apollo_central_sync: use starknet version as single source of truth for non BC classes

[noamsp-starkware]

Note

Medium Risk
Changes the state sync/class-manager integration and compiled-class streaming behavior based on stored starknet_version, which can affect how/when classes and CASMs are persisted and sent to the class manager during sync.

Overview
Switches non-backward-compatible (non-BC) class handling to use the block header’s starknet_version as the single source of truth, removing the previous reliance on the compiler_backward_compatibility_marker and the store_sierras_and_casms_block_threshold config.

State diff processing now sends Sierra classes directly to the class manager only for BC blocks, and persists Sierra classes to storage only for non-BC blocks so the compiled-class stream can later attach CASM and call add_class_and_executable_unsafe. The compiled-class stream now scans headers to stop/pause at the first BC block and batches downloads to include only non-BC ranges; the sync “stuck” detector (check_sync_progress) is updated accordingly.

Removes store_sierras_and_casms_block_threshold from config/schema/deployment overlays and stops updating the compiler-compatibility marker during header writes (marker remains in storage with a TODO to delete).

^{Written by Cursor Bugbot for commit 8c6ec29. This will update automatically on new commits. Configure here.}

[reviewable-StarkWare]

This change is 

[noamsp-starkware]

• apollo_storage: remove compiler backward compatibility marker #13313
• apollo_central_sync: use starknet version as single source of truth for non BC classes #13312 👈 (View in Graphite)
• main

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[github-actions]

Artifacts upload workflows:

• Started at 2026-03-17T15:20:21Z
• Started at 2026-03-17T15:22:49Z

[ShahakShama]

@ShahakShama reviewed 9 files and all commit messages, and made 11 comments.
Reviewable status: all files reviewed, 11 unresolved discussions (waiting on noamsp-starkware).

---

crates/apollo_central_sync/src/lib.rs line 469 at r1 (raw file):

            .expect("Block header must be present before state diff is processed.");

        let is_bc_compatible_block = block_starknet_version >= STARKNET_VERSION_TO_COMPILE_FROM;

bc = backward compatibility. You're saying compatible twice
I personally prefer bc -> backward

---

crates/apollo_central_sync/src/lib.rs line 473 at r1 (raw file):

        // fails we retry the same block.
        if let Some(class_manager_client) = &self.class_manager_client {
            // Non-BC blocks (starknet_version < STARKNET_VERSION_TO_COMPILE_FROM) must be added

In the documentation at least you should have enough space to not use acronym (BC -> backward compatible)

---

crates/apollo_central_sync/src/lib.rs line 493 at r1 (raw file):

            }

            for (class_hash, deprecated_class) in &deprecated_classes {

Add a comment above here that deprecated classes are always backward compatible

---

crates/apollo_central_sync/src/lib.rs line 517 at r1 (raw file):

            if !is_bc_compatible_block {
                debug!(
                    "Storing Sierra classes {:?} in storage (non-BC block {block_number})",

Also in logs avoid using acronyms

---

crates/apollo_central_sync/src/lib.rs line 525 at r1 (raw file):

                }
            } else {
                debug!("Block {} contains non backward compatible classes.", block_number);

Restore this debug log

---

crates/apollo_central_sync/src/lib.rs line 558 at r1 (raw file):

    ) -> StateSyncResult {
        // The compiled class stream pauses when it reaches a BC block, so this function should
        // only be called for non-BC blocks.

same here (BC -> backward compatible)

---

crates/apollo_central_sync/src/lib.rs line 566 at r1 (raw file):

                .map(|v| v < STARKNET_VERSION_TO_COMPILE_FROM)
                .unwrap_or(true),
            "store_compiled_class called for BC block {block_number}"

same here (BC -> backward compatible)

---

crates/apollo_central_sync/src/lib.rs line 859 at r1 (raw file):

            while from < state_marker {
                // The block header is guaranteed to be in storage for any block below state_marker.
                let starknet_version_at_from = txn.get_starknet_version(from)?.expect("Block header must exist for block below state_marker.");

Rename this variable. What is at_from?

---

crates/apollo_central_sync/src/lib.rs line 879 at r1 (raw file):

                );
                pending::<()>().await;
                continue;

Do you really need this continue statement?

---

crates/apollo_central_sync/src/lib.rs line 894 at r1 (raw file):

            // Since starknet_version is monotonically non-decreasing, the non-BC range is always
            // a contiguous prefix.
            let mut up_to = min(state_marker, BlockNumber(from.0 + u64::from(max_stream_size)));

Consider extracting to a helper function

---

crates/apollo_central_sync/src/lib.rs line 990 at r1 (raw file):

            let is_casm_stuck = casm_marker == new_casm_marker
                && new_casm_marker < new_state_marker
                && reader

Move the read to the read that's done above

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