fix(consensus): create CUP shares without waiting for finalized tip to point to CUP height

[pierugo-dfinity]

No description provided.

[Copilot]

Pull request overview

This PR adjusts consensus behavior to allow creating Catch-Up Package (CUP) shares and building/validating blocks even when the finalized tip’s certified_height has not yet caught up to the CUP height, reducing unnecessary blocking during long state computations.

Changes:

• Simplifies ancestor chain iteration to no longer stop at the CUP height, enabling retrieval of past payloads even when a newer CUP exists.
• Removes a gating condition in the CUP maker that required finalized certified_height to be at/above the target CUP height.
• Prevents checkpoint purging below CUP height when the finalized tip’s certified_height is still behind the CUP height, and updates/adds tests for the new behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rs/interfaces/src/consensus_pool.rs	Simplifies ChainIterator API/behavior used by default pool caches.
rs/consensus/src/consensus/validator.rs	Updates validation test expectation to succeed even with a higher CUP present.
rs/consensus/src/consensus/purger.rs	Skips checkpoint purging when finalized certified height lags CUP height; adds coverage.
rs/consensus/src/consensus/catchup_package_maker.rs	Removes finalized-certified-height gating for CUP share creation; updates tests.
rs/consensus/src/consensus/block_maker.rs	Updates block maker test to expect payload generation even with higher CUP present.
rs/artifact_pool/src/consensus_pool_cache.rs	Removes CUP-bounded traversal assumptions in cached chain iteration call sites.

Comments suppressed due to low confidence (1)

rs/interfaces/src/consensus_pool.rs:456

• ChainIterator::get_parent_block now only looks up the parent via validated block_proposal(). If the parent block exists only in the validated catch_up_package() pool (which can happen after purging block proposals but retaining the CUP), the iterator will stop early and callers using the default ConsensusPoolCache::chain_iterator may observe truncated chains. Consider adding a fallback lookup similar to CachedChainIterator (check validated().catch_up_package().get_only_by_height(parent_height) and match the hash) so the iterator can traverse through CUP blocks without relying on block proposals being present.

    fn get_parent_block(&self, block: &Block) -> Option<Block> {
        let height = block.height();
        if height == Height::from(0) {
            return None;
        }
        let parent_height = height.decrement();
        let parent_hash = &block.parent;
        self.consensus_pool
            .validated()
            .block_proposal()
            .get_by_height(parent_height)
            .find_map(|proposal| {
                if proposal.content.get_hash() == parent_hash {
                    Some(proposal.content.into_inner())
                } else {
                    None
                }
            })

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