Implement seamless ledger re-org handling in the indexing engine

[Fatimasanusi]

Description

Blockchain network re-organizations can invalidate previously indexed events, resulting in the backend displaying phantom fractional shares.

Architecture & Context

The indexing engine must maintain a rolling window of "unfinalized" blocks. If a ledger sequence diverges from the expected hash, the backend must systematically rollback database mutations up to the common ancestor and replay the correct events.

Technical Requirements

• Track ledger_hash and previous_ledger_hash in the database.
• Implement a rollback function that deletes events linked to orphaned ledgers.
• Automatically trigger the re-sync pipeline upon detecting a hash mismatch.

Acceptance Criteria

• Simulated chain re-org correctly purges invalid database rows.
• System automatically recovers and syncs the new canonical chain.
• Client APIs temporarily return a 503 Service Unavailable during rollback.