-specific and absent here), so we forward directly.
+    return m_rpc->submit_block_hex(block_hex, ignore_failure);
+}
+
+} // namespace coin
+
+} // namespace dgb

src/impl/dgb/coin/coin_node.hpp

@@ -0,0 +1,70 @@
+#pragma once
+
+// ---------------------------------------------------------------------------
+// dgb::coin::CoinNode -- concrete core::coin::ICoinNode for DGB (family-1 P2
+// WorkView seam, Path A minimal-stub). 1:1 mirror of btc::coin::CoinNode
+// (src/impl/btc/coin/coin_node.{hpp,cpp}), which is itself member-mapped from
+// the ltc::coin::CoinNode reference -- the control flow / sequencing are the
+// load-bearing part and are preserved verbatim:
+//   m_embedded : CoinNodeInterface*       -- embedded in-process source
+//   m_rpc      : NodeRPC*                 -- external coin-RPC client (STUB)
+//   work       : Variable<rpc::WorkData>  -- full per-coin WorkData kept
+//                                            coin-side; only the agnostic
+//                                            WorkView slice crosses the seam
+//
+// DGB Path A status: both work sources behind this adapter are stubs --
+// NodeRPC throws on getwork() (rpc.hpp) and no EmbeddedCoinNode exists until
+// the M3 daemon slice -- so a wired DGB node reports "no template" loudly
+// through the ICoinNode contract rather than fabricating work. The adapter
+// itself is COMPLETE: when either source becomes real, no seam-side change
+// is needed.
+//
+// Build-INERT: defines the type; NOT yet wired into web_server or a
+// main_dgb.cpp (no such binary split exists yet). Registration follows the
+// ci-steward OBJECT-lib convention; see src/impl/dgb/CMakeLists.txt.
+// ---------------------------------------------------------------------------
+
+#include <string>
+
+#include <core/coin/node_iface.hpp>
+#include <core/coin/work_view.hpp>
+#include <core/events.hpp>
+
+#include "rpc.hpp"
+#include "rpc_data.hpp"
+#include "template_builder.hpp"
+
+namespace dgb
+{
+
+namespace coin
+{
+
+class CoinNode : public core::coin::ICoinNode
+{
+    // Embedded in-process template source (EmbeddedCoinNode, M3). May be null
+    // when the node runs RPC-only. is_embedded() reports its presence.
+    CoinNodeInterface* m_embedded = nullptr;
+
+    // External coin-RPC client. May be null in embedded-preferred mode; it is
+    // the sole sink for submit_block_hex(). has_rpc() reports its presence.
+    NodeRPC* m_rpc = nullptr;
+
+    // Full per-coin WorkData retained coin-side via work.set(wd); only the
+    // agnostic WorkView slice crosses the seam into core/web_server.
+    Variable<rpc::WorkData> work;
+
+public:
+    CoinNode(CoinNodeInterface* embedded, NodeRPC* rpc)
+        : m_embedded(embedded), m_rpc(rpc) {}
+
+    core::coin::WorkView get_work_view() override;
+    bool submit_block_hex(const std::string& block_hex, bool ignore_failure) override;
+
+    bool is_embedded() const override { return m_embedded != nullptr; }
+    bool has_rpc()     const override { return m_rpc != nullptr; }
+};
+
+} // namespace coin
+
+} // namespace dgb

