fix(op-reth): surface pruned block bodies as a typed error instead of state-root mismatch

[dhyaniarun1993]

Description

Replace the misleading StateRootMismatch that surfaces when reth has pruned a block we depend on with a dedicated BlockBodyPruned error variant. Detection sits in two places: the engine's tasks::execute_block::run (covers live sync
and any caller of EngineHandle::execute_block) and the backfill's compute_block_backfill_diff (covers the changeset-pruning path that backfill actually reads from).

Tests

Test cases added

Additional context

NA

Metadata

NA

[wiz-0f98cca50a]

Wiz Scan Summary

Scanner	Findings
Vulnerabilities	-
Sensitive Data	-
Secrets	-
IaC Misconfigurations	-
SAST Findings	-
Software Management Findings	-
Total	-

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[sebastianst]

🤖 Claude says: Rust review of the pruned-body detection. The core approach is sound — both detection heuristics are logically correct (engine: transactions_root != EMPTY && empty body; backfill: empty per-block revert + state_root[N] != state_root[N-1], correctly guarded for genesis), and the engine + backfill paths are well tested.

Findings inline, by severity:

• 🔴 High — the unwind.rs guard returns an error before unwinding, contradicting its own comment/message ("unwind proceeds") and turning a safe unwind into a hard failure. Likely meant to be a warn! + continue.
• 🟠 Medium — the new alloy-trie dependency is unnecessary (alloy_consensus::EMPTY_ROOT_HASH is already in scope).
• 🟡 Low — Cargo.toml tabs/trailing-comma; doc comments claim a (non-existent) mirrored check in advance_sync; the backfill test only covers v1 storage settings (acceptable, but worth noting v2 pruning isn't exercised).

Recommend addressing the High finding before merge; the rest are scope-hygiene cleanups.