From fa3f4c5f2c4160b17cbf5a021b4082543de2e958 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Wed, 10 Jun 2026 01:22:26 +0000
Subject: [PATCH] fix(protocol): decouple preconf metadata existence from
 anchorBlockNumber

getPreconfMetadata used "anchorBlockNumber != 0" as the sentinel for "metadata
exists", but anchorBlockNumber is documented as "0 to skip" in BlockParams. A
block legitimately anchored with anchorBlockNumber == 0 was therefore
indistinguishable from a block that was never recorded, causing getPreconfMetadata
to revert and blocking PreconfSlasherL2 from validating faults for that block (or
its predecessor, which also reads the next block's metadata).

Add an explicit "bool stored" marker to PreconfMetadata (packed into the existing
uint48 slot, so the rawTxListHash/parentRawTxListHash sub-slots and the
contract-level storage layout are unchanged) and use it as the existence sentinel.
This preserves the documented "anchorBlockNumber == 0 to skip" semantic.

https://claude.ai/code/session_0187MFZTJHwwQ6zUhRus39we
---
 .../protocol/contracts/layer2/core/Anchor.sol |  7 +++++-
 .../protocol/test/layer2/core/Anchor.t.sol    | 24 +++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/packages/protocol/contracts/layer2/core/Anchor.sol b/packages/protocol/contracts/layer2/core/Anchor.sol
index 1f1b1cc6e6..606d3aa7ea 100644
--- a/packages/protocol/contracts/layer2/core/Anchor.sol
+++ b/packages/protocol/contracts/layer2/core/Anchor.sol
@@ -47,10 +47,14 @@ contract Anchor is EssentialContract {
     }
 
     /// @notice Metadata that will be required for slashing violations of permissionless preconfs.
+    /// @dev `stored` marks an existing entry so callers can distinguish a recorded block whose
+    /// `anchorBlockNumber` is 0 (a valid "skip checkpoint" value) from a block that was never
+    /// recorded. It packs into the same slot as the preceding `uint48` fields.
     struct PreconfMetadata {
         uint48 anchorBlockNumber;
         uint48 submissionWindowEnd;
         uint48 parentSubmissionWindowEnd;
+        bool stored;
         bytes32 rawTxListHash;
         bytes32 parentRawTxListHash;
     }
@@ -205,7 +209,7 @@ contract Anchor is EssentialContract {
         returns (PreconfMetadata memory)
     {
         PreconfMetadata memory preconfMetadata = _preconfMetadata[_blockNumber];
-        require(preconfMetadata.anchorBlockNumber != 0, InvalidBlockNumber());
+        require(preconfMetadata.stored, InvalidBlockNumber());
         return preconfMetadata;
     }
 
@@ -251,6 +255,7 @@ contract Anchor is EssentialContract {
             anchorBlockNumber: _blockParams.anchorBlockNumber,
             submissionWindowEnd: _proposalParams.submissionWindowEnd,
             parentSubmissionWindowEnd: parentPreconfMetadata.submissionWindowEnd,
+            stored: true,
             rawTxListHash: _blockParams.rawTxListHash,
             parentRawTxListHash: parentPreconfMetadata.rawTxListHash
         });
diff --git a/packages/protocol/test/layer2/core/Anchor.t.sol b/packages/protocol/test/layer2/core/Anchor.t.sol
index f698201e83..bd250c9df0 100644
--- a/packages/protocol/test/layer2/core/Anchor.t.sol
+++ b/packages/protocol/test/layer2/core/Anchor.t.sol
@@ -105,6 +105,30 @@ contract AnchorTest is Test {
         assertEq(checkpointStore.getCheckpoint(staleBlockParams.anchorBlockNumber).blockNumber, 0);
     }
 
+    function test_getPreconfMetadata_recordsBlockAnchoredAtZero() external {
+        // A block may legitimately be anchored with `anchorBlockNumber == 0` ("skip checkpoint").
+        // Its preconf metadata must still be retrievable so the slasher can validate faults; the
+        // `stored` marker distinguishes it from a block that was never recorded.
+        Anchor.ProposalParams memory proposalParams =
+            Anchor.ProposalParams({ submissionWindowEnd: 7 });
+        Anchor.BlockParams memory blockParams = _blockParams(0, 0x1234, 0x5678);
+
+        vm.roll(SHASTA_FORK_HEIGHT);
+        vm.prank(GOLDEN_TOUCH);
+        anchor.anchorV4(proposalParams, blockParams);
+
+        Anchor.PreconfMetadata memory meta = anchor.getPreconfMetadata(block.number);
+        assertTrue(meta.stored);
+        assertEq(meta.anchorBlockNumber, 0);
+        assertEq(meta.submissionWindowEnd, 7);
+    }
+
+    function test_getPreconfMetadata_RevertWhen_BlockNotRecorded() external {
+        vm.roll(SHASTA_FORK_HEIGHT);
+        vm.expectRevert(Anchor.InvalidBlockNumber.selector);
+        anchor.getPreconfMetadata(SHASTA_FORK_HEIGHT + 999);
+    }
+
     // ---------------------------------------------------------------
     // Helpers
     // ---------------------------------------------------------------