src/impl/dgb/coin/node.hpp

@@ -0,0 +1,55 @@
+#pragma once
+
+// ---------------------------------------------------------------------------
+// dgb::coin::Node -- per-coin node owner (Path A minimal-stub). TRIMMED mirror
+// of src/impl/btc/coin/node.hpp: owns the NodeRPC client and inherits the
+// dgb::interfaces::Node shared-state surface (work variable + new_block
+// event) that NodeRPC and the seam-side CoinNode bind against.
+//
+// Deliberately ABSENT until M3 (each needs a port dgb does not have yet):
+//   - NodeP2P / p2p_connection (coin P2P block relay; btc's p2p_node.hpp)
+//   - init_rpc() transport connect (NodeRPC is a stub with no transport)
+//   - submit_block_p2p / send_getheaders / handshake surface
+// The ctor keeps btc's (context, config) shape via auto params (no boost
+// include needed in the stub) so M3 restores the body without re-typing
+// construction sites.
+// ---------------------------------------------------------------------------
+
+#include <memory>
+
+#include "node_interface.hpp"
+#include "rpc.hpp"
+
+namespace dgb
+{
+
+namespace coin
+{
+
+template <typename ConfigType>
+class Node : public dgb::interfaces::Node
+{
+    using config_t = ConfigType;
+
+    config_t* m_config = nullptr;
+
+    std::unique_ptr<NodeRPC> m_rpc;
+
+public:
+    Node(auto* /*context*/, auto* config) : m_config(config)
+    {
+    }
+
+    void run()
+    {
+        // Stub NodeRPC: constructed so has-rpc presence wiring can be
+        // exercised, but no transport connect until M3.
+        m_rpc = std::make_unique<NodeRPC>(this);
+    }
+
+    NodeRPC* rpc() { return m_rpc.get(); }
+};
+
+} // namespace coin
+
+} // namespace dgb

src/impl/dgb/coin/node_interface.hpp

@@ -0,0 +1,39 @@
+#pragma once
+
+// ---------------------------------------------------------------------------
+// dgb::interfaces::Node -- coin-node shared-state surface (Path A
+// minimal-stub). Mirrors src/impl/btc/coin/node_interface.hpp TRIMMED to the
+// members the family-1 ICoinNode seam actually binds today:
+//
+//   work      : Variable<rpc::WorkData> -- get_work result (NodeRPC fills,
+//               CoinNode retains coin-side per the WorkView seam contract)
+//   new_block : Event<uint256>          -- block-hash announce (header-chain
+//               feed; uint256 only, no per-coin type needed)
+//
+// Deliberately ABSENT until the M3 type ports land (each pulls a type dgb
+// does not have yet): Event<Transaction> new_tx, Event<vector<
+// BlockHeaderType>> new_headers, Event<BlockType> full_block, TXIDCache
+// txidcache, known_txs map. Restoring them is additive; nothing in the seam
+// depends on their absence.
+// ---------------------------------------------------------------------------
+
+#include <core/events.hpp>
+#include <core/uint256.hpp>
+
+#include "rpc_data.hpp"
+
+namespace dgb
+{
+
+namespace interfaces
+{
+
+struct Node
+{
+    Variable<dgb::coin::rpc::WorkData> work; // get_work result
+    Event<uint256> new_block;                // block_hash
+};
+
+} // namespace interfaces
+
+} // namespace dgb

