From c881aa26a4c0b784a58053186101dfbec84265d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1s=20Gr=C3=BCner?=
 <47506558+MegaRedHand@users.noreply.github.com>
Date: Fri, 6 Feb 2026 11:22:13 -0300
Subject: [PATCH 1/3] fix: check against finalized slot for justifiable search

This is just in case.
---
 crates/blockchain/src/store.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/crates/blockchain/src/store.rs b/crates/blockchain/src/store.rs
index c41af16..93da4a7 100644
--- a/crates/blockchain/src/store.rs
+++ b/crates/blockchain/src/store.rs
@@ -465,11 +465,15 @@ pub fn get_attestation_target(store: &Store) -> Checkpoint {
         }
     }
 
+    let finalized_slot = store.latest_finalized().slot;
+
     // Ensure target is in justifiable slot range
     //
     // Walk back until we find a slot that satisfies justifiability rules
     // relative to the latest finalized checkpoint.
-    while !slot_is_justifiable_after(target_block.slot, store.latest_finalized().slot) {
+    while target_block.slot > finalized_slot
+        && !slot_is_justifiable_after(target_block.slot, finalized_slot)
+    {
         target_block_root = target_block.parent_root;
         target_block = store
             .get_block(&target_block_root)

From 19543b238338e8411cd3c0b673ac86f7812083bc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1s=20Gr=C3=BCner?=
 <47506558+MegaRedHand@users.noreply.github.com>
Date: Fri, 6 Feb 2026 14:48:26 -0300
Subject: [PATCH 2/3] fix: clamp attestation target to source

When a block advances latest_justified during processing (interval 0),
safe_target remains stale until interval 2. This causes
get_attestation_target() to walk back past the new justified checkpoint,
producing attestations where source.slot > target.slot.

Clamp the target to latest_justified when it falls behind, matching
Zeam's approach.

Closes #97
---
 crates/blockchain/src/store.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/crates/blockchain/src/store.rs b/crates/blockchain/src/store.rs
index 93da4a7..b30a6c6 100644
--- a/crates/blockchain/src/store.rs
+++ b/crates/blockchain/src/store.rs
@@ -479,6 +479,20 @@ pub fn get_attestation_target(store: &Store) -> Checkpoint {
             .get_block(&target_block_root)
             .expect("parent block exists");
     }
+    // Ensure target is at or after the source (latest_justified) to maintain
+    // the invariant: source.slot <= target.slot. When a block advances
+    // latest_justified between safe_target updates (interval 2), the walk-back
+    // above can land on a slot behind the new justified checkpoint.
+    let latest_justified = store.latest_justified();
+    if target_block.slot < latest_justified.slot {
+        warn!(
+            target_slot = target_block.slot,
+            justified_slot = latest_justified.slot,
+            "Attestation target walked behind justified source, clamping to justified"
+        );
+        return latest_justified;
+    }
+
     Checkpoint {
         root: target_block_root,
         slot: target_block.slot,

From 9ee480d938b44306515c2233e87ab95a0ee141a5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1s=20Gr=C3=BCner?=
 <47506558+MegaRedHand@users.noreply.github.com>
Date: Mon, 9 Feb 2026 11:07:33 -0300
Subject: [PATCH 3/3] chore: link to Zeam's equivalent

---
 crates/blockchain/src/store.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/crates/blockchain/src/store.rs b/crates/blockchain/src/store.rs
index b30a6c6..5931d67 100644
--- a/crates/blockchain/src/store.rs
+++ b/crates/blockchain/src/store.rs
@@ -483,6 +483,8 @@ pub fn get_attestation_target(store: &Store) -> Checkpoint {
     // the invariant: source.slot <= target.slot. When a block advances
     // latest_justified between safe_target updates (interval 2), the walk-back
     // above can land on a slot behind the new justified checkpoint.
+    //
+    // See https://github.com/blockblaz/zeam/blob/697c293879e922942965cdb1da3c6044187ae00e/pkgs/node/src/forkchoice.zig#L654-L659
     let latest_justified = store.latest_justified();
     if target_block.slot < latest_justified.slot {
         warn!(