From d681232fe650e13b98792b6f261dbe854242f374 Mon Sep 17 00:00:00 2001
From: Potuz <potuz@prysmaticlabs.com>
Date: Fri, 12 Sep 2025 10:58:00 -0300
Subject: [PATCH] Fix setup forkchoice (#15684)

* Insert the head block to forkchoice

* Add test

* Rename file

* add changelog

* Remove test
---
 beacon-chain/blockchain/BUILD.bazel                          | 2 +-
 .../blockchain/{setup_forchoice.go => setup_forkchoice.go}   | 5 ++++-
 beacon-chain/blockchain/setup_forkchoice_test.go             | 2 +-
 changelog/potuz_fix_forkchoice_startup.md                    | 3 +++
 4 files changed, 9 insertions(+), 3 deletions(-)
 rename beacon-chain/blockchain/{setup_forchoice.go => setup_forkchoice.go} (96%)
 create mode 100644 changelog/potuz_fix_forkchoice_startup.md

diff --git a/beacon-chain/blockchain/BUILD.bazel b/beacon-chain/blockchain/BUILD.bazel
index a520194c97..c79f65f95f 100644
--- a/beacon-chain/blockchain/BUILD.bazel
+++ b/beacon-chain/blockchain/BUILD.bazel
@@ -27,7 +27,7 @@ go_library(
         "receive_block.go",
         "receive_data_column.go",
         "service.go",
-        "setup_forchoice.go",
+        "setup_forkchoice.go",
         "tracked_proposer.go",
         "weak_subjectivity_checks.go",
     ],
diff --git a/beacon-chain/blockchain/setup_forchoice.go b/beacon-chain/blockchain/setup_forkchoice.go
similarity index 96%
rename from beacon-chain/blockchain/setup_forchoice.go
rename to beacon-chain/blockchain/setup_forkchoice.go
index 5171935d2d..0761fd707a 100644
--- a/beacon-chain/blockchain/setup_forchoice.go
+++ b/beacon-chain/blockchain/setup_forkchoice.go
@@ -78,7 +78,10 @@ func (s *Service) setupForkchoiceTree(st state.BeaconState) error {
 	}
 	s.cfg.ForkChoiceStore.Lock()
 	defer s.cfg.ForkChoiceStore.Unlock()
-	return s.cfg.ForkChoiceStore.InsertChain(s.ctx, chain)
+	if err := s.cfg.ForkChoiceStore.InsertChain(s.ctx, chain); err != nil {
+		return errors.Wrap(err, "could not insert forkchoice chain")
+	}
+	return s.cfg.ForkChoiceStore.InsertNode(s.ctx, st, chain[0].Block)
 }
 
 func (s *Service) buildForkchoiceChain(ctx context.Context, head interfaces.ReadOnlySignedBeaconBlock) ([]*forkchoicetypes.BlockAndCheckpoints, error) {
diff --git a/beacon-chain/blockchain/setup_forkchoice_test.go b/beacon-chain/blockchain/setup_forkchoice_test.go
index 62cfea7657..481bb074fb 100644
--- a/beacon-chain/blockchain/setup_forkchoice_test.go
+++ b/beacon-chain/blockchain/setup_forkchoice_test.go
@@ -124,5 +124,5 @@ func Test_setupForkchoiceTree_Head(t *testing.T) {
 	require.NotEqual(t, fRoot, root)
 	require.Equal(t, root, service.startupHeadRoot())
 	require.NoError(t, service.setupForkchoiceTree(st))
-	require.Equal(t, 2, service.cfg.ForkChoiceStore.NodeCount())
+	require.Equal(t, 3, service.cfg.ForkChoiceStore.NodeCount())
 }
diff --git a/changelog/potuz_fix_forkchoice_startup.md b/changelog/potuz_fix_forkchoice_startup.md
new file mode 100644
index 0000000000..eace33d3ec
--- /dev/null
+++ b/changelog/potuz_fix_forkchoice_startup.md
@@ -0,0 +1,3 @@
+### Fixed
+
+- Fixed an off-by-one in forkchoice startup.