blockifier: record pre-migration compiled class hash as initial read

[yoavGrs]

When migrating a class's compiled class hash, set_compiled_class_hash_migration
wrote the post-migration (v2) value into the write cache without first recording
the pre-block (v1) value as an initial read. Since get_compiled_class_hash
resolves the write cache before the initial reads, the v2 write shadowed the
pre-block value, so it was never captured. This made to_state_diff panic in
strict_subtract_mappings (the migrated write had no matching initial read to
subtract against) and left the OS without the pre-block class-trie leaf needed to
replay the block.

Force-read the pre-migration compiled class hash into the initial reads before
applying the migration write, and add a unit test covering the fix.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

[reviewable-StarkWare]

This change is 

[yoavGrs]

• blockifier: record pre-migration compiled class hash as initial read #14612 👈 (View in Graphite)
• main

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[cursor]

PR Summary

Medium Risk
Touches block execution state accounting for class-hash migration; the change is small and tested but affects correctness of diffs and OS replay.

Overview
Fixes compiled class hash migration so the pre-block (v1) value is recorded in CachedState initial reads before the v2 write is applied. set_compiled_class_hash_migration now calls get_compiled_class_hash ahead of set_compiled_class_hash, so the v2 cache entry no longer hides the on-chain v1 hash.

That restores correct to_state_diff behavior (avoids strict_subtract_mappings panics when the migrated write had no matching initial read) and preserves the pre-block class-trie leaf data the OS needs for block replay.

Adds a focused unit test that checks the post-migration hash, the diff, and (with reexecution) initial reads.

^{Reviewed by Cursor Bugbot for commit cdbf3ab. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

Artifacts upload workflows:

• Started at 2026-06-23T13:31:02Z
• Started at 2026-06-23T14:42:46Z

[Yoni-Starkware]

@Yoni-Starkware made 1 comment.
Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on yoavGrs).

---

crates/blockifier/src/state/compiled_class_hash_migration.rs line 36 at r1 (raw file):

            // Capture the pre-block (v1) hash as an initial read before the v2 write shadows it.
            self.get_compiled_class_hash(*class_hash)?;

Every migrated class should have triggered a call to get_compiled_class_hash before this point. See here:

sequencer/crates/blockifier/src/utils.rs

Line 126 in a5cbd53

let state_compiled_class_hash = state_reader.get_compiled_class_hash(class_hash)?;

Also, it's clear from the function API - it gets the previous compiled class hash, so not sure why this read is needed

Code quote:

            // Capture the pre-block (v1) hash as an initial read before the v2 write shadows it.
            self.get_compiled_class_hash(*class_hash)?;