Reject abandoned branch hashes - #14

Greptile Summary

The PR introduces a centralized exact-hash denylist for three abandoned or malicious blocks and applies it across consensus validation, header and crosslink verification, block insertion, epoch synchronization, receipt-chain processing, head updates, TiKV forwarding, and off-chain persistence.

• Rejects denied hashes before FBFT caching and PREPARE.
• Rejects direct block/header hashes and embedded beacon crosslinks or incoming receipt source headers.
• Adds focused tests for consensus, engine, core persistence, and crosslink verification paths.

Confidence Score: 5/5

The PR appears safe to merge; the denylist is consistently enforced before the relevant consensus acceptance and persistence boundaries.

The changed paths reject direct and embedded denied hashes before caching, signature acceptance, canonical-head updates, or database writes, and no reachable bypass or regression remains.

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Incoming block or FBFT message] --> B{Exact block hash denied?}
    B -- Yes --> X[Return ErrRejectedBlock]
    B -- No --> C{Embedded crosslink hash denied?}
    C -- Yes --> X
    C -- No --> D{Incoming receipt source hash denied?}
    D -- Yes --> X
    D -- No --> E[Continue signature and semantic validation]
    E --> F[Consensus cache or persistence paths]

_{Reviews (1): Last reviewed commit: "fix: reject abandoned branch hashes" | Re-trigger Greptile}