dash(S8): include leg-1 mempool_ingest + test registration (self-contained slice)

The reception-wire leg-1 header (wire_mempool_ingest) and the
test_dash_node_reception_wire CMake registration were authored in the worktree
but never committed to master -- this PR carries the FULL reception wire
(legs 1+2), so a fresh checkout builds the KAT target and its mempool_ingest
include. No file here is on master; purely additive, dash-only.

Author: frstrtr

src/impl/dash/coin/mempool_ingest.hpp

@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+#pragma once
+// ===========================================================================
+// dash reception wire (leg 1 of 4) -- interfaces::Node::new_tx -> maintainer.
+//
+// #672..#685 landed the node-held embedded coin-state bundle plus its async
+// CoinStateMaintainer, and proved that DRIVING the maintainer's on_*() methods
+// flips select_work() to the embedded arm. But nothing in a LIVE NodeImpl ever
+// subscribed the coin interface's reception events to that maintainer, so in a
+// running node the arm could never flip on its own -- the maintainer sat idle.
+// This is the first of the four reception legs
+// (on_mempool_tx / on_block_connected / on_new_tip / on_mn_list_update): the
+// mempool-relay leg, wired exactly as the dgb sibling (wire_mempool_ingest)
+// but routed through the maintainer's on_mempool_tx() so the readiness /
+// republish bookkeeping stays in one place.
+//
+// PAYLOAD-COMPLETE TODAY: interfaces::Node::new_tx carries a whole
+// coin::Transaction, and on_mempool_tx() never gates publication (an empty
+// mempool still yields a valid coinbase-only template), so this leg needs no
+// chain context. The other three legs are NOT wired here: on_block_connected
+// needs the connected block's HEIGHT (full_block carries none -- see bch's
+// block_connector deriving it from the chain tip), on_new_tip needs
+// bits/mtp/address-version params a bare best_block_hash does not carry, and
+// on_mn_list_update has no source event on interfaces::Node at all. Those are
+// their own slices; opening them touches the interface shape and is a design
+// decision surfaced to the integrator, not guessed here.
+//
+// LIFETIME: the handler captures `maint` by reference, so `maint` (and the
+// NodeCoinState it drives) MUST outlive `node`. The returned EventDisposable
+// lets a caller tear the subscription down explicitly; EventDisposable does
+// NOT auto-dispose on destruction, so if the handle is dropped the
+// subscription persists for the node's life.
+//
+// SCC (#143 / #22 / #39): pulls transaction.hpp (the tx serialization codec),
+// so include this header ONLY from a TU that already links the full dash codec
+// (main_dash + this leg's KAT), never a guard-weight TU -- identical to the
+// dgb mempool_ingest / embedded_tx_select btclibs-SCC trap.
+// ===========================================================================
+#include <memory>
+
+#include <core/events.hpp>
+
+#include "node_interface.hpp"        // dash::interfaces::Node (new_tx feed)
+#include "coin_state_maintainer.hpp" // dash::coin::CoinStateMaintainer::on_mempool_tx
+#include "transaction.hpp"           // dash::coin::Transaction -> MutableTransaction
+
+namespace c2pool::dash
+{
+
+// Subscribe `maint` to `node.new_tx`: every relayed tx is folded into the
+// maintainer's mempool via on_mempool_tx (fee_known=false until a UTXO view
+// feeds it, matching the embedded shaper's conservative default -- a P2P-fed
+// mempool cannot desync coinbasevalue versus a daemon's GBT). The mempool leg
+// never gates publication, so a rejected tx (bad utxo ref / already-in) is a
+// no-op here, not a demotion. Returns the subscription handle so the caller
+// controls teardown.
+inline std::shared_ptr<EventDisposable>
+wire_mempool_ingest(::dash::interfaces::Node& node,
+                    ::dash::coin::CoinStateMaintainer& maint)
+{
+    return node.new_tx.subscribe(
+        [&maint](const ::dash::coin::Transaction& tx)
+        {
+            maint.on_mempool_tx(::dash::coin::MutableTransaction(tx));
+        });
+}
+
+} // namespace c2pool::dash

test/CMakeLists.txt

@@ -560,6 +560,21 @@ if (BUILD_TESTING AND GTest_FOUND)
     target_link_libraries(test_dash_node_embedded_wire PRIVATE c2pool_payout c2pool_hashrate c2pool_merged_mining c2pool_storage pool)  # OBJECT-lib SCC direct-naming (#22/#39)
     gtest_add_tests(test_dash_node_embedded_wire "" AUTO)
 
+    # Reception wire (legs 1-3): interfaces::Node reception Events ->
+    # CoinStateMaintainer. Proves the wire_*_ingest() subscriptions fold off the
+    # real Events (no direct poke), honour dispose(), and reach the embedded
+    # template. Same header-only link set as the maintainer suite (no NodeImpl
+    # -> no pool/storage dep).
+    add_executable(test_dash_node_reception_wire test_dash_node_reception_wire.cpp)
+    target_link_libraries(test_dash_node_reception_wire PRIVATE
+        GTest::gtest_main GTest::gtest
+        dash_x11 core
+        nlohmann_json::nlohmann_json
+        ${Boost_LIBRARIES}
+    )
+    target_link_libraries(test_dash_node_reception_wire PRIVATE c2pool_payout c2pool_hashrate c2pool_merged_mining)  # OBJECT-lib SCC direct-naming (#22/#39)
+    gtest_add_tests(test_dash_node_reception_wire "" AUTO)
+
     # DASH CSimplifiedMNListDiff (mnlistdiff wire, S8.1 leaf): vendored diff
     # round-trip + dashcore field-layout pin + apply_diff semantics. Header-only
     # over the SimplifiedMNList leaf + coin/transaction; no ltc/pool SCC dep.