fix(consensus): require multiplicity-correct MN payment matching after v24

[thepastaclaw]

Issue being fixed or feature implemented

Masternode payment validation currently checks each expected coinbase output with
existence-only matching. If the expected masternode payments contain duplicate
CTxOuts, one actual coinbase output can satisfy multiple expected payments.

This matters after the v24 multi-payout reward-share changes because duplicate
expected outputs can be valid when multiple owner shares resolve to the same
amount and script. Since this tightens consensus validation, the stricter
matching is gated behind DEPLOYMENT_V24 and pre-v24 validation keeps the
legacy behavior.

What was done?

• Added a masternode payment matching helper that can run in legacy
  existence-only mode or strict multiplicity-correct mode.
• Switched CMNPaymentsProcessor::IsTransactionValid to use strict matching
  only after DEPLOYMENT_V24 is active.
• Added focused unit tests covering duplicate expected payments, legacy
  behavior, empty expected payments, missing outputs, and exact amount matching.

How Has This Been Tested?

Ran locally on macOS in
/Users/claw/Projects/dash/worktrees/fix-v24-mn-payment-multiplicity:

./src/test/test_dash --run_test=masternode_payments_tests
./src/test/test_dash --run_test=governance_superblock_tests

Both passed.

Also ran the pre-PR review gate command with the explicit branch ref:

code-review dashpay/dash upstream/develop fix-v24-mn-payment-multiplicity "v24-gated multiplicity-correct masternode payment matching"

The wrapper built the correct 4-file diff, but the Codex reviewer backend failed
with 401 Unauthorized. As a fallback, I ran the same code-reviewer instructions
through local Claude against upstream/develop..HEAD; it returned
Recommendation: ship with no significant findings.

Breaking Changes

This is a consensus tightening after DEPLOYMENT_V24: post-v24 blocks must
include a distinct coinbase output for each expected masternode payment output,
including duplicate expected outputs. Pre-v24 behavior is intentionally
unchanged.

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)

[github-actions]

This pull request has conflicts, please rebase.

[github-actions]

✅ No Merge Conflicts Detected

This PR currently has no conflicts with other open PRs.

[thepastaclaw]

@coderabbitai review

[coderabbitai]

✅ Action performed

Review finished.

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[thepastaclaw]

The current check_merge failure appears unrelated to this PR branch. The job fast-forwarded PR #7377 onto develop successfully:\n\ntext\nUpdating 8c9f166a3..93be20423\nFast-forward\n\n\nIt failed afterward while checking whether develop can fast-forward into master:\n\ntext\ngit checkout master\ngit merge --ff-only base_branch\nfatal: Not possible to fast-forward, aborting.\n\n\nSo the branch itself is mergeable into develop; this looks like the current repo-level develop → master relationship, not a conflict introduced by this PR.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: b693deb2-0cd9-43cb-acbf-e4688bab60fc

📥 Commits

Reviewing files that changed from the base of the PR and between 8c9f166 and 93be204.

📒 Files selected for processing (4)

• src/Makefile.test.include
• src/masternode/payments.cpp
• src/masternode/payments.h
• src/test/masternode_payments_tests.cpp

---

Walkthrough

Added FindUnmatchedMasternodePayment to compare expected and actual masternode payout outputs with optional strict multiplicity. CMNPaymentsProcessor::IsTransactionValid now uses strict matching after Consensus::DEPLOYMENT_V24 activation and logs the unmatched payout on failure. Added a unit test file and included it in BITCOIN_TESTS.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• dashpay/dash#7362: Threads is_v24 into superblock validation and applies distinct-output checking for duplicate payments, which matches the V24-gated matching change here.

Suggested reviewers

• PastaPastaPasta
• UdjinM6

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 27.27% 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 accurately summarizes the consensus change to require multiplicity-correct masternode payment matching after v24.
Description check	✅ Passed	The description matches the implemented changes, including the new helper, v24-gated strict matching, and added tests.
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.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[thepastaclaw]

✅ Review complete (commit 93be204)

[thepastaclaw]

Code Review

Verified one non-blocking in-scope issue: the PR adds a Dash-specific unit test but does not register it in the Dash-only non-backported file list used by local lint gates. Coverage was degraded because the required ACP Claude/Codex reviewer sessions failed authentication; this review is based on native Codex reviewer outputs plus direct source inspection.

🟡 1 suggestion(s)

1 additional finding(s) omitted (not in diff).

🤖 Prompt for all review comments with AI agents

These findings are from an automated code review. Verify each finding against the current code and only fix it if needed.

In `test/util/data/non-backported.txt`:
- [SUGGESTION] test/util/data/non-backported.txt:68: Register the new masternode payment test for Dash-only linting
  This PR adds `src/test/masternode_payments_tests.cpp`, but none of the existing patterns in `test/util/data/non-backported.txt` match that file. Both `.github/workflows/clang-diff-format.yml` and `test/lint/lint-cppcheck-dash.py` build their Dash-specific file lists from this data file, so the new test is skipped by those Dash-only format/cppcheck gates unless it is listed here.