refactor(sync): drop write-only HeadSyncResult.error field

src/lean_spec/node/sync/head_sync.py

@@ -63,16 +63,12 @@ class HeadSyncResult:
     """
     Result of processing a gossip block.
 
-    The SyncService only branches on the processed flag; the error string is
-    retained for incident-response logs and post-mortem inspection.
+    The SyncService only branches on the processed flag.
     """
 
     processed: bool
     """True if the block was immediately integrated into the Store."""
 
-    error: str | None = None
-    """Error message if processing failed."""
-
 
 @dataclass(slots=True)
 class HeadSync:
@@ -236,7 +232,6 @@ async def _process_block_with_descendants(
                 )
                 return HeadSyncResult(
                     processed=False,
-                    error=str(exception),
                 ), store
 
             # Process cached descendants.

tests/node/sync/test_head_sync.py

@@ -270,12 +270,12 @@ def track_processing(s: Any, block: SignedBlock) -> Any:
 class TestErrorHandling:
     """Tests for error handling during block processing."""
 
-    async def test_processing_error_captured_in_result(
+    async def test_processing_error_reported_as_not_processed(
         self,
         genesis_block,
         peer_id: PeerId,
     ) -> None:
-        """Processing errors are captured in the result, not raised."""
+        """Processing errors are swallowed, reported as not processed, never raised."""
         genesis_root = hash_tree_root(genesis_block)
         store = cast(Store, MockForkchoiceStore())
         store.blocks[genesis_root] = genesis_block
@@ -300,7 +300,6 @@ def fail_processing(s: Any, b: SignedBlock) -> Any:
 
         assert head_sync_result == HeadSyncResult(
             processed=False,
-            error="State transition failed",
         )
         assert returned_store is store  # Original store returned on error