test: restore complete spork21 signing coverage

[PastaPastaPasta]

Issue being fixed or feature implemented

PR #7497 merged the default and --spork21 variants of feature_llmq_signing.py based on the assumption that the shared signing-session flow does not depend on spork 21.

That assumption does not hold for the signature-share transport. Mainnet hardens SPORK_21_QUORUM_ALL_CONNECTED to value 1, which keeps the all-connected concentrated QSIGSHARE path enabled for small quorums while LLMQ-100/400 quorums retain the legacy announce/request and QBSIGSHARES path. Both implementations are therefore live and need coverage for the complete signing-session lifecycle.

The shortened mid-test spork section retained basic threshold recovery and recovery-member retry coverage, but no longer exercised conflict handling, quorum aging, recovered-signature cleanup, and session reuse through the spork-21 transport.

What was done?

• Restored the --spork21 option and activation before the first quorum is mined.
• Restored the original spork-specific QSIGSHARE submission, full-connectivity checks, and recovery-member isolation flow.
• Removed the mid-test spork activation and shortened duplicate signing section.
• Re-added feature_llmq_signing.py --spork21 to the functional test runner.

This is limited to the signing-test deduplication from #7497. Its wallet RPC coverage split and spork-23 test optimization remain unchanged.

How Has This Been Tested?

The following checks passed against a current local Dash Core build:

• test/functional/feature_llmq_signing.py
• test/functional/feature_llmq_signing.py --spork21
• python3 -m py_compile test/functional/feature_llmq_signing.py test/functional/test_runner.py
• test/lint/lint-whitespace.py
• git diff --check

test/lint/lint-python.py was also invoked, but skipped because flake8 is not installed in the local environment.

Breaking Changes

None. Test-only change.

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 (not applicable)
• I have assigned this pull request to a milestone (for repository code-owners and collaborators only)

This pull request was created by Codex.

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[coderabbitai]

Walkthrough

The functional test adds a --spork21 mode that enables SPORK 21 before the first quorum and checks quorum connectivity and symmetric recovered-signature messaging. In this mode, valid submit=false signature shares are converted to CSigShare and sent through P2P. Recovery-member isolation uses a later request ID. The test runner adds a base invocation with --spork21.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested reviewers: knst, udjinm6

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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
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.
Title check	✅ Passed	The title clearly states that the change restores complete SPORK 21 signing test coverage.
Description check	✅ Passed	The description directly explains the restored SPORK 21 coverage, test-runner update, validation steps, and test-only scope.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[thepastaclaw]

✅ Final review complete — no blockers (commit 2f0bd0e)

[thepastaclaw]

✅ Final review complete — no blockers (commit 2f0bd0e)

[knst]

utACK 2f0bd0e

[thepastaclaw]

Final validation — Codex + Opus

The PR-specific commit cleanly restores the dedicated --spork21 signing-test variant and registers it with the functional test runner. The restored test is byte-for-byte identical to the established pre-deduplication version, and mine_quorum() waits for the all-connected topology before the subsequent connection and handshake assertions; no in-scope correctness or coverage issues were found.

Review provenance

• Codex reviewers: gpt-5.6-sol — general (completed), gpt-5.6-sol — dash-core-commit-history (completed)
• Verifier: gpt-5.6-sol — final-verifier (Opus verifier fallback)
• Opus reviewers: claude-sonnet-5 — general (failed), claude-sonnet-5 — dash-core-commit-history (failed), claude-sonnet-5 — general (completed), claude-sonnet-5 — dash-core-commit-history (completed)