lndservices: add reorg aware block header cache; use in ChainBridge

[ffranr]

Closes: #1840

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What

• Introduce reusable full block header cache (by height and hash).
• Integrate cache in LndRpcChainBridge.
• Refactor GetBlockTimestamp to read via GetBlockHeaderByHeight and drop the old timestamp cache.

Why

• Avoid stale timestamps from reorged headers.
• Reduce repeated header RPCs.
• Provide a shared, configurable cache for future callers.

Highlights

• Reorg detection with conflicting height handling and orphan invalidation.
• Unsettled vs settled semantics via confirmation depth.
• Configurable capacity and random purge fraction.

Tests

• Basic get and put, capacity and purge, settled semantics, reorg path.

[gemini-code-assist]

Summary of Changes

Hello @ffranr, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a robust, reorg-aware block header cache to the lndservices package. The primary goal is to enhance the reliability of block header lookups by preventing the use of stale data during blockchain reorganizations and to optimize performance by reducing redundant RPC calls to the underlying LND node. The new cache is integrated into the LndRpcChainBridge, and the GetBlockTimestamp function has been refactored to leverage this improved caching mechanism and provide more comprehensive error handling.

Highlights

• Reorg Detection: The new cache includes reorg detection with conflicting height handling and orphan invalidation, ensuring data consistency during blockchain reorganizations.
• Settled Semantics: The cache distinguishes between 'unsettled' and 'settled' block headers based on a configurable confirmation depth, preventing the use of potentially unstable data.
• Configurable Cache: The cache offers configurable capacity and a random purge fraction, allowing for flexible resource management and performance tuning.

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[gemini-code-assist]

Code Review

This pull request introduces a reorg-aware block header cache, which is a great improvement for performance and correctness by avoiding stale data and reducing RPC calls. The implementation is clean and well-tested. The refactoring of GetBlockTimestamp to propagate errors is also a significant enhancement. I have a couple of minor suggestions for improvement, mainly around a small inconsistency in a comment and an opportunity for optimization in the cache purging logic. Overall, this is a solid contribution.

[darioAnongba]

Code looks good to me. Only nit comment is that we should slow down on the comments that add no value, example:

// Calculate the height at which this block would be considered settled.
settledHeight := height + c.cfg.NumConfSettled

Here the code has actually more information in it than the comment IMO.

[jtobin]

Really nice. 👌 Just a couple of questions/comments.

[jtobin]

LGTM. 👍 👍