compactblock: import BIP152-style compact block relay from upstream 1.2.23

Brings src/compactblock.{cpp,h} and test_compactblock.cpp across verbatim
from the upstream-v1.2.23 tag, and gives them a build.

1.2.23 is not a newer release of the line this fork ships. It is a
lightweight tag (7ab5a8c) cut 2026-07-30, on a lineage that upstream/main
(e0be70e, 2026-08-20) does not contain and no remote branch carries -- 272
commits that are not ours, against 376 of ours that are not theirs, from a
merge-base at 56df983. Merging that tag would have deleted 18 files from
src/, selftest.{cpp,h} and the whole 14-test suite among them, so the
content is ported file by file instead.

Compact block relay is the piece worth having: a peer that advertises
sendcmpct gets 48-bit keyed short IDs per transaction rather than the
transaction bytes, and reconstructs the block from its own mempool. It is
purely additive on the wire -- a peer that never sends sendcmpct keeps
receiving full block messages, so no coordinated upgrade is needed.

This commit is the primitives and their unit test only. Nothing calls
BuildCompactBlock or TryReconstructBlock yet: the P2P message handlers
(sendcmpct/cmpctblock/getblocktxn/blocktxn) live in 1.2.23's main.cpp and
are deliberately left for a follow-up, so that no attacker-controlled bytes
reach this code until that wiring is reviewed on its own.

The files needed no API adaptation -- mapTransactions, BEGIN/END and
IMPLEMENT_SERIALIZE are unchanged across the divergence, and it compiled
clean first time. Upstream never wired test_compactblock.cpp into its own
Makefile, so it had never been built there; it links standalone the way
test_bip32 does, supplying its own mapTransactions and GetAppDir to keep
main.cpp out of the link. TEST_LIBS is overridable for the same reason
NODE_LIBS is: the pinned dep tree ships libsodium as a static archive only.

All 17 checks in test_compactblock pass, all 14 selftests still pass, and
the consensus constants are unchanged against e4f898c.

1 files changed, 20 insertions, 4 deletions

diff --git a/src/Makefile b/src/Makefile
index b931007..888110f 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -55,7 +55,8 @@ LIBS = -L$(SECP_LIB) -lsecp256k1 \
 HEADERS = headers_core.h headers.h util.h main.h serialize.h uint256.h \
           key.h bignum.h script.h db.h base58.h net.h nostr.h \
           randomx_pow.h btfaddr.h btfchan.h btfrv.h btftunnel.h \
-          selftest.h walletcmd.h wallet_sqlite.h compat.h sockcount.h proxy.h tor.h font_roboto.h
+          selftest.h walletcmd.h wallet_sqlite.h compat.h sockcount.h proxy.h tor.h font_roboto.h \
+          compactblock.h
 
 IMGUI_OBJS = obj/imgui.o obj/imgui_draw.o obj/imgui_tables.o \
              obj/imgui_widgets.o obj/imgui_impl_glfw.o obj/imgui_impl_opengl3.o
@@ -64,7 +65,7 @@ NODE_OBJS = obj/util.o obj/script.o obj/db.o obj/net.o obj/main.o \
             obj/sha.o obj/nostr.o obj/randomx_pow.o \
             obj/btfaddr.o obj/btfchan.o obj/btfrv.o obj/btftunnel.o obj/rpc.o \
             obj/selftest.o obj/bip32.o obj/walletcmd.o obj/wallet_sqlite.o \
-            obj/proxy.o obj/tor.o
+            obj/proxy.o obj/tor.o obj/compactblock.o
 
 GUI_OBJS = obj/gui.o obj/main_gui.o
 
@@ -194,13 +195,28 @@ fuzz-script-smoke: fuzz-script
         ./fuzz-script -runs=128 ../work/fuzz-corpus/script
 
 clean:
-        rm -rf obj obj-node obj-fuzz bitflash bitflash-node fuzz-net-message fuzz-script test_bip32
+        rm -rf obj obj-node obj-fuzz bitflash bitflash-node fuzz-net-message fuzz-script test_bip32 test_compactblock
 
 test_bip32: test_bip32.cpp bip32.cpp bip32.h bip39_english.h
         $(CXX) $(CXXFLAGS) -o $@ test_bip32.cpp bip32.cpp -lssl -lcrypto
 
-tests: test_bip32 bitflash-node
+# Upstream shipped test_compactblock.cpp with no build rule at all, so it was
+# never compiled there. It links the standalone way test_bip32 does: it supplies
+# its own mapTransactions and GetAppDir so main.cpp stays out of the link, and
+# only needs sha.cpp/util.cpp for Hash() and the logging helpers.
+#
+# TEST_LIBS is overridable for the same reason NODE_LIBS is: the pinned dep tree
+# ships libsodium as a static archive only, so a build against it passes
+# TEST_LIBS="... -l:libsodium.a ...".
+TEST_LIBS ?= -lsodium -lssl -lcrypto -lpthread
+
+test_compactblock: test_compactblock.cpp compactblock.cpp compactblock.h $(HEADERS)
+        $(CXX) $(CXXFLAGS) -o $@ test_compactblock.cpp compactblock.cpp sha.cpp util.cpp \
+          $(TEST_LIBS)
+
+tests: test_bip32 test_compactblock bitflash-node
         ./test_bip32
+        ./test_compactblock
         ./bitflash-node -selftest=wallet-keypool
         ./bitflash-node -selftest=wallet-hd
         ./bitflash-node -selftest=wallet-format