Fix satoshi startup block sync backfill

[macterra]

Summary

Fix satoshi mediator startup sync so it does not treat the latest stored block height as proof that the full configured range has been backfilled.

What changed

• resume startup sync from latest.height + 1 instead of re-adding the latest known block
• skip cleanly when the configured start block is ahead of the current chain tip
• detect partial backfills by verifying the configured start block exists in gatekeeper before declaring sync complete
• report sync progress as a percentage of the configured range from start block to current height

Why

Gatekeeper can contain a recent tail of BTC mainnet blocks without having the full range from the configured start block. In that case the old logic would see the latest stored height at tip and incorrectly skip the missing historical backfill.

[Copilot]

Pull request overview

Improves the Satoshi mediator’s startup block-sync logic so it correctly backfills the full configured block range (from config.startBlock) instead of assuming that reaching the chain tip implies historical coverage in Gatekeeper.

Changes:

• Resume sync from latest.height + 1 when a complete backfill is detected (avoid re-adding the latest stored block).
• Skip startup sync when config.startBlock is ahead of the current chain tip, and detect partial backfills by verifying the configured start block exists in Gatekeeper.
• Add a helper to report sync progress as a percentage of the configured range (startBlock..tip) and use it in both sync paths.

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