From 40c431a17dd229c6b1c36ee62bc5c3f671ee4c86 Mon Sep 17 00:00:00 2001
From: owen <owen@gattaca.com>
Date: Thu, 10 Sep 2026 19:02:10 +0100
Subject: [PATCH] Treat a missing parent state as a temporary sim failure

The simulator returns "no state found for block <hash>" when its node
knows the parent header but does not have that block on its head chain.
A late parent, a reorg, or a lagging node causes this. `is_temporary`
did not match the text, so the relay demoted the builder for a
sim-side condition. Match the reth text and the builder's own
"parent state is not available".

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 crates/builder/src/validation/error.rs |  1 +
 crates/common/src/simulator.rs         | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/crates/builder/src/validation/error.rs b/crates/builder/src/validation/error.rs
index 04642dd7..5f5b311a 100644
--- a/crates/builder/src/validation/error.rs
+++ b/crates/builder/src/validation/error.rs
@@ -30,6 +30,7 @@ pub enum ValidationError {
     PostExecution(String),
     #[error("block state root mismatch: got {got}, expected {expected}")]
     StateRootMismatch { got: B256, expected: B256 },
+    // Text matched by `BlockSimError::is_temporary`; changing it demotes builders.
     #[error("parent state is not available")]
     MissingParentState,
     #[error("could not verify proposer payment")]
diff --git a/crates/common/src/simulator.rs b/crates/common/src/simulator.rs
index f446b20e..def506af 100644
--- a/crates/common/src/simulator.rs
+++ b/crates/common/src/simulator.rs
@@ -64,6 +64,8 @@ const BLOCK_ALREADY_KNOWN: &str = "block already known";
 const BLOCK_TOO_OLD: &str = "block is too old, outside validation window";
 const BLOCK_REQ_REORG: &str = "block requires a reorg";
 const PARENT_BLOCK_NOT_FOUND: &str = "could not find parent block: parent block not found";
+const NO_STATE_FOR_BLOCK: &str = "no state found for block";
+const MISSING_PARENT_STATE: &str = "parent state is not available";
 
 #[derive(Debug, Clone, Error)]
 pub enum BlockSimError {
@@ -110,7 +112,9 @@ impl BlockSimError {
                 PARENT_NOT_FOUND => true,
                 PARENT_BLOCK_NOT_FOUND => true,
                 BLOCK_REQ_REORG => true,
+                MISSING_PARENT_STATE => true,
                 r if r.starts_with(MISSING_TRIE_NODE) => true,
+                r if r.starts_with(NO_STATE_FOR_BLOCK) => true,
                 _ => false,
             },
             BlockSimError::Timeout => true,
@@ -238,6 +242,20 @@ mod tests {
         )
     }
 
+    /// The parent state can be missing while the simulator lags or reorgs, so it must not demote.
+    #[test]
+    fn missing_parent_state_never_demotes() {
+        for reason in [
+            "no state found for block 0xf9d64b1e6815113d8a761cac2d094802520a082b19221dcbeff2940b469adb7d",
+            "parent state is not available",
+        ] {
+            let err = BlockSimError::BlockValidationFailed(reason.to_string());
+
+            assert!(err.is_temporary(), "{err}");
+            assert!(!err.is_demotable(), "{err}");
+        }
+    }
+
     /// A relay-side hydration failure is never the builder's fault, so it must not demote.
     #[test]
     fn relay_hydration_failure_never_demotes() {