fix: deduplicate QRINFO base blocks

[thepastaclaw]

Issue being fixed or feature implemented

QRINFO request handling accepts caller-provided base block hashes and carries the
validated block indexes through quorum rotation response construction. Repeated
base hashes do not add useful information, so this change canonicalizes those
base indexes before the builder phases use them.

Provenance: thepastaclaw/tracker#1450

What was done?

• Sort validated QRINFO base block indexes by height for both construction
  paths.
• Remove duplicate base block index pointers before response construction.
• Add focused unit coverage for repeated base block selection behavior.
• Add RPC functional coverage showing repeated base hashes produce the same
  result as a single base hash.

How Has This Been Tested?

Environment: macOS arm64, local Dash Core worktree based on upstream/develop.

Commands run:

• git diff --check upstream/develop..HEAD — passed
• make -C src -j$(sysctl -n hw.ncpu) test/test_dash — passed earlier in this
  worktree before the final Python-only test addition
• src/test/test_dash --run_test=llmq_snapshot_tests/get_last_base_block_hash_repeated_base_blocks_test
  — passed
• test/functional/feature_llmq_rotation.py — skipped locally because this
  worktree was configured with --disable-wallet
• code-review dashpay/dash upstream/develop fix/qrinfo-dedupe-base-hashes ...
  — passed with recommendation: ship

Also checked:

• gh api repos/dashpay/dash --jq '.default_branch' — develop
• Open PR search for duplicate QRINFO/baseBlockHashes dedupe work — no duplicate
  open PR found

Breaking Changes

None expected.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation
• I have assigned this pull request to a milestone (for repository code-owners and collaborators only)

[thepastaclaw]

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✅ No Merge Conflicts Detected

This PR currently has no conflicts with other open PRs.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 36a2f33d-9858-4cf4-b6ac-378fab424159

📥 Commits

Reviewing files that changed from the base of the PR and between e34105f and 9f30867.

📒 Files selected for processing (2)

• src/llmq/snapshot.cpp
• src/test/llmq_snapshot_tests.cpp

Walkthrough

This PR modifies the quorum rotation snapshot construction to unconditionally sort and deduplicate base block indexes by ascending block height. Previously, this sorting was applied only under legacy construction; now it applies to all paths. The change adds <algorithm> header usage and modifies BuildQuorumRotationInfo to call std::sort and std::unique/erase on baseBlockIndexes. A unit test verifies GetLastBaseBlockHash behavior with repeated block entries, and a functional test confirms the RPC returns consistent results when the same base block hash is provided multiple times.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested reviewers

• UdjinM6
• bigwalter1979-cloud

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: deduplicating QRINFO base blocks, which aligns with the primary objective of the PR.
Description check	✅ Passed	The description comprehensively explains the issue, changes made, testing performed, and breaking changes, all directly related to the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests

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[thepastaclaw]

🔍 Review in progress — actively reviewing now (commit 9f30867)

[thepastaclaw]

Code Review

Both agents converged on no findings for this small, well-scoped fix that sorts and deduplicates QRINFO baseBlockIndexes. CodeRabbit also reported no inline findings. The change is covered by both unit and functional tests.

[PastaPastaPasta]

Might this be a breaking change? Especially how we have the "legacy construction" flag? seems for some reason at some point the exact structure was deemed important?

[thepastaclaw]

Good catch. I narrowed the change in 9f3086755d so the legacy-construction path keeps the old normalization behavior: sort only, no dedupe.

The repeated-base-hash fix now applies to the non-legacy path used by the RPC. I also added a direct unit assertion documenting that duplicates are a no-op for legacy GetLastBaseBlockHash, so we preserve compatibility while still fixing the repeated-base RPC behavior.

Validation:

./src/test/test_dash --run_test=llmq_snapshot_tests