src/impl/dgb/coin/rpc.hpp

@@ -0,0 +1,65 @@
+#pragma once
+
+// ---------------------------------------------------------------------------
+// dgb::coin::NodeRPC -- external coin-RPC client STUB (Path A minimal-stub,
+// "rpc stubs" scope item).
+//
+// btc/ltc NodeRPC is a boost::beast + jsonrpccxx HTTP JSON-RPC client whose
+// header drags in block.hpp / transaction.hpp -- types dgb does not port
+// until M3. This stub keeps the call surface coin_node.cpp and coin/node.hpp
+// consume, with no transport behind it:
+//
+//   getwork()          -> throws std::runtime_error. This is the ICoinNode
+//                         contract for "no template available" -- web_server
+//                         already handles the throw, so a wired-but-stub DGB
+//                         node degrades loudly, not silently.
+//   submit_block_hex() -> false ("no RPC sink"; the same result the null-
+//                         m_rpc guard in CoinNode::submit_block_hex yields).
+//   check()            -> false (never connected).
+//
+// connect()/reconnect()/the RPC method set (getblocktemplate etc.) arrive
+// with the real transport in M3 as a body-only swap mirroring
+// src/impl/btc/coin/rpc.{hpp,cpp}; DGB's getblocktemplate call passes
+// rules=["scrypt"] per the Scrypt GBT filter point (template_builder.hpp,
+// impl plan section 3) so only Scrypt-eligible templates are returned.
+// ---------------------------------------------------------------------------
+
+#include <stdexcept>
+#include <string>
+
+#include "node_interface.hpp"
+#include "rpc_data.hpp"
+
+namespace dgb
+{
+
+namespace coin
+{
+
+class NodeRPC
+{
+    // Shared-state surface the real client fills (work variable); the stub
+    // holds the pointer so the M3 swap does not change construction sites.
+    dgb::interfaces::Node* m_coin = nullptr;
+
+public:
+    explicit NodeRPC(dgb::interfaces::Node* coin = nullptr) : m_coin(coin) {}
+
+    // Never connected: no transport in the stub.
+    bool check() const { return false; }
+
+    rpc::WorkData getwork()
+    {
+        throw std::runtime_error(
+            "dgb: NodeRPC is a Path A stub -- no external RPC transport until M3");
+    }
+
+    bool submit_block_hex(const std::string& /*block_hex*/, bool /*ignore_failure*/)
+    {
+        return false;
+    }
+};
+
+} // namespace coin
+
+} // namespace dgb

src/impl/dgb/coin/rpc_data.hpp

@@ -0,0 +1,63 @@
+#pragma once
+
+// ---------------------------------------------------------------------------
+// dgb::coin::rpc::WorkData -- per-coin work payload for the family-1 P2
+// WorkView seam (Path A minimal-stub).
+//
+// Mirrors src/impl/btc/coin/rpc_data.hpp with ONE deliberate trim: btc's
+// WorkData carries std::vector<Transaction> m_txs, but DGB has no
+// coin/transaction.{hpp,cpp} port yet -- that lands with the M3 embedded
+// daemon slice. The ICoinNode seam contract makes the trim safe: web_server
+// consumes ONLY the agnostic slice (m_data/m_hashes/m_latency); the full
+// per-coin WorkData (incl. txs) never crosses the seam
+// (src/core/coin/node_iface.hpp). When the DGB transaction port lands, m_txs
+// is restored here and the coin-side work.set(wd) retention in
+// CoinNode::get_work_view() carries it without any seam change.
+//
+// V36 master compat: field semantics match p2pool-merged-v36 getwork result
+// (data / txhashes / latency); impl plan section 3 (frstrtr/the, 8ef8d2d).
+// ---------------------------------------------------------------------------
+
+#include <ctime>
+#include <utility>
+#include <vector>
+
+#include <core/uint256.hpp>
+
+#include <nlohmann/json.hpp>
+
+namespace dgb
+{
+
+namespace coin
+{
+
+namespace rpc
+{
+
+struct WorkData
+{
+    nlohmann::json m_data;
+    std::vector<uint256> m_hashes; // transaction hashes
+    time_t m_latency = 0;
+
+    // TODO(M3): std::vector<Transaction> m_txs once coin/transaction.{hpp,cpp}
+    // is ported (DGB txs are bitcoin-family; expected near-verbatim from btc's
+    // port). Kept out of the stub so the rpc chain compiles without the
+    // Transaction/Block types dgb does not have yet.
+
+    WorkData() {}
+    WorkData(nlohmann::json data, std::vector<uint256> txhashes, time_t latency)
+        : m_data(std::move(data)), m_hashes(std::move(txhashes)), m_latency(latency)
+    {
+    }
+
+    bool operator==(const WorkData& rhs) const { return m_data == rhs.m_data; }
+    bool operator!=(const WorkData& rhs) const { return !(*this == rhs); }
+};
+
+} // namespace rpc
+
+} // namespace coin
+
+} // namespace dgb